Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/027—Control of working procedures of a spectrometer; Failure detection; Bandwidth calculation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/28—Investigating the spectrum
  • G01J3/30—Measuring the intensity of spectral lines directly on the spectrum itself
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/02—Details
  • G01J3/10—Arrangements of light sources specially adapted for spectrometry or colorimetry
  • G01J2003/102—Plural sources
  • G01J2003/104—Monochromatic plural sources

Definitions

• the present invention relates to a method and a system for calibrating a spectrometer device of a batch of spectrometer devices. Further, the present invention relates to a computer program and a computer-readable storage medium for performing the method for calibrating a spectrometer device of a batch of spectrometer devices.
• the method and devices can, in particular, be used for calibrating spectrometer devices used for investigation in the infrared spectral region, specifically in the near infrared and the mid infrared spectral regions. However, other spectrometer devices used for optical investigation are also feasible.
• the terms “preferably”, “more preferably”, “particularly”, “more particularly”, “specifically”, “more specifically” or similar terms are used in conjunction with optional features, without restricting alternative possibilities.
• Features introduced by these terms are optional features and are not intended to restrict the scope of the claims in any way.
• the invention may, as the skilled person will recognize, be performed by using alternative features.
• features introduced by "in an embodiment of the invention” or similar expressions are intended to be optional features, without any restriction regarding alternative embodiments of the invention, without any restrictions regarding the scope of the invention and without any restriction regarding the possibility of combining the features introduced in such way with other optional or non-optional features of the invention.
• a method for calibrating a spectrometer device of a batch of spectrometer devices is disclosed.
• spectrometer device as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a device capable of optically analyzing at least one sample, thereby generating at least one item of information on at least one spectral property of the sample.
• the term may refer to a device which is capable of recording a signal intensity with respect to a corresponding wavelength of a spectrum or a partition thereof, such as a wavelength interval, wherein the signal intensity may, preferably, be provided as an electrical signal which may be used for further evaluation.
• An optical element specifically comprising at least one wavelength-selective element, such as an optical filter and/or a dispersive element, may be used for separating incident light into a spectrum of constituent wavelength components whose respective intensities are determined by employing a detector device.
• a further optical element may be used which can be designed for receiving incident light and transferring the incident light to the optical element.
• the spectrometer device generally, may be operable in a reflective mode and/or may be operable in a transmissive mode. For possible embodiment of the spectrometer device, reference is made to the description of the spectrometer device as will be outlined in further detail below.
• calibration the process also being referred to as “calibration”, as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a process of at least one of determining, correcting and adjusting measurement inaccuracies at the spectrometer device.
• the result of the calibration process often also referred to as the “item of calibration information”, may also be or comprise at least one item of information on the result of the calibration process, such as a calibration function, a calibration factor, a calibration matrix or the like, e.g. for transforming one or more measured values into one or more calibrated or “true” values.
• Measurement inaccuracies may, as an example, arise from uncertainties in wavelength determination and/or from intrinsic and/or extrinsic interferences on measurement signals of the spectrometer device.
• Calibrating the spectrometer device may comprise at least one of a wavelength calibration, a stray light calibration, a dark current calibration, a test of a spectral resolution.
• the calibration specifically each of the calibrations, may comprise at least one two-step process, wherein, in a first step, information on a deviation of a measurement signal of the spectrometer device from a known standard is determined, wherein, in a second step, this information is used for correcting and/or adjusting the measurement signal of the spectrometer device in order to reduce, minimize and/or eliminate the deviation.
• the calibration may comprise applying the item of calibration information, for example to a measurement signal and/or to a measurement spectrum of the spectrometer device.
• a calibration of the spectrometer device may improve and/or maintain accuracy of measurements performed with the calibrated spectrometer device.
• the calibrating may comprise preparing the measurement signal and/or the measurement spectrum of the spectrometer device in such a way that the measurement signal and/or the measurement spectrum may be used for further analysis and/or evaluation, such as by preparing the measurement signal and/or the measurement spectrum as input data for one or more trainable models analyzing the measurement signal and/or the measurement spectrum.
• the calibrating may ensure that the measurement signal and/or the measurement spectrum is suitable for being analyzed by the trainable model in order to provide accurate results.
• the calibrating of the spectrometer device specifically may be performed at a manufacturer’s site of the spectrometer device manufacturer.
• the calibrating may also be performed in the field, such as after setup of the spectrometer device at the site of use and/or for maintenance purposes.
• the term “batch” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a plurality of spectrometer device being manufactured in a common manufacturing process.
• the common manufacturing process may comprise a series of manufacturing steps, wherein the series of manufacturing steps yield the plurality of assembled spectrometer devices.
• the common manufacturing process may specifically be a common manufacturing process in terms of time and/or in terms of manufacturing steps.
• the batch of spectrometer device may be manufactured in a timely overlapping fashion. Alternatively or additionally, the batch of spectrometer devices may be manufactured in subsequent manufacturing processes, wherein the subsequent manufacturing processes comprise the same series of manufacturing steps.
• the term “batch of spectrometer device” may also be referred to as “fleet of spectrometer devices” or any grammatical variation thereof.
• the spectrometer device comprises at least one detector device. Specifically, when calibrating the spectrometer device, a calibration of the detector device comprised by the spectrometer device may be necessary and may be performed.
• the term “detector device” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning. The term specifically may refer, without limitation, to an arbitrary device or combination of devices capable of recording and/or monitoring incident light.
• the detector device may be responsive to incident illumination and may be configured for generating an electrical signal indicating an intensity of the illumination.
• the detector device may comprise at least one photodetector such as at least one CCD or CMOS device.
• the detector device specifically may comprise at least one detector array comprising a plurality of pixelated sensors, wherein each of the pixe- lated sensors is configured to detect at least a portion of at least one of the constituent wavelength components.
• the detector device comprises at least one optical element configured for separating incident light into a spectrum of constituent wavelength components.
• optical element as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to an arbitrary element or a combination of elements suitable for one or more of transmitting, reflecting, deflecting or scattering light in a wavelength-dependent manner.
• the optical element may further be configured, specifically after separating incident light into the spectrum of constituent wavelength components, for transmitting the spectrum onto the detector device. Specifically, the wavelength-dependent transmission, reflections, deflection or scattering of incident light at the optical element may result in a spatial separation of the constituent wavelength components of the spectrum which may be transmitted directly or indirectly onto the detector device.
• the term “light” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a partition of electromagnetic radiation which is, usually, referred to as “optical spectral range” and which comprises one or more of a visible spectral range, an ultraviolet spectral range and an infrared spectral range.
• optical spectral range which comprises one or more of a visible spectral range, an ultraviolet spectral range and an infrared spectral range.
• infrared or “I R”, generally, refer to a wavelength of 760 nm to 1000 pm, wherein a wavelength of 760 nm to 3 pm is, usually, denominated as “near infrared” or “NIR” while the wavelength of 3 p to 15 pm is, usually, denoted as “mid infrared” or “MidlR” and the wavelength of 15 pm to 1000 pm as “far infrared” or “FIR”.
• the term “spectrum” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a partition of the optical spectral range, in particular, the IR spectral range, especially at least one of the NIR or the MidlR spectral ranges, being investigated by the spectrometer device.
• Each part of the spectrum may be constituted by an optical signal which is defined by a signal wavelength and the corresponding signal intensity.
• the term “constituent wavelength component” as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to the optical signal forming part of the spectrum.
• the optical signal may comprise the signal intensity corresponding to the respective wavelength or wavelength interval.
• the detector device further comprises a plurality of photosensitive elements, wherein each photosensitive element is configured for receiving at least a portion of one of the constituent wavelength components and for generating a respective detector signal depending on an illumination of the respective photosensitive element by the at least one portion of the respective constituent wavelength component.
• photosensitive element as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to an individual optical sensor comprised by the detector device, wherein each optical sensor has at least one photosensitive area configured for recording a photoresponse of the photosensitive element by generating at least one output signal that depends on an intensity of a portion of one of the constituent wavelength components impinging on the particular photosensitive area.
• the at least one photosensitive area as comprised by each individual optical sensor may, especially, be a single, uniform area which is designated for receiving incident light impinging on the photosensitive area.
• the at least one output signal may, in particular, be used as the detector signal and can, preferably, be provided to an external evaluation unit for further evaluation.
• detector signal is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a signal generated by at least one detector, specifically to the at least one output signal of the photosensitive element.
• the at least one output signal may be selected from at least one of an electronic signal and an optical signal.
• the at least one output signal may be an analogue signal and/or a digital signal.
• the output signals for adjacent photosensitive elements can be generated simultaneously, or in a temporally successive manner.
• the individual photosensitive elements may, preferably, be active pixel sensors which may be adapted to amplify the output signals prior to providing them as detector signals to an external evaluation unit.
• the photosensitive element may comprise one or more signal processing devices, such as one or more filters and/or analogue-digital-converters for processing and/or preprocessing the electronic signals.
• the method comprises the following steps which, as an example, may be performed in the given order. It shall be noted, however, that a different order is also possible. Further, it is also possible to perform one or more of the method steps once or repeatedly. Further, it is possible to perform two or more of the method steps simultaneously or in a timely overlapping fashion. The method may comprise further method steps which are not listed.
• the method comprises the following steps: a) at least one system characterization step comprising determining line spread functions at corresponding wavelengths by comparing at least one spectrum measured by using the spectrometer device with at least one reference spectrum; b) at least one resolution homogenization step comprising for each wavelength converting a resolution of the line spread function to a pre-defined target resolution for a corresponding wavelength, wherein the target resolution for each wavelength is a pre-defined target batch resolution value for the respective wavelength.
• system characterization is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a process of determining one or more system characteristics of the spectrometer device.
• the system characterization step may comprise determining system characteristics related to the spectral data obtained by using the spectrometer device.
• the system characteristics may comprise one or more of spectral resolution, straylight contributions and/or detector characteristics.
• the system characterization step may be performed with each spectrometer device in the fleet of spectrometer devices.
• the system characterization step may determine the one or more system characteristics for each spectrometer devices in the fleet of spectrometer devices.
• the system characteristics may vary for the spectrometer devices in the fleet of spectrometer devices.
• a lowest performing spectrometer device for example a lowest spectral resolution of a specific spectrometer device, may be used as a lower boundary for the following homogenization step.
• the system characterization step may specifically be performed to estimate an instrumental line spread function which provides an estimate of the spectral resolution as a function of the wavelength.
• the system characterization step may comprise determining the system characteristics by analyzing spectral data obtained by using the spectrometer device.
• the characterization step may specifically comprise analyzing spectral data obtained by using the spectrometer device, such as analyzing the spectrum measured by using the spectrometer device and the reference spectrum, to obtain the system characteristics of the spectrometer device.
• reference spectrum is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a spectrum, specifically a spectrum as defined above, obtained by measuring a reference object with a reference spectrometer device.
• the reference object may be an object of known spectral characteristics, such as known reflection and/or transmission characteristics.
• the reference spectrometer device measuring the reference object may be a high-resolution spectrometer device.
• the reference spectrum may be obtained prior to the performance of the method.
• the reference spectrum may be provided by a manufacturer of the reference object and/or by a manufacturer of the spectrometer device.
• broadband light source is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a spe- cial or customized meaning.
• the term specifically may refer, without limitation, to a device emitting light in a broad spectral range, such as light having a spectral width of at least 5 nm, specifically at least 10 nm, e.g. a spectral width of 10 nm to 3000 nm.
• the broad spectral range of the broadband light source may comprise at least one of the visible spectral range, the ultraviolet spectral range and the infrared spectral range.
• pixel position is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to an arbitrary item of location information of the photosensitive element in the detector device.
• the pixel information may describe a position of the photosensitive element in the detector device by using one or more of an absolute position information and a relative position information, specifically in one, two or even three dimensions.
• identification number as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• Step a3) may comprise processing the plurality of detector signals determined in the step a2), thereby obtaining a plurality of processed detector signals.
• the determining of the line spread function in step a3) may comprise determining the line spread function from the plurality of processed detector signals.
• the processing of the plurality of detector signals may specifically comprise transforming the plurality of detector signals. As an example, the plurality of detector signals may be transformed by using at least one Fourier transformation.
• Step aii) may comprise broadening the known spectrum of the monochromatic light sources by using kernel convolution with a theoretical line spread function.
• Step aii) may specifically comprise adjusting parameters of a theoretical kernel until the broadened spectrum of the monochromatic light sources matches the measured spectrum.
• the adjusted kernel parameters may be used to approximate the line spread function at this wavelength.
• the theoretical kernel may be at least one kernel selected from the group consisting of: a Gaussian kernel with only one free parameter; Lorentzian profile; Moffat profile; or Voigt profile; asymmetric kernel. Other kernel may also be feasible.
• the theoretical kernel may be a Gaussian kernel with only one free parameter.
• the free parameter of the Gaussian kernel may be the full width at half maximum (FWHM).
• the system characterization step comprising steps ai) and aii) may comprise using multiple monochromatic light sources with central wavelengths which are spread across the entire wavelength range of the spectrometer device to be characterized.
• the central wavelength of a monochromatic light source may denote the wavelength in the spectrum of the monochromatic light source having the highest intensity.
• a monochromatic light source may be realized using a continuous emitter in conjunction with bandpass filters and/or by using a monochromatic emitter, such as a laser or the like.
• the intrinsic spectral width of the source may preferably be smaller than the line spread function of the spectrometer device at the corresponding wavelength.
• the system characterization step may comprise aa) illuminating at least one reference object by using at least one broadband light source; ab) determining the line spread function by comparing a known spectrum of the reference object with the spectrum measured by using the spectrometer device, wherein the known spectrum of the reference object is predetermined by using at least one high-resolution spectrometer.
• Step ab) may comprise broadening the known spectrum of the reference object by using kernel convolution with a theoretical line spread function.
• Step ab) may comprise adjusting parameters of a theoretical kernel until the broadened spectrum of the reference object matches the measured spectrum.
• the adjusted kernel parameters may be used to approximate the line spread function at this wavelength.
• the theoretical kernel may be at least one kernel selected from the group consisting of: a Gaussian kernel with only one free parameter; Lorentzian profile; Moffat profile; or Voigt profile; asymmetric kernel.
• Step ab) may comprise directly comparing the known spectrum of the reference object with the spectrum measured by using the spectrometer device in signal space and/or comparing at least one derivative of the known spectrum of the reference object with at least one derivative of the spectrum measured by using the spectrometer device, specifically comparing a first-order deri- vate, a second-order derivative and/or higher order derivatives of the spectra.
• the system characterization step comprising steps aa) and ab) may comprise using one or more reference objects for which the intrinsic spectrum may be known, specifically at much higher resolution, and which may be measured beforehand using a high-resolution spectrometer.
• the higher resolution may refer to the situation where the resolution of the intrinsic spectrum may be higher than the resolution of the spectrometer device to be characterized.
• a Gaussian kernel may be used for determining the line spread functions.
• the comparison may be either be done in signal space or using higher derivatives thereof. This may bear the advantage that constant offsets that are not affected by resolution differences, such as due to straylight in the spectrometer system, may not impact the loss function used to find the optimal line spread functions.
• the method may comprise the at least one resolution homogenization step.
• resolution homogenization as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a process of unifying the system characteristics of the spectrometer device across the batch of spectrometer device.
• the resolution homogenization step may comprise unifying the system characteristics of the spectrometer device determined in the system characterization step.
• the system characteristics of the spectrometer device may be identical to the system characteristics of each other spectrometer device of the batch of spectrometer device.
• the resolution homogenization step may specifically comprise unifying the spectral resolution of the spectrometer device across the batch of spectrometer device.
• the resolution homogenization step may comprise using the previously determined is-state of the line spread function of each spectrometer device and computationally converting the is-state of the line spread function to a target state.
• the is-state of the line spread function may refer to the state of the line spread function being determined in step a), specifically indicating a spectral resolution of the spectrometer device at a specific wavelength.
• the is- state may specifically an individual state of the spectrometer device.
• the is-state may be different for different spectrometer devices in the batch of spectrometer devices.
• the resolution homogenization step comprises, for each wavelength, converting the resolution of the line spread function to the pre-defined target resolution for a corresponding wavelength, wherein the target resolution for each wavelength is the pre-defined target batch resolution value for the respective wavelength.
• target resolution is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a resolution, specifically a resolution as defined above, defining a nominal value for the resolution homogenization step.
• the target resolution may be wavelength-dependent.
• the target resolution may be defined for each wavelength of the entire wavelength interval of the spectrometer device.
• the target resolution may be a fixed target resolution.
• the target resolution may be identical for each spectrometer device of the batch of spectrometer devices.
• the target resolution may be lower than the resolution of the individual spectrometer devices of the fleet. This may be required as it is possible to broaden a narrower line spread function, specifically a resolution of the line spread function, to a broader resolution but not vice versa.
• target batch resolution value is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to a target resolution being identical for each spectrometer device of the batch of spectrometer devices.
• the target resolution and the target batch resolution value are predefined.
• the term “predefined”, as used herein, may refer, without limitation, to a situation in which the target resolution and/or the target batch resolution value may be known and/or determined prior to the performance of the method. In other words, the target resolution and/or the target batch resolution value may be defined in advance of the performance of the method.
• a system for calibrating a spectrometer device of a batch of spectrometer devices comprises the spectrometer device comprising at least one detector device.
• the detector device comprises at least one optical element configured for separating incident light into a spectrum of constituent wavelength components.
• the detector device further comprises a plurality of photosensitive elements. Each photosensitive element is configured for receiving at least a portion of one of the constituent wavelength components and for generating a respective detector signal depending on an illumination of the respective photosensitive element by the at least one portion of the respective constituent wavelength component.
• the system further comprises at least one evaluation unit.
• the evaluation unit is configured for performing the method for calibrating a spectrometer device of a batch of spectrometer devices according to the present invention, such as according to any one of the embodiments disclosed above and/or according to any one of the embodiment disclosed in further detail below.
• evaluation unit as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to an arbitrary logic circuitry configured for performing basic operations of a computer or system, and/or, generally, to a device which is configured for performing calculations or logic operations.
• the evaluation unit may be configured for processing basic instructions that drive the computer or system.
• the evaluation unit may comprise at least one arithmetic logic unit (ALU), at least one floating-point unit (FPU), such as a math co-processor or a numeric co-pro- cessor, a plurality of registers, specifically registers configured for supplying operands to the ALU and storing results of operations, and a memory, such as an L1 and L2 cache memory.
• the processor may be a multi-core processor.
• the evaluation unit may be or may comprise a central processing unit (CPU).
• the evaluation unit may comprise one or more processors.
• the evaluation unit may be or may comprise a microprocessor.
• the evaluation unit’s elements may be contained in one single integrated circuitry (IC) chip.
• the evaluation unit may be or may comprise one or more application-specific integrated circuits (ASICs) and/or one or more field-programmable gate arrays (FPGAs) and/or one or more tensor processing unit (TPU) and/or one or more chip, such as a dedicated machine learning optimized chip, or the like.
• the evaluation unit may specifically be configured, such as by software programming, for performing one or more evaluation operations, specifically one or more operations performed in step a) and/or b) of the method as described in further detail above.
• the evaluation unit may be configured for, unidirectionally and/or bidirectionally, exchanging data and/or control commands with other elements of the system, specifically with the detector device.
• the evaluation unit may be configured for receiving the plurality of detector signals from the detector device.
• the evaluation unit may specifically comprise at least one data storage unit configured for storing at least one of the reference spectrum and the target resolution.
• the evaluation unit may comprise at least one retrieving interface configured for retrieving at least one of the reference spectrum and the target resolution, specifically for retrieving at least one of the reference spectrum and the target resolution from a cloud computer network.
• data storage unit as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to an arbitrary memory device configured to store data.
• the data storage unit may be an electronic, magnetic and/or mechanic memory device.
• the data storage unit may further be configured to store data, specifically in an organized way, such as in a database, more specifically in at least one database record.
• the system may further comprise at least one reference object and the at least one broadband light source.
• the system may be configured for performing steps aa) and ab) of the method for calibrating a spectrometer device of a batch of spectrometer devices according to the present invention, such as according to any one of the embodiments disclosed above and/or according to any one of the embodiment disclosed in further detail below.
• the broadband light source may comprise at least one of: an incandescent lamp; a blackbody radiator; an electric filament; a light emitting diode.
• the optical element may comprise at least one wavelength selective element.
• wavelength selective element as used herein is a broad term and is to be given its ordinary and customary meaning to a person of ordinary skill in the art and is not to be limited to a special or customized meaning.
• the term specifically may refer, without limitation, to an optical element configured for selectively transmitting light of different wavelengths.
• the wavelength selective element may be configured for transmitting an incident light beam, whereby a spectral composition of the incident light may be modified upon transmission.
• the modification of the transmitted light may comprise one or more of: a spatial separation of light having different wavelengths; an attenuation of light having different wavelengths.
• the wavelength selective element may be configured for selectively transmitting light in a particular range of wavelengths, while absorbing, filtering and/or interfering the remainder.
• the wavelength selective element may comprise at least one element selected from the group consisting of: a prism; a grating; a linear variable filter; an optical filter.
• the detector device may comprise the plurality of photosensitive elements arranged in a linear array.
• the linear array of photosensitive elements may comprise a number of 10 to 1000 photosensitive elements, specifically a number of 100 to 500 photosensitive elements, specifically a number of 200 to 300 photosensitive elements, more specifically a number of 256 photosensitive elements, most specifically a number of 128 photosensitive elements.
• a computer program comprising instructions which, when the program is executed by the system according to the present invention, such as according to any one of the embodiments disclosed above and/or according to any one of the embodiments disclosed in further detail below, cause the evaluation unit of the system to perform the method for calibrating a spectrometer device of a batch of spectrometer devices according the present invention, such as according to any one of the embodiments disclosed above and/or according to any one of the embodiments disclosed in further detail below.
• At least method step a) and b) as indicated above may be performed by using the evaluation unit of the system executing the computer program.
• one, more than one or even all of method steps a3), aii) and ab) may be performed by using the evaluation unit of the system executing the computer program.
• one, more than one or even all of method steps a1 ), a2), ai) and aa) as indicated above may be at least computer controlled and/or supported by evaluation unit of the system executing the computer program.
• a computer-readable storage medium specifically a non-transient computer- readable storage medium, comprising instructions which, when the instructions are executed by the system according to the present invention, such as according to any one of the embodiments disclosed above and/or according to any one of the embodiments disclosed in further detail below, cause the evaluation unit of the system to perform the method for calibrating a spectrometer device of a batch of spectrometer devices according to the present invention, such as according to any one of the embodiments disclosed above and/or according to any one of the embodiments disclosed in further detail below.
• computer-readable storage medium specifically may refer to non- transitory data storage means, such as a hardware storage medium having stored thereon computer-executable instructions.
• the computer-readable storage medium also referred to as computer-readable data carrier, specifically may be or may comprise a storage medium such as a random-access memory (RAM) and/or a read-only memory (ROM).
• RAM random-access memory
• ROM read-only memory
• the method and system according to the present invention may provide a large number of advantages over known methods and devices.
• the method and the system according to the present invention may provide a global, use-case-independent calibration and correction scheme on the individual spectrometer device level that enables fleet homogenization of the resulting spectral data to the degree that trainable models produce accurate results across the entire fleet of spectrometer devices.
• spectral homogeneity through system characterization and controlled degradation may be achieved for all spectrometer device of a batch of spectrometer devices.
• the method and the system may use a standardized, use-case-independent testing procedure which is capable of characterizing the spectrometer device followed by a digital postprocessing that treats data from different spectrometer devices in a manner such that identical system characteristics may be emulated.
• Embodiment 1 A method for calibrating a spectrometer device of a batch of spectrometer devices, wherein the spectrometer device comprises at least one detector device comprising at least one optical element configured for separating incident light into a spectrum of constituent wavelength components and further comprising a plurality of photosensitive elements, wherein each photosensitive element is configured for receiving at least a portion of one of the constituent wavelength components and for generating a respective detector signal depending on an illumination of the respective photosensitive element by the at least one portion of the respective constituent wavelength component, wherein the method comprises the following steps: a) at least one system characterization step comprising determining line spread functions at corresponding wavelengths by comparing at least one spectrum measured by using the spectrometer device with at least one reference spectrum; b) at least one resolution homogenization step comprising for each wavelength converting a resolution of the line spread function to a pre-defined target resolution for a corresponding wavelength, wherein the target resolution for each wavelength is a pre-defined target batch resolution value for the respective wavelength.
• Embodiment 2 The method according to the preceding embodiment, wherein the pre-defined target batch resolution value A target is selected such that the converted resolution A ⁇ conv for a respective wavelength of the spectrometer device satisfies A ⁇ conv ⁇ A ⁇ target .
• Embodiment 3 The method according to any one of the preceding embodiments, wherein the converting of the respective resolution A ⁇ meas of the line spread function to a pre-defined target resolution comprises convolving the measured spectrum with at least one Kernel with a width described by a quadratic subtraction A iConv
• Embodiment 16 The method according to any one of the three preceding embodiments, wherein step aii) comprises broadening the known spectrum of the monochromatic light sources by using kernel convolution with a theoretical line spread function, wherein step aii) comprises adjusting parameters of a theoretical kernel until the broadened spectrum of the monochromatic light sources matches the measured spectrum, wherein the adjusted kernel parameters are used to approximate the line spread function at this wavelength.
• Figure 4 shows an exemplary line spread function
• the detector device 114 comprises a plurality of photosensitive elements 124, wherein each photosensitive element 124 is configured for receiving at least a portion of one of the constituent wavelength components 120 and for generating a respective detector signal depending on an illumination of the respective photosensitive element 124 by the at least one portion of the respective constituent wavelength component 120.
• the detector device 114 may comprise the plurality of photosensitive elements 124 arranged in a linear array 126.
• the linear array 126 of photosensitive elements 124 may comprise a number of 128 photosensitive elements 124.
• Each photosensitive element 124 may comprise at least one element selected from the group consisting of: a pixelated inorganic camera element, specifically a pixelated inorganic camera chip, more specifically a CCD chip or a CMOS chip; a monochrome camera element, specifically a monochrome camera chip; at least one photoconductor, specifically an inorganic photoconductor, more specifically an inorganic photoconductor comprising PbS, PbSe, Ge, InGaAs, ext. InGaAs, InSb, Si or HgCdTe.
• the system 110 may further comprise at least one broadband light source 128 and at least one optical interferometer 130 arranged to illuminate the spectrometer device 112 with the broadband light source 128 through the optical interferometer 130.
• the broadband light source 128 may comprise, for example, at least one of: an incandescent lamp; a blackbody radiator; an electric filament; a light emitting diode.
• the optical interferometer 130 may comprise at least one interferometer selected from the group consisting of: a Michelson interferometer; a Fabry-Perot interferometer; a cube corner interferometer.
• the system 110 may also comprise the at least one broadband light source 128.
• the system 110 may further comprise at least one reference object 132.
• the reference object 132 may specifically be an object of known spectral characteristics, such as known reflection and/or transmission characteristics.
• the system 110 may further comprise monochromatic light sources 134 with central wavelengths which are spread across a wavelength range of the spectrometer device 112 to be calibrated.
• the system 110 may specifically comprise a plurality of monochromatic light sources 134.
• the monochromatic light sources 134 may comprise a continuous emitter 136, such as the broadband light source 128, in conjunction with bandpass filters 138 or a monochromatic emitter 140, such as a laser or the like.
• the system 110 may not comprise any additional element in between the emitter 140 and the spectrometer device 112.
• An intrinsic spectral width of the monochromatic light sources 134 may be comparable to a line spread function of the spectrometer device 112 at the corresponding wavelength.
• the system 110 further comprises at least one evaluation unit 142.
• the evaluation unit 142 is configured for performing the method for calibrating a spectrometer device 112 of a batch of spectrometer devices 112 according to the present invention, such as according any one of the embodiments described with respect to Figure 2A to 2C.
• the evaluation unit 142 may also be configured for performing the method for calibrating a spectrometer device 112 of a batch of spectrometer devices 112 according to the present invention in any other embodiment disclosed herein.
• the spectrometer device 112, specifically the detector device 114 may be configured for communicating with the evaluation unit 142, specifically for communicating the detector signals to the evaluation unit 142.
• Figures 2A to 2C show exemplary embodiments of a method for calibrating a spectrometer device 112 of a batch of spectrometer devices 112.
• a spectrometer device 112 For possible embodiments of the spectrometer device 112, reference is made to Figures 1 A to 1 C and the corresponding description.
• the embodiments of the method shown in Figures 2A to 2C widely correspond to each other. In the following, Figures 2A to 2C are described in conjunction.
• the method comprises the following step: a) (denoted by reference number 146) at least one system characterization step comprising determining line spread functions at corresponding wavelengths by comparing at least one spectrum measured by using the spectrometer device 112 with at least one reference spectrum; b) (denoted by reference number 148) at least one resolution homogenization step comprising for each wavelength converting a resolution of the line spread function to a pre-defined target resolution for a corresponding wavelength, wherein the target resolution for each wavelength is a pre-defined target batch resolution value for the respective wavelength.
• steps may be performed in the given order. It shall be noted, however, that a different order is also possible. Further, it is also possible to perform one or more of the method steps once or repeatedly. Further, it is possible to perform two or more of the method steps simultaneously or in a timely overlapping fashion. The method may comprise further method steps which are not listed.
• the system 110 as shown in the embodiment of Figure 1 A may be used.
• the system characterization step 146 may comprise: a1 ) (denoted by reference number 150) illuminating, by using the at least one broadband light source 128, the spectrometer device 112 through the at least one optical interferometer 130; a2) (denoted by reference number 152) determining for the plurality of photosensitive elements 124 a plurality of detectors signals depending on the illumination through the optical interferometer 130 in step a1); and a3) (denoted by reference number 154) determining the line spread function from the plurality of detector signals.
• a main frequency of the optical interferometer 130 may be varied over a predetermined spectral range.
• the plurality of detectors signals may be determined depending on the main frequency of the optical interferometer 130.
• the line spread function may be determined by comparing the main frequency of the optical interferometer 130, specifically the main transmission frequency and/or the main reflection frequency of the optical interferometer 130, with at least one of a pixel position and an identification number of the plurality of photosensitive elements 124 generating intensity peaks in the plurality of detector signals associated with the main frequency.
• the optical interferometer 130 may, as an example, comprise at least one beam splitting device for splitting incident light into at least two illumination paths.
• the optical interferometer 130 may further comprise at least one scanning mirror in a first illumination path and at least one stationary mirror in a second illumination path (not shown in Figure 1 A).
• the scanning mirror may be moved along the first illumination path, wherein the stationary mirror may be kept stationary.
• the plurality of detector signals may be determined for a plurality of positions of the scanning mirror in the first illumination path.
• the plurality of positions of the scanning mirror may be different from each other.
• Step a3) may further comprise correlating the plurality of detector signals with the plurality of positions of the scanning mirror.
• the plurality of detector signals correlated to the plurality of positions of the scanning mirror may be used for determining the line spread function.
• Step a3) may comprise processing the plurality of detector signals determined in the step a2), thereby obtaining a plurality of processed detector signals.
• the determining of the line spread function in step a3) may comprise determining the line spread function from the plurality of processed detector signals.
• the processing of the plurality of detector signals may specifically comprise transforming the plurality of detector signals. As an example, the plurality of detector signals may be transformed by using at least one Fourier transformation.
• the system 110 as shown in the embodiment of Figure 1 B may be used.
• the system characterization step 146 may comprise: aa) (denoted by reference number 156) illuminating the at least one reference object 132 by using the at least one broadband light source 128; ab) (denoted by reference number 158) determining the line spread function by comparing a known spectrum of the reference object 132 with the spectrum measured by using the spectrometer device 112, wherein the known spectrum of the reference object 132 is predetermined by using at least one high-resolution spectrometer.
• Step ab) may comprise broadening the known spectrum of the reference object 132 by using kernel convolution with a theoretical line spread function.
• Step ab) may comprise adjusting parameters of a theoretical kernel until the broadened spectrum of the reference object 132 matches the measured spectrum.
• the adjusted kernel parameters may be used to approximate the line spread function at this wavelength.
• the theoretical kernel may be at least one kernel selected from the group consisting of: a Gaussian kernel with only one free parameter; Lorentzian profile; Moffat profile; or Voigt profile; asymmetric kernel.
• Step ab) may comprise directly comparing the known spectrum of the reference object 132 with the spectrum measured by using the spectrometer device 112 in signal space and/or comparing at least one derivative of the known spectrum of the reference object 132 with at least one derivative of the spectrum measured by using the spectrometer device 112, specifically comparing a first-order derivate, a second-order derivative and/or higher order derivatives of the spectra.
• Figure 3 shows a diagram with a reflectance 160 as a function of wavelength 162 , the wavelength 162 being measured in nm.
• Figure 3 shows an exemplary known spectrum 164 of the reference object 132, in this example a rare earth wavelength standard, the known spectrum 164 being measured with the high-resolution spectrometer, in this example a Bruker ® MPA spectrometer.
• Figure 3 further shows the spectrum of the reference object 132 measured by using the spectrometer device 112 (denoted by reference number 166) and broadened known spectra of the reference object 132 by using a Gaussian kernel convolution with a FWHM of 5 nm (denoted by reference number 166), with a FWHM of 10 nm (denoted by reference number 168) and with a FWHM of 15 nm (denoted by reference number 166).
• the best result is achieved by broadening with a FWHM of 15 nm.
• the line spread function in this wavelength region may be approximated with a Gaussian kernel with a FWHM of 15 nm.
• the system 110 as shown in the embodiment of Figure 1 C may be used.
• the system characterization step 146 may comprise: ai) (denoted by reference number 174) illuminating the spectrometer device 112 by using monochromatic light sources 134 with central wavelengths which are spread across a wavelength range of the spectrometer device 112 to be calibrated; aii) (denoted by reference number 176) determining the line spread function by comparing a known spectrum of the monochromatic light sources 134 with the spectrum measured by using the spectrometer device 112.
• Step aii) may comprise broadening the known spectrum of the monochromatic light sources 134 by using kernel convolution with a theoretical line spread function.
• Step aii) may specifically comprise adjusting parameters of a theoretical kernel until the broadened spectrum of the monochromatic light sources 134 matches the measured spectrum.
• the adjusted kernel parameters may be used to approximate the line spread function at this wavelength.
• the theoretical kernel may be at least one kernel selected from the group consisting of: a Gaussian kernel with only one free parameter; Lorentzian profile; Moffat profile; or Voigt profile; asymmetric kernel. Other kernel may also be feasible. However, for example, the theoretical kernel may be a Gaussian kernel with only one free parameter.
• Figure 5 shows exemplary spectra measured by using two different spectrometer devices 112.
• the two different spectrometer devices 112 may be spectrometer devices 112 of the same batch of spectrometer devices 112 and, thus, may be embodied similar with respect to each other.
• the spectrometer devices 112 may specifically be embodied as shown in any one of the Figures 1 to 3.
• Figure 5 specifically shows a diagram with a measured absorbance 194 of the sample as a function of wavelength 196.
• the measured sample is a polyethylene terephthalate (PET) sample being measured in diffuse reflection.
• PET polyethylene terephthalate

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• 2023
  • 2023-09-13 CN CN202380066200.4A patent/CN120225843A/zh active Pending
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