JP2020128997A - Optical measurement system and method - Google Patents

Abstract

To provide a low-noise supercontinuum light source.SOLUTION: A supercontinuum light source (1000) comprising an intermediate supercontinuum light source (100) and a single mode coupling unit (300), an optical measurement system comprising such light source, as well as a measurement method are described. The supercontinuum light source comprises a pulse frequency multiplier (103) for increasing a repetition rate, and the single mode coupling unit is configured to dampen and shape a spectrum from the intermediate supercontinuum light source to allow measurements with a reduced noise floor.SELECTED DRAWING: Figure 3a

Description

The present invention relates to a supercontinuum light source comprising an intermediate supercontinuum (SC) light source and a single mode coupling unit, the supercontinuum light source being a measurement system, eg measured or otherwise analyzed. The sample is suitable for use in a system where the sample is illuminated by light originating from such a supercontinuum light source and the measurement system is arranged to allow detection of the light from the sample. The invention also relates to a system suitable for measuring at least one parameter relating to the object, said system comprising a method for measuring at least one parameter relating to the object of the measuring system, similar to a supercontinuum light source.

Optical measurement systems exist in many variations. Common to these systems is that a light beam is directed at the sample and light from the sample is captured. The captured light may be light emitted from the sample in response to an incident beam, such as light reflected from the sample, light transmitted through the sample, and/or fluorescence.

Octave bandwidth supercontinuum (SC) works well through non-linear fibers such as microstructured fibers, tapered standard fibers and tapered microstructured fibers by pumping the fiber with a pulsed laser (often in a MOPA configuration) as input. Was generated. Such spectrally broad Continium sources are used in many measurement systems, for example in optical coherence tomography (OCT), optical frequency metrology, fluorescence microscopy, coherent anti-Stokes Raman scattering (CARS). It is potentially useful in anti-Stokes Raman scattering) microscopy, two-photon fluorescence microscopy and the like. Unfortunately, for those experiments, the large amplitude variations of conventional Continium sources limit accuracy and/or sensitivity. Previous studies of SC generation have shown that the SC generation process is very sensitive to quantum noise, technical noise, and certain parameters such as input wavelength, duration and chirp of the input laser pulse. Light sources derived from stable Continium will generally improve the utility of SC light sources.

Continuum production in conventional perforated photonic crystals or tapered single-mode long fibers is complicated and leads to undesired unevenly distributed noise and instability for different wavelength regions, leading to time and frequency domain May contain distinctive substructures in. Continuum amplitudes usually show large fluctuations with a significant excess of white noise background, which fluctuations can be revealed using fast detector and RF spectrum analyzer (RFSA) measurements. it can.

A common approach to wavelength conversion is to produce supercontinuum, then spectrally slice a portion of the continuum and use this slice as the light source for a microscopy setup. However, the selected Continium contains possibly large amplitude fluctuations (noise), which may not be suitable for some applications.

In US Pat. No. 6,037,639, the noise from the SC light source is reduced by tapering the non-linear fiber and using a femtosecond pulse source that causes so-called soliton splitting. The abstract of this patent states: "Longitudinal changes in phase-matched state for Cherenkov radiation (CR) and four-wave mixing (FWM) introduced by DMM. Enables the production of low noise supercontinuum." Tapering requires either post-processing techniques that can complicate SC light source fabrication or changes in fiber diameter during fabrication, and the tapering small cross section can limit the amount of light that can be safely transmitted. There is a nature. Moreover, femtosecond pump sources are often relatively complex and expensive.

In (Patent Document 2), a structure having a basic structure capable of generating SC light and capable of shaping a waveform of a spectrum of SC light, adjusting power of SC light, or adjusting a repetition frequency of a pulse train including SC light is disclosed. A light source device having further is described. The light source device of (Patent Document 2) includes an SC fiber pumped at a wavelength of about 1550 nm, and the repetition frequency of the SC optical pulse train from the light source is located at 1 MHz to 100 MHz. Throughout US Pat. No. 6,037,049, noise is discussed only for a single pulse, and it is explained that the noise characteristic of the pulsed light P1 is not affected. Regarding the noise characteristics of the SC optical pulse train P2, it is mentioned that low noise detection is possible through synchronization with a photodetector configured outside the light source device. The noise spectra from SC light sources using different pump wavelengths are different, so the noise suppression may be different. (Patent Document 2) refers to a femtosecond pulse train P1. Such pump sources are often relatively complex and expensive.

US Pat. No. 7,403,688 U.S. Patent Application Publication No. 2011/0116282

In view of the foregoing, it is an object of the present invention to provide a low noise supercontinuum light source, and advantageously a supercontinuum light source with reduced noise effects in the generated supercontinuum (SC). That is. Advantageously, the supercontinuum light source is suitable for use in an optical measurement system.

In an embodiment, the present invention relates to a system suitable for measuring at least one parameter relating to an object, the system including a supercontinuum light source, and further to provide a measuring method using the system. Is.

These and other objects have been solved by the present invention or its embodiments as defined in the claims and as described herein below.
It has been found that the present invention and its embodiments have many additional advantages which will be apparent to those skilled in the art from the following description.

The supercontinuum light source of the present invention includes a light source output unit, an intermediate supercontinuum light source, and a single mode coupling unit, and the intermediate supercontinuum light source is
a. A seed laser configured to provide a seed pulse with a pulse frequency F _seed ;
b. To double the seed pulse, and configured pulse frequency multiplier to convert the _{F seed} pump pulses having a pulse frequency _{F pump:} a _{(PFM pulse frequency multiplier), F} pump is above _{F seed} A large pulse frequency multiplier (PFM),
c. Configured to receive the pump pulse and convert the pump pulse into supercontinuum light having a supercontinuum spectrum spanning from about λ ₁ to about λ ₂ provided as an output of the nonlinear element. A non-linear element having λ ₂ −λ ₁ >about 500 nm.

The output from the non-linear element is coupled to the single mode coupling unit to provide the output from the single mode coupling unit, and the light source output includes the output from the single mode coupling unit. A single mode coupling unit is configured to attenuate and shape the supercontinuum spectrum from the nonlinear element. Preferably, F _pump is at least about 100 MHz, such as at least about 150 MHz, at least about 200 MHz, at least about 300 MHz, at least about 400 MHz, at least about 500 MHz, at least about 600 MHz, at least about 700 MHz, at least about 800 MHz, at least about 1 GHz. ..

In a preferred embodiment of the frequency doubler, the single-mode coupling unit receives the supercontinuum light and spectrums it so that the output spectrum from the single-mode coupling unit extends from λ ₃ to λ _4. Spectrally shaped output spectral output from a single-mode coupling unit, where λ ₃ −λ ₄ >0, λ ₃ ≧λ ₁ and λ ₄ ≦λ ₂ Is different from the spectrum in the wavelength region of λ ₃ to λ ₄ from the intermediate supercontinuum light source.

It has been found that the supercontinuum light source of the present invention has low noise due to the highly improved supercontinuum light source, especially for applications where low noise is beneficial. The term "low noise" is not possible otherwise with prior art white light SC light sources operating at comparable power levels of output power in the spectral domain, for example when the light source is applied in a measurement system. Significantly lower than, for example, significantly lower than would otherwise be possible with prior art supercontinuum sources operating at comparable power levels of output power, and beyond the soliton splitting region It is understood to mean average noise.

The seed laser of the intermediate supercontinuum source can be, for example, a mode-locked fiber laser, preferably mode-locked via SESAM, preferably the gain medium of the fiber laser is YtYb-doped fiber, Er-doped. Fiber and Er/Yb-doped fiber.

In embodiments, the wavelength range “λ _{3 to} λ ₄ ” is greater than about 100 nm, such as greater than about 200 nm, greater than about 300 nm, or greater than about 500 nm. In embodiments, the wavelength λ ₃ is less than about 1000 nm, such as less than about 900 nm, less than about 800 nm, less than about 700 nm, or less than about 600 nm. In embodiments, λ ₄ is greater than about 1070 nm, such as greater than about 1100 nm, greater than about 1200 nm, or greater than about 1300 nm.

In embodiments, the single mode coupling unit includes one or more of the following: a prism, a low pass optical filter, a high pass optical filter, a band pass optical filter, and a single mode fiber. Advantageously, the single mode coupling unit is arranged to shape the spectrum from the intermediate supercontinuum source into a Gaussian spectrum, a double peak spectrum or a flat top spectrum.

In an embodiment, the attenuation of the supercontinuum spectrum in the single mode coupling unit is given by the optical power attenuation coefficient y, which is the optical power attenuation coefficient y in the wavelength region of λ _{4 to} λ ₃ . A measure, the optical power attenuation coefficient y is greater than about 2, for example, greater than about 3, greater than about 4, greater than about 6, greater than about 8, and greater than about 10.

In an embodiment, the single mode coupling unit is provided with at least one of the following: i) a mismatch or mismatch of outputs from the non-linear element to the single mode coupling unit, and ii) a single unit for performing said attenuation. At least one of a splice loss at the input to the one-mode coupling unit and/or at the output from the single-mode coupling unit, and iii) a broadband attenuating filter or a broadband beam splitter such as a neutral density filter.

In an embodiment, the single mode coupling unit is an input for coupling to a non-linear element and a dichroic element at the input of the single mode coupling unit configured to transmit wavelengths below a threshold wavelength λ _5. A dichroic element with λ ₅ >λ ₃ and at least one of the following: a prism, a low-pass optical filter, a high-pass optical filter or a band-pass optical filter, and a single-mode fiber whose output is A single mode fiber, which is the output from the one mode coupling unit. Advantageously, the dichroic element is a single mode fiber, said single mode fiber being a step index fiber or a microstructured fiber comprising a microstructure in the form of air or a low index glass material.

In embodiments, the total optical power at the output from the single mode coupling unit is less than about 100 mW, such as less than about 50 mW, less than about 30 mW, less than about 20 mW.

In embodiments, the seed laser is configured to provide a seed pulse having a pulse width _{t seed,} the pulse width _{t seed} is greater than about 0.1 ps, for example, greater than about 0.25 ps, about 0 >0.5 ps, >0.75 ps, >1 ps, >2 ps, >3 ps, >5 ps, >10 ps, >20 ps, >50 ps, >100 ps Long, longer than about 200 ps, longer than about 300 ps, longer than about 400 ps, longer than about 500 ps, longer than about 1 ns.

In embodiments, the seed laser is configured to provide a seed pulse having a pulse width _{t seed,} the pulse width _{t seed} is less than about 1 [mu] s, for example, shorter than about 500 ns, less than about 200 ns, about Less than 100 ns, less than about 50 ns, less than about 20 ns, less than about 10 ns, less than about 1 ns, less than about 500 ps, less than about 100 ps, less than about 50 ps, less than about 25 ps, less than about 20 ps, about Less than 15 ps and less than about 10 ps.

Advantageously, the non-linear element is an optical fiber, such as tapered and/or non-tapered microstructured fiber.
In an embodiment, the intermediate supercontinuum light source comprises a pulse compressor such as a PBG fiber, the pulse compressor receiving pulses from the pulse frequency multiplier (PFM) and time-compressed pulses. It is configured to output to the non-linear element. Advantageously, the intermediate supercontinuum light source is an incoherent light source.

The system is suitable for measuring at least one parameter relating to an object, comprises a supercontinuum light source according to the invention and comprises at least part of the output of said single mode coupling unit, eg said single mode coupling unit. Configured to illuminate the measurement object at a majority, at least about 90%, of all of the outputs of the system, the system further comprising a detector for detecting light from said object.

Due to the supercontinuum light source of the present invention including a low noise intermediate supercontinuum light source, a very accurate optical measurement system is achieved.
In embodiments, the system includes a subject, which is a part of a human or animal body, such as a mammalian eye or any part thereof. This allows in-vivo and/or in-vitro measurements of parts of the human or animal body.

Advantageously, the detector is longer than 50/F _pump , eg longer than 100/F _pump , longer than 200/F _pump , longer than 500/F _pump , longer than 1000/F _pump , longer than 5000/F _pump . Has a long integration time.

In an embodiment, the measurement system is a reflection mode measurement system configured to measure light reflected from the object, such as a white light interferometry based system, optical coherence tomography (OCT), or the like. Advantageously, the system is based on time domain, frequency domain or swept source OCT.

In embodiments, the measurement system is used to diagnose age-related macular degeneration (AMD), diabetic retinopathy or glaucoma.

In embodiments, the measurement system is used in diagnostics associated with treatments that provide refractive correction of the eye, such as laser eye surgery (LASIK) to correct the refractive state of the eye. In an embodiment, the measurement system is used to measure the boundaries of Bowman's layer inside the human eye.

The method of the invention for measuring at least one parameter relating to an object of measurement comprises providing the supercontinuum light source of the invention and the supercontinuum light source of the invention such as all of the outputs of said single mode coupling unit. Illuminating a measurement object with at least a portion of the output of the single mode coupling unit of, and detecting light from the object by a detector.

Advantageously, due to the high accuracy of the optical measurement system, the subject is a part of the human or animal body, such as the mammalian eye or a part thereof. This allows in-vivo and/or in-vitro measurements of parts of the human or animal body.

In the following, the invention will be explained in the context of silica-based nonlinear fibers. However, as will be apparent to those skilled in the art, the present invention also provides for other materials such as fibers based on other materials such as polymers, chalcogenides and fluoride glasses, nonlinear planar waveguides and gas filled hollow core fibers. It includes an SC light source based on a type of non-linear element. For silica-based fiber parameters, material and/or light guide-based parameters, such as dispersion and nonlinearity, must be adjusted accordingly.

The SC is typically generated by applying a pulsed pump light source configured to pump a non-linear fiber, such as the non-linear fiber as described above. A non-linear process in the non-linear element converts the pump pulse into supercontinuum exiting the fiber. Of particular interest is the case where substantial pump energy is delivered to a wavelength in a nonlinear fiber that exhibits anomalous dispersion. This is because it greatly expands the achievable bandwidth. In particular, supercontinuum production is efficient as described by Dudley et al., Reviews of Modern Physics (Rev. Mod. Phys.), Vol. 78, No. 4, 2006. It is based on the so-called modulation instability in which the pump pulse is split into a series of short pulses (soliton) that allow the generation of a broad supercontinuum spectrum. In the normal dispersion region, supercontinuum production is primarily due to self-phase modulation (SPM), which requires very high peak intensities to induce significant spectral broadening (eg, >100 nm 10 dB bandwidth). Is triggered.

Therefore, in an embodiment, the pump pulse and the non-linear fiber (ie, the non-linear element) are configured such that the supercontinuum spectrum is generated primarily through the splitting of the pump pulse induced by modulation instability (MI). To be done. That is, most of the input pulse power starts at wavelengths located in the anomalous region or close enough to allow initial spectral broadening via the SPM to shift a substantial portion of the power to the anomalous region. To be done. Preferably, greater than 50%, eg, greater than 60%, greater than 70%, greater than 80%, greater than 90%, greater than 95%, 100% of the supercontinuum spectrum produced is MI and the solitons produced by MI. Generated through subsequent processes that include. Any residual pump light exiting the nonlinear element is not considered part of the generated supercontinuum. In embodiments, these percentages are calculated as part of the total power of supercontinuum. In embodiments, the percentage is calculated as a percentage of the bandwidth scanned by SuperContinium.

The high non-linearity of so-called High Nonlinear Fibers (HNLF) is generally the result of a relatively small cross section that causes an increase in peak intensity, but more importantly, the dispersion of these fibers is , Typically low and anomalous for at least some of the wavelengths, the fiber guides at the pump wavelength, for example. High non-linearity ensures a long and effective non-linear interaction length. This is because the peak power is maintained and the peak power supports soliton formation and MI division. In embodiments, soliton formation and MI-induced splitting are the main mechanisms in ultra-wideband light generation from nonlinear fibers. Other non-linear processes such as self-phase modulation, cross-phase tuning, self-steepening, Raman scattering do not require anomalous dispersion, but play a role as well.

The pump pulse and the non-linear element may be arranged such that the center wavelength of the pump pulse is preferably in the anomalous dispersion region. Alternatively, the pump wavelength is ZDW-150 nm or more, ZDW-100 nm or more, ZDW-50 nm or more, ZDW or more, ZDW+10 nm or more, ZDW+20 nm or more, ZDW+30 nm or more, ZDW+50 or more, ZDW+100 nm or more, ZDW+150 nm or more, and an appropriate spectral broadening ( It can be in the normal dispersion region (but sufficiently close to the abnormal region) where a substantial portion of the pump energy can be transferred to the abnormal region (eg via SPM or Raman shift). In embodiments, the shape of the resulting supercontinuum spectrum can be controlled in large part by varying the distance from the pump wavelength to the intersection between normal and anomalous dispersion. This is the so-called zero dispersion wavelength (ZDW: zero dispersion wave length).

The term “substantial pump energy shifted to the anomalous region” means more than 30% of the pulse energy, eg, more than 50%, more than 60%, more than 70%, more than 80%, more than 90%, more than 95%, 100. % Is understood to mean that the pulse enters the abnormal region before it is split.

Dudley et al., "Supercontinuum generation in photonic crystal fiber", Reviews of Modern Physics, Rev. Mod. Phys., Vol. 2006) p. As described by 1159-1162, supercontinuum is incoherent when modulation instability is the dominant process in splitting the pump pulse. Non-interfering supercontinuum can be understood to result from noise, thus impairing the time and spectral stability of the generated light. According to the authors, pump pulses with soliton order (N) in N<10 fibers provide interfering supercontinuum, whereas pump pulses with N>30 provide non-interfering supercontinuum. To do. Values of 10≦N≦30 provide a transition between these two states and the supercontinuum spectrum can be produced interference or incoherently depending on the exact pump and fiber parameters. Here, the soliton order is defined as in (Equation 1).

Where gamma is the fiber nonlinearity, P0 is the pulse peak power, T0 is the pulse width, and β ₂ is the group velocity dispersion of the fiber at the pump wavelength. Therefore, this equation confirms that short pulses reduce the soliton order, which defines a more coherent supercontinuum and thus lower noise.

Coherency can be dramatically reduced (and noise increases dramatically) for N>16. Increasing the value of N causes the modulation instability, which is the pulse splitting induced by quantum noise, to progress faster than the deterministic soliton splitting process. Therefore, the transition from soliton splitting to MI-induced splitting marks the separation between low noise/high interference and high noise/low interference. Fei Lu et al., "Generation of a broadband continuum coherence in tapered single-mode opera- tion". Optics Express, Vol. 2, No. 2, 2004, Jan. 26, 2004, p. In 347-353 (referenced in US Pat. No. 7,403,688 and having authors consistent with the inventors), a short 50 fs pulse provides a relatively low N and the soliton order is tapered. It is further reduced by the ring, providing high spectral coherence and low noise. "Real-time ultra-high-resolution optical coherence tomography (Super continuum generation for real time ultra resolution optical coherence tomography)", Proc. Supercontinuum was generated using a 95 fs pump pulse and it is concluded that only the spectrum generated by pumping in the normal region has sufficiently low noise to be applicable. As mentioned above, such a spectrum is formed by SPM, which is a deterministic process, thus allowing the production of low noise, high interference SC.

In embodiments, the non-linear fiber is not tapered. However, in embodiments, the present invention is combined with the noise reduction effect obtainable via tapering. A new type of tapered fiber suitable for SC generation is described in the international application PCT/Danish Patent Application Publication No. 2011/050328.

However, the soliton order of the pump pulse is substantially 16 or more, for example, 18 or more, 20 or more, 22 or more, 24 or more, 26 or more, 28 or more, 30 or more, 40 or more, 50 or more, 75 or more, 100 or more. , 200 or more, 300 or more, 400 or more, 500 or more, in embodiments such that the non-linear fiber and pump pulses are configured, the present invention provides, in embodiments, a non-interfering or partially non-interfering supercontinuum. Allows the application of Ni. Thereby, the supercontinuum production process proceeds primarily via modulation instability.

In embodiments, the soliton order is defined when the pulse is split, for example, after shifting to an abnormal region and/or after traversing a tapered section of fiber. In embodiments, the soliton order is defined at the time of pump pulse input into the fiber.

In general, the spectral width of the SC produced depends on the peak power of the pump pulse, so for longer pulses the peak power cannot be arbitrarily reduced to reduce the soliton order. Longer pulses, such as those in the ps or ns domain, are often preferred because these pulses often allow for simpler pump laser configurations compared to fs lasers. Thus, in an embodiment, the present invention provides that the pulse width is greater than about 0.1 ps, such as greater than about 0.25 ps, greater than about 0.5 ps, greater than about 0.75 ps, greater than about 1 ps. Greater than 2 ps, greater than about 3 ps, greater than about 5 ps, greater than about 10 ps, greater than about 20 ps, greater than about 50 ps, greater than about 100 ps, greater than about 200 ps, greater than about 300 ps, greater than about 400 ps, about Enables longer pulse width applications, such as applications longer than 500 ps, longer than about 1 ns, longer than about 10 ns.

On the other hand, in SCs generated from very long pump pulses and CWs, pumping suffers from increased noise. While the present invention may reduce sensitivity to noise, it may also be preferable to reduce noise as well through reduction in pulse width, so that in embodiments, the seed laser may have a pulse width t _seed And a pulse width t _seed of less than about 1 μs, for example less than about 500 ns, less than about 200 ns, less than about 100 ns, less than about 50 ns, less than about 20 ns. Short, less than about 10 n, less than about 1 ns, less than about 500 ps, less than about 100 ps, less than about 50 ps, less than about 25 ps, less than about 20 ps, less than about 15 ps, less than about 10 ps.

The variable intervals referred to above may be combined to form closed intervals for pulse widths, such as pulse widths that are 0.1 ps to 1 μs, 0.25 ps to 100 ps, 1 ps to 50 ps.

As mentioned above, SCs are typically generated by applying a pulsed pump light source. In supercontinuum light source of the present invention, the pump pulse is supplied at a repetition rate _{F pump,} the repetition rate _{F pump,} causes amplitude modulation of the generated supercontinuum with the same frequency _{F pump.} On the other hand, the measurement system of the present invention typically has a measurement time longer than 1/F _pump , that is, a measurement time over which the repetition rate is not determined and the measurement is integrated such that the SC appears as CW radiation. Applies to. For that reason, pulsed lasers operating in the MHz region are often referred to as "pseudo CWs". However, the pulsed nature of supercontinuum reduces the effective measurement time in the presence of light. Therefore, in the embodiment, the SC light source has F _pump of 100 MHz or higher, for example, 150 MHz or higher, 200 MHz or higher, 300 MHz or higher, 400 MHz or higher, 500 MHz or higher, 600 MHz or higher, 700 MHz or higher, 800 MHz or higher, 1 GHz or higher, Apply a high repetition rate.

As described further below, pump laser systems typically consist of a main laser oscillator, also referred to as a seed laser, which has one or more optional boosting pulse power levels from the seed laser. Followed by an optical amplifier. That is, the pump laser may include a MOPA configuration. Depending on the type of seed laser, it may not be practical or possible to provide such a high repetition rate. In embodiments, (also referred to as a pump laser system) pump _laser, a seed laser that is configured to provide a seed pulse having a low pulse frequency _{F seed} from _{F pump,} the _{F seed} to convert the _{F pump} One or more pulse frequency multipliers (PFM) configured.

Preferably, the pulse frequency multiplier of the supercontinuum light source of the present invention comprises a splitter configured to split at least one beam of the seed pulse into a number of sub-beams and a first configured to recombine at least some of the sub-beams. Preferably, the pulse frequency multiplier further comprises an adjustable attenuator configured to adjust at least one of the sub-beams.

Beam means herein a pulse train.
The splitter can be any type of splitter. Such splitters are well known in the art.

In embodiments, the pulse frequency multiplier includes an adjustable attenuator configured to receive at least one sub-beam. Preferably, the adjustable attenuator is configured to receive at least one sub-beam with a power above the average sub-beam power, and the pulse frequency multiplier optionally comprises a plurality of adjustable attenuators. Preferably, each attenuator is configured to receive at least one sub-beam having pulses within the selected peak power range. Advantageously, in order to significantly reduce the noise, the adjustable attenuator is arranged such that the pulses of the sub-beams combined in the first combiner have substantially the same peak power value. It is configured to receive a pulse and adjust it to a peak power value corresponding to the peak power value of the pulse in at least one other sub-beam.

In an embodiment, the pulse frequency multiplier is configured to time delay at least one of the sub-beams. The time delay can be provided, for example, by first placing a path from the splitter to the combiner of one sub-beam that is shorter than the second path from the splitter to the combiner of the second sub-beam. Preferably, the pulse frequency multiplier is arranged to delay the at least one sub-beam so that the pulses of the sub-beams recombined in the first combiner are preferably spaced apart at substantially uniform intervals. To be done.

1 shows a schematic intermediate supercontinuum light source suitable for the present invention. ₁ shows an example of a supercontinuum spectrum (10) ranging from λ ₂ at about 460 nm to λ ₁ at about 2400 nm. 1 shows an example of a pulse frequency modulator (PFM) of an intermediate supercontinuum light source according to the present invention. 1 shows an example of a pulse frequency modulator (PFM) of an intermediate supercontinuum light source according to the present invention. 3 shows a measurement setup suitable for measuring intensity noise in the spectrum of an SC light source, such as the SC light source of FIG. Examples of spectral output from the single mode coupling unit 300 are shown, as well as example of supercontinuum spectral output from the intermediate supercontinuum light source 100. 4 shows an exemplary spectral output from a single mode coupling unit. 4 shows an exemplary spectral output from a single mode coupling unit. 4 shows an exemplary spectral output from a single mode coupling unit. 4 shows the average intensity noise of an intermediate supercontinuum source before and after compensation for spectrometer noise. 4 shows the average intensity noise of an intermediate supercontinuum source before and after compensation for spectrometer noise. 1 illustrates an optical measurement system exemplified as an OCT system using an SC light source as a light source. 1 illustrates an example of a single mode coupling unit that includes a dichroic element that is a dichroic mirror, a dispersive element that is a prism, and a single mode fiber configured to shape the spectrum. 1 illustrates an example of a single mode coupling unit including a dichroic element that is a single mode fiber, an attenuating and/or shaping optical element, and a second single mode fiber. Three examples of methods of attenuating optical power are shown. Three examples of methods of attenuating optical power are shown. Three examples of methods of attenuating optical power are shown.

FIG. 1a shows the configuration of a preferred intermediate supercontinuum light source 100 included in a supercontinuum light source according to the present invention. The master oscillator (or seed laser) provides output along the beam path 106. The components are preferably fiber coupled, but may also be coupled via free space optics. The intermediate supercontinuum light source 100 includes two power amplifiers (PA1 and PA2) 102 and 104. As mentioned above, these amplifiers provide an optional but increased pulse energy and peak power as compared to the output from the seed laser 101. The seed lasers 101, PA1 102 and PA4 104 are each pumped by a diode laser, however, other pump sources such as a power source could alternatively be used. An optional regulator 105 is included to show that the intermediate supercontinuum light source can include a feedback system. In this embodiment, a feedback loop is provided by a photodiode 109 that measures a portion of the output 108 and supplies one or more parameters associated with the beam to a decision point 114 that adjusts the input to the nonlinear element 107. ,It is formed. Such a regulator may, by way of example, be formed by a tunable attenuator configured to regulate the optical power entering the nonlinear element 107. Co-pending US patent application Ser. No. 12/865,503 (incorporated herein by reference) describes alternative configurations of the regulator 105 and the photodiode 109, various embodiments of the regulator, beam focusing on the photodiode, And various embodiments of feedback loops in SC light sources (eg, see FIG. 1 and claims), such as the possibility of applying a feedback response to one or more of pump sources 110-112.

The PFM 103 may be placed before the first amplifier, between the amplifiers, and before the nonlinear fiber. In an embodiment, the pulse train saturates the amplifiers (PA1 and/or PA2) such that the peak power of the pulses from the amplifiers is constant regardless of their input power. In FIG. 1, the PFM is placed between two power amplifiers (PA1 and PA2 in this case). This can be preferable. Because in most cases the PFA redistributes the optical power from the seed laser into a larger number of pulses, and when the seed laser output pulse is relatively weak, the pulse train is efficiently amplified in the subsequent amplifier. This is because the PFA may have a significant insertion loss, so that the PFA may produce a pulse train with an average power that is too low to be overcome. For this reason, it is preferred in embodiments to place the PFM after one or more amplifiers, such as between two amplifiers. On the other hand, placing the PFM after the amplifier or amplifiers increases the nominal power loss due to such insertion loss. For this reason, it is preferred in embodiments to place the PFM in front of one or more amplifiers, such as between two amplifiers. This may also have the effect of reducing the peak power of the pulse passing through one or more power amplifiers (or other components in the system), which in turn reduces non-linearities in the pump laser system, etc. It may have one or more benefits. Such non-linearities often have the effect of broadening the pulse, which can result in reduced peak power levels to the non-linear element, which in turn can reduce the spectral width of the supercontinuum produced. In embodiments, multiple PFMs are applied, such as multiple PFMs separated by optical components such as optical amplifiers, attenuators, compressors or filters.

In embodiments, there is an upper limit to the acceptable average optical power that illuminates the object of measurement (also called the sample). An example of such an application is one in which the subject is sensitive to optical power (mean power and/or peak power) above a certain threshold (which would be the case for most biological samples), and especially for mammalian eyes such as the retina. Including uses for parts. Examples of applications where the subject is an ophthalmic mammalian eye include OCT imaging the retina or cornea and imaging using multiphoton fluorescence microscopy of the retina or cornea.

In embodiments, the output of the SC light source or its subsections must match one or more of the laser standard classes 1, 1M, 2, 2M, 3R, 3B. In the embodiment, the output power of the SC light source is higher than that of the above-cited class by the SC light source itself being 100% or higher, 200% or higher, 400% or higher, 800% or higher. Emission level).

In embodiments, relatively low noise caused by the pulse width is desired, so that pulse widths in the range 0.5 ps to 30 ps are preferred, such as pulse widths in the range 1 ps to 20 ps, preferably 2 ps to 20 ps. In embodiments, the average optical power from the SC light source is less than 5 watts output per ps pulse width, eg, less than 3 watts output per ps pulse width, less than 2 watts per ps pulse width, less than 1 watt per ps pulse width. Therefore, an increase in average optical power for this system is undesirable. In one embodiment, the total average optical power in the visible region (400 nm to 850 nm) is configured to be less than 100 mW, such as less than 50 mW, less than 30 mW, less than 20 mW. As mentioned elsewhere, the reduction of average power after output from an SC light source is unnecessarily complicated or impossible because the optical components needed to reduce the power modify the spectrum. Often becomes.

As previously mentioned above, in embodiments, the spectral width of the generated SC depends on the peak power of the pulse, at least up to some saturation level, where a further increase in peak power does not increase the spectral width. Also, the conversion efficiency from pump light to SC light depends on the peak power, which means that for a fixed pulse width, the peak power (and corresponding average power) cannot be reduced at all. Below a certain value, the desired spectral width of the generated spectrum is compromised, and in the end poor conversion efficiency causes too much unconverted pump light to pass through the fiber, which can damage the sample under observation. There is a nature. Therefore, in embodiments, as a result of minimum peak power, insertion of the PFM causes an increase in average optical output power for configurations in which the PFM is omitted. This occurs because the peak power and pulse width are constant while the pump pulse repetition rate is increased. In an embodiment, the optical power is reduced by adjusting the pump energy supplied to the last power amplifier before the non-linear element, but this, as mentioned, impairs the resulting spectral width. there is a possibility.

In embodiments, reducing the average optical power may be performed by introducing attenuation after the non-linear element, such as attenuation of the beam away from the beam path or splitting a portion of the beam. Applications requiring a tunable portion of the generated spectrum directed to the sample may apply AOTF to perform such functions. In embodiments, the AOTF may be controlled to reduce the average amount of optical power introduced into the sample. Applying optical components to the beam and/or damaging the optical element without disturbing the spectral shape can be more difficult for applications requiring broadband illumination, such as in OCT imaging systems. .. In embodiments, the pump laser system includes a pulse compressor, such as a PBG fiber (hollow or solid core), configured to compress the pump pulse and thus increase the peak power. This use of PBG fibers was discussed in PCT application WO 2005041367. In embodiments, by increasing the peak power of the individual pulses, the use of a pulse compressor allows the use of lower average optical power while maintaining the spectral characteristics of the generated spectrum.

In principle, the PFM of the intermediate supercontinuum source of the present invention is any optical component suitable for receiving a pulse train at a certain repetition rate, converting this input into a pulse train with a higher repetition rate. May be. In embodiments, the input and output pulses have substantially the same pulse width and wavelength. In an embodiment, the PFM works by splitting the pulse train at the input into multiple sub-pulse trains, each of which experiences a different delay (optical path length) before being recombined. The relative delay causes a temporal shift of the sub-pulse trains when recombined, so that the combined pulse train contains more pulses than the input. For example, the input pulse train may be split into two sub-pulse trains (or sub-beams), one pulse train being delayed with respect to the other. The repetition rate of the combined columns is then doubled. Preferably, the relative shift between the beams corresponds to half the spacing between two pulses in the input pulse train. In an embodiment, this principle is extended such that the input beam is first split into more than two sub-beams, such as two, three or four sub-beams, which are each delayed and recombined with respect to each other. .. It is well known that optical splitters (or combiners) work in a symmetrical way. Combining several light beams results in the same amount of output beam. In embodiments, only a single output is used/available, while the optical power designated for the other outputs is lost in the optical system. Therefore, in an embodiment, it is advantageous to cascade combiners/splitters, as described below in connection with FIG. 2b.

In an embodiment, the present invention provides a splitter for splitting a beam into sub-beams, an optional adjustable attenuator configured to receive the sub-beams, and a first combiner configured to combine the sub-beams. And a PFM including. In this way, the adjustable attenuator may be adjusted to compensate for manufacturing variations in the splitter and/or combiner as well as coupling variations, resulting in pulses with uniform peak power. Pulse trains can be generated. In embodiments, no exact adjustment of peak amplitude is required and substantial differences between peak powers of the recombined sub-beams are acceptable.

In an embodiment, the one or more splitters and combiners have a non-uniform split ratio (

, Where x is a percentage and is, for example, 45/55, 40/60, 35/65 or 30/70), the attenuator being the most powerful sub-beam (or beam). Of the sub-beams that are more contributive to the combination of the sub-beams, so that when the sub-beams are combined, the more powerful sub-beams may be attenuated to provide equal power levels to other sub-beams. Can be guaranteed. Thereby, the noise is significantly reduced compared to the situation where the sub-beams have different power levels.

In an embodiment, the PFM includes a plurality of attenuators each configured to receive a separate sub-beam. In an embodiment, the splitter splits the beam into two sub-beams. In embodiments, the splitter splits the beam into more than two, eg, three or more, four or more, five or more, six or more, seven or more, eight or more sub-beams. In an embodiment, the first combiner further acts as a splitter that splits the combined beam into a second sub-beam, the second sub-beam being followed by the second combiner. In an embodiment, the PFM comprises an adjustable attenuator configured to receive one of the second sub-beams. This attenuator may be applied to adjust coupling losses and other variations as well as variations in the first and second couplers. In an embodiment, the second combiner is configured to have a non-uniform splitting ratio (and thus also non-uniform coupling of the input beam), and the output from the adjustable attenuator has a larger portion. It is configured to feed the output. Again, the second combiner may ensure that a pulse train with uniform power between the pulses can be supplied by the PFM.

In embodiments, the PFM is formed by free space optics such as a bulk beam splitter. In embodiments, the PFM is formed by a fiber optic splitter and/or combiner, which is often preferred with respect to system cost and robustness.

FIG. 1b shows an example of a supercontinuum spectrum (10) ranging from λ ₂ at about 460 nm to λ ₁ at about 2400 nm. Spectra are obtained from NKT Photonics A/S product Super K EXW-12 (SuperK EXW-12).

2a and 2b show an example of a pulse frequency modulator (PFM) of an intermediate supercontinuum light source according to the invention. FIG. 2a shows an embodiment of PFM 200. The input beam (via free space or via fiber) enters the PFM at input 201. Splitter 214 is illustrated as a 1×2 splitter, but may be any 1×N splitter, or even an M×N splitter. Multiple inputs may be combined for the M×N splitter, or alternatively only one of the M available inputs is used. The first splitter 214 splits the input beam into two sub-beams 202, 203 with a split ratio x ₁ /(1−x ₁ ). As discussed above, in embodiments, the larger of x ₁ and (1-x ₁ ) is sent to adjustable attenuator 204. In an embodiment, the attenuator is omitted, in which case it is preferred that x ₁ be about 0.5 (ie, 50%) so that variations in the peak power of the pulse train at output 207 can be minimized. The sub-beam 202 is provided to the delay line 205, which is preferably arranged to delay the sub-beam 202 by half the period between two pulses in the input beam 201. In embodiments, the delay line is adjustable to absorb variations in the repetition rate of the input beam. In embodiments, small deviations from uniform spacing of pulses in the output beam (eg less than 75%, less than 50%, less than 25%, less than 15%, less than 10%, less than 5%, 1%, etc. Less than) can be tolerated because the delay line is fixed. The sub-beams 202, 203 are combined in a combiner 206 which provides an output 207. Coupler ₂₀₆ has a division ratio of _{x 2 / (1-x 2} ). In an embodiment, either the splitter 214 or the combiner is configured to have a non-uniform splitting ratio, ie x ₁ or x ₂ deviates from 50%, and in this way the attenuator 204 is The beams 202 and 204 may be adjusted to contribute equally so that the pulses at the input that are split into two pulses are recombined to have substantially the same peak power at the output, in this case “Substantially” is meant to include those that are within normal tolerances. The effect of PFM is to double the pulse frequency of the input beam. The combiner 206 further comprises an output 208, which may or may not be a physically available real output. However, if the other optical losses (such as in the coupling and attenuator) are neglected, then the combiner may be a beam splitter/combiner such that the peak power is reduced to about 25% of the input peak power. Output 208 is included to indicate introducing insertion loss due to inherent symmetry. In an embodiment, the beam at output 208 is applied to monitor the beam and adjust attenuator 204.

FIG. 2b shows the PFM of FIG. 2a, but with the second combiner 213 for the PFM to provide quadrupling of the pulse frequency. In principle, quadrupling can also be obtained by extending the splitter 214 to 1×4 and the combiner 206 to a 4×1 combiner. However, in this case, the combiner would impose an insertion loss of about 75% due to the symmetry of the beam splitter, with respect to the loss of about 50% imposed by the second combiner 213. The first delay line is preferably tuned to half the input period at 201, the first delay line doubles the pulse repetition rate after combining at combiner 206, and the second delay line 212 is It is preferably arranged to provide a delay of one half, or one quarter of the input period at 201. The split ratios x ₂ /(1−x ₂ ) are set equal in the embodiment, and x ₁ and x ₃ allow the attenuator 204 to function as described in connection with FIG. 2a. As feasible, the attenuator 211 is non-uniformly configured so that it can perform a similar function of compensating for variations in the split of 206, as well as the combination in the combiner 213. It is worth noting that further doublings can be obtained by adding a coupler and further expanding the PFM without increasing the insertion loss due to the symmetric split.

FIG. 3a shows a measurement setup in which the SC light source 1000 of the present invention is configured to illuminate the spectrometer rather than the measurement object. FIG. 3 a shows that the inventive supercontinuum light source 1000 comprises an intermediate supercontinuum light source 100 and a single mode coupling unit 300. The output from the SC light source 1000 is the output from the single mode coupling unit 300. The output of the intermediate SC light source 100 is the output from the non-linear element 107 (not shown in Figure 3a). This output from the intermediate SC light source 100 is coupled to the input to the single mode coupling unit 300. The output of the intermediate SC light source 100 is at least approximately the output from the non-linear element (107 of FIG. 1a, not shown in FIG. 3a) of the intermediate supercontinuum light source (100 of FIG. 1a). The single mode coupling unit 300 includes adaptations in the form of attenuating and/or shaping the spectrum according to the requirements of the application. In one embodiment, the SM coupling unit 300 comprises one of the embodiments in co-pending PCT application PCT/Denmark Patent Application Publication No. 2011/050475, which is hereby incorporated by reference. In particular, refer to any one of the items and/or claims, as well as the embodiments and variations thereof with respect to Figures 5a, 6, 7, 8-10, 13-15 and 17-19.

FIG. 3b shows an example spectral output from the single mode coupling unit 300 (spectrum 12) as well as an example supercontinuum spectral output from the intermediate supercontinuum light source 100 (spectrum 10). In this example, the spectrum after the single mode coupling unit has a Gaussian distribution, ranging from λ ₄ at about 650 nm to λ ₃ at about 950 nm. Thus, FIG. 3b shows that the spectral shape after the single mode coupling unit is different from the spectral shape in the same wavelength range from the intermediate supercontinuum source.

3c, 3d and 3e show examples of spectral output from the single mode coupling unit 300, namely, Gaussian (FIG. 3c), flat top (FIG. 3d), and dual peak distribution (FIG. 3e) spectral shapes, respectively. Show. The dual peak distribution may be advantageous if the output from the light source is sent through an optical element (such as an optical lens) that is Gaussian like a transfer function before illuminating the object, and Illuminating the object with a flat top distribution is advantageous.

In one embodiment, the spectral shape after the single mode coupling unit is different from the spectrum in the same wavelength region from the intermediate supercontinuum source, such as Gaussian, flat top, or double peak distribution. 4a and 4b show the measurement results from the set-up according to FIG. 3a. The intermediate SC light source was constructed according to FIG.

FIG. 4a shows a Wasatch Cobra UD spectrometer (310) equipped with a Basler Sprint SPL4096-70 km (Basler Sprint SPL4096-70 km) camera as a function of power for a 400-850 nm supercontinuum light source. 3 shows the average intensity noise of the intermediate supercontinuum light source 100 (see FIG. 1) measured at 790-870 nm. FIG. 4a shows the average intensity noise after compensation of the spectrometer noise, while FIG. 4b shows the average intensity noise before compensation of the spectrometer noise. FIG. 4a contains measurements for three different pump pulse frequencies (F _pump ) which are 80 MHz (curve 401), 160 MHz (curve 402) and 320 MHz (curve 403). It can be seen that the noise decreases as the pump pulse frequency increases. Intensity noise is compensated for noise added by the spectrometer.

FIG. 4b shows the intensity noise data from FIG. 4a before compensation for noise from the spectrometer. FIG. 4b contains measurements for three different pump pulse frequencies (F _pump ) which are 80 MHz (curve 411), 160 MHz (curve 412) and 320 MHz (curve 413). Again, it can be seen that the noise decreases as the pump pulse frequency increases.

MO101 is a mode-locked Yb fiber laser with an output having a center wavelength of about 1060 nm and a pulse width of about 6 ps. The laser is passively mode-locked via SESAM and delivers pulses with a repetition rate of 80 MHz. This laser type is well suited for seeding. Because the all-fiber configuration provides a laser that is robust and relatively simple to manufacture for bulk optics setups. The maximum repetition rate is determined by how short the cavity can be manufactured and the response characteristics of SESAM. In practice, these limits often impose a practical upper limit on repetition rates around 100 MHz. In embodiments, other gain media may be applied to provide other output wavelengths, and pulse widths and repetition rates may also be modified within the limits discussed elsewhere.

In an embodiment, the seed laser is a fiber laser such as a mode-locked fiber laser such as a mode-locked via SESAM. The gain medium may be formed by any suitable laser gain, such as Yb-doped fiber, Er-doped fiber and Er/Yb-doped fiber. The seed laser may be, for example, a linear cavity laser or a ring laser.

The non-linear medium 107 is a fine grain formed by a silica core surrounded by a hexagonal pattern of holes configured such that the core is formed by missing holes in the pattern. Structural PCF fiber. The fiber is constructed so that the ZDW of the fiber is relatively close to the pump wavelength, because substantial pump energy is delivered in the anomalous region of the fiber.

As in FIG. 1, fiber optic amplifier sets 102, 104 are placed around an optional PFM. Without PFM, the pump system pumps the fiber at 8 MHz at 8 MHz with 10 W at 80 MHz. By inserting the PFM according to FIG. 2a, the repetition rate is increased to 160 MHz, and by inserting the PFM according to FIG. 2b, the repetition rate is quadrupled to 320 MHz. 4a and 4b comprise a Basler Sprint SPL4096-70km camera configured to measure a spectral range from 790 to 870 nm with 4096 pixels, ie about 0.02 nm/pixel. 7 shows experimental results obtained using a Wasatch Cobra UD spectrometer. A measurement time of 12.9 μs was applied and the power variation measured at each pixel was recorded. A long measurement time such as 1 μs to 1 ms or more and a short measurement time are possible. Short measurement times are often desirable, such as for Fourier domain OCT (see Figure 4b), where real-time imaging is often required. In Figure 4, the average relative standard deviation per pixel in the 790-870 nm spectral region is measured as a function of the visible portion of the spectrum. The standard deviation, and thus the intensity noise, is significantly reduced as the pump pulse repetition rate is doubled, and further when the pump pulse repetition rate is also quadrupled for an equivalent amount of average power in the visible region. To be observed. The amount of power in the visible region depends on how effectively the pump energy is converted to visible light which depends on the peak power of the pump pulse and the total amount of pump power (average power). In FIG. 4a, the estimated noise contribution from the spectrometer was subtracted, whereas this is contained in FIG. 4b.

FIG. 5 shows an optical measurement system illustrated as an OCT system using an SC light source as the light source. The system shown in FIG. 5 is a Fourier domain OCT (FD-OCT) system according to the present invention, and therefore, in the Fourier domain OCT system, the SC light source 1000 is a suitable light source for the optical measurement system according to the present invention. Applied. A 2×2 50/50 directional splitter/combiner (501) coupled to a light source and a spectrometer (310) acting on one side, and a lens (502), a target (503) and a reference on the other side The reflector (504) constitutes the interferometer core of the OCT system. A line scan (depth profile of the sample) is performed by the measurement of the spectrometer, where the measurement depth is determined by the spectral resolution and the spatial resolution at the sample is determined by the spectral width of the measurement. The beam is often scanned over the object to provide a 2D or 3D depth profile of reflectance at the sample. OCT is often a wide area, involving numerous variations in system configuration, which would all benefit from aspects of the present invention. The output spectrum is similar to FIG. 16, for example configured to provide a broad and adjustable spectrum, as shown in FIG. 5a (single band Gaussian spectrum) and FIG. 5 in PCT/Danish Patent Application No. 2011/050475. Gaussian so that in one embodiment the SM coupling unit is configured to shape the spectrum from the SC light source into a Gaussian spectrum, such as the embodiment discussed in connection with 6 (Dual Band Gaussian Spectrum). In one embodiment, the SM combining unit includes a filter configured to provide a Gaussian spectrum. The 50/50 coupler should be configured to handle a broad spectrum, and is typically either a fused fiber coupler or a bulk optical coupler.

FIG. 6 shows an example of a single mode coupling unit 300 that includes a dichroic element that is a dichroic mirror, a dispersive element that is a prism, and a single mode fiber configured to shape the spectrum. Therefore, FIG. 6 illustrates an example of a method of configuring the single mode coupling unit 300. The output of the intermediate supercontinuum light source 100 is guided to the dichroic element 60 and the dispersive element 61. Mirrors and/or angular dispersive elements are connected to the electronic control 6, which enables rotation between these two elements. The system may also optionally include a tunable attenuation filter 62 and/or a tunable spatial filter 63. The light is collimated by lens system 64 and collected by fiber 65, which causes fiber 65 to shape the spectrum. The system may optionally include a broadband splitter 66, which sends a portion of the light to an output 67 and another portion of the light to a detection system 68. The detection system is connected to an electronic control system 6, which is again connected to the supercontinuum light source 100 and/or the dichroic element 500 to stabilize the output power. In one embodiment, the dispersive element is a prism. In one embodiment, fiber 65 is a single mode fiber such as a step-index fiber or a microstructured fiber. In one embodiment, collimating lens system 64 includes a plurality of lenses.

FIG. 7 shows an example of a single mode coupling unit 300 including a dichroic element that is a single mode fiber 60, an attenuating and/or shaping optical element 70, and a second single mode fiber 65.

In one embodiment, the first single mode fiber 60 has a high loss above some threshold wavelength λ ₆ and thus acts as a spectral filter. In one embodiment, the attenuating and/or shaping optics are selected from the list of prisms, optical lowpass, optical highpass and optical bandpass filters, and neutral density filters.

8a-8c show three examples of methods of attenuating the optical power in a supercontinuum light source of the present invention.
In each of FIGS. 8a-8c, a supercontinuum light source is indicated by reference numeral 1000, while an intermediate supercontinuum light source is indicated by reference numeral 100 and a single mode coupling unit is indicated by reference numeral 300. ing.

In FIG. 8 a, the single mode coupling unit 300 includes a damping and shaping unit 81, the mode field diameter at the output of the damping and shaping unit 81 is the mode field of the second single mode fiber 82. Different from diameter. Thus, FIG. 8 a shows the mode field diameter mismatch at the output of the damping and shaping unit 81 of the single mode coupling unit 300.

In FIG. 8b, the single mode coupling unit 300 includes a damping and shaping unit in the form of a shaping element 60 and a damping element 84.
FIG. 8 c shows an example where the attenuation in the single mode coupling unit 300 is obtained by having an optical splice with a large loss 86 between the intermediate supercontinuum light source 100 and the input of the single mode coupling unit 300. Show.

It should be emphasized that the term “comprising” as used herein is to be interpreted as an open term. That is, it should be understood to identify the presence of particular stated features such as elements, units, integers, steps, components and combinations thereof, but one or more other stated Does not exclude the presence or addition of features.

Further, the term "substantially" is meant to include those that are within their normal tolerances.
All features of the invention, including regions and preferred regions, may be combined in various ways within the scope of the invention, unless there is a specific reason not to combine such features.

Claims (1)

An optical measurement system suitable for measuring at least one parameter of an object, said optical measurement system comprising a supercontinuum light source and a detector for detecting light from said object,
The supercontinuum light source is
Having a light source output, and including an intermediate supercontinuum light source and a coupling unit,
The intermediate supercontinuum light source,
a. A seed laser configured to provide a seed pulse with a pulse frequency F _seed ;
b. As doubling the seed pulse, and an _{F seed,} a configuration pulse frequency multiplier to convert the pump pulse with a pulse frequency _{F pump (PFM), F pump} is greater than _{F seed,} The pulse frequency multiplier (PFM),
c. A non-linear element configured to receive the pump pulse and convert the pump pulse into supercontinuum light provided as an output of the non-linear element and having a supercontinuum spectrum ranging from at least about λ ₁ to about λ _2. Wherein λ ₁ −λ ₂ >about 500 nm, and
The supercontinuum light source is configured to illuminate a measurement target with at least a portion of the output of the coupling unit,
The detector is configured to receive light reflected from the measurement object,
The optical measurement system, wherein the detector has an integration time longer than 50/pulse frequency F _pump .