IL322232A

IL322232A - Swept-source optical coherence tomography with enhanced signal detection

Info

Publication number: IL322232A
Application number: IL322232A
Authority: IL
Original assignee: Ipg Photonics Corp
Priority date: 2023-01-23
Filing date: 2024-01-23
Publication date: 2025-09-01
Also published as: CN120659967A; EP4655553A1; MX2025008474A; WO2024158772A1; KR20250136831A; DE112024000612T5

Description

WO 2024/158772 PCT/US2024/012552 SWEPT-SOURCE OPTICAL COHERENCE TOMOGRAPHY WITH ENHANCED SIGNAL DETECTION RELATED APPLICATIONSThe present application claims priority to U.S. Provisional Application Serial No. 63/440,486, titled "SWEPT-SOURCE OPTICAL COHERENCE TOMOGRAPHY WITH ENHANCED SIGNAL DETECTION," filed on January 23, 2023, the content of which is hereby incorporated by reference in its entirety.

BACKGROUNDTechnical FieldThe technical field relates generally to Swept-Source Optical Coherence Tomography (SS-OCT), and more specifically to SS-OCT systems and methods configured with improved imaging capabilities.

Background DiscussionOptical coherence tomography (OCT) is an imaging technology that involves dividing the light output from a light source into an imaging beam and a reference beam, detecting interference signals obtained by superimposing the imaging beam reflected from an object or sample surface with the reference beam, and forming a tomographic image of the object based on the detection result. The tomographic image may comprise two-dimensional cross sections or three-dimensional volume renderings of the object or sample by using information on how the beams are changed upon reflection.A common OCT technique is Fourier domain OCT (FD-OCT), of which there are generally two types: Spectral-Domain OCT (SD-OCT) and Swept-Source OCT (SS-OCT). These two systems differ, how ever, in the type of optical source that they each utilize and how the interference signals are detected.SD-OCT systems use a broadband optical source and a spectrally resolving detector system to determine the different spectral components in a single axial scan (A-scan) of the sample. Thus, SD-OCT systems usually decode the spectral components of an interference signal by spatial separation. As a result, the detector system is typically complex, as it must detect the w avelengths of all optical signals in the scan range simultaneously, and then WO 2024/158772 PCT/US2024/012552 convert them to a corresponding interference dataset. This affects the speed and performance of SD-OCT systems.In contrast, SS-OCT systems encode spectral components in time, not by spatial separation. SS-OCT systems typically utilize instantaneously narrowband imaging sources with an emitted wavelength that varies over time, sometimes referred to as a "Swept Source" or "Swept-Source." SS-OCT systems acquire an A-line by using such light sources along with time-domain optical detection. The spectrogram of the interference light, often referred to as the interferogram, which corresponds to the A-line, is acquired by detecting the interference light sequentially over time as the wavelength of the light source varies. The interference signals are ty pically detected by a non-spectrally resolving detector, one non- limiting example of which includes a balanced detector photodiode detection system.Compared to SD-OCT technology, SS-OCT is less susceptible to sensitivity degradation at longer imaging depths, provides faster scanning speed and improved signal to noise ratio ("SNR"), and reduces the complexity' of the detector system.

SUMMARYAspects and embodiments are directed to methods and systems for the use of SS-OCT in material modification processes.In accordance with one embodiment, there is provided a swept-source optical coherence tomography (SS-OCT) system for performing imaging of a sample treated by a material processing beam, the material processing beam interacting with material of the sample at a processing region on the sample, the SS-OCT system including an interferometer having at least one reference arm, at least one sample arm configured to direct an imaging optical signal to the processing region, and a tunable light source for generating the imaging optical signal, the imaging optical signal having at least one wavenumber k that is variable in time and a sweep rate in a range from 1 kilohertz (kHz) to 20 megahertz (MHz) inclusive, the interferometer configured to direct the imaging optical signal to the at least one reference arm and the at least one sample arm and combine optical signals returning from the at least one reference arm and the at least one sample arm to generate a combined optical signal, an optical detector configured to detect the combined optical signal and generate at least one interferometer output signal, and a processing unit configured to: receive the at least one interferometer output signal, process the at least one interferometer output signal to determine at least one feature of the processing region, detect a distortion in the at least one 2 WO 2024/158772 PCT/US2024/012552 interferometer output signal, the distortion created by a time-vary ing difference in optical path lengths between the at least one sample arm and the at least one reference arm, responsive to detection of the distortion, apply one or more corrections to the at least one interferometer output signal to produce a corresponding corrected interferometer output signal, and process the at least one corrected interferometer output signal to determine the at least one feature of the processing region.In one example, the at least one feature includes depth information of the processing region. In a further example, the depth information includes a range of at least 1 mm inclusive. In a further example, the depth information includes a range of at least 5 mminclusive. In a further example, the depth information includes a range of at least 21 mminclusive. In a further example, the depth information includes a range of at least 50 mminclusive. In another, the material processing beam creates a phase change region (PCR) atthe processing region and the depth information includes keyhole depth of the PCR. In another example, the system further includes at least one directing element that directs the imaging optical signal at one or more selected positions in and/or near the PCR.In one example, the processing unit is further configured to control at least one processing parameter of a material modification process implemented by the material processing beam on the sample based on the at least one feature of the processing region.In one example, the processing unit is further configured to determine a sample position based on the at least one corrected interferometer output signal.In one example, the processing unit is further configured to determine a velocity of the material of the sample based on the at least one corrected interferometer output signal.In one example, the processing unit is further configured to determine one or more alignments and/or one or more offsets in alignment between a coordinate system of a beam delivery system for the material processing beam and a coordinate system of a delivery' system for the imaging optical signal.In one example, the processing unit is configured to control the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt that are associated with one or more interferometer output signals, and the processing unit is configured to calculate the one or more corrections, and calculating the one or more corrections comprises: identifying a distortion in at least one of the one or more interferometer output signals that is associated with at least one of the at least two tuning rates, performing an evaluation of the distortion. 3 WO 2024/158772 PCT/US2024/012552 wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.In one example, the at least two tuning rates dk/dt include at least one positive tuning rate dk/dt and at least one negative tuning rate dk/dt. In a further example, performing the evaluation comprises comparing distortion in at least one interferometer output signal associated with a positive tuning rate dk/dt with distortion in at least one interferometer output signal associated with a negative tuning rate dk/dt.In one example, performing the evaluation comprises comparing distortion in at least two interferometer output signals. In one example, the distortion corresponds to a distortion in one or more geometric aspects encoded in the interferometer output signal. In one example, the one or more geometric aspects includes at least one of a position, symmetry, a width of a peak, a centroid, a geometric second moment, a center of mass, an amplitude, a height to width ratio, and a geometric area under a curve. In one example, performing the evaluation comprises comparing one or more geometric aspects encoded in at least two interferometer output signals.In one example, performing the evaluation comprises comparing one or more geometric aspects to one or more pre-determined thresholds and/or baselines associated with the one or more geometric aspects. In one example, the one or more predetermined thresholds and/or baselines are established based on at least one of; system and/or component requirements, one or more application requirements, one or more calibrations, one or more models, limitations of the hardware and/or software, one or more algorithms, and fundamental physics.In one example, the processing unit is configured to perform the evaluation by comparing the one or more geometric aspects relative to at least one of one or more geometric aspects encoded in at least one other of the one or more interferometer output signals, and one or more predetermined thresholds and/or baselines associated with the one or more geometric aspects.In one example, performing the evaluation comprises applying a predetermined threshold to the distortion and determining whether the distortion exceeds the predetermined threshold. In another example, performing the evaluation comprises determining if a relative difference between two or more distortions exceeds a predetermined threshold.In one example, the processing unit is further configured to generate a mathematical model based at least in part on one or more properties of the SS-OCT system and the 4 WO 2024/158772 PCT/US2024/012552 evaluation of the distortion. In a further example, the mathematical model is further configured to generate an estimate of a magnitude and/or a direction of motion velocity׳ of the sample based on the evaluation of the distortion.In one example, a material modification process implemented by the material processing beam on the sample is a welding process and the material processing beam creates a phase change region (PCR) at the processing region, and the processing unit is configured to use the evaluation to generate one or more corrections, and use the one or more generated corrections to calculate a measurement of one or more features which are in motion in the PCR. In one example, the one or more features which are in motion in the PCR are in motion as a result of the material processing process.In one example, a material modification process implemented by the material processing beam on the sample is a welding process and the material processing beam creates a phase change region (PCR) at the processing region, and the processing unit is configured to use the evaluation to generate an estimate of a velocity of the material being processed in the PCR.In one example, applying the one or more corrections to the at least one interferometer output signal comprises discarding, weighting, promoting, or using the at least one of the one or more interferometer output signals, or selecting the at least one of the one or more interferometer output signals to discard or use at a later time.In one example, the interferometer is a first interferometer and the system further comprises at least one additional interferometer and configured such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element, a first imaging optical signal configured with one of the at least two tuning rates dk/dt is directed to the at least one reference arm and the at least one sample arm of the first interferometer, a second imaging optical signal configured with another of the at least two tuning rates dk/dt is directed to the at least one reference arm and the at least one sample arm of the at least one additional interferometer, and the distortion is identified based on the one or more interferometer output signals of the first interferometer and the at least one additional interferometer. In a further example, the first and second imaging optical signals are directed to the processing region simultaneously.In one example, the time-varying difference in optical path lengths is caused by sample motion. In one example, a motion velocity׳ of the sample is greater than 10 mm/s. In a further example, the motion velocity of the sample is greater than 100 mm/s. In a further 5 WO 2024/158772 PCT/US2024/012552 example, the motion velocity of the sample is greater than 500 mm/s. In a further example, the motion velocity of the sample is greater than 1000 mm/s. In a further example, the motion velocity of the sample is greater than 10,000 mm/s.In one example, the processing unit is configured to derive track data from the at least one interferometer output signal and the one or more corrections is applied to the track data.In one example, the system further includes at least one k-clock module that generates a k-clock signal that indicates when a wavenumber k of the imaging optical signal substantially changes by one or more increments. In one example, a rate of change in the at least one wavenumber k of the imaging optical signal over time (tuning rate dk/dt) is non- uniform, and the at least one k-clock module is configured to trigger the acquisition of the interferometer output signals at uniform increments in wavenumber k. In one example, the processing unit is configured to process the at least one interferometer output signal based on interferometer output signals that are uniformly sampled in wavenumber. In one example, a rate of change in the at least one wavenumber k of the imaging optical signal over time (tuning rate dk/dt) is uniform, and the at least one k-clock module is configured to trigger the acquisition of the interferometer output signals at uniform increments in wavenumber k. In one example, the processing unit is configured to acquire the k-clock signal simultaneously to the acquisition of the interferometer output signals. In one example, the processing unit is configured to use the acquired k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k. In one example, the processing unit is configured to use the acquired k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal. In one example, the processing unit is configured to use the acquired k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k. In one example, the processing unit is configured to acquire the k-clock signal in a manner which is time gated relative to the acquisition of the interferometer output signals, and apply the time gated k- clock signal to the processing of subsequently acquired interferometer output signals. In one example, the processing unit is configured to use the acquired k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k. In one example, the processing unit is configured to use the acquired k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal. In one example, the processing unit is 6 WO 2024/158772 PCT/US2024/012552 configured to use the acquired k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k. In one example, at least one of the interferometer sample and reference arms is configured with one or more optical elements that are used to generate the k-clock signal. In one example, the at least one k-clock module is configured with multiple optical paths that are used to generate the k-clock signal. In a further example, the at least one k-clock module is configured to simultaneously generate the multiple optical paths by splitting the optical signal. In a further example, the at least one k-clock module is configured such that the multiple optical paths are available for selection.In one example, the processing unit is further configured to simulate a k-clock signal that indicates when the at least one wavenumber k of the imaging optical signal substantially changes by one or more increments based at least in part on one or more properties of the SS- OCT system and one or more properties of the tunable light source. In one example, the processing unit is configured to use the simulated k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k. In one example, the processing unit is configured to use the simulated k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal. In one example, the processing unit is configured to use the simulated k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.In one example, the processing unit is further configured to generate a mathematical model of k(t) and/or a tuning rate dk/dt of the imaging optical signal based at least in part on one or more properties of the SS-OCT system and one or more properties of the tunable light source. In a further example, the processing unit is configured to use the mathematical model to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k. In a further example, the processing unit is configured to use the mathematical model to compute at least one correction for one or more distortions in the interferometer output signal. In one example, the processing unit is configured to use the mathematical model to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.In one example, the time-varying difference in optical path lengths is caused by sample motion relative to an axis of the imaging optical signal. In one example, the time-7 WO 2024/158772 PCT/US2024/012552 vary ing difference in optical path lengths is caused by a material modification process implemented by the material processing beam on the sample.In one example, the time-varying difference in optical path lengths is caused by intrinsic sample motion not caused by a material modification process implemented by the material processing beam on the sample.In one example, the processing unit is configured to control the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt. In a further example, the at least two tuning rates dk/dt include at least one negative and at least one positive dk/dt. In one example, the tunable light source is configured such that the imaging optical signal includes a superposition of the at least two tuning rates dk/dt. In a further example, the superposition of the at least two tuning rates dk/dt includes at least one negative and at least one positive dk/dt.In one example, the tunable light source is a first tunable light source and the system further comprises at least one other tunable light source. In one example, the interferometer is a first interferometer and the system further comprises at least one additional interferometer, the first interferometer configured with the first tunable light source, the at least one additional interferometer configured with the at least one other tunable light source, the first interferometer and the at least one additional interferometer configured such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element. In one example, a rate of change in the at least one wavenumber k of the imaging optical signal in time is a tuning rate dk/dt and the processing unit is configured to control the first tunable light source such that a first imaging optical signal generated by the first tunable light source has a first tuning rate dk/dt, and control the at least one other tunable light source such that an imaging optical signal generated by the at least one other tunable light source has a second tuning rate dk/dt that is different than the first tuning rate dk/dt. In one example, at least a portion of the first imaging optical signal and at least a portion of the imaging optical signal generated by the at least one other imaging optical signal are transmitted simultaneously. In one example, the first and second tuning rates are associated with one or more interferometer output signals and the processing unit is configured to calculate the one or more corrections, and calculating the one or more corrections comprises: identifying a distortion in at least one of the one or moreinterferometer output signals that is associated with at least one of the first and second tuning 8 WO 2024/158772 PCT/US2024/012552 rates, performing an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation. In one example, the first tuning rate dk/dt is a positive dk/dt and the second tuning rate dk/dt is a negative dk/dt.In one example, the system further includes a splitter to split the imaging optical signal into at least two arms, and an optical delay element configured such that an output of a first arm of the at least two arms is delayed in time relative to an output of a second arm of the at least two arms. In one example, the processing unit is configured to control the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt. In one example, the at least two tuning rates dk/dt includes a positive tuning rate dk/dt associated with either the first arm or the second arm, and a negative tuning rate dk/dt associated with the other of the first arm or the second arm. In one example, the interferometer is a first interferometer and the system further comprise at least one additional interferometer. In a further example, the first arm is configured to be directed to at least one of: different reference arms, different sample arms, partially overlapped reference arms, and partially overlapped sample arms of the first interferometer and the at least one additional interferometer. In another example, the first arm and the second arm are configured to be directed to at least one sample arm and at least one reference arm of the first interferometer and the at least one additional interferometer. In another example, the first interferometer and the at least one additional interferometer are configured such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element, and the first arm and the second arm of the imaging optical signal are configured to be directed to the first interferometer and the at least one additional interferometer simultaneously. In another example, the first arm is configured to be directed to the first interferometer or the at least one additional interferometer, and the second arm is configured to be directed to the other of the first interferometer or the at least one additional interferometer. In one example, the at least two tuning rates dk/dt of the first and second arms are associated with one or more interferometer output signals and the processing unit is configured to calculate the one or more corrections, and calculating the one or more corrections comprises: identifying a distortion in at least one of the one or more interferometer output signals that is associated with at least one of the positive and negative tuning rates, performing an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.9 WO 2024/158772 PCT/US2024/012552 In one example, an optical frequency of the imaging optical signal varies at a rate in a range of 8 PHz/s - 2 ZHz/s inclusive.In one example, the processing unit is configured to generate an OCT image based on the at least one interferometer output signal and/or the at least one corrected interferometer output signal and transmit the generated OCT image to a display device.In one example, the processing unit is further configured to generate OCT data from the processed interferometer output signal and/or the corrected interferometer output signal, and transmit the OCT data to an external device.In one example, the tunable light source is a tunable vertical-cavity surface-emitting laser (VCSET). In another example, the system further includes an amplifier for amplifying the VCSEL. In one example, the amplifier is configured as a fiber amplifier. In one example, the output power of the amplifier is at least 20 milliwatts (mW). In a further example, the output power of the amplifier is at least 30 mW. In a further example, the output power of the amplifier is at least 50 mW. In a further example, the output power of the amplifier is at least 100 mW. In a further example, the output power of the amplifier is at least 500 mW. In a further example, the output power of the amplifier is at least 1 watt (W). In a further example, the output power of the amplifier is at least 5 W. In one example, the amplifier is configured to have a peak gain at a wavelength between 1010 and 1050 nm. In one example, the amplifier is configured to have a peak gain at a wavelength between 10and 1090 nm. In one example, the amplifier is configured with one, two. or three amplification stages.In one example, the SS-OCT system has a sensitivity of at least 105 dB.In one example, the processing unit is further configured to modulate or demodulate the at least one interferometer output signal using a predetermined carrier frequency.In one example, the system further includes a digitizer configured to digitize the at least one interferometer output signal and generate a corresponding digital signal.In one example, the system further includes a record generator that generates a record of a material modification process implemented by the material processing beam on the sample based on the at least one interferometer output signal at a plurality of times. In a further example, the processing unit is further configured to evaluate quality of a weld produced by a material modification process implemented by the material processing beam on the sample based at least in part on the record.

WO 2024/158772 PCT/US2024/012552 In one example, the system further includes an annunciation generator that generates an annunciation pertaining to a material modification process implemented by the material processing beam on the sample based on the at least one interferometer output signal at a plurality of times.In one example, the system further includes at least one directing element that directs the imaging optical signal. In a further example, the at least one directing element is configured such that the imaging optical signal is within 50 nm of the focal spot of the material processing beam at the processing region.In one example, the system further includes an auxiliary' measurement system configured to measure process radiation.In one example, the system is configured to image sequences of multiple material modification processes that are implemented by the material processing beam on the sample.In one example, the system further includes a safety interlock device integrated into the tunable light source. In another example, a safety interlock device integrated into the tunable light source that is configured to enable an eye-safe operating mode for the tunable light source, the eye-safe operating mode characterized by having a reduced imaging optical emission power.In one example, the system further includes at least one of a material processing energy source that generates the material processing beam and a beam delivery system for the material processing beam and the imaging optical signal. In a further example, the system further includes a laser head that couples to the material processing energy source and houses the beam delivery system. In one example, the processing unit is further configured to control at least one of a material processing energy source that generates the material processing beam and the beam delivery system based on the at least one feature of the processing region.In one example, a material processing system includes the SS-OCT system, a material processing energy source that generates the material processing beam, and a beam delivery' system for the material processing beam and the imaging optical signal. In a further example, the beam delivery system is configured with a dichroic optic configured to combine the imaging optical signal and the material processing beam into a combined optical path. In one example, the dichroic optic is configured with a transmission spectrum having a first band edge, a reflection spectrum having a second band edge, and the first band edge and the second band edge have a maximum wavelength separation of 25 nm. In one example, the 11 WO 2024/158772 PCT/US2024/012552 beam delivery7 system is configured to impinge the imaging optical signal on the dichroic optic over a range of incidence angles.In accordance with another exemplary embodiment, there is provided a swept-source optical coherence tomography (SS-OCT) method for imaging a processing region on a sample being treated by a material processing beam, the method including providing an interferometer having at least one sample arm, at least one reference arm. and a tunable light source configured to generate an imaging optical signal that has at least one wavenumber k that is substantially variable in time and a sweep rate in a range from 1 kilohertz (kHz) to megahertz (MHz) inclusive, directing the imaging optical signal to the at least one reference arm and the at least one sample arm of the interferometer, the at least one sample arm being configured to direct the imaging optical signal to the processing region, generating a combined optical signal from optical signals returning from the at least one reference arm and the at least one sample arm, generating at least one interferometer output signal from the combined optical signal, processing the at least one interferometer output signal to determine at least one feature of the processing region, detecting a distortion in the at least one interferometer output signal, the distortion created by a time-varying difference in optical path lengths between the at least one sample arm and the at least one reference arm, responsive to detecting the distortion, applying one or more corrections to the at least one interferometer output signal to produce a corresponding corrected interferometer output signal, and processing the at least one corrected interferometer output signal to determine the at least one feature of the processing region.In one example, the at least one feature includes depth information of the processing region. In a further example, the depth information includes a range of at least 1 mm inclusive. In a further example, the depth information includes a range of at least 5 mm inclusive. In a further example, the depth information includes a range of at least 21 mm inclusive. In one example, the depth information includes a range of at least 50 mm inclusive. In one example, the material processing beam creates a phase change region (PCR) at the processing region and the depth information includes keyhole depth of the PCR. In a further example, directing the imaging optical signal at one or more selected positions in and/or near the PCR.In one example, the SS-OCT method further includes controlling at least one processing parameter of a material modification process implemented by the material processing beam on the sample based on the at least one feature of the processing region.12 WO 2024/158772 PCT/US2024/012552 In one example, the SS-OCT method further includes determining a sample position based on the at least one corrected interferometer output signal.In one example, the SS-OCT method further includes determining a velocity of a material of the sample based on the at least one corrected interferometer output signal.In one example, the SS-OCT method further includes determining one or more alignments and/or one or more offsets in alignment between a coordinate system of a beam delivery system for the material processing beam and a coordinate system of a delivery system for the imaging optical signal.In one example, the SS-OCT method further includes controlling the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt that are associated with one or more interferometry signals, calculating one or more corrections, wherein calculating the one or more corrections comprises: identifying a distortion in at least one of the interferometer output signals that is associated with at least one of the at least two tuning rates, and performing an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.In one example, the at least two tuning rates dk/dt include at least one positive tuning rate dk/dt and at least one negative tuning rate dk/dt. In one example, performing the evaluation comprises comparing distortion in at least one interferometer output signal associated with a positive tuning rate dk/dt with distortion in at least one interferometer output signal associated with a negative tuning rate dk/dt.In one example, performing the evaluation comprises comparing distortion in at least two interferometer output signals. In one example, the distortion corresponds to a distortion in one or more geometric aspects encoded in the interferometer output signal. In a further example, the one or more geometric aspects includes at least one of a position, symmetry, a width of a peak, a centroid, a geometric second moment, a center of mass, an amplitude, a height to width ratio, and a geometric area under a curve. In a further example, performing the evaluation comprises comparing one or more geometric aspects encoded in at least two interferometer output signals.In another example, performing the evaluation comprises comparing one or more geometric aspects to one or more predetermined thresholds and/or baselines associated with the one or more geometric aspects. In one example, the SS-OCT method further includes establishing the one or more predetermined thresholds and/or baselines, and establishing is 13 WO 2024/158772 PCT/US2024/012552 performed based on at least one of: system and/or component requirements, one or more application requirements, one or more calibrations, one or more models, limitations of the hardware and/or software, one or more algorithms, and fundamental physics.In one example, performing the evaluation comprises comparing the one or more geometric aspects relative to at least one of: one or more geometric aspects encoded in at least one other of the interferometer output signals, and one or more predetermined thresholds and/or baselines associated with the one or more geometric aspects.In one example, performing the evaluation comprises applying a predetermined threshold to the distortion and determining whether the distortion exceeds the predetermined threshold.In one example, performing the evaluation comprises determining if a relative difference between two or more distortions exceeds a predetermined threshold.In one example, the SS-OCT method further includes generating a mathematical model based at least in part on one or more properties of an SS-OCT system and the evaluation of the distortion. In a further example, generating the mathematical model comprises generating an estimate of a magnitude and/or a direction of motion velocity of the sample based on the evaluation of the distortion.In one example, a material modification process implemented by the material processing beam on the sample is a welding process and the material processing beam creates a phase change region (PCR) at the processing region, and the SS-OCT method further includes using the evaluation to generate one or more corrections, and using the one or more corrections generated by the evaluation to calculate a measurement of one or more features which are in motion in the PCR. In a further example, the one or more features which are in motion in the PCR are in motion as a direct result of the material modification process.In one example, a material modification process implemented by the material processing beam on the sample is a welding process and the material processing beam creates a phase change region (PCR) at the processing region, and the SS-OCT method further includes using the evaluation to generate an estimate of a velocity of material being processed in the PCR.In one example, applying the one or more corrections to the at least one interferometer output signal includes discarding, weighting, promoting, or using the at least one interferometer output signal, or selecting the at least one interferometer output signal to discard at a later time.14 WO 2024/158772 PCT/US2024/012552 In one example, the interferometer is a first interferometer and the SS-OCT method further includes providing at least one additional interferometer and configuring the first interferometer and the at least one additional interferometer such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element, directing a first imaging optical signal configured with one of the at least two tuning rates dk/dt to the at least one reference arm and the at least one sample arm of the first interferometer, directing a second imaging optical signal configured with another of the at two tuning rates dk/dt to the at least one reference arm and the at least one sample arm of the at least one additional interferometer, and identifying the distortion based on the one or more interferometer output signals of the first interferometer and the at least one additional interferometer. IN a further example, the SS-OCT method further includes directing the first and second imaging optical signals to the processing region simultaneously.In one example, the time-varying difference in optical path lengths is caused by sample motion. In one example, a motion velocity of the sample is greater than 10 mm/s. In a further example, the motion velocity of the sample is greater than 100 mm/s. In a further example, the motion velocity of the sample is greater than 500 mm/s. In a further example, the motion velocity of the sample is greater than 1000 mm/s. In a further example, the motion velocity of the sample is greater than 10,000 mm/s.In one example, the SS-OCT method further includes deriving track data from the at least one interferometer output signal and applying the one or more corrections to the track data.In one example, the SS-OCT method further includes providing at least one k-clock module configured to generate a k-clock signal that indicates when a wavenumber k of the imaging optical signal substantially changes by one or more increments. In one example, a rate of change in the at least one wavenumber k of the imaging optical signal over time (tuning rate dk/dt) is non-uniform, and the SS-OCT method further includes configuring the at least one k-clock module to trigger the acquisition of the interferometer output signals at uniform increments in wavenumber k. In another example, the SS-OCT method further includes processing the at least one interferometer output signal based on interferometer output signals that are uniformly sampled in wavenumber. In one example, a rate of change in the at least one wavenumber k of the imaging optical signal over time (tuning rate dk/dt) is uniform, and the SS-OCT method further includes configuring the at least one k-clock WO 2024/158772 PCT/US2024/012552 module to trigger the acquisition of the interferometer output signals at uniform increments in wavenumber k.In one example, the provided k-clock module is configured with one or more optical elements present in at least one of the sample and reference arms of the interferometer.In one example, the k-clock signal is acquired simultaneously to the acquisition of the interferometer output signals, and the SS-OCT further includes at least one of: using the acquired k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k, using the acquired k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal, and using the acquired k-clock signal to define a discrete- Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.In one example, the k-clock signal is acquired in a manner which is time gated relative to the acquisition of the interferometer output signals, and the SS-OCT method further includes comprise at least one of: using the acquired k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k, using the acquired k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal, and using the acquired k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.In one example, the SS-OCT method further includes simulating a k-clock signal that indicates when the at least one wavenumber k of the imaging optical signal substantially changes by one or more increments based at least in part on one or more properties of an SS- OCT system and one or more properties of the tunable light source, and the SS-OCT method further includes at least one of: using the simulated k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k, using the simulated k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal, and using the simulated k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.In one example, the SS-OCT method further includes generating a mathematical model of k(t) and/or a tuning rate dk/dt of the imaging optical signal based at least in part on one or more properties of an SS-OCT system and one or more properties of the tunable light 16 WO 2024/158772 PCT/US2024/012552 source, and the SS-OCT method further includes at least one of: using the mathematical model to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k, using the mathematical model to compute at least one correction for one or more distortions in the interferometer output signal, and using the mathematical model to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.In one example, the SS-OCT method further includes controlling the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt that are associated with one or more interferometry signals, and generating a mathematical model of the at least two tuning rates based at least in part on one or more properties of the tunable light source and one or more properties of an SS-OCT system that includes the interferometer and the optical detector. In another example, the SS-OCT method further includes using the mathematical model to associate an estimate of at least one of a value of k and tuning rate dk/dt with data sampled from the interferometer output signal and/or the corrected interferometer output signal, using the associated measurement of the wavenumber k to estimate a value of k at sampled interferometer output signal values, and using the associated measurement of the wavenumber k to perform at least one of sampling, resampling, interpolating, and estimating interferometer output signals at uniform intervals in k. In another example, the SS-OCT method further includes using the mathematical model to compute at least one correction for one or more distortions in the interferometer output signal.In one example, the time-varying difference in optical path lengths is cause by sample motion relative to an axis of the imaging optical signal. In one example, the time-varying difference in optical path lengths is caused by a material modification process implemented by the material processing beam on the sample. In one example, the time-vary ing difference in optical path lengths is caused by intrinsic sample motion not caused by a material modification process that is implemented by the material processing beam on the sample.In one example, the SS-OCT method further includes controlling the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt. In a further example, the at least two tuning rates include at least one negative and at least one positive 17 WO 2024/158772 PCT/US2024/012552 dk/dt. In one example. the tunable light source is controlled such that the imaging optical signal includes a superposition of the at least two tuning rates dk/dt. In a further example, the superposition of the at least two tuning rates dk/dt includes at least one negative and at least one positive dk/dt.In one example, the tunable light source is a first tunable light source and the SS-OCT method further includes providing at least one other tunable light source. In one example, the interferometer is a first interferometer and providing the at least one other tunable light source further includes providing at least one additional interferometer, the first interferometer configured with the first tunable light source, the at least one additional interferometer configured with the at least one other tunable light source, and the first interferometer and the at least one additional interferometer configured such that they share at least one optical element. In another example, a rate of change in the at least one wavenumber k of the imaging optical signal in time is a tuning rate dk/dt and the SS-OCT method further includes controlling the first tunable light source such that a first imaging optical signal generated by the first tunable light source has a first tuning rate dk/dt, and controlling the at least one other tunable light source such that an imaging optical signal generated by the at least one other tunable light source has a second tuning rate dk/dt that is different than the first tuning rate dk/dt. In a further example, at least a portion of the first imaging optical signal and at least a portion of the imaging optical signal generated by the at least one other imaging optical signal are transmitted simultaneously. In a further example, the first and second tuning rates are associated with one or more interferometer output signals and the SS-OCT method further includes calculating one or more corrections, wherein calculating the one or more corrections comprises: identifying a distortion in at least one of the interferometer output signals that is associated with at least one of the first and second tuning rates, performing an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation. In another example, the first tuning rate dk/dt is a positive dk/dt and the second tuning rate dk/dt is a negative dk/dt.In one example, the SS-OCT method further includes providing a splitter to split the imaging optical signal into at least two arms, and an optical delay element configured such that an output of a first arm of the at least two arms is delayed in time relative to an output of a second arm of the at least two arms. In another example, the SS-OCT method further includes controlling the tunable light source such that a rate of change in the at least one 18 WO 2024/158772 PCT/US2024/012552 wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt. In a further example, the at least two tuning rates dk/dt includes a positive tuning rate dk/dt associated with either the first arm or the second arm, and a negative tuning rate dk/dt associated with the other of the first arm or the second arm. In one example, the interferometer is a first interferometer and the SS-OCT method further includes providing at least one additional interferometer. In one example, the first arm is configured to be directed to at least one of: different reference arms, different sample arms, partially overlapped reference arms, and partially overlapped sample arms of the first interferometer and the at least one additional interferometer. In another example, the first arm and the second arm are configured to be directed to at least one sample arm and at least one reference arm of the first interferometer and the at least one additional interferometer. In another example, the first interferometer and the at least one additional interferometer are configured such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element, and the first arm and the second arm of the imaging optical signal are configured to be directed to the first interferometer and the at least one additional interferometer simultaneously. In a further example, the first arm is configured to be directed to the first interferometer or the at least one additional interferometer, and the second arm is configured to be directed to the other of the first interferometer or the at least one additional interferometer. In another example, the at least two tuning rates of the first and second arms are associated with one or more interferometer output signals and the SS-OCT method further includes calculating the one or more corrections, wherein calculating the one or more corrections comprises: identifying a distortion in at least one of the one or more interferometer output signals that is associated with at least one of the positive and negative tuning rates, performing an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.In one example, the tunable light source is configured such that an optical frequency of the imaging optical signal varies at a rate in a range of 8 PHz/s - 2 ZHz/s inclusive.In one example, the SS-OCT method further includes generating an OCT image based on the at least one interferometer output signal and/or the at least one corrected interferometer output signal, and transmitting the generated OCT image to a display device. In another example, the SS-OCT method further includes generating OCT data from the processed interferometer output signal and/or the at least one corrected interferometer output signal, and transmitting the OCT data to an external device.19 WO 2024/158772 PCT/US2024/012552 In another example, the SS-OCT method further includes providing the tunable light source as a tunable vertical-cavity surface-emitting laser (VCSEL). In one example, the SS- OCT method further includes comprising providing an amplifier for amplifying the VCSEL. In one example, the amplifier is configured as a fiber amplifier.In one example, the SS-OCT method further includes directing the imaging optical signal with a directing element. In a further example, the imaging optical signal is directed to be within 50 nm of the material processing beam at the processing region.In one example, the SS-OCT method further includes providing a processing unit that is configured to process the at least one interferometer output signal, detect the distortion, apply the one or more corrections, and process the at least one corrected interferometer output signals.In one example, the SS-OCT method further includes providing a material processing source configured to generate the material processing beam. In another example, the SS- OCT method further includes controlling at least one processing parameter of a material modification process implemented by the material processing beam on the sample based on the at least one feature of the processing region.In one example, the SS-OCT method further includes using an optical detector to generate the at least one interferometer output signal.Still other aspects, embodiments, and advantages of these example aspects and embodiments, are discussed in detail below. Moreover, it is to be understood that both the foregoing information and the following detailed description are merely illustrative examples of various aspects and embodiments, and are intended to provide an ovendew or framework for understanding the nature and character of the claimed aspects and embodiments. Embodiments disclosed herein may be combined with other embodiments, and references to "an embodiment," "an example," "some embodiments," "some examples," "an alternate embodiment," "various embodiments," "one embodiment," "at least one embodiment," "this and other embodiments," "certain embodiments," or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one embodiment. The appearances of such terms herein are not necessarily all referring to the same embodiment.

BRIEF DESCRIPTION OF DRAWINGS WO 2024/158772 PCT/US2024/012552 Various aspects of at least one embodiment are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide an illustration and a further understanding of the various aspects and embodiments, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of any particular embodiment. The drawings, together with the remainder of the specification, serve to explain principles and operations of the described and claimed aspects and embodiments. In the figures, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:FIG. 1 is a schematic representation of one example of an SS-OCT system in accordance with aspects of the invention;FIG. 2 is a schematic representation of a balanced photodetector configuration for optical detection in accordance with aspects of the invention;FIG. 3 is a schematic representation of another example of an SS-OCT system showing alternate locations for the image beam amplification in accordance with aspects of the invention;FIG. 4 is a schematic representation of a beam delivery system in accordance with aspects of the invention;FIG. 5 A is a schematic representation of an SS-OCT system that incorporates auxiliary sensing capability in accordance with aspects of the invention;FIG. 5B is a schematic representation of a beam delivery system that incorporates auxiliary sensing capability in accordance with aspects of the invention;FIG. 6 is a block diagram representing logical modules of a multiplexed system in accordance with aspects of the invention;FIG. 7 A is a schematic representation of an example of an interferometer in accordance with aspects of the invention;FIG. 7B is a schematic representation of an example of an interferometer in accordance with aspects of the invention;FIG. 8 is a comparison of M-Mode data from an SD-OCT system (top graph) and an SS-OCT system (bottom graph) in accordance with aspects of the invention;FIG. 9A is a first example that shows both weld image signal data that is uncorrected and weld image signal data that has been corrected for distortion created by sample motion in accordance with aspects of the invention;21 WO 2024/158772 PCT/US2024/012552 FIG. 9B is a second example that shows both weld image signal data that is uncorrected and weld image signal data that has been corrected for distortion created by sample motion;FIGS. 10A and 10B show interferometry signal data in accordance with aspects of the invention;FIG. 11A shows uncorrected A-line depth versus amplitude data in accordance with aspects of the invention;FIG. 1 IB shows A-line depth versus amplitude data with motion compensation applied, in accordance with aspects of the invention;FIGS. 12A and 12B show M-mode OCT images that are uncorrected and corrected, respectively, in accordance with aspects of the invention;FIGS. 13A and 13B shows OCT image data from a welding process that is uncorrected and corrected, respectively, in accordance with aspects of the invention;FIG. 14A shows raw M-Mode image data from a welding process in accordance with aspects of the invention;FIG. 14B shows motion artifact corrected track image data corresponding to the raw image data from FIG. 14A;FIGS. 14C and 14D show images of cross-sections of the weld performed in the welding process of FIGS. 14A and 14B;FIG. 15 is a block diagram of an exemplary computer control system for performing control and processing in the SS-OCT system in accordance with aspects of the invention;FIGS. 16A, 16B, and 16C, show M-Mode OCT images captured during weld processes on mild steel, aluminum, and copper substrates respectively, in accordance with aspects of the invention;FIG 17A shows an exemplary M-Mode OCT image captured on an SD-OCT system, during a weld process;FIG 17B shows an exemplary M-Mode OCT image captured on an SS-OCT system, which was captured concurrently with the SD-OCT capture of Fig 17A during the same weld process;FIG 17C shows weld image signal data derived from the M-Mode OCT image data of Fig 17 A;FIG 17D shows weld image signal data derived from the M-Mode data of Fig 17B; WO 2024/158772 PCT/US2024/012552 FIG. 18A is a schematic representation of one example of an SS-OCT system showing a double interferometer configuration having interferometers that overlap at a sample arm and have separate light sources in accordance with aspects of the invention;FIG. 18B is a schematic representation of one example of an SS-OCT system showing a double interferometer configuration having interferometers that overlap at a sample arm and features a buffered light source in accordance with aspects of the invention;FIG. 18C is a schematic representation of another example of an SS-OCT system having a double interferometer configuration having interferometers that overlap at a sample arm and features a buffered light source in accordance with aspects of the invention;FIG. 18D is a schematic representation of another example of an SS-OCT system having a double interferometer configuration with separate light sources and displays a variant of the interferometer topology shown in FIG. 18A, in accordance with aspects of the invention;FIG. 18E is a schematic representation of another example of an SS-OCT system having a double interferometer configuration that features a buffered light source and interferometers that overlap at a sample arms in accordance with aspects of the invention;FIG. 19 is a schematic representation of one example of an SS-OCT system showing an interferometer configuration that includes a buffered light source and that produces multiple swept source light signals in accordance with aspects of the invention;FIG. 20A is a graph showing one example of the degradation of quality over time in a process in accordance with aspects of the invention; andFIG. 20B is a graph showing an example of quality degradation in a process over time that is corrected via an AI/ME monitoring technique in accordance with aspects of the invention.

DETAILEDOverview SummanDisclosed herein is an enhanced SS-OCT apparatus and methods for the monitoring of manufacturing processes and especially the monitoring and control of the application of laser and other energy beams for processing materials in industrial material modification processes. Non-limiting examples of material modification processes include welding, cutting, drilling, ablation, brazing, surface texturing, annealing, and additive manufacturing. In accordance with one or more embodiments, certain aspects of the disclosed apparatus 23 WO 2024/158772 PCT/US2024/012552 comprise light sources, amplifiers (especially amplified rapidly tunable light sources with long instantaneous coherence lengths), interferometers, k-clocks, scanning optics, the integration of interferometers into energy beam delivery systems (i.e., beam delivery heads), detection electronics, signal processing electronics, control electronics, and software and feedback loops (e.g., electronic and/or software-enabled feedback loops) by which some aspects of the system control others. These aspects are integrated to perform measurement (and in some embodiments, in real-time) of manufacturing processes including but not limited to inline coherent imaging, which is one of the few known ways of directly measuring laser weld penetration depth in real time and perhaps the only known way that is broadly applicable to serial production in many markets. In accordance with at least one embodiment, the SS-OCT system is based on a rapidly tunable light source that offers significant advantages in speed, sensitivity, flexibility and instantaneous imaging range over other conventional OCT systems. In some embodiments, the tunable light source is a high- pow er light source. Furthermore, implementing such a light source in commercial practice and processing its signals requires special attention to safety systems and dynamic range management. In accordance with certain embodiments, the disclosed SS-OCT system is configured to determine sample position information and/or sample feature information, including geometric information. The sample may be associated with a material modification process, and the feature information may correspond to a position or location in and/or near a phase change region (PCR) at a time point before, during and/or after the material modification process. In accordance with certain embodiments, the disclosed SS-OCT system is configured to determine correct position information and direct measurement of sample motion velocity (e.g., in the axis of the imaging beam) through the evaluation and compensation of motion artifacts caused by a modulation of the interference fringes. In one embodiment, the motion of the sample is motion inherent to the material modification process.In accordance with various aspects, the average return signal intensity seen throughout a given weld is higher on the disclosed SS-OCT system than on a SD-OCT system. Some of the differences in signal level can be attributed to the higher imaging power which is available from the disclosed SS-OCT system. At least some of the differences in signal level between the tw o system configurations may be attributed to the higher imaging sensitivity' that can be achieved with the disclosed SS-OCT system as compared to a state-of- the-art SD-OCT system. However, another discrepancy arises from the manifestation of the 24 WO 2024/158772 PCT/US2024/012552 motion artifact in each of these different approaches to OCT. In the SD-OCT approach, the motion artifact presents as fringe wash-out, which reduces the useful signal level and eliminates the ability to acquire and decode this data. In the disclosed SS-OCT approach, the motion artifact presents as distortion of the interferogram data, resulting in a bright, but possibly distorted, signal. An example of distorted A-lines generated based on distorted interferogram output data is shown in FIG. 11A. FIG. 1 IB shows corrected A-lines generated based on the same interferometer output data, after one or more corrections to the interferometer output data have been applied based on the distortion. These figures are discussed in further detail below. This artifact often presents during the imaging of weld keyholes, since these structures are known to contain metal in rapid motion. Disclosed herein is the implementation of one or more algorithms which enable the correction of this motion artifact.

Overall System DescriptionOne non-limiting example of an SS-OCT system 100 is shown in FIG. 1 in accordance with at least one embodiment. System 100 comprises an imaging light source (which may be considered separately or as a component of the interferometer as described in further detail below), which in this example is a tunable light source 105, which provides coherent narrowband light with a wavelength that varies over time, such as an electronically- tunable swept source MEMS VCSEL. One or more optical amplifiers 106 may be used to amplify the tunable light source 105. Non-limiting examples of a suitable amplifier include Ytterbium fiber amplifiers available from IPG Photonics, Marlborough, MA, USA. The light emitted from the tunable light source and/or the amplified light from the amplifier based on the tunable light source as a seed source may be referred to herein as the swept optical signal, the imaging light, the imaging optical signal, the imaging beam, the ICI beam, and/or the interferometer light, as appropriate based on context.System 100 also comprises a controller 150 (also referred to herein as a control module, processing module, or processing unit) that includes the requisite hardware and software needed to control and communicate with one or more components of system 100. For example, processing unit 150 includes the requisite control electronics for the tunable light source 105 and amplifier 106, and/or other system components. In some embodiments, a light source control module 109 may be included in controller 150 that controls the tunable light source 105 and amplifier 106.25 WO 2024/158772 PCT/US2024/012552 System 100 also comprises an interferometer 120, which in this example includes the tunable light source 105 that generates a swept optical signal, the amplifier 106 that amplifies the swept optical signal power, a splitting element 126 that splits the imaging light (imaging optical signal) into two or more paths within the system, an adjustable delay line to serve as a reference arm 122, a sample arm 124 configured to direct the swept optical signal to a processing region (i.e., on workpiece or sample 102) or a region otherwise related to the material modification process, and a combining element 128 that combines the imaging light after it has traversed its paths. The interferometer 120 is configured to direct the swept optical signal to the reference arm 122 and the sample arm 124 and combine optical signals returning from the reference arm and the sample arm to generate a combined optical signal. In some embodiments, multiple (two or more) sample arms and/or reference arms may be implemented. Certain embodiments with these configurations are described in further detail below. The interferometer embodiment shown in system 100 of FIG. 1 is a Mach-Zender interferometer (MZI) topology, which exhibits improved photon economy in comparison to other interferometer configurations, and the ability to implement balanced detection. The Mach-Zender interferometer also includes fiber-optic circulators 121. 123 and polarization controllers 127 that are also included in the embodiment shown. However, it is to be appreciated that other interferometer topologies, such as Michelson interferometers, are also within the scope of this disclosure.System 100 also comprises a material processing beam source 110 and a respective beam delivery system 115 (which may also be referred to as a beam delivery module, and may be housed in a laser head) whereby the imaging light is at least partially combined with the material processing beam using a dichroic 117, to be subsequently applied to a workpiece 102 (also referred to herein as a "sample"). The workpiece 102 or sample may be any object or surface undergoing a material modification process (e.g., welding) or otherwise being treated by the material processing beam 112 (also referred to herein as simply a processing beam or process beam). The material processing beam 112 interacts with material of the sample 102 at a processing region 103 on the sample 102. For instance, imaging can be performed in some embodiments on a sample that is about to undergo or has just undergone a material modification process. Contained within the beam delivery system 115, there may be beam directing elements, such as galvanometers, which deflect or otherwise steer (e.g., scanner 116, 118) the imaging beam 108, the material processing beam 112, or both. In some embodiments, the material processing beam 112 creates a phase change region (PCR) at the 26 WO 2024/158772 PCT/US2024/012552 processing region 103. In one embodiment, at least one directing element directs the imaging beam at one or more selected positions in and/or near the PCR. System 100 also comprises an optical detector 130 (also referred to as simply a detector) or multiple detectors which receive imaging light, such as the combined optical signal from the reference and sample arms of the interferometer 120. The detector 130 is configured to generate at least one interferometer output signal from the detected combined optical signal. One non-limiting example of a detector 130 is a balanced photodetector (BPD), an example of which is shown schematically in FIG. 2, which in this embodiment enhances system performance by reducing common mode noise. According to one embodiment, detector 130 is configured as a BPD with an integral transimpedance amplifier.For SS-OCT. a laser source (for imaging) with an instantaneously narrowband wavelength that can be tuned at high speeds is often required. In accordance with at least one embodiment, the tunable light source 105 generates an imaging optical signal that has at least one wavenumber k that is variable in time and a sweep rate in a range from 1 kilohertz (kHz) to 20 megahertz (MHz) inclusive. The term sweep rate as used herein refers to a rate of repetition in the time-varying spectral output of the imaging optical signal. It is the inverse of the sweep interval/sweep period. This could also be considered as the inverse of the amount of time which it takes to acquire one A-line. In accordance with certain aspects, the imaging optical signal substantially has at least one wavenumber k that is variable in time. The following cases are examples of imaging optical signals which are encompassed within this definition:A) An imaging optical signal, with an instantaneous coherence length of 1 mm or longer, containing at least one spectral feature and/or peak, the feature and/or peak containing a plurality of wavenumbers, each feature and/or peak having a characteristic wavenumber k (e.g. corresponding to a center, a centroid, a highest intensity point in the instantaneous spectrum, the intensity weighted centroid of the instantaneous spectrum etc.), the characteristic wavenumber k of the feature and/or being variable in time; andB) An imaging optical signal as outlined in A, which additionally contains other spectral features (e.g. secondary peaks, amplified spontaneous emission), which may or may not partially or completely overlap with the peak at any time during the operation of the imaging optical signal.

WO 2024/158772 PCT/US2024/012552 The term tuning rate as used herein refers to the rate of change in the at least one wavenumber k of the imaging optical signal in time. The term tuning rate may interchangeably be referred to as ‘dk/dt‘ or ‘tuning rate dk/dt‘.The imaging optical signal may comprise any other optical signal which would be suitable for SS-OCT as recognized by those of ordinary7 skill in the art.For a linear tuning profde, different beat frequencies in the combined optical signal (sometimes referred to or otherwise known as the "Interferogram") correspond to different delays or reflections from different depths in the sample. In practice, most lasers do not exhibit an ideal linear relationship between wavenumber k and time. For at least this reason, system 100 may also comprise at least one k-clock module 145 (also referred to herein as a k- clock). In some embodiments, system 100 includes multiple K-clock modules 145. K-clock module 145 provides a k-clock output whose frequency is proportional to the wavelength being output by light source 105. If this clock is used as a sampling clock, the analog to digital output is sampled in a substantially linear way in k-space. In one embodiment, the k- clock module is configured as an optical interferometer designed to produce a reference beat frequency which corresponds to a known delay based on the tuning rate of the tunable light source 105 and is implemented through a low-power tap (e.g., about 1%, and in some embodiments less) of the tunable light source 105. The k-Clock, if included, requires its own detector 147.System 100 also comprises a digitizer 135 that captures the detector signals. In certain embodiments, the digitizer is configured to digitize at least one interferometer output signal and generates a corresponding digital signal. Processing unit 150 may incorporate a signal processor that receives the digitized signals from the digitizer 135 and computes data and/or other relevant information derived from these signals. In general, modules associated with processing unit 150 include (but are not limited to) data processing modules, communication modules, safety modules, and feedback and control modules. As used herein, the term "module" refers to logical groupings of design functions including but not limited to optical, electronic, simulated, analytical, and/or computational embodiments of such functions. A "module" does not necessarily imply that modules are nominally physically separable from one another. Discussed in further detail below are embodiment options for multiplexing one or more components, but it is to be appreciated that according to certain embodiments modules may be shared with other modules and are thus not always employed in a 1:1 ratio.28 WO 2024/158772 PCT/US2024/012552 In accordance with at least one embodiment, tunable light source 105 is comprised of a micro-electromechanical system (MEMS) tunable vertical cavity surface emitting laser (VCSEL) that is amplified by a rare earth doped optical fiber amplifier 106 (also referred to herein as a "fiber amplifier"). In one embodiment, the fiber amplifier 106 has a peak gain at a wavelength between 1010 and 1050 nm. In another embodiment, the fiber amplifier 1has a peak gain at a wavelength between 1050 and 1090 nm. Common dopants include Erbium and Ytterbium. According to certain embodiments, the fiber amplifier 106 has one, two, or three amplification stages. In some embodiments, the fiber amplifier architecture may include optical isolation in-between the amplifier stages where applicable, in the form of compact isolators and/or semi-compact isolators and/or bulk isolators. In accordance with at least one embodiment, the output power of the fiber amplifier is at least 30 milliwatts (mW). In some embodiments, the output power is at least 20 mW, at least 50 mW, at least 100 mW, at least 500 mW, at least 1 watt (W), and/or at least 5 W. These higher powers are considered to be novel because most coherent imaging and OCT systems are conventionally designed for imaging living tissue which would be destroyed by such high power levels. Laser material processing is one of the very few application spaces where the management of high energy laser hazards is commercially routine. A fiber amplifier is an attractive option because, in addition to its high power scalability, it has high reliability and redundancy. In addition, with sufficient economies of scale, a fiber amplifier may be less costly to manufacture than a semiconductor optical amplifier (SOA) of equivalent output and/or reliability. As used herein with regard to amplifiers, reliability' refers to the stability׳ of the power output of the amplifier over a long period of time. Fiber amplifiers can be made very reliable when combined with redundant pump diodes that can be held in reserve and brought online if the output of other pump diodes begin to drop or otherwise fail. In certain embodiments, a safety module (not explicitly featured in FIG. 1) controls the energy ultimately being provided to one or more amplifier stages through redundant means so that the device complies with IEC 60825-1.In accordance with certain aspects, the higher emission powers offered by implementation of fiber amplifier 106 functions at least in part to increase the sensitivity of the system. It is to be appreciated that other factors, such as improved photon economy, balanced detection, detector resolution, etc. also contribute to system sensitivity. As used herein, sensitivity' refers to the weakest reflection from the sample or workpiece 102 that is resolvable above the noise floor of the system. In accordance with at least one embodiment. 29 WO 2024/158772 PCT/US2024/012552 the SS-OCT systems disclosed herein have a sensitivity of at least 105 dB. This is several orders of magnitude greater than conventional OCT systems used in material processing. According to at least one embodiment, the disclosed SS-OCT systems are capable of providing weld image depths of at least 21 mm inclusive. In some embodiments, the disclosed SS-OCT system is capable of providing a weld image depth of at least 17 mm, of at least 20 mm inclusive, at least 30 mm inclusive, at least 40 mm inclusive, and/or at least mm inclusive. All of these depths are greater than those provided by conventional coherent imaging systems used in material processing applications.In a preferred embodiment, the interferometer 120 of system 100 includes the imaging light source 105 and corresponding fiber amplifier 106, and is configured as a Mach-Zehnder interferometer with a 90:10 splitting ratio between the sample arm 124 and the reference arm 122 respectively, but it is to be appreciated that other splitting ratios as required to enable greater sensitivity are also within the scope of this disclosure. The reference arm 122 may be configured with an adjustable delay line. The beam delivery7 system 115 may be configured as or otherwise implemented into a laser welding head, such as the FLW-D50 welding head available from IPG Photonics. Oxford, MA. USA. Beam delivery system 115 may include a beam steering apparatus, such as galvanometer scanner 116 for the imaging beam. In some embodiments, more than one galvanometer may be used.According to one embodiment, material processing beam source 110 is configured as a Yb:fiber laser. A non-limiting example of such a fiber laser includes the IPG YLS- 2000/4000-SM-AMB and/or other YLS-series fiber lasers available from IPG Photonics. The material processing beam source 110 produces a material processing beam 112 that interacts with material of the sample 102 at a processing region on the sample 102. The material modification processes discussed herein are implemented by the material processing beam 112.The k-clock module 145 is implemented in one embodiment by tapping (at beam splitter 104) the imaging light source 105 after the amplifier stage(s) to illuminate an additional MZI with slightly mismatched optical path lengths which is coupled to a second optical detector 147, which in one embodiment is configured as a balanced photodetector. As used herein, k refers to the optical wavenumber, an inverse expression of optical wavelength. The k-clock produces an interference signal that significantly aids accurate processing of the primary7 interferometry signal in the event that the tuning function of the light source is not linear in time (t). i.e. k(t) is not linearly proportional to t. One application of the k-clock 30 WO 2024/158772 PCT/US2024/012552 signal is to use it to discipline the sampling rate of the digitizer 135 of the processing module 150 such that signal samples are collected in uniform spacing in wavenumber (k).The digitizer 135 (also referred to as an analog-to-digital conversion module) receives the interferometer output signal from the optical detector 130 and generates a corresponding digital signal. The digitizer 135 in some embodiments also receives the signal from the k- clock detector 147 and digitizes it and/or uses it to discipline the sampling rate. The processing module 150 then processes the at least one interferometer output signal to determine at least one feature of the processing region, and detects a distortion in the at least one interferometer output signal. In accordance with various embodiments, the distortion is created by the motion of the sample, but more broadly the distortion is created by a time- varying difference in optical path lengths between the at least one sample arm and the at least one reference arm. In accordance with various aspects, the time-varying difference in optical path lengths is caused by sample motion. In accordance with certain aspects, sample motion refers to a time-varying change in the optical path length of the sample arm, i.e., the distortion is created by a time-varying optical path length of the sample arm and may not be caused by intrinsic motion of the sample itself, but the optical path length may also be changed by other external factors that change, e g., the environment. The time-varying optical path length of the sample arm may also be caused by intrinsic motion of the sample. The time-varying optical path length of the sample arm may be caused by a combination of intrinsic motion and environmental factors. Responsive to detection of the distortion, processing module 150 applies one or more corrections to the interferometer output signal to produce a corresponding corrected interferometer output signal, and processes the at least one corrected interferometer output signal to determine the at least one feature of the processing region. For example, in some embodiments, the processing module 150 receives the digital data, optionally performs spectral shaping and background subtraction operations, and calculates a frequency analysis and noise floor equalization of the resulting signal to yield a function of workpiece reflectivity vs. optical path length know n to those with skill in the art as an axial line or "A-line." Other operations may also be added in this processing chain to compensate for optical dispersion or other distortions present in the interferogram. In some embodiments, the system is configured to automatically compensate for optical dispersion by first training it on a known flat surface. In some embodiments, additional operations may be added in this processing chain to compensate for image artifacts introduced by rapid motion of the imaging target. In some embodiments, additional operations may be added in this31 WO 2024/158772 PCT/US2024/012552 processing chain to digitally re-sample the data digitized by digitizer 135 to be substantially linear in k, in cases where digitizer 135 is not set up to digitize signals in a manner that is substantially linear in k. Such operations may employ digitized captures of the k-clock signal, models of the optical source and/or system including mathematical models, or other information to aid in such resampling.Beam delivery system 115 of system 100 comprises at least one directing element such as scanner 116 configured to adjust the position of the imaging beam 108 relative to the processing beam 112. In accordance with one embodiment, the at least one directing element directs the swept optical signal (imaging beam 108). In another embodiment, the at least one directing element is configured such that the imaging optical signal (focal spot) is within nm or less of the (focal spot) of the material processing beam 112 at the processing region. According to some embodiments, the ability to adjust the position of the imaging beam relative to the processing beam enables the acquisition of subsequent A-lines at various locations in and about a phase change region (PCR). During processes such as laser welding (one example of a material modification process), a PCR is created where the material localized to the bonding region changes dynamically from solid to a liquid and/or a gas state and back to a solid again at the completion of the weld. By acquiring subsequent A-lines in or about a PCR that is created by the material processing beam 112, a variety7 of measurements of the processing region/workpiece geometry7 (i.e., features, including geometrical features) can be made in order to guide, influence and/or monitor the quality of the process and the resulting workpiece.

Various System Components and FeaturesImaging Light SourceA number of possible configurations exist for the imaging light source 105 of the SS- OCT systems disclosed herein. The general construction of the light source contains at least a seed source that produces the wavelength swept signal (also referred to herein as the imaging optical signal or swept optical signal), which can be referred to as a swept source, which may be based on some input (referred to as the driving signal), and may contain any number of amplifiers, optical buffers, feedback mechanisms, and other elements. Certain requirements that the light source must satisfy include the availability of wavelength sweeping, sufficiently narrow instantaneous linewidth, sufficiently broadband sweeping range, sufficiently rapid sweeping rate, sufficient phase stability7, and power requirements, as 32 WO 2024/158772 PCT/US2024/012552 well as wavelength requirements, and various other requirements per the parameters of the system. Overall, the precise selection of the light source is highly dependent on the requirements of the application. Non-limiting examples of an appropriate seed swept source include solid-state MEMS (Micro-Electro-Mechanical System) swept-source VCSELs (Vertical Cavity Surface Emitting Lasers) among other possible configurations. One non- limiting example of a suitable MEMS VCSEL light source includes the SL 10280 available from Thorlabs, Inc., Newton, NJ, USA. According to at least one embodiment, the tunable laser light source 105 is a tunable VCSEL. The selection and/or design of the optical amplifier 106 for embodiments of the invention which incorporate an amplifier must take into consideration the properties of the seed source, including seed/output power, wavelength swept range, instantaneous linewidth, response time, safety requirements, and other requirements. Non-limiting examples of appropriate amplifiers 106 include a doped fiber amplifier, such as diode-pumped Erbium (doped) or Ytterbium (doped) fiber amplifiers.As mentioned previously, according to at least one embodiment, the tunable laser light source 105 is a high power light source. In accordance with various embodiments, the tunable laser light source 105 has a power of at least 1 microwatt (uW), at least 30 pW, at least 100 pW, at least 500 pW, at least 1 mW, at least 5 mW, at least 10 mW, at least 20 mW, at least 50 mW, at least 100 mW, at least 500 mW, and/or at least 1W. In one embodiment, the tunable laser light source 105 has a power in a range from 30 pW to 500 pW inclusive.

Optical AmplifierAs mentioned above, some embodiments of the invention include an amplifier 106 to increase the power available to levels greater than those possible when using the seed swept source 105 on its own. In some embodiments the amplifier for amplifying the VCSEL is configured as a fiber amplifier (as used in the examples herein), although it is to be appreciated that other types of amplifiers are also within the scope of this disclosure, such as a semiconductor optical amplifier (SOA) or solid-state amplifiers. Some embodiments utilize constant gain, while other embodiments use variable gain, for example to implement feedback control of the output power of the amplifier 106. More advanced embodiments may incorporate manual or software-based feedback control incorporating (but not limited to) the detectors and the amplifier, for example to prevent detector saturation, effectively increasing system dynamic range.

WO 2024/158772 PCT/US2024/012552 In preferred embodiments of the system, a doped fiber amplifier is used, examples of such amplifiers include Erbium and Ytterbium-doped fiber amplifiers. In some embodiments of the system a solid-state amplifier may be used. In other embodiments of the system an SOA may be used. The selection and/or design of an appropriate amplifier may be informed by the requirements of the application, including for example the desired wavelength, time dynamics, and gain requirements.Certain embodiments may use custom population inversion or time-dynamic pumping to optimize the gain ratio of the amplifier at each point in the swept-source sweep. In embodiments where the seed swept-source is known to vary in output power over time, power level feedback may be used to compensate for long-term source degradation. In embodiments where the emission power of the seed source varies predictably and regularly based on instantaneous emission wavelength, the amplifier constmction can be optimized using parameters including length and population inversion, to compensate partially or completely for the power variability. Amplifier pumping can also be implemented in a time- dynamic manner which is synchronized with the tuning signal in order to compensate for output power variability across the swept spectrum.In some embodiments of the system, feedback control (e.g., via processing unit 150) can be implemented to maximize amplifier power output stability7. In some embodiments, feedback control can also be implemented in the amplifier system to increase the effective dynamic range of the system by adjusting the amplifier gain, and thereby the imaging power, based on return signals such as from the primary detector 130 or other sensors throughout the system, for example to increase imaging power when imaging a low reflectivity surface, or decrease imaging power if a detector is saturating. Other embodiments of the system may incorporate variable gain without feedback, for example by designing a variable gain signal for the amplifier drive based on imaging requirements designed for a given process. Feedback control may also be implemented to compensate for decreased optical transmission or performance e.g. on account of degradation with system age.Some embodiments of the system may incorporate more than one amplifier 106. Amplifiers may be deployed in series to increase the overall gain available. In accordance with certain embodiments, amplifiers may also be placed at various positions within the interferometer itself where appropriate based on specific design requirements. One non- limiting example of an SS-OCT system with alternate amplifier placement is shown in system 400 of FIG. 3. One or more of amplifiers 406 as shown in FIG. 3 may be34 WO 2024/158772 PCT/US2024/012552 implemented either in addition to or without an amplifier (not shown in FIG. 3) directly following the seed source 405. Examples of amplifier placement include placing the amplifier into the sample arm of the system immediately after it is split from the reference arm 422 to deliver increased power to the sample (e.g., amplifier 406a), or placement of the amplifier at the last phases of the sample arm to increase amplitude of the return signal for imaging (e.g., 406b). Some embodiments of the system may incorporate more than one amplifier. For example, multiple amplifiers may be placed at different locations within the interferometer itself.In system embodiments with an amplifier, the electrical configuration can incorporate interlock features to allow the system to switch between different laser safety classes, e.g., Class 2 vs Class 3b, for different processes, such as manual alignment vs. cell operation.

Delay LinesAll embodiments incorporate one or more delay lines within the interferometer topology to match path lengths between the sample arm 124 and the reference arm 122. In some embodiments, delay lines are designed to enable the adjustment of the optical path length, for example by incorporating precision mechanical components and motors to move mirrors or other optical components. In certain embodiments, the delay line is adjustable manually, while in certain embodiments automatic adjustment using e.g. electronically controlled devices may be implemented. In some embodiments, automatic delay line motion may be used to effectively extend the imaging range by adjusting the delay line responsive to different optical path lengths present in the sample arm of the system. Such delay line adjustments may be implemented based on pre-programmed algorithms that account for expected variability in sample height within the field of view. Alternatively, such delay line adjustments may be implemented responsive to system conditions, e.g. via feedback control.Certain embodiments incorporate an adjustable delay line on the reference arm of the system. This topology7 enables adjustment of the depth field-of-view of the OCT system, thereby allowing the imaging target of interest to be positioned within the field of view without need to change the mechanical setup of the target, greatly simplifying the setup and increasing flexibility.Some embodiments of the system will incorporate an adjustable delay line in the k- clock interferometer 145. The adjustment of path length in the k-clock in turn enables adjustment of the k-clock frequency, allowing k-clock optimization for a single system at a 35 WO 2024/158772 PCT/US2024/012552 number of different seed source sweeping rates. For example, if a seed source sweeping rate is slowed down, the length of the k-clock path length separation can be increased, resulting in a larger available imaging depth and more available points for acquisition within a sweep, while maintaining appropriate frequency characteristics for the sampling and digitization system (due to the slower sweeping of the seed source and therefore the slower dk/dt). Alternatively, techniques which generate and/or switch between multiple different optical paths (e.g.. shutters, mechanical devices) may be used to achieve a similar effect by making a number of discrete paths of different lengths available to the k-clock.

Feedback ControlIn some embodiments, active feedback control (per the functionality of processing unit 150) is implemented within and between a variety of system components and/or modules, including but not limited to the optical swept source 105, the amplifier 106, the delay lines (as in reference arm 122), and the optical detector 130. In some embodiments, feedback control or feedback loops may comprise the implementation of electronic and/or software-enabled feedback loops.According to at least one embodiment, various feedback controls of the optical amplifier 106 are implemented. Within the amplifier module, feedback control can be implemented to maintain stable power output throughout changing operating conditions. Amplifier module control may also receive inputs from the system controller 150, for example to allow for the automatic increase of beam power to compensate for less-reflective imaging target materials, enabling the OCT system to achieve higher sensitivity. Output power control in all embodiments will be dependent on the required interlocks and other safety measures that are compliant with relevant laser safety product standards.To take advantage of optimization for a variety of situations, feedback control may also be applied to system components including but not limited to the k-clock arm length, the reference arm length, the source sweep rate, and the source sweep span.According to further embodiments (and as discussed elsewhere in this disclosure), feedback control is implemented to control the material processing laser source 110 and/or the beam delivery system 115 using information acquired from the SS-OCT system 1(and/or other components, such as auxiliary measurement system 160) and processed by controller 150. For example, controller 150 may control one or more processing parameters (non-limiting examples given below) of the beam delivery system 115 and/or the material 36 WO 2024/158772 PCT/US2024/012552 processing beam source 110 using processed output obtained from interferometer 120 (and/or associated components such as the optical detector 130. digitizer 135, etc.). Processed output may include, for example, at least one feature of the phase change region.

DetectionSS-OCT and time-domain imaging approaches typically do not use detectors that can substantially discriminate between different frequencies of light. This means that they are more vulnerable to being overloaded by the incoherent emissions of the process and/or by the high power modification energy. The addition of blocking filters at various locations in the interferometer, such as in the material processing beam delivery head (e.g. dichroic optics), inside the fiber line (e.g., fiber Bragg gratings, etc.), or at the detector, to isolate the imaging light from the unwanted signals may be employed for the material processing applications described herein. Balanced detection is another method of rejecting these unwanted signals, which may be applied in addition to or instead of blocking filters.In accordance with at least one embodiment, optical detector 130 is configured as a balanced photodetector (BPD). A BPD circuit is employed to convert differential interferometry signals from the optical domain to the electronic domain for both the OCT data and the k-clock data. The detection of differential signals using a BPD can eliminate common-mode noise and DC elements from the interferogram data collected in an OCT capture, and can improve the amplitude of the acquired signal relative to non-balanced detection methods. A schematic example of an optical detector 130 configured as a balanced photodetection apparatus is shown in FIG. 2.In accordance with one or more embodiments, analog electronic gain of the BPD signal is adjustable to and/or selectable to enable ideal signal levels for digitization. In some embodiments, feedback control is implemented to automatically optimize BPD gain levels. In other embodiments, the gain control is implemented by the user, or some combination of user control and feedback control.In certain embodiments an electronic amplifier is included in the BPD circuit with characteristics of noise reduction, appropriate bandwidth, and rejection of common mode and DC signals. Analog bandwidth filtering for the specific purpose of anti-aliasing is also considered in the design of the detection module of one or more embodiments. Additional amplifier optimizations can be introduced to other system embodiments as needed. The WO 2024/158772 PCT/US2024/012552 amplifier topology is designed using circuit techniques known to those of ordinary skill in the art.In accordance with other embodiments, alternative optical signal detection methods may be used, including photodiodes and other detector techniques known to those of ordinary skill in the art. These embodiments may also contain variable gain, either feedback controlled or not under feedback control, and amplifier topologies optimized for specific applications. Embodiments employing a variety of methods of photodetection, e.g., different detection methods in the k-clock and OCT signal portions of the system, are also possible.In some embodiments, different portions of the output of the interferometer are split tow ards multiple detectors. In this w ay, as one detection channel becomes saturated if the reflected signal becomes too bright, another detector channel may still read the signal. In this w ay, the dynamic range of the overall system could be substantially increased. In certain embodiments, additional attenuation, in the optical and/or the electronic domain, may be included in different levels for different detectors to enhance this effect and provide even greater dynamic range.

K-Clocking MethodsSwept-Source OCT (SS-OCT) systems may use a signal that indicates when the w avenumber k of the imaging optical signal or signal spectrum substantially changes by one or more increments, as known to those of ordinary skill in the art as a k-clock. Some embodiments of the invention may use a sampling clock which is sampled in uniform intervals of time. Some embodiments of the invention may use a sampling clock w hich is uniform in wavenumber k, which may be based on a k-clock signal. The relationship between time and wavenumber k may or may not be linear depending on the imaging source tuning method and other system considerations.In accordance with at least one embodiment, the imaging source produces a sw ept optical signal for w hich the rate of change of wavenumber k over time (referred to as the tuning rate dk/dt) is variable. In some embodiments, the tuning rate dk/dt can be equivalently expressed in dimensions of a rate of change of optical frequency, and is in a range of 1 PHz/s - 2 ZHz/s (inclusive), and in some embodiments is in a range of 8 PHz/s - 2 ZHz/s (inclusive). Most practical implementations of SS-OCT systems require resampling or k- clock control of the interferometer output signal sampling to compensate for variations, including instability of sweep phase, variability in dk/dt throughout the sweep, and/or non- 38 WO 2024/158772 PCT/US2024/012552 linearity7 in the tuning of the swept source (such as a non-linear relationship between wavenumber k and time t). The use of a signal which provides some reference for the relative or absolute wavenumber of the imaging source light over time, referred to herein as a "k-clock signal," to assist in the sampling, signal processing (including interpolation and re- sampling), and/or analysis of the OCT interferometer output signal is referred to herein as "K-clocking." Variations in dk/dt may be caused by non-symmetric behavior of the light source due to intentional driving, fundamental properties of the light source, or unavoidable consequences of the light sources’ manufacture, for example.According to some embodiments, at least one of the interferometer sample and reference arms is configured with one or more optical elements that are used to generate the k-clock signal. In some embodiments, these optical elements are already present, and in other embodiments, these one or more optical elements are added and used to generate the k- clock signal.In accordance with at least one embodiment, the SS-OCT system requires that a Fourier transform be applied to interferometer data to produce an OCT image. To generate an OCT image which is appropriately scaled in meaningful units of physical space, the Fourier transform must be performed either on a signal which is sampled uniformly in k, or otherwise employ a method which corrects for know n non-uniformity in sampling in k-space (e.g. Homodyne matrix DFT). In such embodiments for which dk/dt is variable, the incorporation of k-clocking (including but not limited to optical methods, electronic methods, simulated methods) is required to appropriately process or sample the interferometer output signal for the Fourier transform and/or appropriately construct a Fourier transform for the interferometer output signal.The k-clock may in some embodiments be generated by an optical k-clock module (e.g., k-clock module 145) that generates a signal indicating every time the swept source 1tunes through a predetermined k (inverse of frequency) increment of the scan band. The k- clock may in some embodiments be generated by an electronic k-clock module which estimates the time-domain behavior of the w avenumber k of the swept optical source output based on the tuning signal applied to the swept source. The k-clock may also in some embodiments be simulated based on a model of the system. A combination of the described approaches may be used in some embodiments. The k-clock is used to correct for non- linearity7 in the time domain of the frequency sweeping of the swept source 105.

WO 2024/158772 PCT/US2024/012552 In one embodiment, the k-clock module 145 is configured to trigger sampling of the interferometer output signals by the optical detector 130 at uniform intervals in wavenumber k. The rate of change in wavenumber k may or may not be uniform in time. This embodiment represents a preferred implementation of k-clocking in SS-OCT systems where dk/dt of the imaging swept source 105 is non uniform over time. In embodiments of the system implemented with sampling at uniform intervals in wavenumber, the processing unit may be configured to process interferometer output signals uniformly sampled in wavenumber, which may provide advantages e.g. in terms of precision of measurement or computational efficiency. In another embodiment, the controller 150 is configured to acquire the k-clock signal simultaneously to acquisition of the interferometer output signals. In some embodiments, the controller 150 (processing unit) is configured to acquire the k-clock signal simultaneously to the acquisition of the interferometer output signals, where both signals are acquired simultaneously at uniform time increments. In one or more of these embodiments, the k-clock measured signal and any derived quantities from this signal may be used by the processing unit 150 for sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k using digital processing approaches. The k-clock measured signal may also be used by the processing unit 150 to compute at least one correction for one or more distortions in the interferometer output signal. The k-clock signal may also be used by the processing unit 150 to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal which may not be uniformly sampled in k. One example of such a method would be using the k-clock signal as an input to compute an appropriate matrix for the implementation of a matrix DFT that may be applied to interferometer output data that is uniformly sampled in time but not uniformly sampled in k. In one embodiment, the k-clock module 145 is temperature stabilized.The use of the k-clock as a sample clock yields interference data that are evenly spaced in the optical wavenumber domain, or k-space, which provides maximal SNR and axial imaging resolution for subsequent Fourier transform-based signal processing upon the acquired interferometer output signals. The Fourier transform provides the A-scan information, or axial scan depth profile within the sample. OCT systems may also digitally resample or interpolate interference datasets using wavenumber information obtained via sampling the k-clock signal in the time domain in order to achieve even k-space sample spacing.

WO 2024/158772 PCT/US2024/012552 In accordance with at least one embodiment, a k-clock module is used. A k-clock signal is generated to aid in the processing of the OCT interferometer data of the system. Fourier Transform processing of the OCT interference signal is simplified when the discrete signal samples are spaced evenly in units of wavenumber (k). Tunable laser sources such as tunable light source 105 often do not tune in such a way that their wavenumber is linearly proportional to time. A k-clock generates a signal in time that oscillates in equal spacing of wavenumber. By detecting the oscillations of the k-clock (typically defined by "zero crossings" of the signal after low frequency components are removed), a relationship can be established between the time domain and a domain that is substantially linear in k. In accordance with one or more aspects, the k-clock measured signal and any derived quantities from this signal may be used for sampling, resampling, interpolating, or estimating OCT interferometer output signals at uniform intervals in wavenumber k. Sampling, resampling, interpolation, or estimation may be executed using digital processing approaches, analog continuous time signal processing, either in the electrical or optical domain, and may alternatively be performed before, during or subsequent to digitization of the signals.In some embodiments, the k-clock signal is generated using an optical path that is independent of the optical path used for OCT measurements. The design of an independent k-clock can incorporate devices including but not limited to free-space and fiber-based optical devices, in fixed and/or adjustable configurations that are known to those of ordinary skill in the art. For example, the k-clock can include a delay line and/or an adjustable delay line. In some instances multiple k-clocks may be used that can be selected or hot-swapped. In some embodiments, the k-clock includes multiple reflectors that are designed to tune to a variety of desired frequencies.In other embodiments, the k-clock signal is generated using the same optical path as is used for OCT measurements. One or more mechanical and/or optical features may be included within the OCT system to facilitate k-clock signal generation. The mechanical features may be fixed (e.g., physical surfaces), or dynamic (e.g., galvanometers), and a k- clock optical path may include any combination of such elements as well as others. The optical features may include, but are not limited to, specular and diffuse reflective elements, partially transparent or partially reflective elements (e.g., protective cover glass of the processing head), and other elements that are known to those of ordinary skill in the art. In other embodiments, features that are already present in the OCT system (i.e., not added for WO 2024/158772 PCT/US2024/012552 the express purpose of creating a k-clock path) may comprise some or all of the elements in the k-clock optical path.In some embodiments, a k-clock signal may be acquired (e.g., by the processing unit 150) in a manner that is time-gated relative to the interferometer signal, such as during a calibration phase, and stored to be applied to at least one subsequently acquired interferometer capture. Such an approach may be implemented using optical features in the OCT interferometer, and eliminate the need for a separate K-clock optical path. The application of time-gating may also eliminate the need for a separate detection module for the k-clock signal.In some embodiments, various k-clock paths are available and the k-clock path in use can be switched during operation or during idle time. Multiple k-clocks can be generated by splitting the swept optical signal into multiple simultaneous paths, and in other embodiments k-clock paths can contain actuated elements that modify a single path, and in still further embodiments k-clock paths may contain multiple fixed or active paths that can be selected using an optical device, such as a shutter or switch. The k-clock in use can be selected using optical means, and multiple k-clocks can be active simultaneously and selection can occur via electronic control of the data acquisition and sampling system.In some embodiments, the k-clock module 145 comprises at least one optical component. In certain embodiments, the k-clock module comprises at least one electronic component. In some embodiments, the k-clock module 145 comprises at least one computational and/or simulated component. According to certain embodiments, the k-clock module 145 comprises at least two of the following: at least one optical component, at least one electronic component, and at least one computational and/or simulated component.In accordance with at least one embodiment, non-limiting examples of optical components which may be included in the K-Clock Module 145 can include fiber-based and/or free space optical components, and/or some combination thereof. For example, in an embodiment where the k-clock signal is generated using an optical path that is independent of the optical path used for OCT measurements, this optical path may comprise beam splitters in the form of fused fiber couplers or beam splitter cubes, in order to split light coming into the K-Clock apparatus along multiple paths. As another example, in an embodiment where the K-clock is generated using the same optical path as is used for OCT measurements, partially reflective optical elements such as optics with dichroic coatings may be used.

WO 2024/158772 PCT/US2024/012552 Electronic components in some embodiments may fulfill various functions in a given K-Clock embodiment, including electronic photodetectors and associated electronics for signal processing and/or digitization of the K-clock signal. Electronic components may also be used for example in simulation, timing synchronization, and/or control of opto-mechanical components, applying techniques known to those of ordinary7 skill in the art.The term "simulated"’ or "simulation" as used herein generally refers to the solution of a model by numerical or analytical methods. According to some embodiments, simulated components may be implemented in system computers or processors, based on various electronic inputs, programmable inputs, and mathematical and/or analytical and/or numerical computer models which model the behavior of system components, or compute various other useful outputs. According to at least one embodiments, simulated components may take as inputs to the simulation input values measured based on the physical system. Such values may include values measured during operation by the system itself. Such values may include values measured prior to operation using at least one of system components and/or other instrumentation and input to the system (e.g., calibration data). For example, a simulated K- clock component may be synchronized to the line trigger of an SS-OCT system via an electronic signal, and produce a simulated time-domain trace of a K-Clock which corresponds to the required behavior of the K-clock trace after such a trigger, based on programmed, calibrated, and/or detected conditions.In some embodiments, the processing unit 150 is further configured to generate a mathematical model of dk/dt based at least in part on one or more properties of the SS-OCT system and one or more properties of the tunable light source. This mathematical model may be applied to associate an estimate of at least one of a value of k or the tuning rate dk/dt with data sampled from the interferometer output signal. In some embodiments, the processing unit 150 is configured to simulate a k-clock signal that indicates when the wavenumber k of the imaging optical signal or signal spectrum substantially changes by one or more increments. The simulated k-clock and/or mathematical model of k (also referred to as k(t)) or tuning rate dk/dt that is thus obtained may be used to facilitate any of the operations described above as being facilitated by׳ a physical, optical or electronic embodiment of the k- clock, including as appropriate, triggering the acquisition of the interferometer output signals at uniform intervals in wavenumber k. This model and/or simulated k-clock may also be used to facilitate re-sampling, interpolating, or estimating the values of sampled interferometer output signals at uniform intervals in wavenumber k where the original 43 WO 2024/158772 PCT/US2024/012552 sampling clock was not uniform in wavenumber k. This model and/or simulated k-clock may also be used to compute at least one correction for one or more distortions in the interferometer output signal. This model and/or simulated k-clock may also be used to compute a discrete-Fourier transform method which can be directly applied to an interferometer output signal which may not be uniformly sampled in k. In some embodiments of the system, the simulated k-clock and/or mathematical model of dk/dt uses as an input the tuning signal provided to the swept optical source, and this model may be capable of modeling dk/dt based on a source tuning waveform of arbitrary complexity.According to at least one embodiment, the processing unit is configured to control the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt. In some embodiments the at least two tuning rates dk/dt are associated with one or more interferometer output signals. In some embodiments, the at least two tuning rates include at least one positive tuning rate dk/dt and at least one negative tuning rate dk/dt. In some embodiments where there is an interferometer output signal where dk/dt varies in time, the at least two tuning rates dk/dt are associated with one or more interferometer output signals which correspond to different points in time.According to at least one embodiment, the sweep rate of the light source is varied to adjust the range/depth field of view of the system (typically at the expense of imaging frequency). As noted previously, the term sweep rate refers to a rate of repetition in the time- varying spectral output of the imaging optical signal. It is the inverse of the sweep interval/sweep period. This could also be considered as the inverse of the amount of time that it takes to acquire one A-line. As the sweep rate of the system is reduced, the frequency of a signal provided by a fixed k-clock is also reduced. In some embodiments where sample rate is independent of k-clock frequency, the number of samples acquired by the primary detector between ticks of the k-clock may be increased (e.g., to increase the axial resolution of an A-line), or the sample rate may be adjusted to maintain the original ratio of sampling clock to k-clock. In some embodiments where sample rate is dependent on k-clock frequency, no adjustment of sampling is necessary׳ when sweep rate is adjusted. In some embodiments where sample rate is dependent on k-clock frequency, the k-clock may be adjusted through mechanical, optical, digital, or other means in tandem with the imaging frequency, to enable other imaging performance, e.g. lengthening a k-clock delay while WO 2024/158772 PCT/US2024/012552 slowing down tuning of the source in order to increase imaging distance without increasing frequency.As mentioned previously, in some embodiments the tunable light source 105 has a sweep rate in a range from 1 kHz to 20 MHz inclusive. In accordance with at least one aspect, this range is selected to accommodate certain digitizer (e.g., digitizer 135) configurations (which can generally incorporate a maximum sampling rate) and/or any later interpolation techniques (e.g., interpolating sweep), thus making these respective approaches more effective.In accordance with certain embodiments, the k-clock frequency is monitored relative to another electronic clock in the processing electronics. By monitoring/measuring the rate of change of k of the light source (i.e., dk/dt in Leibniz notation, or k-dot, or light source wavenumber sweep velocity/tuning rate), important information can be collected for the compensation of distortions caused by the motion of the workpiece during the sweep of the waveform, known to those of ordinary skill of the art as motion artifacts. In some embodiments, time domain sampling of the k-clock may be implemented in addition to using a k-clock signal to drive the sample clock of the OCT interferometer, this can be achieved using electronic design techniques known to those of ordinary skill in the art. Such time domain measurement of the k-signal is motivated by the utility of this signal in some embodiments of motion artifact compensation. Further information regarding the concept of motion artifacts and the consequences of these artifacts for the design and performance of the system, and more specifically of the k-clock, are discussed in the Correction for Motion Artifact section below .According to some embodiments a line-start signal is generated at a particular wavelength in every sweep, to provide additional information (e.g.. for system synchronization). This signal may be generated by an optical band-pass device, examples including but not limited to a Bragg Grating or Fiber Bragg Grating. This signal may be generated inline with the chosen k-clock or OCT optical path embodiment, and it may also be generated using a tap of the source, separate from other optical paths.In certain embodiments signal processing operations are performed on the k-clock signal to enhance the system data. One example of such an operation is the computation of the k-space uniform FFT of the k-clock signal, which can provide a reference point for depth calibration of A-line signals and compensate for phase variability in the source, using methods known to those of ordinary skill in the art. In one embodiment, the value of k at at 45 WO 2024/158772 PCT/US2024/012552 least one point in the sweep is measured separately and recalled as needed as part of a calibration procedure. Many other k-clock signal processing operations are possible to enhance data collected from the system, as will be appreciated by those skilled in the art, which are also within the scope of this disclosure.

Optimized Swept-Source DrivingSS-OCT system 100 includes an imaging light source 105 configured as a swept source, which can be driven by a driving signal (e.g. an electrical signal sent by controller 150). The appropriate selection of a driving source and pattern to generate the driving signal is considered important to the function of the device, as the driving has a strong influence on the interferograms produced by the optical modules of the device. There may exist nonlinear relationships between the driving pattern applied and the spectral emission of the swept- source.Certain embodiments may use standard waveforms, such as ramp functions, sawtooth functions, or sinusoids, to drive the swept source. Other embodiments may incorporate more complex drive waveforms, for example drive signals specifically designed to produce a swept laser signal that is linear in wavenumber k, or drive signals designed to maximize device lifetime. Some embodiments may incorporate a variety of sweep driving waveforms, to permit the adjustment of sweep rate, tuning rate, span, or waveform shape for monitoring different aspects of the laser process, such as keyhole measurement or finished weld scanning during laser welding (for example). The adjustment of a sweep driving waveform of the swept source, including as non-limiting examples adjustment of sweep driving frequency, sweep driving waveform rate of change (slope), and/or sweep driving waveform repetition rate, may also be used to adjust the imaging range or sensitivity of the system, or manage (in some embodiments suppress, but in some embodiments enhance) motion artifacts. Some embodiments of the system may employ swept source driving modes that are slow relative to other available modes, for the specific purpose of increasing the available imaging range in scenarios where fringe frequency, and not coherence length, is the limiting factor.To increase the effective sweep rate, certain embodiments may incorporate optical buffering or interleaving of the swept source light. These embodiments of the invention may incorporate a combination of optical paths, shutters, couplers, and other optics to achieve an effective sweep rate greater than the phy sical sweep rate of the source. Optical buffering may WO 2024/158772 PCT/US2024/012552 be implemented at any point in the system, including, for example, either before or after the amplifier 106, as is appropriate for application-specific performance.In some embodiments, the rate of swept source driving may be changed between tasks, or, in some instances, during a task, to enable optimization of source sweeping. Vary ing the source sweeping rate has been demonstrated in experiments to change performance of the system.Certain embodiments may use drive waveforms specifically designed to account for different modes of operation of the sw ept source. For example, the mechanism of tuning of a MEMS VC SEE may be different for a sw eep from low-to-high w avelengths compared to high-to-low wavelengths. A tuning waveform may therefore be designed such that one direction of sweep is tuned differently from the other direction of sweep, such that the sweep behavior is optimized for each sweep direction.

Wavelength SelectionIn accordance with various embodiments, OCT systems at different wavelengths may be implemented, as swept-sources are available at a number of wavelengths. Each wavelength option presents distinct strengths.In some embodiments, the w avelength of the imaging system is matched to the w avelength of the material processing laser beam. For example, in specific applications of laser weld monitoring with a 1070 nm processing laser source 110, swept sources centered on approximately 1030 nm are advantageous due to their proximity to the wavelength of the material processing beam, while also presenting suitable resolution for w eld imaging. A further advantage is the commercial availability of solid state swept sources at this wavelength. The proximity of this wavelength to typical process beam wavelengths of 10nm reduces undesirable effects that arise from process beam optics (such as chromatic aberration), but presents the challenge of developing an appropriate dichroic coating to separate the imaging beam from the process beam.In some embodiments, the imaging system spectral range is designed to take advantage of low-cost spectral ranges, such as telecom. Sources centered at 1550 nm take advantage of a common telecommunications wavelength, w hich allows for the use of less expensive commercial-off-the-shelf components in the optical system, however these wavelengths present a coarser axial resolution for a given sweep bandwidth (in nm), as WO 2024/158772 PCT/US2024/012552 compared to the axial resolution available from a system centered at a shorter wavelength such as 1030 nm, with the equivalent sweep bandwidth (in nm).In some embodiments, the imaging system spectral range is designed to maximize resolution. System embodiments based on sources centered at shorter wavelengths, such as 800 nm may provide better axial resolution of OCT data in practical implementations.In some embodiments, the imaging system spectral range is designed to match the reflectivity (or in some cases the transmissivity) of at least part of the material undergoing laser processing or treatment. For example, in dissimilar plastic material lap welding applications, the spectral range may be designed so that the top material is at least partially transparent to the imaging system.Choice of wavelength as implemented by the disclosed systems and methods is dependent on the context in which it is being applied, including but not limited to resolution requirements, market availability of components, material properties for the material being imaged, and other processes that are occurring concurrently to the imaging. The principles of operation and general topology׳ of the SS-OCT systems and methods described herein are the same for SS-OCT systems at any wavelength. Therefore, possible embodiments theoretically exist at any wavelength, and practical embodiments can be considered to exist at all wavelengths where suitable technology exists.

Data ProcessingFor practical application of embodiments of the system, the capture and processing of interferogram data is necessary. This can be implemented by processing unit 150. Overall, a given embodiment of the system will be engineered to ensure adequate signal levels, data rates, timing characteristics, data precision, and other parameters so that sufficient data integrity is preserved from the optical signal through to the OCT image, and any derived quantities as applicable. Many of the required design practices are known to those of ordinary׳ skill in the art, but certain key elements of the system design where they present unique aspects are discussed in further detail below.

Optical-to-Electronic Signal ConversionEmbodiments disclosed herein include a system to convert the optical OCT signals into electronic signals. In some embodiments this stage of signal processing can be implemented by using a balanced photodetector configuration, thereby reducing or 48 WO 2024/158772 PCT/US2024/012552 eliminating DC components of the OCT signal, and amplifying the electronic signal generated to a level optimized for the digitization system. A high-level schematic outlining an example balanced photodetector configuration with electronic amplifiers is shown in FIG. 2. Other optical detection methods as are known to those of ordinary skill in the art are also appropriate for the optical-to-electronic signal conversion.Some embodiments may incorporate feedback electronic amplifiers to maintain a consistent output signal amplitude and maximize the SNR of the interferogram, and other embodiments may have multiplexed or multi-stage amplifiers to achieve a higher dynamic range for the system. Some embodiments may use analog electronic filter networks in order to filter or otherw ise enhance the signal produced by the photodetectors. Embodiments of the system without balanced detection are also within the scope of this disclosure, as well as embodiments with alternative detection techniques.In embodiments of the system which contain a k-clock, both the k-clock signal and the interferogram signal are converted from optical interferograms to analog electronic signals. Circuitry for the detection, amplification, and handling of these distinct signals is configured based on the nature of each signal, and in some embodiments different methods will be employed for each respective signal.

DigitizationAccording to at least one embodiment, the disclosed SS-OCT systems and methods employ the use of a digitizer 135. The digitizer 135 is configured to digitize at least one interferometer output signal, or modified interferometer output signal, or corrected interferometer output signal, or amplified interferometer output signal, with analog electronic signal processing applied as appropriate, and generate a corresponding digital signal. Digitization of the detected interferogram enables the further processing and storage of the OCT data. The resolution, range and sampling rate of digitization is dependent upon specific parameters of the physical system, including seed source tuning rate, optical power, and clocking requirements, as well as other physical parameters.In some embodiments, specialized digitization circuitry is implemented to allow the interferogram signal to be sampled in a domain that is linearly proportional to wavenumber k of the OCT sw ept source 105, and not necessarily sampled uniformly in time. These implementations may involve any combination of optical and/or analog electronic and/or simulated digital and/or simulated analog k-clocking signals to achieve appropriate sampling.49 WO 2024/158772 PCT/US2024/012552 This implementation presents advantages as it eliminates computationally expensive interpolation operations from the data processing. Digitization approaches which are linearly proportional to wavenumber k are discussed in the "K-Clocking Methods" section above.Other embodiments may involve digitization sampling that is uniform in time. In some embodiments that involve digitization sampling that is uniform in time, the imaging light source sweeping is implemented in such a way that wavenumber k is substantially linearly related to time in regions of interest. In preferred embodiments where digitization sampling of the OCT interferometer output signal is uniform in time, a K-clock signal is digitized using a sampling method which is also uniform in time. The K-clock signal may be acquired based on methods discussed in the above "K-Clocking Methods" section. The K- clock signal in such cases may be used to extract information which can be used to relate the sampling that is uniform in time-domain to the k-domain. This relation is important for the application of computational methods (e.g. Fourier transform, Homodyne matrix) which enable the extraction of depth information from an interferometer output signal.In some embodiments, the controller 150 may be configured to compute a resampled digital signal based on one or more digitally sampled interferogram signals. In some embodiments, a K-Clock interferogram signal may be digitized on the same clock as the OCT interferogram signal. This may be accomplished using electronic design approaches known to those of ordinary' skill in the art, e.g. by implementing a dual-channel ADC.

K-Clock AcquisitionOne or more embodiments of the system comprise an interferometer which serves as a phy sical optical k-clock 145, supplied with light tapped from the imaging source 105. Such embodiments also include the necessary electronic circuitry to detect k-clock signals, e.g., detector 147). In some embodiments, the k-clock signal (after appropriate conditioning) may be used to directly drive the sampling clock on the OCT signal digitizer, resulting in a digitization which is not necessarily linear in time but is substantially linear in k. This embodiment presents the advantage of eliminating computationally intensive resampling steps while still allowing the generation of an interferogram with uniform k spacing, which may enable the use of FFT methods during the processing phase. A further advantage of this method is that the use of an optical k-clock directly related to the imaging sw ept source can synchronize acquisition rates automatically to any sweep rate within specification. In some embodiments, the k-clock signal (after appropriate conditioning) may be digitized on some50 WO 2024/158772 PCT/US2024/012552 other clock, such as a clock which is uniform in the time domain. In some embodiments, digital signal processing of the digitized k-clock signal is used to determine a basis which is substantially linear in k, and resample other signals in the system to such a basis.In other embodiments of the system, the k-clock can serve to compute dk/dt using direct optical clocking methods sampled on a uniform electronic clock, or by employing at least one Fiber Bragg Grating and/or at least one electronic oscillator to determine a piecewise function. Simulated approaches to k-clocking are also within the scope of this disclosure. Implementations of embodiments where dk/dt is determined through measurements along a reference configuration of the primary interferometer are included herein, and dk/dt can be saved or modelled electronically and/or computationally to help with the development of appropriate transforms and processing methods. More detailed discussion of k-clocking methods may be found in the section "K-Clocking Methods" above, including details on different approaches for processing OCT data based on the k-clocking methodologies applied.

Processing ApproachesThe general data processing approach employed in the generation of A-lines from interferograms, and subsequent images (M-Modes (A-lines acquired at a fixed transverse position over time) or B-Scans (two-dimensional, cross-sectional view)) is related to another aspect of the disclosure. An overview of key steps in the data flow in accordance with one embodiment includes pre-processing, Fourier transform, and post-processing.In some embodiments, pre-processing includes all digital operations which may be performed prior to the application of a transform to enhance the interferogram data and improve the final result. This may include windowing acquisitions with analytical or arbitrary envelope functions. Digital filtering may also be applied to the data, as well as DC signal subtraction. Many additional pre-processing methods have been developed for OCT applications, and may be deployed as a component of the system as they are known to those of ordinary skill in the art. In the specific case of compensation for motion artifact, which is extensively developed below, pre-processing may include (but is not limited to) windowing a digital signal representing an interferogram in two or more different ways to extract data captured at portions of the sweep with different dk/dt.In accordance with at least one embodiment. OCT data may not be sampled uniformly in K-space (e.g. a signal sampled uniformly in time in a sweeping methodology where K and 51 WO 2024/158772 PCT/US2024/012552 time are not linearly related). In such embodiments, acquired digital data may be re-sampled to generate an OCT dataset that is sampled uniformly in K-space. The relation between time and K-space may be mapped to assist in the re-sampling using a variety7 of methods, including the acquisition of an optical K-clock signal, the implementation of calibration methods to characterize the source sweep in the time-domain and/or the K-domain, the simulation of a K-clock signal based on system and optical source parameters, and/or some combination of methods. Based on the relation between time and K-space, digital resampling methods may be applied to the time-domain OCT data capture. Digital resampling methods include those known to those of ordinary skill in the art, such as linear interpolation, spline interpolation, and/or the application of sliding window' signal processing functions. A mismatch in optical dispersion between the arms of the interferometer may distort the relation between time and K-space, as detailed in the section "Dispersion Compensation," (discussed in further detail below). In some embodiments, this distortion can be estimated and calculated a priori and a compensation for this distortion may be incorporated into the re- sampling of the interferometer output signals. In such embodiments, the dispersion correction can be applied with minimal additional real-time computing load.A variety of methods exist to perform the step of the transform from interferogram data in k-space to data in the depth domain, known as an axial line or A-line. In some embodiments, transform methods can be chosen based on what is most appropriate for a given application of the system. For example, depending on sampling methods, an FFT may be employed (for embodiments uniformly sampled in k), a homodyne matrix DFT may also be used (for embodiments not uniformly sampled in k, for example those sampled uniformly in time where k varies in a non-linear way in time), or a Fractional FFT may be used (also for embodiments not uniformly sampled in k). Factors including the stability of the tuning source, the tuning rate, and the available processing power may be taken into account when selecting a transform processing approach. Some transform processing approaches may incorporate compensation for various physical and optical effects which impact the accuracy and resolution of the data, which is discussed in more detail below. A non-limiting example of such effects is the motion artifact discussed below, or the effects of optical dispersion.Post-processing in accordance with some embodiments includes operations which track geometric properties (features) of a singular A-line, as well as operations which track properties across many A-lines. The features/geometric aspects which are tracked are encoded in the interferometer output signal used to generate the A-line.52 WO 2024/158772 PCT/US2024/012552 Non limiting examples of features (e.g., geometric properties) which may be tracked for a singular A-line include a position, a symmetry, a width of a peak, a centroid, a geometric second moment, a center of mass, an amplitude, a height to width ratio, and a geometric area under a curve. In accordance with certain embodiments of the invention, certain A-lines may be represented based on some set of parameters, features, measurements, including geometric parameters and features, or other parameters extracted from the imaging data, which may be derived from the properties of that A-line. Such representations of A- lines can be referred to as "tracked A-line data" or simply "tracked data" and/or "track data." In accordance with the requirements of the application, in some embodiments the processing system may be configured to output only track data, or track data in addition to raw A-line data. The incorporation of track data into embodiments of the system can offer insight into the key features/geometric aspects of the sample which are being measured via SS-OCT at a considerably lower data density than that of raw data, which can make this approach advantageous from a computational standpoint.Post-processing operations are designed in at least one embodiment to extract quantitative parameters from composite imaging data derived from a plurality of A-lines, such as M-Modes or B-Scans or 3D volumetric scans. In some embodiments, this includes assessing groups of A-lines based on analysis of shared features. Some embodiments include the development of metrics which quantify correlation between subsequent A-lines. Filtering of a group of A-lines may be performed by the application of filter methods known to those of ordinary skill in the art, such as Kalman filtering. In some embodiments, B-scan or M- mode data may be handled analogously to an image, and in such embodiments appropriate image processing algorithms and approaches may be applied to extract data or manipulate data to assist in further interpretation. Representations of A-lines and more generally representations of features (e.g., geometrical or geometric features) within the OCT capture derived based on the extraction of parameters from composite imaging data can also be referred to as "tracked data" or "track data." Track data based on only one A-line may be more specifically referred to as "A-line track(ed) data" and/or "track(ed) A-line data." Track data based on more than one A-line may be more specifically referred to as "bulk track(ed) data" and/or "track(ed) bulk data." In some embodiments, operations including statistical analysis, mathematical analysis, geometric analysis and/or signal processing may be applied to a collection of more than one A-line track data corresponding to more than one A-line in WO 2024/158772 PCT/US2024/012552 order to generate bulk track data. In some embodiments, such operations as described may be applied to a collection of more than one A-line in order to generate bulk track data.Additional methods of extracting simplified data from A-lines or B-scans, M-Modes, etc., including those known to those of ordinary skill in the art of signal processing and/or artificial intelligence (AI) and/or machine learning (ML) may also be employed, and are considered to be within the scope of this disclosure.Signal processing approaches/methods known to those of ordinary skill in the art may be employed as part of processing approaches, in pre-processing (e.g. of interferometer output signals in the analog or digital time and/or K-domains) or post-processing (e.g. of A- lines or groups of A-lines). Digital or analog high-pass or low-pass filtering and Kalman filtering are examples of such approaches. Further examples of such methods include smoothing filters, such as median and percentile filters. Image processing approaches, for example those developed for analysis and feature extraction may also be applied to data and can be particularly meaningful when handling the image-like outputs produced when combining multiple A-lines (such as B-scans, M-Modes, or volumetric scans). Examples of image processing approaches include signal processing operations designed to work on 2- or 3- dimensional digital imaging data, such as convolutional filters, frequency domain masking (including 2-D Fourier-Domain based methods), and others known to those of ordinary skill in the art. Signal and image processing approaches may be applied at any level of the data - for instance, in post-processing one filter may be applied to each individual A-line. while a separate filter may be applied to the complete B-Scan. The filters may be applied to extract the same information from an image, or each filter may be applied to extract different information from an image, e.g. one filter may be developed and optimized to extract features of the PCR from a B-Scan, while another filter may be developed to suppress noise on a B- Scan.The application of ML and/or AI methods to the processing of data may be applied at various levels of the data. For example, ML training techniques known to those of ordinary skill in the art (such as backpropagation and logistic regression) may be applied to train an algorithm (such as commonly applied algorithms, for example neural networks, CNNs, regression algorithms, self-organizing map, k-nearest neighbor) which acts on SS-OCT data to extract useful information, such as the evolution of a w eld keyhole and/or other features of the processing region/workpiece, including the geometry of a w orkpiece. Algorithms which are trained using ML techniques may be used in conjunction with algorithms which do not54 WO 2024/158772 PCT/US2024/012552 use ML, algorithms which comprise at least one component developed with ML methods are referred to herein as ML-trained and/or ML-augmented algorithms (used interchangeably).ML-trained algorithms may in some embodiments take as inputs raw SS-OCT data, possibly including interferometer output signals, A-Lines, B-Scans, and/or M-Modes. ML- trained algorithms may in some embodiments take as inputs one or more features/geometric characteristics e.g., position, shape, symmetry, width of one or more peak(s), centroid(s), geometric second moment(s), center(s) of mass, amplitude(s), height to width ratio(s), geometric area(s) under one or more curve(s), of signals and/or A-lines and/or groups of A- lines (such as B-Scans or M-Modes). ML-trained algorithms may in some embodiments take as inputs some combination of these data types, and/or other data ty pes. In some embodiments, ML-trained algorithms may take as inputs SS-OCT data and data from other detectors within a system, examples may include photodiode data or acoustic data (other detectors are discussed in the section titled "Auxiliary7 Detectors" below). An ML- or AI- augmented algorithm may be used to extract track data from A-lines and/or groups of A- lines. An ML- or Al-augmented algorithm may be used to extract features of interest from data and/or track data. In some cases, an ML-augmented processing paradigm may involve a pre-trained algorithm which is applied as part of the data processing. When developing this algorithm, care must be taken to ensure that the training data used is appropriate to the conditions for which the ML-augmented algorithm is applied. For example, an ML algorithm may be trained on SS-OCT weld keyhole data, using as a ground truth a longitudinal section of the imaged welds to employ supervised learning methods. Such an algorithm may then be applied to the post-processing of keyhole data, to estimate the depth of the keyhole based on the imaging signal. It may be desirable in some cases, to further narrow7 the scope of the training set to apply ML techniques to produce an algorithm with greater specificity for a given problem. As an example, ML techniques may be applied to train an algorithm on only data from single mode copper welds. This may allow7 the ML training methods to extract features specific to single mode laser welding dynamics and copper material properties (and the interaction of the two). The resultant ML-enhanced post-processing algorithm may have improved performance when extracting features (e.g.. geometric features) of the PCR from copper welds as compared to an algorithm trained on data derived from numerous materials or processes. Numerous sources of ground truth are available for application to supervised learning methods for ML-trained SS-OCT algorithms in the context of laser material processing. Examples of training data sources include datasets concurrently captured during 55 WO 2024/158772 PCT/US2024/012552 material processes using another instrument (e.g. X-ray synchrotron data, SS-OCT data), datasets based on analysis of finished welds (e.g. metallographic analysis, X-ray computed tomography) or synthetic/simulated datasets. In some embodiments, unsupervised learning methods may be applied to develop ML-trained algorithms. In some embodiments, ML and/or AI algorithms in the SS-OCT system may use a combination of supervised and unsupervised learning methods, and/or other algorithm development methods as appropriate.ML and/or AI algorithms may be applied to the identification, evaluation, and/or correction of artifacts in an OCT signal, including motion artifact. Motion artifact and the application of AI/ML algorithms is further discussed below in the section titled "ML/Al Algorithms and Motion Artifact."In some embodiments, it may be appropriate to employ ML/AI methods on a broader, trend-based approach to the outputs of the SS-OCT system. For example, an AI based monitor may monitor the quality metrics such as QA outputs of one or more SS-OCT systems within a plant, and based on the evolution of SS-OCT data over time, provide timely updates to assist human operators in the proactive management of problems. In this example, an AI program may take in data from seam tracking or keyhole depth measurements, and identify general trends over the course of many hours, days, or more time, in the positioning and welding of parts. It is common for process parameters to drift slightly over time, e.g. due to wear on fixtures or the buildup of contaminants such as weld fume on system components, this process drift commonly impacts quality metrics of the process product. As the process parameters drift, an SS-OCT system produces bulk data indicative of this shift in quality metrics, which may be analyzed in aggregate to understand the shift of average process parameters closer to the bounds of the acceptable process. As process quality metrics shift away from nominal, the real-time feedback provided by SS-OCT may help maintain the process within the set bounds, but at a certain level of process drift intervention may be required to re-establish nominal performance e.g. through a maintenance or calibration operation. The AI program can produce an alert for the human operator and identify cells which may need maintenance based on the SS-OCT data trends before the process goes too far out of specification and starts producing failing parts. An illustration of process drift over time is included in FIGS. 20A and 20B. FIG. 20A illustrates the typical statistical nature of process parameter and quality metric distribution, the quality metrics being derived at least in part from SS-OCT data associated with the process, and demonstrates the gradual degradation of quality metrics over time resultant from process drift. FIG. 20B illustrates the 56 WO 2024/158772 PCT/US2024/012552 impact of process supervision by an AI/ML supervisor or monitor: the AI/ML monitor identifies the statistical trend where the quality metric begins to drift out of specification, allowing for corrective action before a part is flagged outside of the bounds of the quality metric. Such AI supervision, with the aid of a network of QA and feedback systems may be able to proactively manage production assets to ensure timely maintenance and limit the number of failures across full production facilities and/or supply chains.In some embodiments. AI and/or ML methods may be employed on interferograms, A-Lines, or groups of such datatypes. In some embodiments, AI and/or ML methods may be employed to identify and/or measure and/or characterize specific features of the PCR, including weld depth. As mentioned previously, filtering methods known to those of ordinary skill in the art of signal processing may be applied, for example percentile filters or Kalman filters, as an additional method for generating simplified track data.The application of track data has key roles according to some embodiments of the system, primarily reducing the data footprint required to store meaningful measurement information, and enabling the development of Quality Assurance (QA) algorithms. In embodiments of the system where the SS-OCT system is integrated with a laser material processing system, the QA metrics may be developed in accordance with material processing objectives, and SS-OCT data, being track data or otherwise, may be applied to provide feedback on the material processing. A pertinent example of the application of track data is for embodiments of the system which capture at least some interferometer data for which the imaging beam is aligned with the keyhole of a laser weld, such that at least some data is collected representing the OCT return from the bottom of the keyhole. Features, including geometric features derived from such an A-line may be processed to produce track data representing the bottom of the keyhole, which may be used to help track keyhole depth of the PCR throughout a weld process for example. In the present disclosure, "keyhole depth" refers to the maximum depth of the vapor capillary, as understood by those skilled in the art.

Processing Hardware and Hardware ImplicationsIn some embodiments, data is pipelined into a specifically coded FPGA for real-time processing, which can include any or all of the pre-processing, transform, or post processing steps. Such embodiments enable the possibility' of real-time output, with the potential to use OCT data as a feedback mechanism within a process. Further processing methods may also be implemented on the FPGA. including but not limited to depth tracking or motion artifact 57 WO 2024/158772 PCT/US2024/012552 correction, which is extensively explained below. Tracking methods may be developed that incorporate data from multiple A-lines, such as percentile tracking or averaging, to reduce the effects of instantaneous chaotic variability, especially when tracking keyhole (welding) processes. In some embodiments, digitized data is processed using programs on one or more CPUs and/or GPUs. In some embodiments, digitized data is processed using an ASIC (application-specific integrated circuit). In some embodiments, digitized data is processed using some combination of processing hardware, which may include, as non-limiting examples, FPGAs, CPUs, GPUs ASICs, microcontrollers, and other processing hardware which is know n to those of ordinary skill in the art. In some embodiments, the computation of weld metrics, such as keyhole depth, or finished weld surface height, may be performed in real-time when the processing is configured to enable it. In some embodiments, Quality Assurance (QA) metrics can also be developed to provide rapid feedback on the suitability of an imaged part for industrial application.

Correction for Motion ArtifactGeneral Problem DescriptionA known physical effect which impacts all swept-source OCT systems is distortion of A-lines when the imaging target moves (sample motion) during the acquisition time of a single A-line. This effect is known to those of ordinary skill in the art as motion artifact. The motion artifact can manifest as a shift, which may be greater than the actual displacement of the imaging target during the imaging time. The motion artifact can additionally manifest as a broadening, blur, or distortion of the A-line in addition to or instead of the shift. In laser weld monitoring applications, motion is known to exist in a number of desirable imaging targets, particularly at the bottom and the side walls of the keyhole. As such, understanding and compensating for this motion artifact is important for purposes of generating accurate weld monitoring information, such as keyhole depth.In some embodiments, the time-vary ing difference in optical path lengths (between the at least one sample arm and the at least one reference arm of the interferometer) is caused by sample motion relative to an axis of the imaging optical signal. In some embodiments, the time-varying difference in optical path lengths is caused by the material modification process that is implemented by7 the material processing beam on the sample. In some embodiments, the time-vary ing difference in optical path lengths is caused by intrinsic sample motion not caused by the material modification process. The motion artifact causes a modulation in the WO 2024/158772 PCT/US2024/012552 interference spectrum that results in an improper depth being registered for moving reflectors when processed with conventional means. The magnitude of the motion artifact depends on dk/dt of the imaging source, so a careful analysis of the variations of dk/dt are useful for compensating for the shifts.In accordance with certain embodiments, one or more algorithms are used to identify, address, and correct the effect of the motion artifact (distortion). According to certain embodiments, the processing unit is further configured to determine a sample position based on the at least one corrected interferometer output signal. In some embodiments, a working principle is that the motion artifact detected is related to the change in the source wavenumber over time (tuning rate dk/dt). The source is swept such that interferometer output signals corresponding to portions of the source sweep at two or more (at least two) tuning rates dk/dt are captured. This enables identification of distortions which can be attributed to the motion artifact. Based on these distortions, a correction is computed and applied to produce a motion artifact corrected A-line or M-Mode or other motion artifact corrected data. In some embodiments, correction of the motion artifact includes correction of higher-order distortions which affect the shape and characteristics of the complete raw A- line. Other embodiments of motion artifact correction include only correction of key image features, such as the tracked A-line peak. To handle noise, which is still present after the motion artifact correction, in some embodiments smoothing and tracking algorithms are applied.Selection of appropriate methodologies of motion artifact compensation depends upon the specific requirements demanded by the application, including requirements of accuracy, resolution, data rate, computational power, operation speed, output data requirements, and more. Details of a variety of general approaches are disclosed below, however specific steps within these approaches can sometimes be interchanged where appropriate, either with other steps disclosed below or with operations of similar mathematical utility' and effect known to those of ordinary7 skill in the art (e.g. interchanging the use of median, mean, and mode in cases where averaging is required, per the performance of the application).

Distinction from medical OCTResearch on the topic of medical OCT has led to work on the correction of motion artifact. However, a number of differences exist between the application of OCT to medical fields and the application of OCT to material processing, and as such, there is a material 59 WO 2024/158772 PCT/US2024/012552 difference in the magnitude and nature of motion artifact observed, as well as in the requirements for motion artifact correction.For example, in the case of medical OCT, consideration must be taken within the system to work at wavelengths and powers which are not harmful to biological tissue and/or material being imaged, whereas in material processing, considerably higher powers may be applied for OCT without damaging the sample. Additionally, medical OCT often concerns itself with imaging a substance which is at least partially transparent to the OCT wavelength, where sub-surface structures are of interest. Such imaging requires signal-to-noise characteristics that make it possible to clearly distinguish low-brightness features within the sample volume. Common material processing applications employ sample materials which are opaque to typical OCT wavelengths, including metals. As such, surface features are of more concern, especially the interface between the solid processing material and the surrounding gas. Also, for samples materials which are opaque to typical OCT wavelengths features within the sample volume cannot be accessed by OCT.Additionally, the motion observed in medical OCT typically consists of low velocity bulk motion of the sample during acquisition, with typical values reported in the range of less than I mm/s. Motion observed in OCT applied to material processing may include bulk sample motion at considerably higher speeds, intrinsic sample motion caused by the material modification process, motion which is non-uniform in time and space within or pertaining to the sample volume or parts of the sample volume, and generally arbitrarily complex and rapid motion. Certain material modification processes induce intrinsic motion at the PCR and/or in other regions of interest in the sample which can be considerably and chaotically variable on the timescales of SS-OCT acquisitions. Motion may also be intrinsic sample motion not caused by the material modification process. Such motion may also include high velocity components, where the motion velocity of the sample being imaged is greater than 10 mm/s, greater than 100 mm/s, greater than 500 mm/s, greater than 1000 mm/s, greater than 50mm/s or even greater than 10,000 mm/s. In some cases this sample motion velocity may be intrinsic to the material modification process. Of particular interest is the motion of material within the keyhole of a laser weld, which has been demonstrated under some conditions to display some of the characteristics described above. Techniques known to those of ordinary skill in the art of medical SS-OCT are not sufficient for such cases.Medical OCT is typically applied in contexts where a qualified human operator supervises the images and may repeat images if bulk motion is perceived to degrade the 60 WO 2024/158772 PCT/US2024/012552 image to an unacceptable degree. Unlike medical OCT, material processing OCT is often employed in automated processes where images must be processed using algorithms to produce e.g. a quality assurance result. In many material processing cases, the OCT image may also only be acquired once, for example a situation where a repeat is not practical or not possible, as it is linked to a single material modification process such as a weld, and must be acquired during the processing time. These differences mean that the development of motion artifact correction algorithms specific to material modification process monitoring OCT presents a novel challenge as compared to medical OCT motion artifact management and/or correction. The challenge is further heightened by the demands of automation and the rigorous quality assurance and reliability׳ requirements in the manufacturing space. Outlined below are motion artifact identification and correction algorithms specifically developed to address the capabilities and challenges of the application of OCT to material modification processes.

Identification of Motion Artifact Distortion in SS-OCT DataIn embodiments of the system where motion artifact compensation or correction is required, the first step is to identify the motion artifact distortion and characterize it. According to certain embodiments, the distortion corresponding to the motion artifact corresponds to one or more geometric aspects encoded in the interferometer output signal (such as the geometric characteristics of the A-line, which are encoded within the frequency of the interferometer output signal). Adequate information can be derived based on information contained within an un-corrected interferometer output signal when sample settings of the system are set appropriately to capture interferometer output signals corresponding to swept optical signals at two or more tuning rates dk/dt. In some embodiments, to extract the motion artifact features of an un-corrected interferometer output signal, the signal capture must include at least two separable segments of data for which the imaging source has different dk/dt. Different dk/dt may comprise different rates of tuning of the imaging source, and/or may comprise positive and negative dk/dt. By evaluating the frequency components seen in the at least two interferometer output signals associated with at least two imaging source dk/dt, information on the distortion of the interferometer output signal during the time of the acquisition can be extracted, and this distortion information can be related to motion and/or velocity of the imaging sample. Evaluation of the distortion may include but is not limited to measurement of the amplitude of individual frequency61 WO 2024/158772 PCT/US2024/012552 components or groups of frequency components within the un-corrected interferogram signal segments, the evaluation of the frequency components observed at the different dk/dt’s, the evaluation of one or more geometric aspects or characteristics encoded within interferometer output signals including, but not limited to, position, shape, symmetry, width of one or more peak(s), centroid(s), geometric second moment(s), center(s) of mass, amplitude(s), height to width ratio(s), geometric area(s) under one or more curve(s), of signals and/or A-lines and/or groups of A-lines (such as B-Scans or M-Modes) corresponding to un-corrected data. In accordance with certain embodiments, performing an evaluation of the distortion comprises comparing the distortion in at least one of the at least two interferometer output signals relative to the distortion in at least one other of the at least two interferometer output signals. In some embodiments, performing the evaluation comprises comparing distortion in at least one interferometer output signal associated with a positive tuning rate dk/dt with distortion in at least one interferometer output signal associated with a negative tuning rate dk/dt. In certain embodiments with multiple interferometers (systems configured with multiple interferometers are discussed in more detail below), a sample arm of a first interferometer and a sample arm of at least one additional interferometer share at least one optical element, and a first imaging signal configured with one of at least two tuning rates dk/dt is directed to the at least one reference arm and the at least one sample arm of the first interferometer, a second imaging signal configured with another of the at least two tuning rates dk/dt is directed to the at least one reference arm and the at least one sample arm of the at least one additional interferometer, and the distortion is identified based on the one or more interferometer output signals of the first interferometer and the at least one additional interferometer. In additional embodiments the first and second imaging optical signals are directed to the processing region simultaneously.According to certain embodiments, the distortion corresponds to one or more geometric aspects of the interferometer output signal and/or A-line. The one or more geometric aspects may include at least one of position(s), symmetry (symmetries), shape(s) of signals, a shape(s) of envelope functions, width(s) of one or more peaks, displacement(s) of one or more peaks, amplitude(s), centroid(s), height to width ratio(s). center(s) of mass, geometric area(s) under (a) curve(s), and geometric second moment(s). In accordance with certain embodiments, performing the evaluation of the distortion comprises comparing one or more geometric aspects encoded in at least one of the at least two interferometer output signals relative to one or more geometric aspects encoded in at least one other of the at least 62 WO 2024/158772 PCT/US2024/012552 two interferometer output signals. In accordance with some embodiments, performing the evaluation of the distortion comprises comparing one or more geometric aspects encoded in at least one of the at least two interferometer output signals to one or more pre-determined thresholds and/or baselines associated with the one or more geometric aspects. Such pre- determined baselines and/or thresholds may be established based on one or more of the following: system requirements, component requirements, one or more application requirements, one or more calibrations, one or more models, one or more algorithms, fundamental physics, limitations of the hardware and/or limitations of the software.The geometric aspects which are distorted by the motion artifact can include aspects known by those of ordinary7 skill in the art as aspects which correspond to features, including geometric features, of the phase change region (and more generally the processing region) and more generally to features, including geometric features, of the sample. As such, the identification and subsequent correction of the motion artifact is crucial to obtaining an accurate measurement of one or more features, including geometric features, of interest in the sample when the sample is in motion. A pertinent example of features or geometric aspects to be measured when the sample is in motion is obtaining an accurate measurement of keyhole geometry while the molten metal at the bottom and side walls of the keyhole is in motion.It is to be appreciated that there are instances where no distortion is detected in the interferometer output signal by controller 150 and this scenario is encompassed by one or more embodiments disclosed herein. As such, the controller 150 will process the interferometer output signal to determine at least one feature (e.g., depth information) of the processing region. However, when the controller 150 detects a distortion in the at least one interferometer output signal, in response the controller 150 will apply one or more corrections to the at least one interferometer output signal as discussed herein.

Imaging Target Velocity Estimation and CompensationA theoretical framework and corresponding mathematical model can be developed, based at least in part on one or more properties of the SS-OCT system, to relate the distortion of the at least one of the at least two interferometer output signals at different dk/dt to the magnitude and/or direction of motion velocity7 of the sample, especially where the motion of the sample is relative to an axis of the imaging optical signal. This has enabled the development of correction factors (also referred to as simply a "correction") which can be 63 WO 2024/158772 PCT/US2024/012552 applied to an interferogram to correct the effects of motion artifact. The appropriate correction to compute a given corrected A-line can be computed based on this theoretical model combined with information extracted from analysis of geometric aspects encoded within the interferometer output data, examples of which are described above, the interferometer output data containing at least two segments or portions of the source sweep which have different dk/dt. Put another way, the computation of a given corrected A-line can be based at least in part on a theoretical model. The theoretical model can be built and/or updated based at least in part on interferometer output data, K-clock data, analytical and/or numerical models of the SS-OCT system and/or its components, or results derived from some combination thereof. The theoretical model can be combined with information extracted from analysis of geometric aspects encoded within the interferometer output data, where the interferometer output data contains at least two segments or portions of the source sweep which have different dk/dt. Information extracted from the frequency analysis of the un- corrected interferogram, combined with the theoretical framework and knowledge of key physical parameters of the OCT imaging system, can be used to compute an estimate of the velocity of the sample at the time of the A-line capture which was effected by the observed motion artifact. Based on this compensation, it is therefore possible to extract position data as well as velocity data from an OCT system scan.In accordance with some embodiments, the computed correction factors are applied at the transform phase of OCT imaging, by means of a correction factored into each element of a DFT matrix, similar to dispersion compensation. Therefore, the controller 150 is configured to transform the time domain interference signals (interferometer output signals) into respective frequency domain signals by calculating a corrected DFT matrix which is applied by multiplication to the time domain interference signals.In accordance with some embodiments, the time domain measurement of k and/or dk/dt provided by a K-clock signal, and/or simulated/modeled k-clock signal, is used to compute at least one correction for one or more distortions in the interferometer output signal.The motion artifact distorts both position and other geometric aspects of the signal (e.g. symmetry, full-width at half-maximum, amplitude above noise floor). In some embodiments of the system, the implementation of appropriate correction factors includes the corrections required to compensate for higher order effects of motion artifact, and the WO 2024/158772 PCT/US2024/012552 corrected A-line presents improved symmetry and/or improved amplitude and/or decreased full-width at half-maximum when compared to the un-corrected A-line.In embodiments of the system where varied motion conditions are anticipated for the imaging target, numerous DFT matrices with velocity compensation included as required may be pre-calculated and stored in look-up tables for rapid processing of datasets with variable velocities present. Other embodiments where velocity is less variable may be calibrated based on their characteristic velocity on occasion and designed to compensate every A-line for the characteristic velocity7 based on the calibration of a singular common transform matrix. Depending on the specific needs of a process, including computational speed, sample rate, source sweep rate, and precision requirements, a variety of approaches can be applied to develop an optimal velocity compensation methodology7 to meet the needs of that application. One example of an embodiment of the system where varied motion conditions are anticipated for the imaging target is where the SS-OCT system is configured to image a welding process, and the material processing beam creates a phase change region (PCR) at the processing region. In such an embodiment, the imaging beam may be directed toward a region of the process which is in motion, such as the weld keyhole, an imaging target known to be in motion with varied velocities as the process evolves over time and/or space. Evaluation of the distortion corresponding to motion artifact in such an embodiment can be used to generate a corrected A-line which corresponds to the geometry7 of the PCR, and/or is used to generate an estimate of a velocity of the material being processed in the PCR.

Track Data and Correction for Motion ArtifactFor application specific reasons, it may be preferred in some embodiments of the invention to derive simplified tracking data, herein referred to as track data, from the interferometer output signal or its corresponding A-lines, B-Scans, M-Modes etc. The concept of track data has been discussed previously. Track data may be developed in a way that is specific to the SS-OCT application, and may include expressions of pertinent information related to the geometry of the sample, possibly including the phase change region (PCR) and/or the processing region. For instance, A-lines may be employed to identify and/or measure and/or characterize specific features of the PCR, especially weld depth. Some non-limiting examples of tracking data include signal position, symmetry7, a width of a WO 2024/158772 PCT/US2024/012552 peak, a centroid, a geometric second moment, a center of mass, an amplitude, a height to width ratio, and geometric area under a curve.Additional methods of extracting simplified data from A-lines or B-scans, M-Modes, etc., including those known to those of ordinary skill in the art of image processing and/or artificial intelligence (AI) and/or machine learning (ML) may also be employed, and are considered to be within the scope of this disclosure. For instance, in some embodiments, AI and/or ML methods may be employed on interferograms. A-Lines, or groups of interferograms. In some embodiments, AI and/or ML methods may be employed to identify to identify and/or measure and/or characterize specific features of the PCR, including weld depth. As mentioned previously, filtering methods known to those of ordinary skill in the art of signal processing may be applied, for example percentile filters or Kalman filters, as an additional method for generating simplified track data.In the context of identification of SS-OCT motion artifact, and compensation for SS- OCT motion artifact, it is to be understood that in some embodiments the application of tracking methods to extract key information from raw OCT data is an integral part of the approach. Tracking methods may be used on data prior to correction or compensation, in order to establish and quantify the observed distortion and generally characterize the un- corrected signal, as w ell as for other purposes. Tracked data from more than one interferometer output signals captured at more than one tuning rate dk/dt may be employed to perform the necessary evaluation to establish the presence of absolute or relative distortions which are used as a basis for motion artifact compensation.In some embodiments of the invention, at least one correction for motion artifact is to be applied to tracked or simplified data extracted from the un-compensated interferometer output signal. The resulting corrected track data is understood to be corrected data. In some embodiments of the invention, at least one correction for motion artifact is computed based on tracked or simplified data derived from the interferometer output.Embodiments of the invention where the distorted component, the correction, and the corrected data, as well as any intermediate data or other relevant quantities, are derived based on either complete interferometer output signals or data that is tracked and simplified or some combination of the two are all to be considered as covered in the scope of this disclosure.

Geometric Compensation for Motion Artifact without Velocity Estimation WO 2024/158772 PCT/US2024/012552 In some embodiments of the system, it may be appropriate to apply simpler methodologies to compute corrections for detected motion artifact which do not involve incorporating a theoretical model or velocity estimation. The motivation for simplifying the compensation methodologies varies, but commonly timing and computational power, (especially in e.g. real time metrology7 systems), are limited and of concern. In such cases, it may be favorable to forgo the full complexity motion compensation method and instead apply a simpler approach. Although this may come at the fundamental expense of data density or accuracy, it must be understood that this can be suitable for numerous applications.The compensation of motion artifacts without velocity7 modelling and estimation still requires the frequency analysis of an interferogram signal capture including at least two segments of the source sweep which have different dk/dt. Based on this analysis, a correction can be computed for application directly to at least one of the at least two un-corrected A- lines. This correction may include a shift of the A-line, the application of an amplify ing or attenuating factor, a filter, or other signal processing manipulation or method known to those of ordinary skill in the art. In some cases, it is appropriate to first track key features of the at least two un-corrected A-lines, and apply the correction only to the tracked features. Such tracked features may be features of geometrical interest in or on the sample, as previously discussed.

Filtering by Artifact SizeIn some embodiments of correction for motion artifact, the data from at least two different dk/dt portions or subsets in a given interferogram signal is analyzed to identify the magnitude of the motion artifact and/or the corresponding distortion in the interferometer output signal. The motion artifact distorts both position and other geometric aspects of the signal (e.g. a position, symmetry, a width of a peak, a centroid, a geometric second moment, a center of mass, an amplitude, a height to width ratio, geometric area under a curve, and/or amplitude above noise floor). A signal with a smaller magnitude of motion artifact is likely to also have less distortion in these other respects. The motion artifact magnitude may therefore be used as an indicator of the relative quality and/or accuracy of the A-line produced from a given interferometer output signal. By selecting the A-lines with the smallest motion artifacts, it is possible to reduce noise, improve tracking accuracy, and view features of the target process with greater accuracy. In some embodiments, performing the evaluation of distorted components (including two or more distortions) comprises 67 WO 2024/158772 PCT/US2024/012552 determining if a relative difference between the distorted components exceeds a predetermined threshold. In some embodiments, the magnitude of distortion of some geometric aspects of one or more distorted interferograms may be considered in absolute terms, and/or relative to a predetermined threshold when evaluating the motion artifact. In some embodiments, applying corrections to the at least one interferometer output signal pursuant to assessment of the motion artifact comprises discarding, weighting, promoting, or using the interferometer output signal based on assessment of the motion artifact, or evaluating a signal for disposal and/or processing later on.According to at least one embodiment, the one or more corrections that are applied to the at least one interferometer output signal by controller 150 include discarding, weighting, or using the interferometer output signal, or any derivative values and signals from this signal. For instance, an analysis performed by controller 150 between at least two segments of the source sweep that have different dk/dt may have the outcome that the relative difference between the at least two segments is of a value or magnitude such that the data is unusable and the data is therefore discarded. The decision to discard, not discard, to promote, to modify, or leave the data unmodified constitutes a correction per the use of this term described herein. The motivation for including as options discarding, leaving unmodified, and modify ing is that the noise in the system can be sufficient to wash out information for A- lines under certain motion artifact conditions, so in certain cases no information is lost by discarding data, and a reduction in noise as well as an increase in efficiency can be gained. As such, this method is a pertinent correction. Flagging the data based on whether it passes key thresholds to inform later processing is also possible for managing the variable quality of return data as a component of motion artifact compensation.This phenomenon may be used to filter un-motion-corrected A-lines by, for example, selecting only A-lines below a given (pre-determined) motion artifact magnitude threshold. This has the effect of selecting those A-lines on which motion compensation will provide the most high-quality and/or accurate resultant A-lines, and apply motion compensation to only those A-lines. Such methods have been shown to improve the tracking accuracy of certain methods of analysis on some processes. Motion-artifact magnitude based downsampling can also effectively reduce the noise seen in M-Modes and in track data, creating a clearer view of the material modification process and its key features being imaged, and allowing for more accurate analysis.

WO 2024/158772 PCT/US2024/012552 It is to be understood that this filtering can be applied in addition to the geometric correction or motion compensation outlined above.Whether using corrected and/or uncorrected interferometer output signals, controller 150 can process these signals to determine at least one feature of the processing region, such as depth information of the processing region. Depth information includes keyhole depth of the PCR, seam tracking, finished weld surface height, workpiece height, and other measurements related to the workpiece geometry at time points that occur during, and both pre- and post- processing. In some instances, the controller 150 is also configured to control at least one processing parameter of the material modification process based on the at least one feature. In some embodiments, the at least one processing parameter comprises at least one property of the material processing beam and/or material processing laser source, non- limiting examples of which include on/off state, average power, pulse duration, peak intensity, energy density, fluence, wavelength, pulse repetition rate, pulse energy, pulse shape, scan speed, focal diameter, focal position, spatial pattern (on the sample). Other non- limiting examples of processing parameters include material feed rate, cooling media flow rate, cover/assist gas flow rate, cover/assist gas pressure, cover/assist gas blend, and additive material feed rate.

ML Al Algorithms and Motion ArtifactThe application of ML and AI algorithms to SS-OCT need not be limited by the capabilities of currently available industrial OCT systems, which are dominantly based on SD-OCT. Certain exciting possibilities in SS-OCT are derived from its capacity to capture data from a target, even when that target is in motion. This capability, and approaches to address the resultant artifacts, are discussed in herein. ML/AI techniques present possibilities to extract information from the motion artifact. For example, a keyhole collapse event will produce rapid motion in the phase change region which washes out imaging signal in an SD- OCT context. However, in SS-OCT, this event will produce a data signature, albeit one which is distorted on account of the motion which is occurring. ML algorithms may be developed to identify such collapses in SS-OCT imaging data based on the motion artifact signatures which they produce. ML algorithms may also be developed to identify the SS- OCT data signatures resultant from motion in the material processing region characteristics of events such as pore formation, weld blowouts, or other process anomalies and/or fluctuations.

WO 2024/158772 PCT/US2024/012552 The detection of such events provides novel opportunities for ensuring the quality and integrity of welds.Additional examples of the application of ML include using ML algorithms to identity' and/or correct distortions in the data resultant from the motion artifact, identify the velocity' of a target or other characteristics of its motion resultant from the motion artifact, etc. For example, an ML algorithm may be trained on SS-OCT A-line data taken with one or more known sample motion patterns in the data. Once trained, such an algorithm may be applied, depending on the specifics of implementation, toward the identification and/or correction of the motion artifact. For example, an AI or ML algorithm could be implemented to extract velocity' information from SS-OCT A-line data, identity' distortions in interferometer output signals resultant from sample motion, to correct distortions in interferometer output signals resultant from sample motion, to reconstruct distorted signals, and/or to achieve any of the other corrections for motion artifact as outlined above (as appropriate), including filtering and/or selection operations.

Example of imaging Target Velocity Estimation and CompensationAs referenced herein, an interferogram or an interference pattern can be a pattern formed by interference of waves of light from the reference arm 122 and the sample arm 1of SS-OCT system 100. An interferogram can also be thought of as a time vary ing signal which can be converted to a digital electronic signal using an optical detector 130 and an analog to digital converter (digitizer 135). Light reflected from the reference arm 122 and sample arm 124 are combined into a combined optical signal and directed to optical detector 130, which generates at least one interferometer output signal. Signals generated at the optical detector 130 can be converted from an analog to digital signal (by digitizer) and processed by controller 150. Controller 150 is configured to enable the information generated at the optical detector 130 to be sampled by digital converter 135. In some embodiments, the analog electronic signal is sampled at even intervals in k, and the k-clock 145 is detected using detector 147 and the resultant signal is passed to digital converter 1where it is used to time these even intervals.FIG. 10A is anon-limiting example of a captured interferometry signal that is in the time domain prior to capture and represents what will eventually become one or more A- line(s). It is to be appreciated that to produce a cross-sectional image (B-scan) or repeated A- lines acquired at a fixed transverse position over time (M-mode), many of the interferometry 70 WO 2024/158772 PCT/US2024/012552 signals shown in FIG. 10A need to be captured. For instance, according to one embodiment an M-mode OCT image comprises a set of subsequent A-lines that are shown in intensity׳ contrast adjacent to each other for purposes of capturing the evolution of a target (e.g., a weld keyhole) over time. The interferometry signal as it is captured may contain information at a variety׳ of dk/dt sweep states.According to at least one embodiment, the tunable light source 105 is controlled such that the tuning rate dk/dt of the imaging optical signal includes at least two tuning rates dk/dt that generate or are otherwise associated with respective interferometer output signals. In some embodiments the processing unit 150 is configured to control the tunable light source such that the imaging optical signal includes at least two tuning rates dk/dt that are associated with one or more interferometer output signals. In some embodiments the at least two tuning rates dk/dt include at least one negative dk/dt and at least one positive dk/dt. In one embodiment, both the positive and negative tuning rates are captured as shown in the interferometry signal of FIG. 10B. An appropriate Fourier transform method is applied to each of the positive/forward and negative/reverse interferogram portions to produce two A- lines. The A-lines are scaled to be in units corresponding to depth based on one or more properties of the light and/or the system. The peaks in such an A-line thus correspond to the depth at which a reflective sample interface is found (relative to the reference of the depth of the reference interface). In the case where the sample interface is in motion during the interferogram capture, a distortion is present in the resultant A-lines. Such a distortion is one example of the "motion artifact" as described above. The motion artifact causes the forward (positive) and reverse (negative) dk/dt A-lines to both be distorted. The distortion has effects which vary based on dk/dt rates present within the interferogram used to generate the A-line. An example of this distortion is show n in the A-line depth versus amplitude data of FIG.A, which shows one A-line generated using a positive dk/dt interferogram portion with no motion compensation or correction applied, referred to as the "Positive A-line," and one A- line generated using a negative dk/dt interferogram portion with no motion compensation or correction applied, referred to as the "Negative A-line." The distortion is visible as a displacement between the forward and reverse A-line peaks, as well as an asymmetry and distorted shape of each peak. This is just one example of a distortion in at least two of the two or more interferometer output signals and is identified by controller 150. The controller 150 performs an evaluation of the distortion of each of the at least two interferometer output WO 2024/158772 PCT/US2024/012552 signals and computes and applies a correction to the at least one interferometer output signal based on this evaluation.According to certain embodiments, the distortion corresponds to one or more geometric aspects of the interferometer output signal, as specified above (in the "Identification of Motion Artifact Distortion in SS-OCT Data" section). Calculating the correction(s) comprises the analysis of the frequency content of two or more interferometer output signals, and evaluating the frequency content of the two or more signals. Various correction methodologies may be applied to A-lines following this evaluation. Non limiting examples of possible correction methodologies include developing a full motion compensation matrix as outlined above, applying a geometric correction as informed by the evaluation as outlined above, or determining whether the relative difference between the frequency content of the at least two interferometer output signals exceeds a certain threshold.Returning to the example of FIG. 11 A, based on the evaluation of the distortion of the A-lines generated by the forward and reverse interferogram directions, the required correction can be computed. In some embodiments, the evaluation of the distortion is also used to compute an estimate of sample velocity during the time of acquisition. In some embodiments, the evaluation of the distorted components of each of the at least two interferometer output signals is used by controller 150 to generate an estimate of a velocity of the material being processed in the PCR.In accordance with one embodiment, the correction is computed based on a mathematical model that includes a set of functions that describe the relationship between different variables, including motion in the keyhole, the behavior of swept-source tuning, and the timing properties of the physical system. In one embodiment, the controller 150 is configured to generate a mathematical model based at least in part on one or more properties of the SS-OCT system and the evaluation of the distortion. In some embodiments, the controller 150 is configured to generate a mathematical model of the tuning rate dk/dt based at least in part on one or more properties of the SS-OCT system and one or more properties of the tunable light source 105. In another embodiment, a second model is configured to provide an estimate of the motion of the sample on the time scales of the k-clock. In some embodiments, these two models are used to estimate the time elapsed between k-clock samples, and/or to estimate the displacement of the target (sample) on these time scales and/or in some embodiments to compute an adequate correction.72 WO 2024/158772 PCT/US2024/012552 Once the correction is calculated (e.g., by the processing unit 150), in some embodiments it is then incorporated into the construction and modification of a new modified DFT matrix. For the example shown in FIG 11A, a transform matrix which incorporates the correction is computed for each of the positive and negative dk/dt interferogram portions and the new matrix is applied to the respective portion of the interferogram to produce the corrected A-line, which displays the corrected depth of the interface. FIG. 1 IB shows an example of the corrected A-line depth versus amplitude data of FIG. 11A. In other embodiments, the correction is computed and/or applied based on geometric factors only.According to at least one embodiment, corrected A-lines can be tracked, filtered, and analyzed to discern material modification process features, such as keyhole depth in a welding process. In addition, if multiple interferograms (e.g.. M-mode or B-scan images) have distortion from the same motion velocity, one (corrected) modified DFT matrix can be used to correct all of them. However, if multiple interferograms have distortion from different or changing velocities, then each interferogram requires a modified DFT matrix which corresponds to its velocity. An example of an uncorrected M-mode OCT image is shown in FIG. 12A. This M-mode image is taken from a benchtop experiment and offers a view of a sample target in uniform motion. FIG. 12A clearly displays the gap between the positive and negative dk/dt sweep portions that is indicative of the motion artifact. FIG. 12B shows the same M-mode OCT image with the motion artifact correction applied.FIGS. 13A and 13B show uncorrected and corrected OCT image M-Mode data, respectively, of a bead-on-plate keyhole welding process. The OCT image data is captured inline with the weld process, and data represents the evolution of the weld keyhole throughout the process. The bead-on-plate process was on a copper substrate, the process speed was 150 mm/s and the processing laser, an IPG Photonics YLS-6000, was configured with a weld head to emit a beam having 6 kW of power and a 200 pm focal spot size. The corrections applied to the data to generate the corrected FIG. 13B include methods described in "Identification of Motion Artifact Distortion in SS-OCT Data" and "Imaging Target Velocity Estimation and Compensation" discussed above.

Head IntegrationIntegration into Laser Material Processing HeadsTo achieve Inline Coherent Imaging (ICI) of laser material processing applications, according to at least one embodiment one or more components of the system are integrated 73 WO 2024/158772 PCT/US2024/012552 with a laser processing head. A schematic showing one possible configuration for such integration, which includes elements for steering the imaging beam and steering the combined imaging + processing beam, can be seen in the non-limiting example of laser head 715 of FIG. 4. Some embodiments of the system will employ the use of a dichroic mirror (7.8) for the purpose of combining the material processing beam and the imaging beam and separating them on their reflection from the process. In cases where the imaging beam and the process beam have similar wavelengths, the optical design of the dichroic is critical.Various embodiments of the invention can be integrated into different types of laser material processing heads, including but not limited to scanner heads, where active beam steering occurs on the process beam (e.g. using galvanometers, 7.9 and 7.10), wobble heads, where the process beam is manipulated in repetitive xy patterns to enhance material processing, and fixed optics. Application of the disclosed SS-OCT systems and methods to material processing heads designed for other laser processing operations, e.g. cutting, cleaning, and additive manufacturing, can be developed based on the same general principles of process and imaging beam integration.In some embodiments, the laser processing head may include special considerations for the imaging system. Such embodiments may include dedicated optical paths and targets for the purpose of compensating for thermal drift in the OCT system. Some embodiments may include dedicated k-clock optical paths within the head. Some embodiments may include one or more reference arm paths within the head. Such optical paths may be realized by beam splitting the imaging beam path (e.g., with 50:50 or 99:1 non-polarizing beam splitters), spectrally splitting the imaging beam (e.g., with a dichroic mirror and a sub- spectral region of the light source), or with electromechanical optics. Some embodiments may direct light into other paths based on optical intensity׳ (controlled by the amplifier). Some embodiments may include one or more imaging beam targets within the head which provide a scaling or calibration benchmark. Such benchmark paths may be realized by splitting the imaging beam, using partially reflective optics, or with electromechanical optics.In some embodiments, multiple sample arm beam paths may be introduced for purposes of imaging multiple positions relative to the processing beam 112 (e.g.. aligned, in front, behind, left, right, etc.). Measurements may be performed simultaneously or may be temporally gated. Such measurements, may, for example, be used in laser welding to direct the imaging beam to the keyhole (in line or just behind the processing beam), the surface of the material, the solidified weld surface (trailing the processing beam), or at regions of74 WO 2024/158772 PCT/US2024/012552 interest on the welded material (e.g., the seam position). Optical paths may be engineered with intentional delays so that measurements from each path may be distinguished based on location within the total Z field of view of the system. Optical paths may be engineered with intentional attenuation to compensate for reflectivity differences on the sample (e.g., keyhole vs surface). Optical paths may be configured such that they may be spectrally selected by controlling the swept source wavelength and sweep parameters.In some embodiments of the system, the OCT sample arm imaging beam optical path will contain at least one directing element, e.g., galvanometer(s) or other beam steering element(s) (7.3, 7.4) which can be used to position the sample arm beam path at multiple positions relative to the processing beam (e.g., aligned, in front, behind, left, right, etc.). In certain embodiments, the steering elements will operate at a high enough speed such that multiple positions relative to a beam may be imaged repeatedly within a single process. In certain embodiments the imaging beam steering elements may be used to assist in alignment, or to align the imaging beam so as to compensate for optical phenomena impacting the imaging beam, such as chromatic aberration caused by material processing beam optics.In some embodiments, a common mode interferometry setup may be employed, wherein the reference arm path shares at least part of the imaging system’s beam delivery path to the sample (i.e., sample arm path). For example, the coatings of the laser head’s coverglass (7.12) may be designed to partially reflect the imaging w avelength band, creating a common mode reference arm path ending at the output of the laser head. Such a path may be used in conjunction with a long Z FOV system to reduce the effects of thermal drift on absolute OCT measurements.

Dichroic MirrorTo partially or completely combine the imaging beam with the material processing beam (e.g., into a combined optical path), as it relates to embodiments involving laser material processing, an optic must be designed to combine the beams. This optic must also be able to separate the imaging beam(s) from other beams (e.g.. process beams) and/or emissions (e.g., blackbody thermal radiation from the process) subsequent to the reflection and/or backscattering of the imaging beam from the workpiece. A typical optical device which may be implemented in this function is a dichroic mirror, which has different reflective/transmissive characteristics at different wavelengths. Such mirrors can be simulated and designed for specific wavelengths, and different embodiments of the invention 75 WO 2024/158772 PCT/US2024/012552 will incorporate different dichroic mirrors as needed, based on design parameters including the wavelength of the imaging beam, the wavelength of the material processing beam, and the respective powers of each beam, along with other design requirements as needed.In accordance with at least one embodiment, the beam delivery system (e.g., bead delivery system 115) is configured with a dichroic optic configured to combine the imaging optical signal and the material processing beam into a combined optical path. In some embodiments, the beam delivery system is configured to impinge the imaging optical signal on the dichroic optic over a range of incidence angles. According to one embodiment, the dichroic optic is configured with a transmission spectrum having a first band edge, a reflection spectrum having a second band edge, and the first band edge and the second band edge have a maximum wavelength separation of 25 nm.Although the laser processing head examples described herein include the use of a dichroic mirror, it is to be appreciated that other configurations are also within the scope of this disclosure. For instance, off-axis integration of the imaging beam into the material processing beam, by methods known to those of ordinary skill in the art, is also within the scope of this disclosure.

Beam Steering and AlignmentIn at least one embodiment, the imaging beam path will contain steering/deflecting elements (e.g. galvanometers, resonant mirrors, polygon mirrors, acousto-optic devices, electro-optic devices) which specifically align its position relative to the process beam. These elements enable more precise alignment of the imaging beam to different process regions, such as the keyhole or the seam, which may be of particular interest for measurement purposes. In some embodiments, steering elements may be used to steer the beam in patterns which enable the collection of data on numerous process regions within the weld throughout a process (e.g. keyhole depth, seam tracking, finished weld surface height). In some embodiments, steering elements may be used to scan the imaging beam across a workpiece. In embodiments that implement imaging beam steering, the steering is typically applied before the imaging beam is combined with the process beam.In accordance with at least one embodiment, control for scanning of the imaging beam is synchronized to the imaging light source tuning cycle. In some embodiments, the imaging light source tuning cycle is synchronized to the control for scanning of the imaging beam. The synchronization functions to reduce positional jitter in the resulting geometrical 76 WO 2024/158772 PCT/US2024/012552 measurements of a workpiece. Through precise synchronization of the imaging beam scanning and the imaging light source tuning, transverse resolution of 20 microns or better on an OCT system may be achieved.In some embodiments, the alignment between the imaging beam and the material processing beam must be maintained. In some embodiments, design of the laser material processing head may be sufficient to maintain this alignment, and in other embodiments active correction of alignment using e.g., the imaging beam path steering elements, is also appropriate.

ApplicationsExamples of ApplicationsThe disclosed SS-OCT systems and methods can be employed for a variety of applications. Various embodiments of the invention can be optimized for imaging and quality assurance of a number of applications, including but not limited to laser material processing (e.g. welding, cutting, marking, brazing, cleaning, scribing, sintering, powder bed additive manufacturing, wire fed additive manufacturing). Particularly in laser material processing applications, the imaging beam can be integrated into a material processing beam for precise imaging of a process during the process, a.k.a. Inline Coherent Imaging (ICI). Such imaging may provide information on the features of the processing region. One example of features which may be characterized by such imaging is depth information of the processing region. Depth information on the processing region may in some applications include a range of at least 1 mm inclusive, a range of at least 5 mm inclusive, a range of at least 21 mm inclusive, and/or a range of at least 50 mm inclusive.

ScanningSome embodiments of the system incorporate the imaging beam into beam delivery heads where optical or opto-mechanical elements (e.g. galvanometers) are used to move the material processing beam, such as scanner heads. Non-limiting examples of such heads include 2-dimensional scanner heads, such as the IPG Photonics 2D High-Power scanner, 3- dimensional scanner heads (e.g. heads where the focal distance and the position within the focal surface of the material processing beam may be adjusted by the beam delivery optic) such as the IPG Photonics 3D High-Power scanner, and advanced scanner configurations, such as polygon scanner systems.77 WO 2024/158772 PCT/US2024/012552 In some embodiments, wavelengths of the imaging and material processing beam are selected to be spectrally close together, in order to minimize the chromatic aberration caused as the combined image and process beam are steered towards the edges of scanner head optics. For example, to minimize chromatic aberration in an embodiment configured to work with a 1070 nm fiber-laser in a scanner head, some embodiments of the system may be designed using swept sources in the nearby 1000 to 1050 nm wavelength range. Alternatively, if the material processing laser operates closer to 1030 nm (e.g. a disc laser), then the imaging system could be centered closer to the 1040 to 1070 nm wavelength range. In some embodiments of the system, software and/or opto-mechanical methods may be used to correct for chromatic aberration, for example using beam steering corrections on the imaging beam to re-align as desired in regions of operation where chromatic aberration is observed.In embodiments of the system where the material processing beam and the imaging beam are actively steered/scanned using elements in the beam delivery head, the optical path length to the workpiece may substantially vary throughout the scan range of the beam delivery setup. In embodiments of the invention which incorporate 3D scanner heads, optical path lengths and specifically the distance between the beam delivery head and the workpiece may be substantially and deliberately variable. However, variability in the optical path length to the workpiece may also be present in many other beam delivery head configurations, such as 2D scanners. In some embodiments, the parameters of the system may be set such that the imaging range is adequate to capture the full variation optical path length over the beam delivery head field-of-view without the adjustment of the delay line. The considerable (>mm) coherence length available from certain SS-OCT implementations enables this approach. In some embodiments which incorporate scanning, an active delay line may be included to adjust the imaging range responsive to the variation of the optical path length to the workpiece throughout the scan range.In embodiments of the system which incorporate 3D scanning, the focusing and collimation apparatus of the imaging beam may be equipped with electronic, opto- mechanical, or opto-electronic devices that enable active adjustment of the imaging beam focus, such that the focal surface of the imaging beam may be actively adjusted to be partially or fully co-incident with the focal surface of the material processing beam. In 3D scanning applications where the focal distance of the material processing beam is varied throughout a WO 2024/158772 PCT/US2024/012552 weld, the imaging system may be used to provide active feedback, e.g. on workpiece height and/or keyhole penetration, to guide and validate the 3D scanning performance.In some embodiments of the system, a calibration may be performed to characterize the optical path length at various locations in the available field-of-view of the beam delivery head (e.g. the scan field-of-view of the scanner head). In some embodiments of the system, a calibration may be performed to characterize the chromatic aberration (CA) of the imaging beam relative to the process beam at various locations in the available field-of-view of the beam delivery head (e.g., the scan field-of-view of the scanner head). Either or both of these calibrations may form the basis for the application of compensation methods to correct for variability in these parameters. Compensation methods may involve computational corrections (e.g., algorithms), and/or physical corrections (e.g., imaging beam steering, reference arm adjustment). The calibration may also be performed to characterize the field of view of the imaging beam steering optics, either independently or concurrently with the material processing beam steering optics.Additional applications of embodiments of the system are possible with various active scanner and/or beam steering configurations implemented in the beam delivery head. For example, some embodiments of the system may incorporate polygon scanners in the beam delivery head, which may be applied to welding, cutting, surface treatment, coating removal, patterning, and web processing.

High Power WeldingCertain embodiments of the system may be designed for high-power and very-high- power weld monitoring (>20 kW). The imaging depth field of view of some tested embodiments of the disclosed SS-OCT system is larger compared to conventional SD-OCT systems (e.g., 12 mm for a conventional SD-OCT system vs. more than 50 mm for certain embodiments of the SS-OCT systems disclosed herein). The greater imaging depth available through SS-OCT unlocks the possibility of imaging welds of much greater depth while still monitoring additional metrics like the workpiece surface and the finished weld surface. Embodiments of the system designed for high power welding may require that material processing head design and integration is suitable for handling the levels of energy and heat developed in such processes.

Reflectivity Measurements79 WO 2024/158772 PCT/US2024/012552 In some embodiments, reflectivity measurements are performed in addition to, as an alternative to, or in between coherent measurements to monitor additional aspects of the process. In one embodiment, the same light source (imaging light source 105) is used for both the reflectivity measurements and the coherent measurements. The amplifier 106 in some embodiments may be used to increase DC signal levels for improved measurement signal to noise ratios (SNRs). In such instances, a feedback signal sampled from the output of the amplifier 106 may be used to control amplifier stabilization for purposes of more accurate reflectivity measurements. Additionally, back-reflected measurement beam light from the sample may also be used as an amplifier control signal to normalize measurements from the surface of the part (workpiece).

Sequence ModeIn some embodiments, the system may be designed to capture a set of multiple OCT captures, comprising A-lines, B-Scans, M-Modes, Volume Captures, or other imaging formats known to those or ordinary skill in the art, corresponding to one or more subsequent tasks and/or material modification processes. Such a set of captures is referred to as a sequence of imaging tasks. Such sequences may include any combination of measurements of various sample targets, such as fixtured parts, seams, weld keyholes, finished surfaces after processing, and more. In some embodiments, imaging tasks within a sequence may be concurrent with material processing. In some embodiments imaging tasks within a sequence may occur before and/or after material processing, or may correspond to a metrology task or capture. In some embodiments some or all of these types of imaging tasks are incorporated. Sequence imaging may comprise in some embodiments repeated measurements of aspects of identical processes, or in other embodiments of a set of measurements of subsequent different processes.Imaging processes within the sequence mode may incorporate one or more processing elements described in this disclosure, non-limiting examples include dispersion compensation, motion artifact compensation, or generating tracked data. In accordance with some embodiments, imaging tasks within a sequence may be used to develop Quality Assurance (QA) metrics, which may correspond to the quality of the process corresponding to the current imaging task, or may be used to extract parameters for feedback control of either the current processing task or a subsequent processing task within the sequence. In WO 2024/158772 PCT/US2024/012552 some embodiments, QA metrics may be developed based on the result of multiple imaging tasks within a sequence, up to all the tasks within a sequence.In some embodiments of the system, a programmed sequence of imaging tasks can continuously monitor a given process in an unsupervised automated manner. Such embodiments may be integrated with a quality assurance alarm to produce an alert and/or annunciation when quality assurance metrics are not met for a task within a sequence or for the full sequence itself. Such embodiments may׳ be integrated with another method of generating annunciations based on the outcome of sequences.

Pre-Weld Workpiece CharacterizationIn certain embodiments of the system, the imaging system may be used to characterize the material modification sample or workpiece at a time other than during the material modification process. In such cases the imaging beam may still be integrated into the beam delivery׳ apparatus for the material processing beam, to enable the imaging of the workpiece inline with or in close proximity to the material processing beam location. In some such configurations, the imaging beam may be steered independently from the material processing beam, using separate beam steering elements in the imaging beam path. In some such configurations, the imaging beam may be steered by beam steering elements in the material processing beam path. In some such configurations, the imaging beam may not be actively steered.In some embodiments of the system, the SS-OCT system may be configured to measure the distance between a workpiece and the focal surface of the material modification beam optic. In material modification optics for which the material modification beam is actively steered, e.g. scanner heads, the SS-OCT system may additionally be configured to characterize the entire focal space or focal surface over which the material modification beam may travel. Such a characterization may be completed as a calibration prior to the material modification processing step. In embodiments of the system integrated with material modification optics for which the focal distance may be actively adjusted, the SS-OCT system may be used to provide feedback on sample and/or workpiece features/geometry. such as a distance between the focal surface of the material modification beam optic and the workpiece surface, or a measurement of position and geometry׳ of fixture parts to evaluate fit- up. In such systems, the workpiece geometry measurement may be used in active feedback WO 2024/158772 PCT/US2024/012552 control of the material processing beam head, such as to provide "auto-focus" or weld path correction capability.

Top Surface Reference Point Measurement (TSRP)In some embodiments, one or more imaging beam positions may be used to measure a top surface reference point(s) (TSRP), with further embodiments including the ability to simultaneously measure the TSRP and weld depth using multiple imaging beams. The TSRP is a reference position(s) established using points on the sample surface and in instances where the sample is substantially flat, at least one TSRP can be used to define a top surface reference plane. Although mentioned here within the context of setting a TSRP before a welding process, it is to be appreciated that the TSRP may be set. measured, or calibrated before, during, or after the welding process. This may be achieved by taking a baseline depth measurement or measurements at locations on the sample unaffected by the welding process. In some instances the TSRP can be determined by taking one or more measurements of the material immediately before the weld begins. If the material is sufficiently flat relative to the weld motion, then this initial measurement can define the TSRP for the rest of the weld. Other techniques for measuring TSRP are known in the art.

Seam TrackingIn certain embodiments of the system that involve laser welding, the imaging system may be used to obtain measurements taken at a specific distance sufficiently far ahead of the processing beam focal spot along the path of the material processing beam during processing such that measurements are unaffected by the process itself, but close enough to the focal spot such that accurate measurements of the part fit-up and/or geometry (e.g., the seam-line between the two components being joined by the welding process) may be used to determine if the focal spot is sufficiently aligned to the seam-line. In certain embodiments, the imaging system may be used to obtain measurements of the part fit-up and/or geometry prior to the beginning of the material processing, e.g. as a pre-scan, or after the material processing. In one example, a scanner may be used in combination with the imaging beam to locate one or more surface features (e.g., a groove) which can be used to provide measurements of the location and/or geometry of the seam before the material processing beam arrives at a given location in the process. In certain instances, these measurements may be further used to WO 2024/158772 PCT/US2024/012552 dynamically correct misalignment, for example by providing real time feedback to the material processing beam steering apparatus.Besides seam tracking, the scope of this disclosure also includes other desired features (e.g., workpiece height) that can be tracked by the imaging beam prior to or during a material modification process. As with seam tracking, in some embodiments the imaging beam can be configured to scan the desired feature prior to the start of the material modification processes. In embodiments of the system which enable pre-material processing scans, processor 1may be set up to provide real-time feedback based on the imaging of a desired feature, for the purpose of closed-loop feedback control of a material modification process.In some embodiments, measurements of the location and/or geometry of the seam, or other notable pre-weld features which are measured, may be used in the development of Qualify Assurance (QA) metrics.

Post-Weld CharacterizationIn certain embodiments of the system that involve laser welding, the imaging system may be used to obtain measurements taken at a specific distance sufficiently far behind the processing beam focal spot along the path (geometry/directi on) of the material processing beam during processing such that measurements are unaffected by the process itself, but close enough to the focal spot such that accurate measurements of the finished weld surface may be used to determine aspects relating to the qualify of the weld.In some embodiments the finished weld surface measurements, or other notable post- weld geometric aspects, may be used in the development of QA metrics.In accordance with at least one embodiment, the scope of this disclosure also includes monitoring of desired features that can be tracked by the imaging beam subsequent to a weld process. For instance, measurements may be used to inspect the seam surface subsequent to welding, and identify geometric features and/or the presence of physical defects (e.g., blowouts). In some embodiments, the imaging beam can be configured to scan the desired feature subsequent to the completion of the material modification process.

Additive ManufacturingIn certain embodiments, the material modification may be part of an additive manufacturing process, a subtractive manufacturing process, or some combination thereof. The additive manufacturing process may comprise powder bed fusion, directed energy 83 WO 2024/158772 PCT/US2024/012552 deposition, wire fed additive manufacturing, laser sintering, or a variant and/or combination thereof. Embodiments of the invention which are applied to material modification processes which can be broadly categorized as additive and/or subtractive may include features which provide feedback of specific interest to such processes, some non-exclusive examples of which are detailed below.Embodiments of the invention which are designed to work with additive manufacturing processes that involve the delivery of additive manufacturing precursor materials (e.g. powder, wire) may be configured to produce measurement outputs which characterize relevant metrics of precursor delivery and/or quality. One example of such a metric is the flatness of a layer of powder deposited during a powder bed fusion additive manufacturing process. In some embodiments, the additive manufacturing set-up may be set to make corrections in response to the measurement information acquired by the SS-OCT system. For example, selective laser ablation and/or re-melting may be applied to correct the flatness of a part based on OCT measurements taken during or after deposition. Additional measurements, such as measurements of features/geometric characteristics of the keyhole, measurements of deposited track surface trailing the keyhole, and measurements of the geometry of the part being constructed, may also be performed. In some embodiments, the SS-OCT system may be used to track measurements of a manufactured part relative to a model, (e.g. a CAD model). Some embodiments of the system may be set up to provide real- time feedback to update and modify build parameters of the additive process to maintain desired characteristics.

General Feedback ControlReal time feedback provided by the imaging system may be used to change process variables in a way that compensates for variations in feedstock (e.g., poor fit up) and instabilities (e.g., variable weld depth) in the process as it is accelerated to higher speeds and/or pushed to greater depths. This may extend the usability of laser welding systems to include lower cost input feedstock, higher processing speeds, and/or deeper penetration while maintaining acceptable quality. The real-time feedback may also be applied to enable greater consistency in process outputs over time, for example real time feedback may be used to control the power of a diode laser used for material processing, and power of the laser may be increased via feedback mechanisms when keyhole depth, as measured by the system, deviates from the target value. There are many factors which may cause such deviation in weld84 WO 2024/158772 PCT/US2024/012552 keyhole depth in a ty pical material processing system, including degradation of the output power of laser modules over time, pollution or obstruction of the beam path (e.g. smoke, or weld spatter on beam delivery optics), and more. Changes which occur within the timespan of one material processing process, such as inconsistency in the material parameters of the sample being processed, or changes which occur over the course of many material processing processes, such as changes in the ambient conditions, may in some cases contribute to changes in the output quality of a process such that critical process metrics are no longer within the target specification. Real time feedback provided by the imaging system may in some cases be applied to the active feedback control of process parameters to keep weld processes within the target metrics. In some cases, real time feedback methods may implement control loops and/or theories known to those of ordinary skill in the art. including proportional control, and/or, proportional-integral-derivative control. Implementations of feedback control may be based on feedback derived from measurements and or signals provided by the SS-OCT system, and may additionally incorporate one or more of the signals and or signals provided by auxiliary sensors in the SS-OCT system, measurements and or signals of other sensors within the material processing system, and models of various components of the material processing beam system.The transient effects during the start or finish of a welding procedure may have a negative effect on the outcome of a weld (e.g., inconsistent seam depth, underfill). For example, quantifying the amount of underfill along the surface of the seam is important information for determining the strength of the weld, its resistance to corrosion, and its compatibility with subsequent coating processes such as priming and painting. According to at least one embodiment, feedback provided by the imaging system may be used to reduce these defects by controlling one or more process parameters to compensate for the transient behavior of the weld at its start, at its finish or both.

Additional System Capabilities and FeaturesAuxiliary Measurement SystemIn accordance with at least one embodiment, SS-OCT systems as disclosed herein may also include an auxiliary measurement system 160 that is in communication with controller 150 and includes auxiliary sensors such as visible and/or IR-sensitive photodiodes, and/or cameras and/or spectrometers, which in some instances may be coupled to a w elding head by way of optical fibers. The auxiliary measurement system 160 may be configured to 85 WO 2024/158772 PCT/US2024/012552 measure process radiation, for example, within a spectral band between 100 nm to 20 WO 2024/158772 PCT/US2024/012552 It should be noted that unlike the biological applications of coherent imaging, material processing applications, as is the primary focus of this disclosure, often feature the presence of incoherent optical sources that are incoherent with the imaging light in the form of blackbody radiation and the material processing beam light itself. In spectrally discriminated SD-OCT approaches, a great deal of this light is discarded automatically by the spectrometer. In accordance with at least one embodiment, additional filtering elements (in the form of FBGs, WDMs and other filters known to those of ordinary skill in the art) are added at one or more places in the sample arm of the SS-OCT system to ensure that these incoherent optical signals do not reach the main detector (e.g., detector 130 of FIG. 1). However, it is potentially useful to divert these signals to auxiliary detectors. Some possible placements of such auxiliary detectors within the sample arm of an interferometer are outlined in FIG. 5 A. One possible method of diversion is shown in the example of beam delivery head 315 in FIG. 5B, where a schematic of the material processing beam head 315 is shown that comprises an additional dichroic (3.4) to separate blackbody radiation signals to a detector (3.5) in the imaging beam portion of the head. The diversion of these samples may also be achieved in the fiber portions of the interferometer. Blackbody radiation signals may be coupled back into the sample arm fiber, and subsequently split from the OCT signal using e.g. a wavelength division multiplexer, such as WDM 614 in FIG. 5 A to enable detection on a dedicated detector, such as Auxiliary' Detector 611 in FIG. 5 A, such that concurrent detection of blackbody radiation and SS-OCT data may occur. To enhance back-coupling of broadband blackbody radiation, in some embodiments a double-clad fiber may be employed, such that blackbody radiation is coupled into the multi-mode inner-cladding portion while the imaging beam light reflected from the workpiece is coupled into the single-mode core portion of the fiber. Examples of the incorporation of blackbody detection into an OCT system via a double clad fiber in the sample arm are described in more detail in US Patent No. 10,898,969, which is hereby incorporated by reference.One non-limiting example of an implementation including auxiliary' detection is to position one or more photodiode sensors for blackbody radiation detection in a beam steering module for the imaging beam, as in the case of auxiliary sensor 613 in FIG. 5A. One configuration possible for such an auxiliary detector is shown in laser head 315 of FIG. 5B and described in more detail below. Note that to enable blackbody detection simultaneously with OCT imaging, it may be necessary to include an additional detector (e.g. blackbody sensor 3.5 of FIG. 5B), and ensure that the desired blackbody wavelength can pass through 87 WO 2024/158772 PCT/US2024/012552 one or more dichroic optics (e.g. the dichroic mirror 3.8 of FIG. 5B which splits the imaging beam and the material processing beam upon their reflection from the process) while being correctly separated from the OCT beam by using appropriate optics (e.g. Blackbody Signal Dichroic 3.4 of FIG. 5B).One non-limiting example of an implementation including auxiliary' detection involves the inclusion of double clad fiber including a single mode core with an additional inner cladding which is designed to enable the propagation of multi-mode light. This set-up is represented by double-clad fiber 610 and Auxiliary detector 612 in FIG. 5 A. A detail of double-clad fiber (61OA) is show n in FIG. 5A, displaying the multi-mode inner cladding (61 OB) and the single mode core (6IOC). An advantage of implementing double-clad fiber for the detection of blackbody signals is that the larger surface area of the multi-mode inner cladding enables a greater back-coupling of the broadband and incoherent light produced by blackbody and/or thermal radiation, enabling a stronger signal for detection at the auxiliary detector (e.g. auxiliary detector 612 in FIG. 5A). To enable the detection of blackbody radiation, the multi-mode light captured in the inner cladding of the double clad fiber may be coupled out into a separate multi-mode fiber.The practice of coupling additional optical signals, such as blackbody radiation or back-reflected processing beam, into the sample arm be generally referred to as wavelength multiplexing the sample arm return signal. In some embodiments, this multiplexed return signal(s) can be detected and used as additional metrics for process quality control and also to aid the alignment of the coordinate systems of the process beam and imaging systems. The latter approach is performed by using one or more directing elements to scan the imaging system about the region where the material processing beam source is striking a workpiece, calibration target and/or a test coupon of material. While this happens, the material processing beam source is operated (preferably at a low intensity) so as to either a) produce reflected material processing beam energy7, b) produce blackbody7 radiation, or c) both. As the directing element scans over this region, the main detector and/or auxiliary7 detectors receive radiation that can be correlated to the scan location. In this way, the energy distribution and location of the material processing beam source can be determined through means including peak finding, maximum finding, Gaussian curve fitting, supergaussian curve fitting and other fitting functions used for beam characterization that are known to those of ordinary skill in the art. By selecting which wavelengths of radiation are allowed to the detector(s). this approach conveniently allows chromatic aberration of the beam delivery88 WO 2024/158772 PCT/US2024/012552 system to be compensated and mapped. This mapping can be stored in a memon׳ and used by the control module and/or directing element control electronics to allow directing element(s) to compensate for chromatic aberrations. PCT Patent Application No. PCT/US2021/027672, owned by Applicant and incorporated by reference herein, examines and outlines this process in more detail.Capturing the energy spot width of blackbody radiation or back-reflected processing beam and using it as a proxy for the material processing beam can be used to produce additional beam characterization measurements such as beam caustics and focal surface determination. In some embodiments, spectral filtering may be used to intentionally remove back reflected process beam light and blackbody radiation from the OCT optical detection elements. However, in some embodiments, the OCT optical detection elements and the back- reflected processing beam and blackbody radiation collection elements may be shared (i.e., use common optical paths) to reduce optical complexity and cost. In such cases OCT signals may be distinguished from back-reflected process beam and blackbody radiation signals through different photodiode detection schemes (e.g., balanced vs unbalanced), through digital processing (e.g., lowpass. bandpass, or high pass filtering), through time gating (e.g., collection of the OCT signal at different times from the auxiliary radiation), or some combination thereof. Time gating may be achieved by turning off the OCT system light source, reducing it at the amplifier, or through additional filtering elements.In some embodiments, the detected process blackbody radiation may be used to compute an estimate of the temperature of the process or of a location within the process. This metric may be used to track the stability of process temperature over time, and record absolute or relative values. When accompanied by beam steering of the imaging beam, such a measurement may also be used to estimate absolute or relative temperature throughout a process in space.In some embodiments, a portion of the sample arm includes a double clad MM/SM mode stripper fiber component such as the Castor Optics DC1060LE (Montreal, QC, Canada). This allows a variety of functions including integrated time of flight (TOP )/frequency modulated continuous wave (FMCW) light detection and ranging (LIDAR) detection and optionally with the help of further filtering elements, the ability' to detect larger amounts of incoherent emissions (for higher SNR auxiliary sensing). The multimode channel can also be used to collect additional reflected imaging light that is transmitted to an auxiliary photodetector in order to perform closed-loop feedback of the imaging light source emission 89 WO 2024/158772 PCT/US2024/012552 power. The multimode channel may also be used to collect back-reflected process beam light, blackbody radiation, or a combination thereof.

Interferometer FeaturesIn some embodiments, the interferometer has at least two reference arm paths, of similar or dissimilar length. The reference arm may also be configured with at least one actuator that causes one or more of the paths to be selected or deselected. The means of selection or deselection may include adding attenuation to the beam path. Attenuation of the path can be caused by moving a lens, closing a shutter, actuating an optical switch, adding an absorbing or reflecting optic to the path, changing polarization of the light, rotating a polarizing optic and/or changing the alignment of a mirror in the beam path, including the end mirror. Path selection may also be selected spectrally, wherein a spectrally-selective optical element (e.g., a dichroic minor) may be used in conjunction with dividing the swept source spectral band into two regions (one dedicated to each reference arm). The reference arm(s) are designed such that all of the paths may be illuminated simultaneously, and deselected by the control module. interestingly. illuminating two or more reference paths would create a common path interference signal that would be suppressed by the balanced detection scheme show n in SS-OCT system 100 of FIG. 1. However, it could still be recovered by monitoring a single-ended (i.e., unbalanced) detection output from the BPD. This is a means of simultaneously measuring a K-clock signal from a single interferometer and has the added benefit of being able to compare two known paths simultaneously in order to confirm the axial calibration of the system. Lastly, while simultaneous illumination of multiple reference paths may be looked upon as wasteful of optical pow er by someone of ordinary skill, it should be emphasized that the light source described herein develops an unusual abundance of imaging light, meaning that less efficient, but more powerful/practical approaches like this can be considered without significant loss to image quality.In accordance with at least one embodiment, the amount of optical power returning from at least one reference arm is adjusted in order to shift the dynamic range of the imaging system. In situations where strong reflections are returning from the sample, it may be desirable to attenuate the reference arm so as not to saturate the detector(s). This can be performed as a closed-loop control with the main BPD signal, single ended BPD signal, or an auxiliary photodiode serving as the input and a variable attenuator and/or any of the means of attenuating the reference path described in the previous paragraph serving as the actuator.90 WO 2024/158772 PCT/US2024/012552 Proportional (P), Proportional-Integral (PI), and Proportional-Integral-Differential (PID) control schemes are all possible via the control and/or feedback modules of the system. Another way reference power and dynamic range may be effected is through modulation of the light source power, as described herein.In accordance with certain embodiments, a visible light "guide" or "pointing" beam is injected into the imaging beam, e.g.. via the sample arm and transmitted through the head to the workpiece. This can be done by means of a WDM device or other similar components known to those of ordinary skill in the art. The addition of a guide beam into the imaging system provides a variety of benefits. Since the imaging fiber core diameter is often much smaller than the process fiber, it produces a sharper point on the focal surface and less modal interference in the fiber. This makes the point easier to see accurately. By steering the guide beam with the directing element, visible patterns can be drawn on the surface of the workpiece to aid in the teaching and alignment of the material modification process as well as the imaging system itself. Showing a visible beam that represents scanning of the imaging system also aids in interpretation of imaging system data. In a further optimization of this approach, the timing of the imaging system acquisition, the scanning path of the directing element and the emission of the guide beam may be tuned to compensate for transverse chromatic aberration in the beam delivery system such that the true imaging path is represented by the guide beam.In some embodiments, one or more booster amplifiers may be added to the sample arm of the interferometer in order to increase the sample arm optical pow er as shown in FIG. 3. For example, amplifier 406b is configured to amplify the returned imaging light, since other optical signals have been blocked. Dispersion and optical path length introduced by the introduction of such an amplifier may be compensated for by the addition of appropriate compensating elements to the reference arm. By choosing a short amplifier with a low amount of stored energy and pump power, spontaneous emission is reduced and, from a relative perspective, weak signals are amplified more than strong ones. This has the added benefit of effectively compressing the dynamic range of the system. The control module and/or feedback module (not explicitly shown in FIG. 3, but is analogous to processing unit 150 of FIG. 1) controls the gain on this amplifier by modulating the pump current for its diodes.According to some embodiments, high population inversions are employed in order to shift the gain of the amplifier to shorter wavelengths, thereby tuning the operation spectrum 91 WO 2024/158772 PCT/US2024/012552 of the imaging system further away from the spectrum of a high power laser that is used for material processing such as welding. For example, a high population inversion YDFA may be employed to produce an amplifier gain peak in the region of to 1020 to 1050 nm, which keeps the operation spectrum of the imaging system away from the typical 1070 nm operating wavelength of select Ytterbium-Doped Fiber lasers.Because differential stress or temperature changes in the fiber of the interferometer can cause path length variations in the reference arm or sample arm of the interferometer, in some embodiments mechanisms may be included in the sample arm to compensate, including adjustable mandrels, motorized stages containing optical components, adjustable mirrors, and other optical mechanisms known to those of ordinary skill in the art. In some embodiments, a dedicated correction path may be included, in the form of a mechanical or optical feature in the sample or reference arm, which can be used for automatic compensation or manual compensation.In accordance with at least one embodiment, e.g., one that employs an imaging light source having a wavelength near 1550 nm, the system is configured with dispersion shifted fiber to reduce chromatic dispersion in the interferometer allowing air path lengths to be compensated with fiber with a reduced dispersive effect on the point spread function of the imaging system.According to certain embodiments, one or more portions of the interferometer is configured with polarization maintaining (PM) fiber. In this configuration, it is advantageous to illuminate interferometer(s) with a single polarization to reduce path length degeneracy due to the birefringence of the fiber. The benefit of using PM fiber is that manipulation of the sample and reference arm fiber causes less of a variation in the interference signal received at the BPD. In order to achieve this, in some embodiments, polarization optics are added in the light source module to align the polarization of the light that it emits to the preferred polarization of the interferometer.

MultiplexingIn accordance with at least one embodiment, the imaging light source module is shared/multiplexed between multiple interferometers which may be associated with multiple beam delivery systems, material processing beam sources, detectors, etc. An example configuration is shown in FIG. 6. Using a swept laser in a multiplexed configuration requires special care to be taken when selecting the lengths of fibers and signal cables so that any92 WO 2024/158772 PCT/US2024/012552 phase shift between the interferometers is either minimized or compensated for. In some embodiments, the length of fiber between the light source module and each multiplexed interferometer unit is matched to less than 1 ns of propagation time. In other embodiments, the matching is less than 10 ns.In some embodiments, a single k-clock positioned in or before one of the interferometers is used as a k-clock for multiple interferometers when one light source is shared between multiple imaging systems. This configuration implies that the time delay between various multiplexed interferometers/detectors has to be considered when applying the k-clock signal to the signal processing chain. However, in other embodiments the k-clock is implemented by sampling the reference arm signal instead.In some embodiments, the imaging system scanning control is synchronized to the imaging light source tuning cycle to reduce positional jitter in the resulting geometrical measurements of a workpiece. In at least one embodiment, the light source tuning cycle phase and frequency is measured and used to calculate a positional offset that is added to geometrical measurements to compensate for jitter/variations in the start phase of the light source tuning cycle. Ideally. the clocks running the deflection system and the light source tuning signal are themselves synchronized to a common electronic clock.According to certain embodiments, interferometer unit(s) are additionally equipped with a shutter or other beam-blocking device that is operated by a safety module to ensure optical safety. One way this can be achieved is to monitor the position of one or more of the directing elements and use safety logic to ensure that the light source cannot be operated at a potentially hazardous power (in combination with the directing element that allows the beam to exit the beam delivery system) unless the safety interlock is satisfied.

Autofocus for Applications with Considerable Imaging, Depth VariabilityCertain embodiments may take advantage of the available deep imaging field of view to an extent where the imaging depth field of view is greater than the depth range over which the focus of the imaging beam is adequate. In such applications, optical, mechanical, and/or electronic elements which allow the shift in the focus depth may be integrated into the system. One example which enables focal depth shifting within the field of view is focus- tunable lenses, an electro-optical technology'. Some embodiments of the system may take advantage of feedback control between focusing elements and return power or image data to enable "autofocus" operations. Possible optimizations in focusing include, but are not limited 93 WO 2024/158772 PCT/US2024/012552 to optimizing the focus of the imaging beam to align with the workpiece surface or with the bottom of the keyhole or with the finished weld surface.Sweeping the focal depth surface of the imaging beam presents the possibility for numerous useful measurement algorithms. Fitting the back-reflected intensity for a wavelength can be used to detect the focal surface of a system. Measuring the peak possible amplitude of all interfaces in the imaging frame by sweeping the focus across the whole Z- range can help in identifying the true brightest interface(s) by algorithmically correcting for the effects of defocus. Focus can also be tuned to track a variable interface depth, for example, by using pre-weld scan imaging data to evaluate upcoming interface depth and adjust focus responsive to the upcoming depth.

Interferometer TopologiesAccording to various embodiments, the interferometer is implemented using fiber- based optical path components, or free-space optical path components, or some combination of fiber-based and free-space optical path components. In some embodiments of the system which include fiber-based interferometer components, polarization-maintaining fibers may be used. In some embodiments of the system which include fiber-based interferometer components, single mode fibers may be used. The dispersion present in the sample arm and the reference arm of the interferometer may in some embodiments be designed to be as well- matched as possible, to improve imaging performance. The interferometer implementation in a specific embodiment of the invention may vary based on the requirements of that embodiment, and may incorporate interferometer components and methods known to those of ordinary7 skill in the art.According to some embodiments, a Mach-Zehnder interferometer (an example of which is shown in FIG. 1) is preferable because it simultaneously allows for easy adjustment of the initial splitting ratio from the imaging light source as well as balanced detection. How ever, ty pical implementations of this topology require two Faraday devices which can increase cost and complexity. In the Mach-Zehnder interferometer configuration, care needs to be taken in the interferometer design to ensure that the two paths to the BPD 130 are approximately matched so that the positive and negative interference signals arrive at the BPD simultaneously.Since the pow er of the amplifier light source may be (for practical intents and purposes) sufficiently high to not be a limiting factor in optical design, in some embodiments, 94 WO 2024/158772 PCT/US2024/012552 a Michelson interferometer may be used with (e.g., detector 130 of FIG. 1) or without (e.g., detector 230 of FIG. 7A) balanced detection with little overall penalty to the signal to noise ratio (SNR)/sensitivity. FIG. 7A is a schematic representation of an SS-OCT system 2configured with a Michelson interferometer and shows how this could be accomplished in terms of interferometer topology7. In some embodiments where pow er of the amplifier light source is considered not to be a limiting factor, an interferometer similar to a Mach-Zender may be constructed by replacing the circulators (121, 123 in FIG. 1) with 50:50 splitters (521, 523 in Fig 7B), one example of such an interferometer is shown in FIG. 7B. This configuration may provide cost advantages over an implementation which includes circulators. Although such an interferometer would have worse photon economy than a more standard Mach-Zender embodiment, it is to be noted that in some embodiments the amplifier may provide an unusual abundance of power, enabling high return interferometer power even in such interferometers as shown in FIG 7B. In either interferometer configuration, care needs to be taken in the interferometer design to ensure dispersion mismatch is minimized. Although not explicitly shown, one or more imaging source amplifiers similar to amplifier 106 of FIG. 1 may also be included in system 200 and/or in system 500.In system 100 of FIG. 1, a 90:10 splitting ratio is used between the sample arm and the reference arm. This has the benefit of greater photon economy betw een source, workpiece and detector. It is recognized that a variety7 of other splitting ratios could be used (e.g. 99:1, 95:5) to shift dynamic range and further optimize the photon economy of the system.In some embodiments, the interferometer topology is a demodulation interferometer.In accordance with certain embodiments, the reference path contains elements which enable the control of reference signal power. This may be achieved through the construction and selection of different reference paths, using splitting methods and optical elements known to those of ordinary7 skill in the art. This may alternately be achieved by introducing attenuation into a single reference path as needed. Illuminating reference paths with different output powers or modifying the output power of a given reference path can be used to match power levels delivered to the BPD by the sample and reference arm respectively. This can be applied to enhance the dynamic range of the system by allowing the full BPD detection range at different sample power return conditions, and preventing saturation. In embodiments applied to processes where multiple reflectivity conditions exist or may exist on the sample arm, this configuration of the reference path enables the optimization of return power for the 95 WO 2024/158772 PCT/US2024/012552 various sample powers, improving the dynamic range of the system at each individual return power condition and thereby effectively increasing the dynamic range of the balance of the system. Illuminating reference paths of different lengths or modifying the length of a single reference path (such as in accordance with the methods described in "Interferometer Features" above), in conjunction with adjusting any system timing as necessary7, can for example modify the imaging range of the system or the axial resolution of a given system during operation.

Double Interferometer/Double or Buffered Source SS-OCT TopologiesAs noted herein, information from measurements taken with differing dk/dt values can be applied to compute corrections which reduce or otherwise eliminate the effect of the motion artifact. A further concept described herein allows for the capability to acquire forward (positive) and reverse (negative) sweeps (dk/dt) simultaneously. Several concepts related to this capability are outlined below7, with physical embodiments and further details also included below. Overarching concepts include the use of a single imaging light source or multiple imaging light sources that are used to illuminate multiple optical interferometers simultaneously, interferometers with sample arms that share at least one optical element (e.g., interferometers w ith at least partially overlapping sample arms (multiple interferometers "sharing" a common sample arm)), the implementation of delay lines, especially delay lines incorporated into a source module which enable the output of delayed imaging optical signals simultaneously with non-delayed imaging optical signals from a source module, and an imaging light source configured such that it simultaneously generates distinct (i.e., substantially different) swept light signals.In some embodiments, the processing unit 150 is configured to control the tunable light source 105 such that a rate of change in the at least one wavenumber k (tuning rate dk/dt) of the imaging optical signal includes at least two tuning rates dk/dt. In some embodiments, the at least two tuning rates dk/dt include at least one negative and at least one positive dk/dt. In some embodiment, the tunable light source 105 is configured such that the imaging optical signal includes a superposition of multiple optical signals. In some embodiments, the multiple optical signals that are superposed to create the imaging optical signal have distinct wavenumbers k and/or distinct tuning rates dk/dt. In such embodiments, the distinct tuning rates dk/dt may overlap each other, including e.g., sharing one or more optical element. In some embodiments, the tunable light source 105 is configured to generate 96 WO 2024/158772 PCT/US2024/012552 multiple distinct imaging optical signal outputs. In some embodiments, the distinct outputs produce imaging optical signals which differ at the output, e.g., differ in optical power, wavenumber k, and/or tuning rate dk/dt. In some embodiments, the tunable light source 1is configured such that the imaging optical signal includes a superposition of the at least two tuning rates dk/dt. In further embodiments, the superposition of the different tuning rates dk/dt includes at least one negative and at least one positive dk/dt.According to at least one embodiment, the SS-OCT system includes a first tunable light source and at least one other tunable light source. Non-limiting examples of such a configuration are shown in FIGS. 18A and 18D (e.g., tunable light sources 805a and 805b). A first interferometer is configured with the first tunable light source (e.g., 805a of FIGS. 18A and 18D) and the at least one additional interferometer is configured with the at least one other tunable light source (e.g., 805b of FIGS. 18A and 18D). In accordance w ith at least one embodiment, the first interferometer and the at least one additional interferometer are configured such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element. For example, in FIGS. 18A and 18D. sample arms 824a (of the first interferometer) and 824b (of the at least one additional interferometer) share at least one optical element, e.g., fiber of the overlapped sample arm prior to introduction to the beam delivery head 815. It is to be appreciated that optical fiber is just one non-limiting example, and other optical elements that may be shared include collimators, free space beam directing elements (e.g., beam directing elements that position the imaging beam relative to the process beam), dichroic optics (e.g., dichroic optics configured to combine the dual interferometer sample arms with the beam path of the material processing beam), any other beam delivery optics that are shared between the interferometer sample arm and processing beam (e.g.. scanning/wobble galvos. processing beam lenses, other lenses, cover glass), and/or any other fiber based elements (e.g., circulators, isolators, fused fiber couplers, or other fiber elements specific to a particular design or topology ). In a further embodiment, the processing unit 150 is configured to control the first tunable light source such that a first imaging optical signal generated by the first tunable light source has a first tuning rate dk/dt and to control the at least one other tunable light source such that an imaging optical signal generated by the at least one other tunable light source has a second tuning rate dk/dt that is different than the first tuning rate dk/dt. In another embodiment, the first tuning rate dk/dt is a positive dk/dt and the second tuning rate dk/dt is a negative dk/dt. In a further embodiment, at least a portion of the first 97 WO 2024/158772 PCT/US2024/012552 imaging optical signal and at least a portion of the imaging optical signal generated by the at least one other imaging optical signal are transmitted simultaneously. In a further embodiment, the first and second tuning rates are associated with one or more interferometer output signals, and the processing unit is configured to calculate the one or more corrections (that are applied in response to detection of the distortion), which may include identifying a distortion in at least one of the one or more interferometer output signals that is associated with at least one of the first and second tuning rates, and performing an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.In some embodiments, the SS-OCT system further includes a splitter to split the imaging optical signal into at least two arms, and an optical delay element. Non-limiting examples of such a configuration are shown in FIGS. 18B, 18C, and 18E (e.g., optical delay element 825 in FIGS. 18B and 18C and 18E). The optical delay element (e.g., 825) is configured such that an output of a first arm of the at least two arms is delayed in time relative to an output of a second arm of the at least two arms. In a further embodiment, the processing unit 150 is configured to control the tunable light source (e.g.. 805 in FIGS. 18B. 18C, 18E) such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt. In some embodiments, the at least two tuning rates dk/dt includes a positive tuning rate dk/dt associated with either the first arm or the second arm. and a negative tuning rate dk/dt associated with the other of the first arm or the second arm. In accordance with various embodiments, the first arm is configured to be directed to at least one of different reference arms, different sample arms, partially overlapped reference arms, and partially overlapped sample arms of a first interferometer and at least one additional interferometer. This is shown in FIGS. 18B, 18C, and 18E). For instance, in FIGS. 18B, 18C, and 18Ethe delayed arm (passes through optical delay element 825) is directed to partially overlapped sample arms of the first interferometer and the at least one additional interferometer (e.g., in FIGS. 18B, 18C and 18E, sample arms 824a (of the first interferometer) and 824b (of the at least one additional interferometer) share at least one optical element, e.g., fiber of the overlapped sample arm prior to introduction to the beam delivery head 815. It is to be appreciated that this is just one non-limiting example and other embodiments exist where the delayed arm is directed to different reference arms of multiple interferometers, different sample arms of different interferometers, and/or partially overlapped reference arms of multiple98 WO 2024/158772 PCT/US2024/012552 interferometers. In some embodiments, the first arm and the second arm are configured to be directed to at least one sample arm and at least one reference arm of the first interferometer and the at least one additional interferometer. In some embodiments, the first interferometer and the at least one additional interferometer are configured such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element. For example, in FIGS. 18B, 18C, and 18D, sample arms 824a (of the first interferometer) and 824b (of the at least one additional interferometer) share at least one optical element, e.g., fiber of the overlapped sample arm prior to introduction to the beam delivery head 815. Other examples of optical elements that may be shared were discussed above. In a further embodiment, the first arm and the second arm of the imaging optical signal are configured to be directed to the first interferometer and the at least one additional interferometer simultaneously. For example, the delayed arm and the "non-delayed" arm of the imaging optical signal can be directed to one or more sample arm(s) and/or reference arm(s) of the first interferometer and the at least one additional interferometer at the same time. In a further embodiment, the first arm is configured to be directed to the first interferometer or the at least one additional interferometer, and the second arm is configured to be directed to the other of the first interferometer or the at least one additional interferometer. For example, the delayed arm may be directed to the sample and/or reference arms of the first interferometer, and the second (non-delayed) arm may be directed to the sample and/or reference arms of the at least one additional interferometer (or vice versa). In a further embodiment, the at least two tuning rates dk/dt of the first and second arms are associated with one or more interferometer output signals, and the processing unit is configured to calculate the one or more corrections (that are applied in response to detection of the distortion), and calculating the one or more corrections comprises; identifying a distortion in at least one of the one or more interferometer output signals that is associated with at least one of the positive and negative tuning rates, and performing an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.

In accordance with at least one embodiment, the SS-OCT system may be configured such that more than one substantially distinct swept sources of imaging light are used to illuminate the sample.99 WO 2024/158772 PCT/US2024/012552 In some embodiments, the SS-OCT system may be configured such that one or more substantially distinct swept sources of imaging light are used to illuminate two or more optical interferometers simultaneously. Some embodiments may involve the two or more interferometers overlapping (at least partially) at the sample (or sharing a common "sample arm"). Details of such embodiments are discussed below.

In accordance with at least one embodiment, the SS-OCT system may be configured such that the sample is illuminated with more than one substantially distinct swept sources of imaging light. In this case, substantially distinct sources of imaging light refer to swept sources which differ from each other in at least one characteristic, examples of characteristics include the wavelength of light emitted, the frequency of source sweeping, the phase of source sweeping, the polarization, or the coherence with a given reference. The substantially distinct swept sources of imaging light may be derived from more than one light source. Alternately, substantially distinct sources of imaging light may be derived from light emitted from one light source. For example, a light signal may be split and at least one of the split light signals may be modified or delayed by methods known to those of ordinary skill in the art (delay lines, optical buffering, etc.) prior to arriving at the sample arm, such that at the time each distinct light signal arrives at the sample arm the imaging light substantially differs from other imaging light at the sample arm.Numerous topologies exist for the generation of more than one substantially distinct sources of imaging light. For example, more than one separate light source may be used to create substantially distinct imaging light. Such light sources may be synchronized or coordinated using various electronic signals to enable functionalities of the optical system. A schematic of one non-limiting example of such a topology, incorporated into an interferometer SS-OCT topolog)׳ having separate light sources and a shared sample arm is shown in FIG. 18A.Another example incorporates the concept that more than one substantially distinct sources of imaging light may be generated by splitting the light from a single source along two paths and one of these paths may be directed over a substantially different distance than the other path. At the output of the paths, the light from one path will be substantially delayed compared to the light from another path. Directing light to paths of select optical path lengths for the purpose of introducing delay into its propagation is commonly referred to by those skilled in the art as implementing (an) optical delay line(s). A schematic example of 100 WO 2024/158772 PCT/US2024/012552 such a topology, where a single light source and an optical delay line are used to generate two substantially distinct light incorporated into a double interferometer SS-OCT topology is shown in FIG. 18B.The optical delay line may be designed in accordance with one or more desired characteristics of the imaging light sources generated, for example to provide a specific phase or timing delay. The wavelength tuning of light which has been delayed by the delay line may be, for example, 180 degrees out of phase relative to the wavelength tuning of light which has not been delayed when it arrives at the sample arm, due to the selected design parameters of the delay line. The optical paths may be designed in such a way that the difference in path length is greater than the coherence length of the source, which means that after the light transits the optical delay line it will also be temporally less coherent. The degradation of the phase relationship (temporal coherence) of the light which transits through one path relative to the other will lead to a reduction or an elimination of interference between the two paths if or when they are overlapped.A non-limiting example of an embodiment which takes advantage of a single light source and a delay line is as follows. In the case of a swept light source emitting 1060 +/- nm light in a fiber with refractive index of 1.4, to build an optical delay line for a 180 degree delay on a 100 kHz sweep frequency, approximately 1071.4 m of fiber path length difference between the separate paths would be required to introduce the desired delay.In accordance with at least one embodiment, the above methods for the generation of two or more light sources may be combined, for example more than one separate light source may be split and delayed as many times as necessary to generate the required light sources.

In accordance with at least one embodiment, the SS-OCT systems as disclosed herein shall be configured such that one or more substantially distinct swept sources of imaging light are used to illuminate two or more optical interferometers simultaneously. Preferred embodiments may involve the two or more interferometers at least partially overlapping at the sample (or "sample arm’־) so that each interferometer may be used to image the same sample. Three examples of topologies where tw o distinct interferometers are at least partially overlapped are shown in FIGS. 18A, 18B, 18C. 18D, and 18E. It is to be understood that variants of such interferometers are also possible and considered within the scope of this disclosure, for example a version of the interferometer in FIG. 18B with K-Clock module included as an optical K-clock but without K-clock module 2, where K-clocking for the 101 WO 2024/158772 PCT/US2024/012552 buffered light signal is handled by applying a time-delayed copy of the signal from K-clock Module 1. FIG. 18A illustrates an embodiment with two distinct partially overlapping interferometers that are configured such that each interferometer has a separate tunable light source. FIGS. 18B and 18C illustrate embodiments where an optical delay line 825 is implemented, such as by applying the techniques described in the above section "Multiple Light Sources,־’ to produce distinct swept optical signals for input to each of the partially overlapping interferometers. FIG. 18D is another example of a configuration with two separate tunable light sources, which illustrates an interferometer topology which can be constructed without the use of optical circulators, and FIG 18E illustrates this concept of an interferometer without circulators with a buffered source providing distinct swept optical signals for input to each of the partially overlapping interferometers. Variants of double interferometer topologies based on the interferometer features, topologies, and functions described in this document are also considered within the scope of this disclosure.In accordance with at least one embodiment, the multiple interferometers are configured such that multiple interferometers are illuminated by only one swept source, so that the light in each of the interferometers is not substantially distinct. For example, an SS- OCT system may be configured with only one light source, but multiple interferometers which all overlap at the sample arm have distinct reference arms. By configuring each reference arm differently in accordance with requirements of the system, this method enables the simultaneous capture of multiple different depth ranges within the field of view.In accordance with at least one embodiment, the multiple interferometers are configured such that multiple interferometers are illuminated by substantially distinct sources of imaging light. For example, each different interferometer may be configured with swept source light corresponding to a different tuning rate. In cases where light in each interferometer is emitted by a different light source, there may not be sufficient spatial and temporal coherence between the two light sources such that light from one light source will interfere with light from another light source corresponding to a different interferometer. In cases where the substantially distinct light sources are generated by means of a single light source, a splitter, and a delay line, then light paths which are delayed by more than the coherence length of the source relative to one another will also lack sufficient spatial and temporal coherence to substantially produce interference with each other. In this way, as long as the relative coherence of the light in any pair of the multiple interferometers is negligible, those interferometers and their respective interferometer output signals may be 102 WO 2024/158772 PCT/US2024/012552 considered independently for analysis and processing of the interferograms despite their overlap at the sample arm.In accordance with at least one embodiment, two interferometers are illuminated with substantially distinct light sources such that the instantaneous rate of change of the wavenumber k of the light source corresponding to one interferometer with respect to time (dk/dt) (for at least some portion(s) of the light source sweep duration) is substantially different than the instantaneous rate of change of the wavenumber k of the light source corresponding to the other interferometer with respect to time (dk/dt).An example of the application of such an embodiment is where at least two interferometers are illuminated with substantially distinct swept sources, such that for the swept light source in one interferometer, dk/dt is substantially different compared to the dk/dt of at least one other interferometer at a given point (or series of points) in time. Differences in dk/dt may include differences in the sign of dk/dt. All of these interferometers are combined such that they share a sample arm, and all substantially distinct swept sources simultaneously illuminate this sample arm. As discussed previously, information related to motion artifact distortion can be extracted by evaluating the frequency components in interferometer output signals associated with at least two different values of dk/dt. For this case, with at least two interferometers illuminated with sources substantially differing in dk/dt at a given point in time, interferometer output signals associated with at least two different values of dk/dt may be produced simultaneously. This enables the evaluation of motion artifact effects on time scales shorter than those required to acquire the data to produce a complete A-line for a given system (sub-A-line timescales), as well as greater time-domain precision about the position and velocity characteristics of a w orkpiece. Differences observed between the interferometer output signals may be used in the evaluation of motion artifact.In specific embodiments of the at least two interferometers illuminated with sources substantially differing in dk/dt at a given point in time, symmetry7 between the sw eeping patterns and dk/dt of the different interferometer sources may be exploited. This symmetrybetween, for example, a positive dk/dt and a negative dk/dt sweep can make available additional information that would not be present if data w as captured only from either a positive or a negative dk/dt.In specific embodiments of the at least two interferometers illuminated with sources substantially differing in dk/dt at a given point in time, where the interferometers share a 103 WO 2024/158772 PCT/US2024/012552 common sample arm, the signals recovered from the different interferometers/different sources may all correspond to the same sample and show the same interface(s). Importantly, for interferometers with substantially differing dk/dt, the interferometer output signal corresponding to a static interface would typically present at a matching depth in each signal, while the interferometer output signal corresponding to an interface in motion would present with distortion which differs based on the differing dk/dt.Embodiments of an interferometer capable of simultaneously outputting more than one interferometer output signals corresponding to more than one dk/dt are of particular interest due to possibilities which such embodiments present in regards to the identification, characterization and correction for motion artifact in SS-OCT. As described in the section "Correction for Motion Artifact," in order to identify, characterize, and/or correct for SS- OCT motion artifacts, one can use information corresponding to swept optical signals at two or more tuning rates dk/dt. In embodiments of an interferometer for SS-OCT with at least two interferometers overlapping at the sample arm and illuminated with sources substantially differing in dk/dt at a given point in time, swept optical signals corresponding to two or more tuning rates dk/dt may be collected simultaneously. As such, the methods for handling motion artifacts developed in the section above may be applied using these simultaneously collected signals. This can present a number of advantages, including the possibility7 of motion artifact handling on much shorter time scales, the ability to exploit certain symmetries in motion artifact-related distortions, and the ability to more precisely characterize and compensate rapid time-dynamics in samples containing motion, especially motion which changes on the timescales which are close in duration to or shorter than the duration of the acquisition of one A-line. This approach can also, due to the simultaneous capture of signals corresponding to the same sample but different dk/dt, provide enhanced information on instantaneous sample position and velocity relative to methods which rely on capturing the signals corresponding to different dk/dt in a substantially time-gated manner. This is because the simultaneously captured signals, if the sample arm is suitably overlapped, are based on identical sample conditions, where time-gated signals may reflect slightly different conditions due to the evolution of the sample with the elapsed time. In general, any method which is developed in the section "Correction for Motion Artifact," including those methods which leverage advanced signal processing methods and/or ML/AI, are considered to be applicable/adaptable to interferometer topologies which are capable of simultaneously outputting interferometer output signals corresponding to more than one dk/dt.104 WO 2024/158772 PCT/US2024/012552 In some embodiments the output from the fiber amplifier may be split using a beam splitter. The beam splitter may be configured to achieve a balance of power (imaging beam) that strikes the workpiece from each optical path, and/or apply such other signal balancing techniques as known to those of ordinary skill in the art.

In accordance with at least one embodiment, a light source is configured such that the light emitted contains two or more substantially distinct swept light signals, and this light source is used to illuminate an interferometer for SS-OCT. The distinct swept light signals may differ in instantaneous wavelength or wavenumber, dk/dt, sweep rate, or other pertinent characteristics. In preferred embodiments, the distinct swept light signals are not coherent with one another. One example of a configuration which is shown in FIG. 19 illustrates an embodiment where an optical buffer implemented as a delay line fiber is included in the light source to produce an output light which is substantially distinct from the non-delayed light. In accordance with at least one embodiment, and as illustrated in FIG. 19, the system may include a light source that sweeps in two substantially distinct ways at once. The delayed and non-delayed light may substantially differ in instantaneous wavenumber k and/or tuning rate dk/dt, and if the length of the optical fiber buffer is longer than the coherence length of the light source, then the light from the buffered arm will not be coherent with the light from the non-buffered arm (and vice-versa). In the case of the example shown in FIG. 19, the substantially distinct swept light from the optically buffered and non-optically buffered paths are recombined and used to illuminate the balance of an SS-OCT interferometer, including a K-Clock.Like the dual interferometer topologies above, this interferometer topology enables the sample to be simultaneously illuminated by more than one light source with more than one dk/dt. For example, in at least one embodiment the light source is configured such that a swept light signal with a negative dk/dt and a swept light signal with a positive dk/dt are swept simultaneously illuminating the sample for at least part of the duration of the imaging process. The interferometer output signals derived from such a configuration may be used to evaluate sample position, in addition to sample velocity based on the relation between dk/dt and the motion artifact of the scans. Additionally, these interferometer output signals which contain information from multiple dk/dt be used to extract the information required to identify and/or correct one or more distortions in the signal resultant from motion artifact, and more generally support or implement approaches described in the prior section titled105 WO 2024/158772 PCT/US2024/012552 "Correction for Motion Artifact." In accordance with at least one aspect, combining information from differing dk/dt values in such a way that is coincident in both time and space allows for the correction to the motion artifact to be performed more effectively. Examples of increased motion artifact correction effectiveness enabled by the topologies are similar to those described for the "Double Interferometer Topologies" section above.

Dispersion CompensationIn some embodiments of the system, optical elements in the sample or reference arm may cause a mismatch in optical dispersion between the arms of the interferometer. In some embodiments, optical elements may be added to the reference and/or sample arm of the interferometer to substantially reduce and/or eliminate observed effects of optical dispersion mismatch. For example, in some embodiments the reference arm contains optics (not shown in figures) that allow for dispersion control. For example, an optic may be placed in the free space portion of the reference arm for purposes of matching dispersion introduced by free space optics in the sample arm. In some embodiments, computational methods may be applied to numerically compensate for dispersion mismatch in the measured interferometer output signal. Dispersion compensation methods known to those of ordinary skill in the art may be applied to this system.In some embodiments, optical components in the sample and reference arms are matched (in certain embodiments the group delay and higher order dispersion terms) for purposes of reducing any dispersion mismatch between the two arms. This may improve axial imaging resolution. It may also be beneficial to change this dispersion compensation in the reference arm to match additional dispersion caused by material present in the sample. In some embodiments approximately equal amounts of each optical material in both the reference and sample arm paths (that include air/vacuum) may be used.In accordance with one embodiment, at least one of a pre-calculated interferogram and a measured interferogram is shaped to compensate for dispersion mismatch. Compensation may, for example, be achieved through a controlled modulation of the complex phase and amplitude of the individual elements of the synthesized interferogram. The amount of modulation can be determined from at least one of experimental calibration of the apparatus, mathematical modelling of optical propagation, a theoretical analysis of the system response, and a combination of the above. For instance, for a fixed dispersive 106 WO 2024/158772 PCT/US2024/012552 element, the relative phase lag/advance of each wavelength arising from the dispersive terms of the material can be added to each element in the synthesized interferogram.Optical dispersion induced by a sample being measured can have an adverse effect on the axial resolution of coherent images. In some embodiments, the sample can induce a wavelength dependent phase shift on the interference pattern that may be dependent on the depth that the light has propagated in the sample. A complex phase and amplitude modulation algorithm, for example, as described above, can be used to compensate for these effects. The dispersion coefficients of the materials in the sample can, in some embodiments, be calculated a priori, or, in other embodiments, be determined iteratively. One may begin by assuming that the phase shifts induced by the sample increase linearly with increasing penetration into the sample. In this way, each sample acquired at wavenumber ־k' may have a certain phase shift dictated by the instantaneous wavenumber ‘k’ of the imaging optical beam and what depth in the sample the signal is returning from. If the wavenumber k associated with each interferometer output signal and the depth associated with each interferometer output signal can both be known a priori (for example, the w avenumber k or a pertinent related quantity may be known based on the k-clocking methods described above), this distortion can be estimated and calculated a priori and a compensation for this distortion may be incorporated into the processing of the interferometer output signals. Alternatively, measurement of the optical signal propagating through the system may also provide dispersion mismatch information used for compensation. A dispersion compensation lookup table can be prepared before imaging is performed. In such embodiments, the dispersion correction can be applied with zero additional real-time computing load.

Frequency-Modulation and Frequency-Demodulation Enhanced Swept Source OCTThe time-domain interference signal (interferometer output signal) in some embodiments of an SS-OCT system is captured by a photodetector and converted to an analog electronic signal, or an RF analog electronic signal. This signal may have variable frequency content and/or variable instantaneous frequency content. In some embodiments of the system, it may be advantageous to define a carrier frequency of the signal and de- modulate the interferogram using this carrier frequency, using signal processing techniques known to those of ordinary' skill in the art, such as techniques ty pically associated with FM de-modulation. The process of de-modulation of the signal can produce a signal of low er frequency than the original analog electronic signal. In embodiments of the system where the 107 WO 2024/158772 PCT/US2024/012552 frequency of the analog electronic signal associated with the output of one or more SS-OCT system photodetectors is higher than the frequency which can accurately be digitized by the ADC, the demodulation can preserve information earned in the signal, while decreasing the frequency of the signal, thereby enabling the signal to be accurately digitized while limiting the loss of information. In some embodiments of the system, the de-modulation may be motivated by the design constraints involved in the analog signal transmission, as a signal with lower frequency content may have improved transmission characteristics and simplified design requirements as compared to a signal with higher frequency content.In some embodiments, the analog electronic signal may instead be modulated by a selected carrier frequency.According to at least one embodiment, the processing unit 150 is configured to modulate or demodulate the at least one interferometer output signal using a predetermined carrier frequency. For example, in some embodiments, it may be desirable to modulate and/or demodulate the analog electronic signal corresponding to the interferometer output signal by several different carrier frequencies, either in series or in parallel, based on characteristics and requirements of the system. In some embodiments, a signal may be demodulated and/or modulated by one carrier frequency selected from a set of possible carrier frequencies, such a set may additionally include the option of not modulating or de- modulating the original signal. The carrier frequency selected for modulation or de- modulation may be selected and/or adjusted based wholly or in part on feedback mechanisms within the system. For example, the modulation may be adjusted based on a detected change in sample depth, or based on feedback of reference arm position.In some embodiments, the modulation or de-modulation frequency may be selected responsive to some feedback regarding system state. In an SS-OCT system, for given light source settings, faster interferogram fringes are typically produced when the path length difference between a sample arm and a reference arm of an interferometer is larger. De- modulation approaches, as described above, may therefore be useful to reduce the frequency content of interferometer output signals associated with greater path length differences in an SS-OCT capture, enabling the effective capture of data for example of a greater range of sample arm depths without exceeding the Nyquist frequency of the ADC. In some embodiments, it may be preferable to tune the swept light source at different frequencies for different imaging functions. The frequency (in time) of interferometer output signal will change based on the light source tuning frequency. De-modulation or modulation settings 108 WO 2024/158772 PCT/US2024/012552 may be changed responsive to changes in light source tuning frequency in order to allow a system with a given ADC sample frequency to preserve imaging range for higher light source tuning frequencies.In preferred embodiments, a digitized de-modulated signal may be processed in a way that recovers the signal to an equivalent of the original modulated state. In preferred embodiments, a digitized modulated signal may be processed in a way that recovers the signal to an equivalent of the original de-modulated state.A key practical implication of modulation and de-modulation approaches as applied to swept source OCT systems is that applying such techniques could help extend imaging range without needing to digitize arbitrarily high digital frequencies. This could increase accuracy of a signal or imaging rate and/or range of a system, in some cases where analog bandwidth of hardware is limiting.

Alignment to Material Processing Beam or Process Region using Motion SignaturesIn accordance with certain embodiments, identified motion artifact distortion may be used to aid in the alignment of various coordinate systems, including but not limited to the coordinate system(s) of the material processing beam delivery system(s), and coordinate system(s) of the imaging system(s). In some embodiments, the processing unit is configured to determine one or more alignments and/or one or more offsets in alignment between a coordinate system of a beam delivery system for the material processing beam and a coordinate system of a delivery system for the imaging optical signal. Examples of material processing beam delivery systems include fixed optical heads, 2D and/or 3D scanner heads, an example of a suitable scanner head is the 2D high-power scanner system available from IPG Photonics. Material processing beam delivery systems may also include, for example, robotic elements which are configured to move the entirety of the beam delivery head. The coordinates of such robotic systems is included in the scope of coordinate systems that can be aligned through the use of motion artifact distortion. In some embodiments the determination of the one or more alignments and/or the one or more offsets in alignment is based at least in part on the spatial distribution of the distortion in the interferometer output signal.In certain embodiments, the alignment of the imaging system coordinate system(s) and the material processing beam coordinate systems is performed by using one or more directing elements to scan the imaging beam about the region where the material processing beam source is striking a workpiece, calibration target and/or a test coupon of material.109 WO 2024/158772 PCT/US2024/012552 While this happens, the material processing beam is operated to cause material modification resulting in motion of the sample. In accordance with various embodiment, the beam delivery system for the imaging optical signal includes one or more directing elements that are configured to adjust or otherwise control a position of the imaging optical signal relative to a position of the material processing beam, and the directing elements are controlled during the acquisition of one or more interferometer output signals such that interferometer output signals are obtained that are associated with different positions of the imaging optical signal relative to the position of the material processing beam.In preferred embodiments, the imaging beam scan pattern is based in a coordinate system which is defined relative to the material modification beam. Embodiments where the imaging beam scan pattern is based in other coordinate systems, such as those defined in absolute terms, or relative to other elements of the material modification system, are also possible. SS-OCT data is captured as the directing element scans over this region, SS-OCT data may include A-lines, which can then be combined with information derived from the directing elements to form a 2D data capture, such as B-Scan(s) and/or M-Modes, or a 3D volumetric data capture, such as a point cloud. By identifying the motion artifact distortion in each A-line of this 2D or 3D data, motion artifact distortion can be correlated to the imaging beam location. In this way, the location of maximum motion artifact distortion can be determined. A non-exhaustive list of methods which may be applied to the 2D or 3D data to assist in this determination include peak finding, maximum finding, and curve fitting. In some embodiments, motion artifact distortion over the B-scan(s) may be processed prior to determining the location of maximum motion artifact distortion, through means including integration, outlier removal, and/or other data filtering methods known to those with ordinary experience in the art.When considering this method of alignment, it is important to note that motion of a sample undergoing material modification (and therefore motion artifact distortion when imaging this process with SS-OCT) can change based on the characteristics of the material modification process. For example, in the material modification process known to those of ordinary skill in the art as keyhole welding, the motion of the sample in e.g. the heat-affected zone, the melt pool, and the keyhole is known to differ, due to the material being in a molten vs. solidified state for example, allowing the observation of distinct motion artifact distortion for each of these regions. 110 WO 2024/158772 PCT/US2024/012552 In some embodiments, motion artifact distortion may be used to help locate the origin of the material processing beam coordinate system, relative to the origin of the imaging beam coordinate system, and align the origins of the two coordinate systems.In some embodiments, motion artifact distortion may be used to help characterize optical phenomena impacting the position of the imaging beam relative to that of the material processing beam, and align the imaging beam to compensate for such phenomena, such as chromatic aberration caused by material processing beam optics. For example, if the material processing beam and imaging beam of different wavelengths are both directed using a (pre- objective) scanner, each beam will experience different refractive indices within the scanner lens optical elements due to their differing wavelengths, which will result in them having differing propagation directions at the output of the scanner lens and a different position on the workpiece. Chromatic aberration of this kind is dependent on the angle of incidence of the beams on the scanner lens, and will differ when directing the beams to different positions within the scanner field of view. As such, one beam may be actively steered relative to the other to correct for the change in relative position of the beams on the workpiece based on the relative difference in chromatic aberration between the two wavelengths.In some embodiments, motion artifact distortion may be used to align the imaging beam to different process regions, such as the keyhole or the seam, which may be of particular interest for measurement purposes.In some embodiments, the material processing beam source is operated such that the location of maximum motion artifact distortion is correlated with the location of the material processing beam source at the workpiece. Data taken from an imaging beam scan during such an operation can enable the establishment of a relative mapping between the location of the material processing beam at the workpiece and the imaging beam at the workpiece.In some embodiments, the material processing beam source is operated such that the location of maximum motion artifact distortion is correlated with the location of a process region. For example, this method can aid in the location of the keyhole process region by using one or more directing elements to direct the material processing beam and imaging beam along the same processing path and/or at the same processing location, while using one or more additional directing elements to independently direct the imaging beam about the material processing beam. When combined with information from the directing elements, motion artifact distortion can then be correlated to the location of the imaging beam relative to the material processing beam. The location of maximum motion artifact relative to the ill WO 2024/158772 PCT/US2024/012552 material processing beam, which may be correlated to the location of the keyhole process region, can then be identified over the entirety of the processing path or segments thereof. The keyhole process region may be of particular interest for measurement and/or quality assurance purposes and its location relative to the material processing beam is known to be highly dependent on process parameters, including the processing path, to those with ordinaryskill in the art.For certain process parameters, the location of the keyhole process region is known to those with ordinary skill in the art to change significantly at different points/times along the processing path. In some embodiments, the imaging beam may be directed to the same location(s) relative to the material processing beam more than one time over the duration of the processing path. In this way, the location of the keyhole process region may be identified over more than one segment of the processing path.

Computer SystemFIG. 15 is a schematic functional diagram of exemplary computer hardware used to control system 100 of FIG. 1. As shown in FIG. 15, the computer 150 includes a central processing unit (CPU) 152, a storage memory (ROM/RAM) 154, a user input/output (FO) interface 156, and a system interface 158. The various components of the computer 1communicate with each other via physical and logical data lines (DATA BUS).CPU 152 (also referred to as a "processor" and ־־computer processor") may be a single core or multi core processor, or a plurality of processors for parallel processing and can execute a sequence of machine-readable instructions, which can be embodied in a program or software. The instructions may be stored in a memory7 location, such as memory 154. The instructions can be directed to the CPU 152. which can subsequently program or otherwise configure the CPU 152 to implement methods of the present disclosure.Storage memory 154 includes one or more computer-readable and/or writable media, and may include, for example, a magnetic disc (e.g., a hard disk drive HDD), an optical disc (e.g., a DVD, a Blu-ray®, or the like), a magneto-optical disk, semiconductor memory (e.g., a non-volatile memory card. Flash® memory, a solid state drive, SRAM. DRAM), an EPROM, an EEPROM, etc. Storage memory 154 may store computer-readable data and/or computer- executable instructions including Operating System (OS) programs, and control and processing programs. 112 WO 2024/158772 PCT/US2024/012552 The user interface 156 provides a communication interface (electronic connections) to input/output (I/O) devices, which may include a keyboard, a display device (LCD or CRT), a mouse, a printing device, a touch screen, a light pen, an external optical storage device, a scanner, a microphone, a camera, a drive, communication cable and a network (either wired or wireless). For instance, OCT images based on the interferometer output signals can be generated by the CPU and output to a display device. In other embodiments, OCT data from the processed interferometer output signal is transmitted to an external device and/or a component of the SS-OCT system, such as storage memory 154 or an external memory or a separate controller or PLC.The system interface 158 also provides an electronic interface (electronic connection circuits) for one or more components of system 100, such as tunable light source 105, optical detector 130, digitizer 135, and k-clock module detector 147. The system interface 158 may include programmable logic for use with a programmable logic device (PLD), such as a Field Programmable Gate Array (FPGA) or other PLD, discrete components, integrated circuitry (e.g., an Application Specific Integrated Circuit (ASIC)), or any other components including any combination thereof.The function of the user interface 156 and of the system interface 158 may be realized at least in part by computer executable instructions (e.g., one or more programs) recorded in storage memory 154 and executed by CPU 152. Moreover, the computer 150 may comprise one or more additional devices, for example, components such as a communications or network interface for communicating with other external devices.

Record GeneratorIn some embodiments, system 100 also comprises a record generator 155 that generates a record of the material modification process based on the interferometry/detector output at a plurality of times and stores the record on a memory component (e.g., storage memory 154). Controller 150 is also configured to evaluate quality7 of a material process result, e.g., a weld, based at least in part on the record. For example, a quality evaluation may include a determination of whether or not any defect is present in the welded portion of the sample, such as lack of penetration or incomplete penetration, lack of fusion or incomplete fusion, undercut, spatter, cracks, craters, porosity, mechanical damage, overlap, lamellar tearing, slag inclusion, bum through, excess reinforcement, whiskers, and misalignment.113 WO 2024/158772 PCT/US2024/012552 SafetyThe SS-OCT systems and methods disclosed herein are designed with safety as atop consideration. As some embodiments contain lasers operating at wavelengths and powers that could harm people or equipment if misused, safety interlocks (also referred to herein as simply an interlock) will be implemented in the system. Interlocks are implemented on critical connectors, device chassis, and other locations where necessary. Interlocks are capable of integration with other interlock/safety systems, including but not limited to safety PLCs. Resistance-sensing interlocks and redundant interlock channels can be applied to make the system even more fail-safe. Power supply monitoring will be implemented to ensure the maintenance of safe operating conditions.In embodiments where multistage amplifiers are included, the end stage of the amplifier is interlocked to prevent unsafe operation. In some embodiments where multiple power output modes of operation are possible, interlocking may be implemented such that operation in an "eye safe" operating mode is available when interlock conditions are not satisfied. As used herein, the term "eye safe" operating mode or "eye safe mode" refers to an operating mode where the imaging light source is operated in such a way that emitted light complies with the requirements set out in one or more national or international standards (e.g., ANSI Z136) such that people can work safely with the system without requiring PPE or light-tight enclosures.

EXAMPLESFunctions and advantages of the embodiments of the SS-OCT systems and techniques disclosed herein may be more fully understood based on the examples described below. The following examples are intended to illustrate various aspects of the disclosed SS-OCT system.

Example 1 - Comparison of signals in SD-OCT vs SS-OCT systemA prototype of an SS-OCT system similar to SS-OCT system 100 of FIG. I was constructed and used to capture ICI data of a keyhole weld process. A commercial SD-OCT system (an LDD-700 inline welding process monitoring system available from IPG Photonics) was used to capture data for the same process and used as a source of comparison. Welding of stainless steel was performed using a material processing beam having a power of 114 WO 2024/158772 PCT/US2024/012552 2 kW with an approximate spot size of 260 m and speed of 50 mm/s using a two- dimensional high powered scanner beam delivery system from IPG Photonics. The power of the imaging beam was approximately 44.5 mW for the SS-OCT system.M-Mode data obtained from both systems is shown in FIG. 8. It is to be noted that since the weld speed was 50 mm/s, the weld duration of 300 ms corresponds to a 15000 m weld length. Of particular interest is the substantially higher signal density and intensity obtained from the SS-OCT system. Additionally the available imaging depth is greater on the SS-OCT system.

Example 2 - Capture of OCT data from a 21 mm deep weld keyholeAn SS-OCT system such as that of system 100 of FIG. 1 built by Applicant has been used to image weld keyholes deeper than 21 mm using the ICI approach, which is at least mm greater than the 12 mm weld imaging depth obtained by an SD-OCT system. The weld was generated using a YLS-AMB laser provided by IPG Photonics using a beam configured with a central core output power of 6 kW and a ring output power of 6 kW and a 20 mm/s scan velocity. As mentioned previously, the 21 mm weld image depth is limited by material processing laser power, and thus the imaging of weld keyholes with depths greater than mm (which may be achieved in higher power laser configurations) are within the scope of this disclosure. To the extent Applicant was able to ascertain, there was no sign of a limit to how deep a weld could be measured with an embodiment of this invention configured to have sufficient imaging range. M-Mode raw data from a weld process with a 21 mm keyhole depth is shown in FIG. 14A, and FIG. 14B shows motion artifact corrected tracked image data corresponding to the raw image data from FIG. 14A for this weld. Microscope images of two cross-sections of this weld are shown in FIGS. 14C (taken at 1 mm ± 0.5 mm) and 14D (taken at 6 mm ± 0.5 mm). FIG. 14C is marked with a measurement that demonstrates the mm depth of the weld keyhole. The position (within ± 0.5mm, corresponding to ± 25 ms on the x-axis) and depth of the section shown in FIGS. 14C and 14D are marked with a solid line crosshair and a dashed line crosshair respectively in FIGS. 14A and 14B.

Example 3 - Correction of Motion Artifact in Weld Kevhole & Validation with Weld Cross SectionsAs described above, a set of algorithms was developed by Applicant to identify, address, and correct and/or compensate the effect of the motion artifact. To handle noise, 115 WO 2024/158772 PCT/US2024/012552 which is still present after motion artifact correction and/or compensation, smoothing and tracking algorithms are optionally applied. The output of the algorithms can be verified against weld sections to confirm that correction and/or compensation, smoothing, and tracking provides accurate data which corresponds to the geometry of the weld keyhole. An example of this motion correction is seen in the keyhole depth data show n in FIGS. 9A and 9B. Tracking algorithms, as described above, are applied to generate a tracked keyhole depth measurement based on the M-Mode data. The shift caused by the motion artifact is evident in FIGS 9A and 9B, which include both the tracked data from the dk/dt forward (grey, deepest track) and dk/dt reverse (grey, shallowest track) portions of the sweep, w ithout motion compensation, where the shift caused by the motion artifact is evident. Additionally, the motion-compensated track is shown (black, middle track). The keyhole depth data shown in FIGS. 9A and 9B was collected during weld processes with the following conditions: FIG. 9ABead on plate weld with mild steel material Power of 580 W and weld speed of 100 mm/s Welded using a YLS-6000 Fiber Laser (IPG Photonics) which w as set up to provide a focal spot size of 200 m FIG. 9BBead on plate weld with copper materialPower of 3 kW and weld speed of 200 mm/sWelded using a YLS-6000 Fiber Laser (IPG Photonics) which was set up to provide a focal spot size of 200 m To validate the depth measurements generated by the system, the weld was subsequently sectioned and etched using metallurgical analysis techniques known to those of ordinary skill in the art, to produce a physical measurement of weld depth at a variety of cross-sectional positions throughout the weld. The accuracy of the keyhole depth measured using the motion compensated track is confirmed by comparing to the measurements of keyhole depth which were generated by cross-sectioning the weld (shown as grey squares in FIGS. 9A and 9B).

Example 3 - Sensitivity7 Measurement of SS-OCT System116 WO 2024/158772 PCT/US2024/012552 A prototype of an SS-OCT system similar to SS-OCT system 100 of FIG. I was constructed in-lab and used to characterize system performance. The sensitivity of this system was characterized using a reflective target in the sample arm. To quantify sensitivity, a neutral density absorptive filter was included in the sample arm to manage signal levels. The attenuation of the neutral density7 absorptive filter was measured to be 51.8 dB, based on optical power measurements of 27.1 mW before the attenuator and 69.5 W after. Dark readings were captured to characterize the noise floor of the system. Subsequently, A-lines were captured to determine the signal-to-noise ratio and sensitivity of the system.

Once optical return levels were optimized using techniques known to those of ordinary skill in the art, an A-line was captured with an amplitude of 54.7 dB above the noise floor in the condition of 51.8 dB attenuation in the reference arm, demonstrating an OCT system sensitivity of 106.5 dB.

Example 4 - Example SS-OCT Data for Various MaterialsA prototype of an SS-OCT system similar to SS-OCT system 100 of FIG. I was constructed in-lab and used to capture ICI data of a keyhole weld process. ICI data of keyhole laser weld processes was gathered for welds with a variety of different materials. Materials welded included mild steel, aluminum, and copper, due to their prevalence in laser welding markets including but not limited to automotive, battery manufacturing, e-mobility, aerospace, and more.

M-Modes captured during ICI of the keyhole weld process are shown in FIGS. 16A-C for these various materials. For all captures in FIG. 16A-C, the imaging beam was combined with the process beam via a dichroic optic, using the imaging port on the laser weld head, and the imaging beam was aligned substantially coaxial with the process beam. The imaging system was configured such that the imaging beam power on the sample was approximately mW, focused to a spot size of 60 m at the substrate surface. FIG. 16A shows keyhole data collected during a bead-on-plate weld on a mild steel substrate. The processing laser (IPG Photonics YLS-6000) was set to a nominal power of 3 kW, and focused to a nominal spot size of 200 m at the substrate surface. The process speed was set to 100 mm/s. FIG. 16B shows keyhole data collected during a bead on plate weld on a 1000-series aluminum substrate. The processing laser (IPG Photonics YLS-6000) was set to a nominal power of kW, and focused to a nominal spot size of 200 m at the substrate surface. The process speed 117 WO 2024/158772 PCT/US2024/012552 was set to 30 mm/s. FIG. 16C shows keyhole data collected during a bead on plate weld on a copper substrate. The processing laser (IPG Photonics YLS-6000) was set to a nominal power of 3 kW, and focused to a nominal spot size of 200 m at the substrate surface. The process speed was set to 200 mm/s. Different weld process parameters were used for different materials due to fundamental differences in their properties as it relates to materials processing. These fundamental differences in properties also produce different characteristics when the keyhole is imaged with an imaging system, including variability in the characteristics of the A-lines observed. Some of this variability is due to the different motion dynamics within the weld keyholes for different materials, which leads to materially different motion artifact distortions observed in keyhole measurement A-lines. Such differences manifest in the features, including geometric characteristics of the A-lines and the geometric characteristics of their distortions. Some of these material differences may be observed by comparison of the M-Mode frames of keyhole data for different materials shown in FIG. 16. Some of the differences in the motion artifact characteristics for different materials are evident with the help of additional analysis of the OCT data, which may include A-lines, the interferograms, and/or the populations of such readings, which may be treated statistically or in bulk.

Example 5 - Concurrent Capture of SS-OCT weld data and SD-OCT weld dataA prototype of an SS-OCT system similar to SS-OCT system 100 of FIG. I was constructed in-lab and an opto-mechanical setup was constructed such that the prototype SS- OCT system could be used concurrently with a commercial SD-OCT system (an LDD-7inline welding process monitoring system available from IPG Photonics). The concurrent SS- OCT/SD-OCT setup was interfaced to an IPG Photonics weld head via an imaging port and a dichroic. Both imaging systems were aligned to the weld process beam, and an M-Mode capture of a keyhole weld process was captured concurrently on both OCT systems. One keyhole weld process captured in such a way involved a head-on plate weld on a copper substrate, the process speed was 150 mm/s and the processing laser, an IPG Photonics YLS- 6000, was configured with a weld head to emit a 200 pm spot size beam having 3 kW of power. FIG. 17A demonstrates the M-Mode of this process captured using the commercial OCT system, where FIG. 17B demonstrates the concurrently captured M-Mode of this process which was captured with the SS-OCT System. FIGS. 17C and 17D show the brightest pixels of A-lines which pass certain amplitude and quality filter parameters from 118 WO 2024/158772 PCT/US2024/012552 both systems, showcasing the agreement between the two systems. Also clearly visible on examination of FIG. 17 (FIGS. 17A-17D) is several cases of anomalous weld behavior, some of which are visible to the SS-OCT system but not to the LDD-700. For example, a keyhole collapse event at approximately 80 ms weld time, circled in 17C and 17D, can be clearly seen on the SS-OCT (FIG. 17D) data, but there is no evidence of this event in the LDD-700 data (FIG. 17C).The aspects disclosed herein in accordance with the present invention, are not limited in their application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. These aspects are capable of assuming other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, acts, components, elements, and features discussed in connection with any one or more embodiments are not intended to be excluded from a similar role in any other embodiments.Also, the phraseology׳ and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to examples, embodiments, components, elements or acts of the systems and methods herein referred to in the singular may also embrace embodiments including a plurality׳, and any references in plural to any embodiment, component, element or act herein may also embrace embodiments including only a singularity׳. References in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of "including," "comprising," "having," "containing," "involving," and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to "or" may be construed as inclusive so that any terms described using "or" may indicate any of a single, more than one, and all of the described terms. In addition, in the event of inconsistent usages of terms between this document and documents incorporated herein by reference, the term usage in the incorporated reference is supplementary to that of this document; for irreconcilable inconsistencies, the term usage in this document controls. Moreover, titles or subtitles may be used in the specification for the convenience of a reader, which shall have no influence on the scope of the present invention.Having thus described several aspects of at least one example, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. For instance, examples disclosed herein may also be used in other contexts. Such 119 WO 2024/158772 PCT/US2024/012552 alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the scope of the examples discussed herein. Accordingly, the foregoing description and drawings are by way of example only. 120

Claims

WO 2024/158772 PCT/US2024/012552 CLAIMSWhat is claimed is:

1. A swept-source optical coherence tomography (SS-OCT) system for performing imaging of a sample treated by a material processing beam, the material processing beam interacting with material of the sample at a processing region on the sample, the SS-OCT system comprising:an interferometer havingat least one reference arm,at least one sample arm configured to direct an imaging optical signal to the processing region, anda tunable light source for generating the imaging optical signal, the imaging optical signal having at least one wavenumber k that is variable in time and a sweep rate in a range from 1 kilohertz (kHz) to 20 megahertz (MHz) inclusive, the interferometer configured to direct the imaging optical signal to the at least one reference arm and the at least one sample arm and combine optical signals returning from the at least one reference arm and the at least one sample arm to generate a combined optical signal;an optical detector configured to detect the combined optical signal and generate at least one interferometer output signal; anda processing unit configured to:receive the at least one interferometer output signal;process the at least one interferometer output signal to determine at least one feature of the processing region;detect a distortion in the at least one interferometer output signal, the distortion created by a time-varying difference in optical path lengths between the at least one sample arm and the at least one reference arm;responsive to detection of the distortion, apply one or more corrections to the at least one interferometer output signal to produce a corresponding corrected interferometer output signal; andprocess the at least one corrected interferometer output signal to determine the at least one feature of the processing region. 121 WO 2024/158772 PCT/US2024/012552

2. The SS-OCT system of claim 1, wherein the at least one feature includes depth information of the processing region.

3. The SS-OCT system of claim 2, wherein the depth information includes a range of at least 1 mm inclusive.

4. The SS-OCT system of claim 3, wherein the depth information includes a range of at least 5 mm inclusive.

5. The SS-OCT system of claim 4, wherein the depth information includes a range of at least 21 mm inclusive.

6. The SS-OCT system of claim 5, wherein the depth information includes a range of at least 50 mm inclusive.

7. The SS-OCT system of claim 2, wherein the material processing beam creates a phase change region (PCR) at the processing region and the depth information includes keyhole depth of the PCR.

8. The SS-OCT system of claim 7, further comprising at least one directing element that directs the imaging optical signal at one or more selected positions in and/or near the PCR.

9. The SS-OCT system of claim 1, wherein the processing unit is further configured to control at least one processing parameter of a material modification process implemented by the material processing beam on the sample based on the at least one feature of the processing region.

10. The SS-OCT system of claim 1, wherein the processing unit is further configured to determine a sample position based on the at least one corrected interferometer output signal.

11. The SS-OCT system of claim 1, wherein the processing unit is further configured to determine a velocity of the material of the sample based on the at least one corrected interferometer output signal.122 WO 2024/158772 PCT/US2024/012552

12. The SS-OCT system of claim 1, wherein the processing unit is further configured to determine one or more alignments and/or one or more offsets in alignment between a coordinate system of a beam delivery system for the material processing beam and a coordinate system of a delivery system for the imaging optical signal.

13. The SS-OCT system of claim 1, whereinthe processing unit is configured to control the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt that are associated with one or more interferometer output signals, andthe processing unit is configured to calculate the one or more corrections, and calculating the one or more corrections comprises:identifying a distortion in at least one of the one or more interferometer output signals that is associated with at least one of the at least two tuning rates;performing an evaluation of the distortion.wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.

14. The SS-OCT system of claim 13, wherein the at least two tuning rates dk/dt include at least one positive tuning rate dk/dt and at least one negative tuning rate dk/dt.

15. The SS-OCT system of claim 14, wherein performing the evaluation comprises comparing distortion in at least one interferometer output signal associated with a positive tuning rate dk/dt with distortion in at least one interferometer output signal associated with a negative tuning rate dk/dt.

16. The SS-OCT system of claim 13, wherein performing the evaluation comprises comparing distortion in at least two interferometer output signals.

17. The SS-OCT system of claim 13, wherein the distortion corresponds to a distortion in one or more geometric aspects encoded in the interferometer output signal. 123 WO 2024/158772 PCT/US2024/012552

18. The SS-OCT system of claim 17, wherein the one or more geometric aspects includes at least one of a position, symmetry, a width of a peak, a centroid, a geometric second moment, a center of mass, an amplitude, a height to width ratio, and a geometric area under a curve.

19. The SS-OCT system of claim 17, wherein performing the evaluation comprises comparing one or more geometric aspects encoded in at least two interferometer output signals.

20. The SS-OCT system of claim 17, wherein performing the evaluation comprises comparing one or more geometric aspects to one or more pre-determined thresholds and/or baselines associated with the one or more geometric aspects.

21. The SS-OCT system of claim 20, wherein the one or more predetermined thresholds and/or baselines are established based on at least one of:system and/or component requirements,one or more application requirements,one or more calibrations,one or more models,limitations of the hardware and/or software, one or more algorithms, and fundamental physics.

22. The SS-OCT system of claim 17, wherein the processing unit is configured to perform the evaluation by comparing the one or more geometric aspects relative to at least one of one or more geometric aspects encoded in at least one other of the one or more interferometer output signals, andone or more predetermined thresholds and/or baselines associated with the one or more geometric aspects.

23. The SS-OCT system of claim 13, wherein performing the evaluation comprises applying a predetermined threshold to the distortion and determining whether the distortion exceeds the predetermined threshold.124 WO 2024/158772 PCT/US2024/012552

24. The SS-OCT system of claim 13, wherein performing the evaluation comprises determining if a relative difference between two or more distortions exceeds a predetermined threshold.

25. The SS-OCT system of claim 13, wherein the processing unit is further configured to generate a mathematical model based at least in part on one or more properties of the SS- OCT system and the evaluation of the distortion.

26. The SS-OCT system of claim 25, wherein the mathematical model is further configured to generate an estimate of a magnitude and/or a direction of motion velocity of the sample based on the evaluation of the distortion.

27. The SS-OCT system of claim 13, wherein a material modification process implemented by the material processing beam on the sample is a welding process and the material processing beam creates a phase change region (PCR) at the processing region, and the processing unit is configured touse the evaluation to generate one or more corrections, anduse the one or more generated corrections to calculate a measurement of one or more features which are in motion in the PCR.

28. The SS-OCT system of claim 27, wherein the one or more features which are in motion in the PCR are in motion as a result of the material processing process.

29. The SS-OCT system of claim 13, wherein a material modification process implemented by the material processing beam on the sample is a welding process and the material processing beam creates a phase change region (PCR) at the processing region, and the processing unit is configured touse the evaluation to generate an estimate of a velocity of the material being processed in the PCR.

30. The SS-OCT system of claim 13, wherein applying the one or more corrections to the at least one interferometer output signal comprises125 WO 2024/158772 PCT/US2024/012552 discarding, weighting, promoting, or using the at least one of the one or more interferometer output signals, orselecting the at least one of the one or more interferometer output signals to discard or use at a later time.

31. The SS-OCT system of claim 13, wherein the interferometer is a first interferometer and the system further comprises at least one additional interferometer and configured such thata sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element,a first imaging optical signal configured with one of the at least two tuning rates dk/dt is directed to the at least one reference arm and the at least one sample arm of the first interferometer,a second imaging optical signal configured with another of the at least two tuning rates dk/dt is directed to the at least one reference arm and the at least one sample arm of the at least one additional interferometer, andthe distortion is identified based on the one or more interferometer output signals of the first interferometer and the at least one additional interferometer.

32. The SS-OCT system of claim 31, wherein the first and second imaging optical signals are directed to the processing region simultaneously.

33. 33 The SS-OCT system of claim 1, wherein the time-varying difference in optical path lengths is caused by sample motion.

34. The SS-OCT system of claim 33, wherein a motion velocity of the sample is greater than 10 mm/s.

35. The SS-OCT system of claim 34, wherein the motion velocity of the sample is greater than 100 mm/s.

36. The SS-OCT system of claim 35, wherein the motion velocity of the sample is greater than 500 mm/s.126 WO 2024/158772 PCT/US2024/012552

37. The SS-OCT system of claim 36, wherein the motion velocity of the sample is greater than 1000 mm/s.

38. The SS-OCT system of claim 37, wherein the motion velocity7 of the sample is greater than 10,000 mm/s.

39. The SS-OCT system of claim 1, wherein the processing unit is configured to derive track data from the at least one interferometer output signal and the one or more corrections is applied to the track data.

40. The SS-OCT system of claim 1, further comprising at least one k-clock module that generates a k-clock signal that indicates when a wavenumber k of the imaging optical signal substantially changes by one or more increments.

41. The SS-OCT system of claim 40, wherein a rate of change in the at least one wavenumber k of the imaging optical signal over time (tuning rate dk/dt) is non-uniform, and the at least one k-clock module is configured to trigger the acquisition of the interferometer output signals at uniform increments in wavenumber k.

42. The SS-OCT system of claim 41, wherein the processing unit is configured to process the at least one interferometer output signal based on interferometer output signals that are uniformly sampled in wavenumber.

43. The SS-OCT system of claim 40, wherein a rate of change in the at least one wavenumber k of the imaging optical signal over time (tuning rate dk/dt) is uniform, and the at least one k-clock module is configured to trigger the acquisition of the interferometer output signals at uniform increments in wavenumber k.

44. The SS-OCT system of claim 40, wherein the processing unit is configured to acquire the k-clock signal simultaneously to the acquisition of the interferometer output signals. 127 WO 2024/158772 PCT/US2024/012552

45. The SS-OCT system of claim 44, wherein the processing unit is configured to use the acquired k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k.

46. The SS-OCT system of claim 44, wherein the processing unit is configured to use the acquired k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal.

47. The SS-OCT system of claim 44, wherein the processing unit is configured to use the acquired k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.

48. The SS-OCT system of claim 40, wherein the processing unit is configured to acquire the k-clock signal in a manner which is time gated relative to the acquisition of the interferometer output signals, and apply the time gated k-clock signal to the processing of subsequently acquired interferometer output signals.

49. The SS-OCT system of claim 48, wherein the processing unit is configured to use the acquired k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k.

50. The SS-OCT system of claim 48, wherein the processing unit is configured to use the acquired k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal.

51. The SS-OCT system of claim 48, wherein the processing unit is configured to use the acquired k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.

52. The SS-OCT system of claim 48, wherein at least one of the interferometer sample and reference arms is configured with one or more optical elements that are used to generate the k-clock signal. 128 WO 2024/158772 PCT/US2024/012552

53. The SS-OCT system of claim 40, wherein the at least one k-clock module is configured with multiple optical paths that are used to generate the k-clock signal.

54. The SS-OCT system of claim 53, wherein the at least one k-clock module is configured to simultaneously generate the multiple optical paths by splitting the optical signal.

55. The SS-OCT system of claim 54, wherein the at least one k-clock module is configured such that the multiple optical paths are available for selection.

56. The SS-OCT system of claim 1, wherein the processing unit is further configured to simulate a k-clock signal that indicates when the at least one wavenumber k of the imaging optical signal substantially changes by one or more increments based at least in part on one or more properties of the SS-OCT system and one or more properties of the tunable light source.

57. The SS-OCT system of claim 56, wherein the processing unit is configured to use the simulated k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k.

58. The SS-OCT system of claim 56, wherein the processing unit is configured to use the simulated k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal.

59. The SS-OCT system of claim 56, wherein the processing unit is configured to use the simulated k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.

60. The SS-OCT system of claim 1, wherein the processing unit is further configured to generate a mathematical model of k(t) and/or a tuning rate dk/dt of the imaging optical signal based at least in part on one or more properties of the SS-OCT system and one or more properties of the tunable light source. 129 WO 2024/158772 PCT/US2024/012552

61. The SS-OCT system of claim 60, wherein the processing unit is configured to use the mathematical model to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k.

62. The SS-OCT system of claim 60, wherein the processing unit is configured to use the mathematical model to compute at least one correction for one or more distortions in the interferometer output signal.

63. The SS-OCT system of claim 60, wherein the processing unit is configured to use the mathematical model to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.

64. The SS-OCT system of claim 1, wherein the time-varying difference in optical path lengths is caused by sample motion relative to an axis of the imaging optical signal.

65. The SS-OCT system of claim 1, wherein the time-varying difference in optical path lengths is caused by a material modification process implemented by the material processing beam on the sample.

66. The SS-OCT system of claim 1, wherein the time-varying difference in optical path lengths is caused by intrinsic sample motion not caused by a material modification process implemented by the material processing beam on the sample.

67. The SS-OCT system of claim 1, wherein the processing unit is configured to control the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt.

68. The SS-OCT system of claim 67, wherein the at least two tuning rates dk/dt include at least one negative and at least one positive dk/dt.

69. The SS-OCT system of claim 67, wherein the tunable light source is configured such that the imaging optical signal includes a superposition of the at least two tuning rates dk/dt. 130 WO 2024/158772 PCT/US2024/012552

70. The SS-OCT system of claim 69, wherein the superposition of the at least two tuning rates dk/dt includes at least one negative and at least one positive dk/dt.

71. The SS-OCT system of claim 1, wherein the timable light source is a first tunable light source and the system further comprises at least one other tunable light source.

72. The SS-OCT system of claim? 1. wherein the interferometer is a first interferometer and the system further comprises at least one additional interferometer,the first interferometer configured with the first tunable light source,the at least one additional interferometer configured with the at least one other tunable light source,the first interferometer and the at least one additional interferometer configured such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element.

73. The SS-OCT system of claim 72, wherein a rate of change in the at least one wavenumber k of the imaging optical signal in time is a tuning rate dk/dt and the processing unit is configured tocontrol the first tunable light source such that a first imaging optical signal generated by the first tunable light source has a first tuning rate dk/dt, andcontrol the at least one other tunable light source such that an imaging optical signal generated by the at least one other tunable light source has a second tuning rate dk/dt that is different than the first tuning rate dk/dt.

74. The SS-OCT system of claim 73, wherein at least a portion of the first imaging optical signal and at least a portion of the imaging optical signal generated by the at least one other imaging optical signal are transmitted simultaneously.

75. The SS-OCT system of claim 74, whereinthe first and second tuning rates are associated with one or more interferometer output signals andthe processing unit is configured to calculate the one or more corrections, and calculating the one or more corrections comprises:131 WO 2024/158772 PCT/US2024/012552 identifying a distortion in at least one of the one or more interferometer output signals that is associated with at least one of the first and second tuning rates;performing an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.

76. The SS-OCT system of claim 75, wherein the first tuning rate dk/dt is a positive dk/dt and the second tuning rate dk/dt is a negative dk/dt.

77. The SS-OCT system of claim 1, further comprisinga splitter to split the imaging optical signal into at least two arms; andan optical delay element configured such that an output of a first arm of the at least two arms is delayed in time relative to an output of a second arm of the at least two arms.

78. The SS-OCT system of claim 77, wherein the processing unit is configured to control the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt.

79. The SS-OCT system of claim 78, wherein the at least two tuning rates dk/dt includes a positive tuning rate dk/dt associated with either the first arm or the second arm, and a negative tuning rate dk/dt associated with the other of the first arm or the second arm.

80. The SS-OCT system of claim 79, wherein the interferometer is a first interferometer and the system further comprise at least one additional interferometer.

81. The SS-OCT system of claim 80, wherein the first arm is configured to be directed to at least one of: different reference arms, different sample arms, partially overlapped reference arms, and partially overlapped sample arms of the first interferometer and the at least one additional interferometer.

82. The SS-OCT system of claim 80, wherein the first arm and the second arm are configured to be directed to at least one sample arm and at least one reference arm of the first interferometer and the at least one additional interferometer.132 WO 2024/158772 PCT/US2024/012552

83. The SS-OCT system of claim 80, whereinthe first interferometer and the at least one additional interferometer are configured such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element, andthe first arm and the second arm of the imaging optical signal are configured to be directed to the first interferometer and the at least one additional interferometer simultaneously.

84. The SS-OCT system of claim 83, whereinthe first arm is configured to be directed to the first interferometer or the at least one additional interferometer, andthe second arm is configured to be directed to the other of the first interferometer or the at least one additional interferometer.

85. The SS-OCT system of claim 83, whereinthe at least two tuning rates dk/dt of the first and second arms are associated with one or more interferometer output signals andthe processing unit is configured to calculate the one or more corrections, and calculating the one or more corrections comprises:identifying a distortion in at least one of the one or more interferometer output signals that is associated with at least one of the positive and negative tuning rates;performing an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.

86. The SS-OCT system of claim 1, wherein an optical frequency of the imaging optical signal varies at a rate in a range of 8 PHz/s - 2 ZHz/s inclusive.

87. The SS-OCT system of claim 1, wherein the processing unit is configured to generate an OCT image based on the at least one interferometer output signal and/or the at least one corrected interferometer output signal and transmit the generated OCT image to a display device.133 WO 2024/158772 PCT/US2024/012552

88. The SS-OCT system of claim 1, wherein the processing unit is further configured to generate OCT data from the processed interferometer output signal and/or the corrected interferometer output signal, and transmit the OCT data to an external device.

89. The SS-OCT system of claim 1, wherein the tunable light source is a tunable vertical- cavity surface-emitting laser (VCSEL).

90. The SS-OCT system of claim 89, further comprising an amplifier for amplifying the VCSEL.

91. The SS-OCT system of claim 90, wherein the amplifier is configured as a fiber amplifier.

92. The SS-OCT system of claim 90, wherein the output power of the amplifier is at least milliwatts (mW).

93. The SS-OCT system of claim 92, wherein the output power of the amplifier is at least mW.

94. The SS-OCT system of claim 93, wherein the output power of the amplifier is at least mW.

95. The SS-OCT system of claim 94, wherein the output power of the amplifier is at least 100 mW.

96. The SS-OCT system of claim 95, wherein the output power of the amplifier is at least 500 mW.

97. The SS-OCT system of claim 96, wherein the output power of the amplifier is at least watt (W). 134 WO 2024/158772 PCT/US2024/012552

98. The SS-OCT system of claim 97, wherein the output power of the amplifier is at least W.

99. The SS-OCT system of claim 90, wherein the amplifier is configured to have a peak gain at a wavelength between 1010 and 1050 nm.

100. The SS-OCT system of claim 90, wherein the amplifier is configured to have a peak gain at a wavelength between 1050 and 1090 nm.

101. The SS-OCT system of claim 90, wherein the amplifier is configured with one, two, or three amplification stages.

102. The SS-OCT system of claim 90, having a sensitivity of at least 105 dB.

103. The SS-OCT system of claim 1, wherein the processing unit is further configured to modulate or demodulate the at least one interferometer output signal using a predetermined carrier frequency.

104. The SS-OCT system of claim 1, further comprising;a digitizer configured to digitize the at least one interferometer output signal and generate a corresponding digital signal.

105. The SS-OCT system of claim 1, further comprising a record generator that generates a record of a material modification process implemented by the material processing beam on the sample based on the at least one interferometer output signal at a plurality of times.

106. The SS-OCT system of claim 105, wherein the processing unit is further configured to evaluate quality of a weld produced by a material modification process implemented by the material processing beam on the sample based at least in part on the record.

107. The SS-OCT system of claim 1, further comprising an annunciation generator that generates an annunciation pertaining to a material modification process implemented by the 135 WO 2024/158772 PCT/US2024/012552 material processing beam on the sample based on the at least one interferometer output signal at a plurality of times.

108. The SS-OCT system of claim 1, further comprising at least one directing element that directs the imaging optical signal.

109. The SS-OCT system of claim 108. wherein the at least one directing element is configured such that the imaging optical signal is within 50 nm of the focal spot of the material processing beam at the processing region.

110. The SS-OCT system of claim 1, further comprising an auxiliary measurement system configured to measure process radiation.

111. The SS-OCT system of claim 1, further configured to image sequences of multiple material modification processes that are implemented by the material processing beam on the sample.

112. The SS-OCT system of claim 1, further comprising a safety interlock device integrated into the tunable light source.

113. The SS-OCT system of claim 1, further comprising a safety interlock device integrated into the tunable light source that is configured to enable an eye-safe operating mode for the tunable light source, the eye-safe operating mode characterized by having a reduced imaging optical emission power.

114. The SS-OCT system of claim 1, further comprising at least one of a material processing energy source that generates the material processing beam and a beam deliverysystem for the material processing beam and the imaging optical signal.

115. The SS-OCT system of claim 114, further comprising a laser head that couples to the material processing energy7 source and houses the beam delivery system. 136 WO 2024/158772 PCT/US2024/012552

116. The SS-OCT system of claim 115, wherein the processing unit is further configured to control at least one of a material processing energy source that generates the material processing beam and the beam delivery system based on the at least one feature of the processing region.

117. A material processing system, comprising;the SS-OCT system of claim 1;a material processing energy source that generates the material processing beam; and a beam delivery system for the material processing beam and the imaging optical signal.

118. The material processing system of claim 117, wherein the beam delivery system is configured with a dichroic optic configured to combine the imaging optical signal and the material processing beam into a combined optical path.

119. The material processing system of claim 118, wherein the dichroic optic is configured with a transmission spectrum having a first band edge, a reflection spectrum having a second band edge, and the first band edge and the second band edge have a maximum w avelength separation of 25 nm.

120. The material processing system of claim 118, wherein the beam delivery system is configured to impinge the imaging optical signal on the dichroic optic over a range of incidence angles.

121. A swept-source optical coherence tomography (SS-OCT) method for imaging a processing region on a sample being treated by a material processing beam, the method comprising:providing an interferometer having at least one sample arm, at least one reference arm, and a tunable light source configured to generate an imaging optical signal that has at least one wavenumber k that is substantially variable in time and a sweep rate in a range from kilohertz (kHz) to 20 megahertz (MHz) inclusive; 137 WO 2024/158772 PCT/US2024/012552 directing the imaging optical signal to the at least one reference arm and the at least one sample arm of the interferometer, the at least one sample arm being configured to direct the imaging optical signal to the processing region;generating a combined optical signal from optical signals returning from the at least one reference arm and the at least one sample arm;generating at least one interferometer output signal from the combined optical signal;processing the at least one interferometer output signal to determine at least one feature of the processing region;detecting a distortion in the at least one interferometer output signal, the distortion created by a time-varying difference in optical path lengths between the at least one sample arm and the at least one reference arm;responsive to detecting the distortion, applying one or more corrections to the at least one interferometer output signal to produce a corresponding corrected interferometer output signal; andprocessing the at least one corrected interferometer output signal to determine the at least one feature of the processing region.

122. The SS-OCT method of claim 121, wherein the at least one feature includes depth information of the processing region.

123. The SS-OCT method of claim 122, wherein the depth information includes a range of at least 1 mm inclusive.

124. The SS-OCT method of claim 123, wherein the depth information includes a range of at least 5 mm inclusive.

125. The SS-OCT method of claim 124, wherein the depth information includes a range of at least 21 mm inclusive.

126. The SS-OCT method of claim 125, wherein the depth information includes a range of at least 50 mm inclusive. 138 WO 2024/158772 PCT/US2024/012552

127. The SS-OCT method of claim 122, wherein the material processing beam creates a phase change region (PCR) at the processing region and the depth information includes keyhole depth of the PCR.

128. The SS-OCT method of claim 127, further comprising directing the imaging optical signal at one or more selected positions in and/or near the PCR.

129. The SS-OCT method of claim 121, further comprising controlling at least one processing parameter of a material modification process implemented by the material processing beam on the sample based on the at least one feature of the processing region.

130. The SS-OCT method of claim 121, further comprising determining a sample position based on the at least one corrected interferometer output signal.

131. The SS-OCT method of claim 121, further comprising determining a velocity of a material of the sample based on the at least one corrected interferometer output signal.

132. The SS-OCT method of claim 121, further comprising determining one or more alignments and/or one or more offsets in alignment between a coordinate system of a beam delivery system for the material processing beam and a coordinate system of a delivery׳ system for the imaging optical signal.

133. The SS-OCT method of claim 121, further comprising:controlling the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt that are associated with one or more interferometry׳ signals;calculating one or more corrections, wherein calculating the one or more corrections comprises;identifying a distortion in at least one of the interferometer output signals that is associated with at least one of the at least two tuning rates; andperforming an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation. 139 WO 2024/158772 PCT/US2024/012552

134. The SS-OCT method of claim 133, wherein the at least two tuning rates dk/dt include at least one positive tuning rate dk/dt and at least one negative tuning rate dk/dt.

135. The SS-OCT method of claim 134, wherein performing the evaluation comprises comparing distortion in at least one interferometer output signal associated with a positive tuning rate dk/dt with distortion in at least one interferometer output signal associated with a negative tuning rate dk/dt.

136. The SS-OCT method of claim 133, wherein performing the evaluation comprises comparing distortion in at least two interferometer output signals.

137. The SS-OCT method of claim 133, wherein the distortion corresponds to a distortion in one or more geometric aspects encoded in the interferometer output signal.

138. The SS-OCT method of claim 137, wherein the one or more geometric aspects includes at least one of a position, symmetry, a width of a peak, a centroid, a geometric second moment, a center of mass, an amplitude, a height to width ratio, and a geometric area under a curve.

139. The SS-OCT method of claim 137, wherein performing the evaluation comprises comparing one or more geometric aspects encoded in at least two interferometer output signals.

140. The SS-OCT method of claim 137, wherein performing the evaluation comprises comparing one or more geometric aspects to one or more predetermined thresholds and/or baselines associated with the one or more geometric aspects.

141. The SS-OCT method of claim 140, further comprising establishing the one or more predetermined thresholds and/or baselines, and establishing is performed based on at least one of:system and/or component requirements,one or more application requirements, one or more calibrations.140 WO 2024/158772 PCT/US2024/012552 one or more models,limitations of the hardware and/or software, one or more algorithms, and fundamental physics.

142. The SS-OCT method of claim 137, wherein performing the evaluation comprises comparing the one or more geometric aspects relative to at least one of:one or more geometric aspects encoded in at least one other of the interferometer output signals, andone or more predetermined thresholds and/or baselines associated with the one or more geometric aspects.

143. The SS-OCT method of claim 133, wherein performing the evaluation comprises applying a predetermined threshold to the distortion and determining whether the distortion exceeds the predetermined threshold.

144. The SS-OCT method of claim 133, wherein performing the evaluation comprises determining if a relative difference between two or more distortions exceeds a predetermined threshold.

145. The SS-OCT method of claim 133, further comprising generating a mathematical model based at least in part on one or more properties of an SS-OCT system and the evaluation of the distortion.

146. The SS-OCT method of claim 145, wherein generating the mathematical model comprises generating an estimate of a magnitude and/or a direction of motion velocity of the sample based on the evaluation of the distortion.

147. The SS-OCT method of claim 133, wherein a material modification process implemented by the material processing beam on the sample is a welding process and the material processing beam creates a phase change region (PCR) at the processing region, and the method further comprisesusing the evaluation to generate one or more corrections, and141 WO 2024/158772 PCT/US2024/012552 using the one or more corrections generated by the evaluation to calculate a measurement of one or more features which are in motion in the PCR.

148. The SS-OCT method of claim 147, wherein the one or more features which are in motion in the PCR are in motion as a direct result of the material modification process.

149. The SS-OCT method of claim 133, wherein a material modification process implemented by the material processing beam on the sample is a welding process and the material processing beam creates a phase change region (PCR) at the processing region, and the method further comprises using the evaluation to generate an estimate of a velocity of material being processed in the PCR.

150. The SS-OCT method of claim 133, wherein applying the one or more corrections to the at least one interferometer output signal includesdiscarding, weighting, promoting, or using the at least one interferometer output signal, orselecting the at least one interferometer output signal to discard at a later time.

151. The SS-OCT method of claim 133, wherein the interferometer is a first interferometer and the method further comprisesproviding at least one additional interferometer and configuring the first interferometer and the at least one additional interferometer such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element,directing a first imaging optical signal configured with one of the at least two tuning rates dk/dt to the at least one reference arm and the at least one sample arm of the first interferometer,directing a second imaging optical signal configured with another of the at two tuning rates dk/dt to the at least one reference arm and the at least one sample arm of the at least one additional interferometer, andidentifying the distortion based on the one or more interferometer output signals of the first interferometer and the at least one additional interferometer. 142 WO 2024/158772 PCT/US2024/012552

152. The SS-OCT method of claim 151, further comprising directing the first and second imaging optical signals to the processing region simultaneously.

153. The SS-OCT method of claim 121, wherein the time-varying difference in optical path lengths is caused by sample motion.

154. The SS-OCT method of claim 153, wherein a motion velocity of the sample is greater than 10 mm/s.

155. The SS-OCT method of claim 154, wherein the motion velocity of the sample is greater than 100 mm/s.

156. The SS-OCT method of claim 155, wherein the motion velocity of the sample is greater than 500 mm/s.

157. The SS-OCT method of claim 156, wherein the motion velocity of the sample is greater than 1000 mm/s.

158. The SS-OCT method of claim 157, wherein the motion velocity of the sample is greater than 10,000 mm/s.

159. The SS-OCT method of claim 121, further comprising deriving track data from the at least one interferometer output signal and applying the one or more corrections to the track data.

160. The SS-OCT method of claim 121, further comprising providing at least one k-clock module configured to generate a k-clock signal that indicates when a wavenumber k of the imaging optical signal substantially changes by one or more increments.

161. The SS-OCT method of claim 160, wherein a rate of change in the at least one wavenumber k of the imaging optical signal over time (tuning rate dk/dt) is non-uniform, and the method further comprises configuring the at least one k-clock module to trigger the acquisition of the interferometer output signals at uniform increments in wavenumber k.143 WO 2024/158772 PCT/US2024/012552

162. The SS-OCT method of claim 161, wherein the method further comprises processing the at least one interferometer output signal based on interferometer output signals that are uniformly sampled in wavenumber.

163. The SS-OCT method of claim 160, wherein a rate of change in the at least one wavenumber k of the imaging optical signal over time (tuning rate dk/dt) is uniform, and the method further comprises configuring the at least one k-clock module to trigger the acquisition of the interferometer output signals at uniform increments in wavenumber k.

164. The SS-OCT method of claim 160, wherein the provided k-clock module is configured with one or more optical elements present in at least one of the sample and reference arms of the interferometer.

165. The SS-OCT method of claim 160, wherein the k-clock signal is acquired simultaneously to the acquisition of the interferometer output signals, and the method further comprises at least one of:using the acquired k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k,using the acquired k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal, andusing the acquired k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.

166. The SS-OCT method of claim 160, wherein the k-clock signal is acquired in a manner which is time gated relative to the acquisition of the interferometer output signals, and the method further comprise at least one of;using the acquired k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k,using the acquired k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal, and144 WO 2024/158772 PCT/US2024/012552 using the acquired k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.

167. The SS-OCT method of claim 121, wherein the method further comprises simulating a k-clock signal that indicates when the at least one wavenumber k of the imaging optical signal substantially changes by one or more increments based at least in part on one or more properties of an SS-OCT system and one or more properties of the tunable light source, and the method further comprises at least one of:using the simulated k-clock signal to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k,using the simulated k-clock signal to compute at least one correction for one or more distortions in the interferometer output signal, andusing the simulated k-clock signal to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.

168. The SS-OCT method of claim 121, wherein the method further comprises generating a mathematical model of k(t) and/or a tuning rate dk/dt of the imaging optical signal based at least in part on one or more properties of an SS-OCT system and one or more properties of the tunable light source, and the method further comprises at least one of:using the mathematical model to perform at least one of sampling, resampling, interpolating, and/or estimating interferometer output signals at uniform intervals in wavenumber k,using the mathematical model to compute at least one correction for one or more distortions in the interferometer output signal, andusing the mathematical model to define a discrete-Fourier transform method which can be directly applied to an interferometer output signal that is not uniformly sampled in k.

169. The SS-OCT method of claim 121, further comprisingcontrolling the tunable light source such that a rate of change in the at least one w avenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt that are associated with one or more interferometry signals; and145 WO 2024/158772 PCT/US2024/012552 generating a mathematical model of the at least two tuning rates based at least in part on one or more properties of the tunable light source and one or more properties of an SS- OCT system that includes the interferometer and the optical detector.

170. The SS-OCT method of claim 169, further comprisingusing the mathematical model to associate an estimate of at least one of a value of k and tuning rate dk/dt with data sampled from the interferometer output signal and/or the corrected interferometer output signal,using the associated measurement of the wavenumber k to estimate a value of k at sampled interferometer output signal values, andusing the associated measurement of the wavenumber k to perform at least one of sampling, resampling, interpolating, and estimating interferometer output signals at uniform intervals in k.

171. The SS-OCT method of claim 169, further comprising using the mathematical model to compute at least one correction for one or more distortions in the interferometer output signal.

172. The SS-OCT method of claim 121, wherein the time-varying difference in optical path lengths is cause by sample motion relative to an axis of the imaging optical signal.

173. The SS-OCT method of claim 121, wherein the time-varying difference in optical path lengths is caused by a material modification process implemented by the material processing beam on the sample.

174. The SS-OCT method of claim 121, wherein the time-varying difference in optical path lengths is caused by intrinsic sample motion not caused by a material modification process that is implemented by the material processing beam on the sample.

175. The SS-OCT method of claim 121, further comprising controlling the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt. 146 WO 2024/158772 PCT/US2024/012552

176. The SS-OCT method of claim 175, wherein the at least two tuning rates include at least one negative and at least one positive dk/dt.

177. The SS-OCT method of claim 175, wherein the tunable light source is controlled such that the imaging optical signal includes a superposition of the at least two tuning rates dk/dt.

178. The SS-OCT method of claim 177, wherein the superposition of the at least two tuning rates dk/dt includes at least one negative and at least one positive dk/dt.

179. The SS-OCT method of claim 121, wherein the tunable light source is a first tunable light source and the method further comprises providing at least one other tunable light source.

180. The SS-OCT method of claim 179, wherein the interferometer is a first interferometer and providing the at least one other tunable light source further includes providing at least one additional interferometer, the first interferometer configured with the first tunable light source, the at least one additional interferometer configured with the at least one other tunable light source, and the first interferometer and the at least one additional interferometer configured such that they share at least one optical element.

181. The SS-OCT method of claim 180, wherein a rate of change in the at least one wavenumber k of the imaging optical signal in time is a tuning rate dk/dt and the method further comprisescontrolling the first tunable light source such that a first imaging optical signal generated by the first tunable light source has a first tuning rate dk/dt, andcontrolling the at least one other tunable light source such that an imaging optical signal generated by the at least one other tunable light source has a second tuning rate dk/dt that is different than the first tuning rate dk/dt.

182. The SS-OCT method of claim 181, wherein at least a portion of the first imaging optical signal and at least a portion of the imaging optical signal generated by the at least one other imaging optical signal are transmitted simultaneously. 147 WO 2024/158772 PCT/US2024/012552

183. The SS-OCT method of claim 182, wherein the first and second tuning rates are associated with one or more interferometer output signals and the method further comprises calculating one or more corrections, wherein calculating the one or more corrections comprises:identifying a distortion in at least one of the interferometer output signals that is associated with at least one of the first and second tuning rates;performing an evaluation of the distortion.wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.

184. The SS-OCT method of claim 183, wherein the first tuning rate dk/dt is a positive dk/dt and the second tuning rate dk/dt is a negative dk/dt.

185. The SS-OCT method of claim 121, further comprising providing a splitter to split the imaging optical signal into at least two arms; and an optical delay element configured such that an output of a first arm of the at least two arms is delayed in time relative to an output of a second arm of the at least two arms.

186. The SS-OCT method of claim 185, further comprising controlling the tunable light source such that a rate of change in the at least one wavenumber k of the imaging optical signal in time (tuning rate dk/dt) includes at least two tuning rates dk/dt.

187. The SS-OCT method of claim 186, wherein the at least two tuning rates dk/dt includes a positive tuning rate dk/dt associated with either the first arm or the second arm, and a negative tuning rate dk/dt associated with the other of the first arm or the second arm.

188. The SS-OCT method of claim 187, wherein the interferometer is a first interferometer and the method further comprises providing at least one additional interferometer.

189. The SS-OCT method of claim 188, wherein the first arm is configured to be directed to at least one of: different reference arms, different sample arms, partially overlapped reference arms, and partially overlapped sample arms of the first interferometer and the at least one additional interferometer.148 WO 2024/158772 PCT/US2024/012552

190. The SS-OCT method of claim 188, wherein the first arm and the second arm are configured to be directed to at least one sample arm and at least one reference arm of the first interferometer and the at least one additional interferometer.

191. The SS-OCT method of claim 188, whereinthe first interferometer and the at least one additional interferometer are configured such that a sample arm of the first interferometer and a sample arm of the at least one additional interferometer share at least one optical element, andthe first arm and the second arm of the imaging optical signal are configured to be directed to the first interferometer and the at least one additional interferometer simultaneously.

192. The SS-OCT method of claim 191, whereinthe first arm is configured to be directed to the first interferometer or the at least one additional interferometer, andthe second arm is configured to be directed to the other of the first interferometer or the at least one additional interferometer.

193. The SS-OCT method of claim 191, wherein the at least two tuning rates of the first and second arms are associated with one or more interferometer output signals and the method further comprisescalculating the one or more corrections, wherein calculating the one or more corrections comprises;identifying a distortion in at least one of the one or more interferometer output signals that is associated with at least one of the positive and negative tuning rates;performing an evaluation of the distortion, wherein the one or more corrections to the at least one interferometer output signal is based on the evaluation.

194. The SS-OCT method of claim 121, wherein the tunable light source is configured such that an optical frequency of the imaging optical signal varies at a rate in a range of PHz/s - 2 ZHz/s inclusive.149 WO 2024/158772 PCT/US2024/012552

195. The SS-OCT method of claim 121, further comprisinggenerating an OCT image based on the at least one interferometer output signal and/or the at least one corrected interferometer output signal, andtransmitting the generated OCT image to a display device.

196. The SS-OCT method of claim 121, further comprisinggenerating OCT data from the processed interferometer output signal and/or the at least one corrected interferometer output signal. andtransmitting the OCT data to an external device.

197. The SS-OCT method of claim 121, further comprising providing the tunable light source as a tunable vertical-cavity surface-emitting laser (VCSEL).

198. The SS-OCT method of claim 197, further comprising providing an amplifier for amplifying the VCSEL.

199. The SS-OCT method of claim 198, wherein the amplifier is configured as a fiber amplifier.

200. The SS-OCT method of claim 121, further comprising directing the imaging optical signal with a directing element.

201. The SS-OCT method of claim 200, wherein the imaging optical signal is directed to be within 50 nm of the material processing beam at the processing region.

202. The SS-OCT method of claim 121, further comprising providing a processing unit that is configured to process the at least one interferometer output signal, detect the distortion, apply the one or more corrections, and process the at least one corrected interferometer output signals.

203. The SS-OCT method of claim 121, further comprising providing a material processing source configured to generate the material processing beam.150 WO 2024/158772 PCT/US2024/012552

204. The SS-OCT method of claim 203, further comprising controlling at least one processing parameter of a material modification process implemented by the material processing beam on the sample based on the at least one feature of the processing region.

205. The SS-OCT method of claim 121, further comprising using an optical detector to generate the at least one interferometer output signal. 151