An on-line calibration system and method for spectral peaks in dual-comb coherent Raman spectroscopy measurement

Abstract

An on-line spectral peak calibration system and method for dual-comb coherent Raman spectroscopy measurement. By setting a calibration sample with Raman shift wave numbers corresponding to known spectral peaks in the spectral peak calibration module, and measuring its coherent Raman spectrum to calculate the transformation function between the delay and the Raman shift wave number, the on-line spectral peak calibration of dual-comb coherent Raman spectroscopy measurement is realized, which is beneficial to reducing the spectral peak calibration deviation caused by system fluctuations. It is characterized in that it includes a comb light source module, a dispersion control module, a spectral peak calibration module and a sample detection module connected in sequence. The comb light source module generates pump light and Stokes light with different frequencies and perpendicular polarizations. The dispersion control module forms a combined beam of the pump light and the Stokes light. The spectral peak calibration module divides the combined beam into transmitted light and reflected light. The reflected light acts on the calibration sample to generate a calibration spectral signal. The transmitted light acts on the sample to measure the coherent Raman spectral signal of the sample, and is recorded and input into the upper computer together with the calibration spectral signal by a high-speed data acquisition system.

Description

Technical Field

[0001] The present invention relates to the technical field of coherent Raman spectroscopy measurement, and particularly relates to a system and method for on-line calibration of spectral peaks in dual-comb coherent Raman spectroscopy measurement. By setting a calibration sample with a Raman shift wave number corresponding to a known spectral peak in a spectral peak calibration module, measuring its coherent Raman spectrum, and calculating a transformation function between the delay and the Raman shift wave number, on-line calibration of spectral peaks in dual-comb coherent Raman spectroscopy measurement is achieved, which is beneficial to reducing the spectral peak calibration deviation caused by system fluctuations and improving the accuracy of spectral measurement. Background Art

[0002] Coherent Raman scattering is a Raman scattering technique based on non-linear effects. This method utilizes the multi-beam interference effect to obtain a coherent Raman signal with a greatly increased intensity. The coherent Raman spectrum signal directly reflects the internal molecular vibration modes of substances and has the ability of non-destructive and non-labeled detection. At the same time, due to the high signal-to-noise ratio, its measurement time is extremely short, so it can be widely applied in the fields of biomedical imaging, chemical real-time analysis, industrial environmental monitoring, etc. The dual-comb coherent Raman spectroscopy technique uses two optical comb light sources as the pump light and the Stokes light (Stokes light) to realize the excitation of coherent Raman scattering. The center frequency difference between the two optical combs determines the excited molecular vibration frequency. In order to achieve wide-spectrum range and high-speed spectral measurement, the spectral focusing method is used for excitation. This method applies linear chirps to the pump light and the Stokes pulses, so that the instantaneous frequency of the pulses changes linearly with time, and different delays of the pulses correspond to the excitation of different molecular vibration frequencies; then the delay difference between the pump light and the Stokes light is scanned, and the abscissa of the obtained time-domain signal is the delay, and the ordinate is the vibration intensity. Therefore, it is necessary to calibrate the measured signal to convert the delay into the Raman wave number, so as to obtain an accurate coherent Raman spectrum signal.

[0003] The inventor of the present invention has learned that when the two optical combs in the coherent Raman spectroscopy measurement system are affected by environmental temperature, vibration, etc., parameters such as the repetition frequency and the repetition frequency difference of the output laser pulses will change, which causes the relative delay of the two optical comb laser pulses to jitter. Due to the use of spectral focusing excitation, this results in the shift of the wave number of the generated coherent Raman spectrum signal and the distortion of the signal. The inventor believes that if the Raman shift wave number and the delay at the sample measurement moment can be calibrated on-line, even if the system parameters fluctuate, the transformation function between the Raman shift wave number and the delay at this moment can be obtained, so as not to be affected by the system parameter fluctuations. Therefore, if a spectral peak calibration module is additionally set in the system and the method of obtaining the transformation function between the Raman shift wave number and the delay at this moment by using a sample with a known spectral peak position is used, on-line calibration of spectral peaks can be completed, which helps to know the influence of system fluctuations on measurement and improve the accuracy of spectral measurement. At present, there is no system and method for on-line calibration of spectral peaks in dual-comb coherent Raman spectroscopy. In view of this, the inventor of the present invention has completed the present invention. Summary of the Invention

[0004] Aiming at the defects or deficiencies of the prior art, the present invention provides an online spectral peak calibration system and method for dual-comb coherent Raman spectroscopy. By setting a calibration sample with Raman shift wavenumbers corresponding to known spectral peaks in the spectral peak calibration module, measuring its coherent Raman spectrum, and calculating the transformation function between the delay and the Raman shift wavenumber, the online spectral peak calibration of dual-comb coherent Raman spectroscopy is realized, which is beneficial to reducing the spectral peak calibration deviation caused by system fluctuations and improving the spectral measurement accuracy.

[0005] The technical solution of the present invention is as follows:

[0006] An online spectral peak calibration system for dual-comb coherent Raman spectroscopy, characterized in that it includes a optical frequency comb light source module, a dispersion control module, a spectral peak calibration module and a sample detection module connected in sequence. The optical frequency comb light source module generates a pump light and a Stokes light (Stokes light) with different frequencies and perpendicular polarizations. The dispersion control module applies equal dispersion to the pump light and the Stokes light and compensates their delay difference to form a combined beam of light. The spectral peak calibration module divides the combined beam of light into a transmitted light and a reflected light. The reflected light acts on the calibration sample to generate a calibration spectral signal. The transmitted light enters the sample detection module to act on the sample to measure the coherent Raman spectral signal of the sample, and is recorded by a high-speed data acquisition system together with the calibration spectral signal and input into a host computer for processing to realize the online spectral peak calibration of the sample coherent Raman spectrum.

[0007] The optical frequency comb light source module includes a first optical frequency comb and a second optical frequency comb respectively connected to a reference source. The output side of the first optical frequency comb is connected to a first grating pair in the dispersion control module, and the output side of the second optical frequency comb is connected to a second grating pair in the dispersion control module through a 1 / 2 wave plate.

[0008] The dispersion control module includes a polarization beam splitter prism. The output side of the polarization beam splitter prism is connected to a depolarization beam splitter in the spectral peak calibration module. The first input side of the polarization beam splitter prism is connected to the second grating pair, and the second input side of the polarization beam splitter prism is sequentially connected to the first grating pair through an aspherical lens pair, a first mirror and a retroreflector.

[0009] The spectral peak calibration module includes a first photomultiplier tube. The output side of the first photomultiplier tube is connected to the high-speed data acquisition system in the sample detection module. The input side of the first photomultiplier tube is sequentially connected to the reflection side of the depolarization beam splitter through a first focusing lens, a first filter, a second objective lens, a calibration sample and a first objective lens. The transmission side of the depolarization beam splitter is connected to a second mirror in the sample detection module.

[0010] The sample detection module includes a sample stage. The input side of the sample stage is connected to a second reflector through a third objective lens, and the output side of the sample stage is connected to a host computer through a fourth objective lens, a second filter, a second focusing lens, a second photomultiplier tube, and a high-speed data acquisition system in sequence.

[0011] The reference signal provided by the reference source has a frequency of 100 MHz. The center frequency repetition frequency of the first optical frequency comb is 100 MHz, and the repetition frequency of the second optical frequency comb is 100 MHz. The repetition frequency difference between the first optical frequency comb and the second optical frequency comb is adjustable, and the adjustable range of the repetition frequency difference is 0 to 100 Hz. The output spectral range of the first optical frequency comb is from λ 1-min to λ 1-max , where λ 1-min is the minimum value of the first wavelength λ 1 , and λ 1-max is the maximum value of the first wavelength λ 1 . The output spectral range of the second optical frequency comb is from λ 2-min to λ 2-max , where λ 2-min is the minimum value of the second wavelength λ 2 , and λ 2-max is the maximum value of the second wavelength λ 2 , where λ 1-max < λ 2-min .

[0012] The gratings in the first grating pair and the second grating pair are blazed gratings. The blazed wavelength of the grating in the first grating pair is near λ 1 , and the blazed wavelength of the grating in the second grating pair is near λ 2 .

[0013] The transmission - reflection ratio of the depolarization - eliminating beam splitter is 7:3. The Raman spectrum of the calibration sample has at least 5 Raman spectral peaks with known peak positions in the wavenumber range from to .

[0014] Both the first filter and the second filter are low - pass filters, and the cut - off wavelength is .

[0015] A method for online calibration of spectral peaks in dual - optical - comb coherent Raman spectroscopy, characterized in that the above - mentioned spectral peak online calibration system for dual - optical - comb coherent Raman spectroscopy is used to perform online calibration on the dual - optical - comb coherent Raman spectroscopy measurement system, including the following steps:

[0016] Step 1: Turn on the first optical frequency comb and the second optical frequency comb, lock their repetition frequency difference, adjust the position of the retro - reflector, and observe the spectral signal of the calibration sample in the host computer until its signal is maximum and near the center position of the time axis;

[0017] Step 2, observe the spectral signal of the calibration sample in the host computer, select 5 spectral peaks, and record the Raman shift wave numbers w 1 、w 2 、w 3 、w 4 and w 5 , and their time-axis delays d 1 、d 2 、d 3 、d 4 and d 5 ;

[0018] Step 3, use the formula to fit the transformation function between the delay x and the Raman shift wave number y. The formula is:

[0019]

[0020] where w i 、w j are the recorded Raman shift wave numbers, and d i 、d j are the recorded delays;

[0021] Step 4, use the host computer to record the coherent Raman spectral signal of the sample, and use the formula in Step 3 to convert its delay on the time axis into a wave number, thereby completing the online calibration of the wave number.

[0022] The technical effects of the present invention are as follows: The present invention relates to an online calibration system and method for spectral peaks in dual-comb coherent Raman spectroscopy measurement. By setting a calibration sample with known Raman shift wave numbers corresponding to spectral peaks in the spectral peak calibration module, measuring its coherent Raman spectrum, and calculating the transformation function between the delay and the Raman shift wave number, the online calibration of spectral peaks in dual-comb coherent Raman spectroscopy measurement is realized, which is beneficial to reducing the spectral peak calibration deviation caused by system fluctuations and improving the spectral measurement accuracy. The present invention is a system and method for online calibration of spectral peaks in a dual-comb coherent Raman spectroscopy measurement system by applying the conversion of the transformation function between Raman shift wave number and delay using a sample with known Raman shift of spectral peaks.

[0023] The advantages of the present invention compared with the prior art are as follows: (1) Compared with the conventional coherent Raman scattering spectroscopy measurement device, using a sample with known Raman wave numbers corresponding to spectral peaks to calculate the transformation function between Raman shift wave number and delay in real time solves the problem of unable to perform real-time spectral peak calibration and improves the spectral measurement accuracy. (2) The real-time monitoring of the delay can be realized without separately setting a delay monitoring module, which simplifies the system. (3) Using a high-speed data acquisition system to collect spectral information improves the spectral measurement and online spectral peak calibration speed. Brief Description of the Drawings

[0024] Figure 1The present invention is a schematic structural diagram of a spectrum peak online calibration system for dual-comb coherent Raman spectroscopy measurement. Figure 1 The system includes a light comb light source module, a dispersion control module, a spectrum peak calibration module, and a sample detection module which are connected in sequence.

[0025] Figure 2 The present invention is a schematic flow chart of a method for online calibration of spectrum peaks in dual-comb coherent Raman spectroscopy measurement. Figure 2 The method comprises the steps of: 1, opening the first optical frequency comb and the second optical frequency comb, locking their repetition frequency difference, and adjusting the position of the retroreflector so that the spectral signal is maximized and near the center of the time axis; 2, observing the spectral signal of the calibration sample in the host computer, selecting 5 spectral peaks, and recording the Raman shift wavenumbers corresponding to the spectral peaks and the delay on the time axis; 3, using a formula to fit the transformation function of the delay x and the Raman shift wavenumber y; and 4, using the host computer to record the coherent Raman spectral signal of the sample, and using the formula to convert its delay on the time axis into wavenumbers.

[0026] Figure 3 It is the measured spectrum of the calibration sample. Figure 3 The horizontal axis is delay (ps, scale value -10, -8, ···, 10), and the vertical axis is signal strength (au- arbitrary unit, scale value 0, 5000, ···, 20000). Figure 3 The calibration specimen involved is PS (polystyrene) sample.

[0027] Figure 4 It is the Raman shift wavenumber diagram of the calibration sample. Figure 4 The horizontal axis is the Raman shift wave number (cm -1 , scale value 2800, 2850, ···, 3200), the vertical axis is the signal strength (au, scale value 0, 5000, ···, 20000). Figure 4 The calibration specimen involved is PS (polystyrene) sample.

[0028] Figure 5 This is the fitted delay and Raman shift wavenumber conversion function diagram. Figure 5 The horizontal axis is the delay (ps, scale value -10, -8, ···, 10), and the vertical axis is the Raman shift wave number (cm -1 , scale values ​​2800, 2850,..., 3200). Figure 5 The dots in the middle represent the actual measured values, and the oblique lines associated with the dots are the fitted curves.

[0029] The description of the reference numerals in the drawings is as follows: 1 - first optical frequency comb; 2 - second optical frequency comb; 3 - reference source; 4 - half-wave plate; 5 - first pair of gratings; 6 - second pair of gratings; 7 - retroreflector; 8 - first mirror; 9 - pair of aspherical lenses; 10 - polarization beam splitter prism; 11 - depolarizing beam splitter; 12 - first objective lens; 13 - calibration specimen; 14 - second objective lens; 15 - first filter; 16 - first focusing lens; 17 - first photomultiplier tube; 18 - second mirror; 19 - third objective lens; 20 - sample stage; 21 - fourth objective lens; 22 - second filter; 23 - second focusing lens; 24 - second photomultiplier tube; 25 - high-speed data acquisition system; 26 - host computer. Detailed implementation manners

[0030] The present invention will be described below in conjunction with the drawings ( Figures 1 - 5 ), and embodiments.

[0031] Figure 1 is a schematic structural diagram of a system for online calibration of spectral peaks in a dual-comb coherent Raman spectroscopy measurement implementing the present invention. Figure 2 is a schematic flowchart of a method for online calibration of spectral peaks in a dual-comb coherent Raman spectroscopy measurement implementing the present invention. Figure 3 is a spectrogram of the calibration specimen measured. Figure 4 is a Raman shift wavenumber diagram of the calibration specimen. Figure 5 is a graph of the delay and Raman shift wavenumber transformation function obtained by fitting. Refer to Figures 1 to 5 As shown, a system for online calibration of spectral peaks in a dual-comb coherent Raman spectroscopy measurement includes an optical comb light source module, a dispersion control module, a spectral peak calibration module, and a sample detection module connected in sequence. The optical comb light source module generates pump light and Stokes light (Stokes light) with different frequencies and perpendicular polarizations. The dispersion control module applies equal dispersion to the pump light and Stokes light and compensates for their delay difference to form a combined beam of light. The spectral peak calibration module divides the combined beam of light into transmitted light and reflected light. The reflected light acts on the calibration specimen 13 to generate a calibration spectral signal. The transmitted light enters the sample detection module to act on a sample (the sample is in the sample stage 20) to measure the coherent Raman spectral signal of the sample, and is recorded together with the calibration spectral signal by the high-speed data acquisition system 25 and input into the host computer 26 for processing to achieve online calibration of the spectral peaks of the sample coherent Raman spectrum.

[0032] The optical frequency comb light source module includes a first optical frequency comb 1 and a second optical frequency comb 2 respectively connected to a reference source 3. The output side of the first optical frequency comb 1 is connected to a first grating pair 5 in the dispersion regulation module, and the output side of the second optical frequency comb 2 is connected to a second grating pair 6 in the dispersion regulation module through a half-wave plate 4. The dispersion regulation module includes a polarization beam splitter prism 10. The output side of the polarization beam splitter prism 10 is connected to a depolarization beam splitter 11 in the spectral peak calibration module. The first input side of the polarization beam splitter prism 10 is connected to the second grating pair 6, and the second input side of the polarization beam splitter prism 10 is sequentially connected to the first grating pair 5 through an aspheric lens pair 9, a first reflector 8, and a retroreflector 7.

[0033] The spectral peak calibration module includes a first photomultiplier tube 17. The output side of the first photomultiplier tube 17 is connected to a high-speed data acquisition system 25 in the sample detection module. The input side of the first photomultiplier tube 17 is sequentially connected to the reflection side of the depolarization beam splitter 11 through a first focusing lens 16, a first filter 15, a second objective lens 14, a calibration specimen 13, and a first objective lens 12. The transmission side of the depolarization beam splitter 11 is connected to a second reflector 18 in the sample detection module. The sample detection module includes a sample stage 20. The input side of the sample stage 20 is connected to the second reflector 18 through a third objective lens 19. The output side of the sample stage 20 is sequentially connected to a host computer 26 through a fourth objective lens 21, a second filter 22, a second focusing lens 23, a second photomultiplier tube 24, and a high-speed data acquisition system 25.

[0034] The reference signal frequency provided by the reference source 3 is 100 MHz. The center frequency repetition frequency of the first optical frequency comb is 100 MHz, and the repetition frequency of the second optical frequency comb is 100 MHz. The repetition frequency difference between the first optical frequency comb and the second optical frequency comb is adjustable, and the adjustable range of the repetition frequency difference is 0 to 100 Hz. The output spectral range of the first optical frequency comb is from λ 1-min to λ 1-max , where λ 1-min is the minimum value of the first wavelength λ 1 , and λ 1-max is the maximum value of the first wavelength λ 1 . The output spectral range of the second optical frequency comb is from λ 2-min to λ 2-max , where λ 2-min is the minimum value of the second wavelength λ 2 , and λ 2-min is the maximum value of the second wavelength λ 2 , where λ 1-max < λ 2-min . The gratings in the first grating pair and the second grating pair are blazed gratings. The blazed wavelength of the grating in the first grating pair is near λ 1 , and the blazed wavelength of the grating in the second grating pair is near λ2 nearby

[0035] The transmission - reflection ratio of the depolarizing beam splitter is 7:3, and the Raman spectrum of the calibration sample has at least 5 Raman spectral peaks with known peak positions in the wavenumber range from to the wavenumber range.

[0036] Both the first filter and the second filter are low - pass filters, and the cut - off wavelength is .

[0037] A method for on - line calibration of spectral peaks in dual - comb coherent Raman spectroscopy. Using the above - mentioned on - line calibration system for spectral peaks in dual - comb coherent Raman spectroscopy to perform on - line calibration of spectral peaks for a dual - comb coherent Raman spectroscopy measurement system, including the following steps: Step 1, turn on the first optical frequency comb and the second optical frequency comb, lock their repetition frequency difference, adjust the position of the retro - reflector, and observe the spectral signal of the calibration sample in the upper computer until its signal is maximum and is near the center position on the time axis; Step 2, observe the spectral signal of the calibration sample in the upper computer, select 5 spectral peaks, record the Raman shift wavenumbers w 1 , w 2 , w 3 , w 4 and w 5 corresponding to the spectral peaks, as well as their time - axis delays d 1 , d 2 , d 3 , d 4 and d 5 ; Step 3, use the formula to fit the transformation function of the delay x and the Raman shift wavenumber y. The formula is:

[0038]

[0039] where w i , w j are the recorded Raman shift wavenumbers, and d i , d j are the recorded delays;

[0040] Step 4, use the upper computer to record the coherent Raman spectral signal of the sample, and use the formula in Step 3 to convert its time - axis delay into a wavenumber, thereby completing the on - line calibration of the wavenumber.

[0041] An on - line calibration system and method for spectral peaks in dual - comb coherent Raman spectroscopy. By setting a calibration sample with Raman shift wavenumbers corresponding to known spectral peaks in the spectral peak calibration module, measuring its coherent Raman spectrum, and calculating the transformation function of the delay and the Raman shift wavenumber, on - line calibration of spectral peaks in dual - comb coherent Raman spectroscopy is achieved, which is beneficial to reducing the spectral peak calibration deviation caused by system fluctuations and improving the spectral measurement accuracy.

[0042] Reference Figure 1 As shown, a spectral peak on-line calibration system for dual-comb coherent Raman spectroscopy measurement includes an optical comb light source module, a dispersion control module, a spectral peak calibration module, and a sample detection module connected in sequence. The optical comb light source module generates pump light and Stokes light with different frequencies and perpendicular polarizations. The dispersion control module applies equal dispersion to the pump light and Stokes light and compensates for their delay difference to form a combined beam of light. The spectral peak calibration module divides the combined beam of light into transmitted light and reflected light. The reflected light acts on the calibration sample 13 to generate a calibration spectral signal. The transmitted light enters the sample detection module to act on the sample to measure the coherent Raman spectral signal of the sample, and is recorded together with the calibration spectral signal by the high-speed data acquisition system 25 and input into the upper computer 26 for processing to achieve on-line calibration of the spectral peak of the sample coherent Raman spectrum.

[0043] The optical comb light source module includes a half-wave plate 4. The half-wave plate 4 is connected to the output side of the second optical frequency comb 2. The first optical frequency comb 1 and the second optical frequency comb 2 are respectively connected to the reference source 3. The output side of the first optical frequency comb 1 and the output side of the half-wave plate 4 are respectively connected to the dispersion control module.

[0044] The dispersion control module includes a first pair of gratings 5 and a second pair of gratings 6. The input side of the first pair of gratings 5 is connected to the output side of the first optical frequency comb 1. The output side of the first pair of gratings 5 is connected to the input side of the retroreflector 7. The output side of the retroreflector 7 is sequentially connected to the first reflector 8 and the aspherical lens pair 9 and then connected to the first input side of the polarization beam splitter 10. The input side of the second pair of gratings 6 is connected to the output side of the half-wave plate 4. The output side of the second pair of gratings 6 is connected to the second input side of the polarization beam splitter 10. The output side of the polarization beam splitter 10 is connected to the spectral peak calibration module.

[0045] The spectral peak calibration module includes a depolarizing beam splitter 11 and a calibration sample 13. The input side of the depolarizing beam splitter 11 is connected to the output side of the polarization beam splitter 10. The reflection side of the depolarizing beam splitter 11 is sequentially connected to the first objective lens 12, the calibration sample 13, the second objective lens 14, the first filter 15, the first focusing lens 16 to the first photomultiplier tube 17. The signal of the first photomultiplier tube 17 is connected to the high-speed data acquisition system 25 of the sample detection module. The transmission side of the depolarizing beam splitter 11 is connected to the second reflector 18 of the sample detection module.

[0046] The sample detection module includes a second photomultiplier tube 24, a second focusing lens 23, a second filter 22, a fourth objective lens 21, a sample stage 20, a third objective lens 19, and a second reflector 18 connected to the transmission side of the depolarizing beam splitter 11. The signal of the second photomultiplier tube 24 is connected to the upper computer 26 through the high-speed data acquisition system 25.

[0047] The reference signal frequency provided by the reference source 3 is 100 MHz. The center frequency repetition frequency of the first optical frequency comb 1 is 100 MHz, and the repetition frequency of the second optical frequency comb 2 is 100 MHz. The difference between the repetition frequencies of the first optical frequency comb 1 and the second optical frequency comb 2 is adjustable, and the adjustable range of the difference between the repetition frequencies is 0 to 100 Hz. The output spectral range of the first optical frequency comb 1 is from λ 1-min to λ 1-max , and the output spectral range of the second optical frequency comb 2 is from λ 2-min to λ 2-max , where λ 1-max < λ 2-min .

[0048] The gratings in the first grating pair 5 and the second grating pair 6 are blazed gratings. The blazing wavelength of the grating in the first grating pair 5 is near λ 1 , and the blazing wavelength of the grating in the second grating pair 6 is near λ 2 .

[0049] The transmission - reflection ratio of the depolarization - eliminating beam splitter 11 is 7:3. The Raman spectrum of the calibration sample 13 has more than 5 Raman spectral peaks with known peak positions in the wavenumber range from to .

[0050] Both the first filter 15 and the second filter 22 are low - pass filters, and the cut - off wavelength is .

[0051] A method for on - line calibration of spectral peaks in dual - comb coherent Raman spectroscopy. Using the above - mentioned on - line calibration system for spectral peaks in dual - comb coherent Raman spectroscopy to perform on - line calibration on the dual - comb coherent Raman spectroscopy measurement system, it includes the following steps:

[0052] Step 1: Turn on the first optical frequency comb 1 and the second optical frequency comb 2, lock their difference between the repetition frequencies, adjust the position of the retro - reflector 7, and observe the spectral signal of the calibration sample 13 in the upper computer 26 until its signal is maximum and near the center position on the time axis;

[0053] Step 2: Observe the spectral signal of the calibration sample 13 in the upper computer 26, select 5 spectral peaks, and record the Raman shift wavenumbers corresponding to the spectral peaks as w 1 , w 2 , w 3 , w 4 and w 5， as well as their time - axis delays d 1 , d 2 , d 3 , d 4 and d 5 ;

[0054] Step 3: Use a formula to fit the transformation function of the delay x and the Raman shift wave number y. The formula is as follows:

[0055]

[0056] where w i and w j are the recorded Raman shift wave numbers, and d i and d j are the recorded delays.

[0057] Step 4: Use the host computer 26 to record the sample coherent Raman spectrum signal, and use the formula in Step 3 to convert the delay on the time axis into a wave number, thereby completing the online calibration of the wave number.

[0058] Specifically, the laser emitted by the optical comb light source module obtains equal amounts of linear chirp through the first grating pair 5 and the second grating pair 6 in the dispersion control module, and then after the time coincidence is adjusted by the retroreflector 7 and the spatial coincidence is adjusted by the aspheric lens pair 9, and then a combined beam of light is formed through the polarization beam splitter prism 10. After the combined beam of light is split into two beams by the depolarizing beam splitter 11, the reflected beam of the depolarizing beam splitter 11 acts on the calibration sample (taking a PS (polystyrene) sample as an example) 13 corresponding to the known spectral peak Raman shift, and the calibration sample spectrum as shown in Figure 3 is obtained. At this time, observe its spectrum through the host computer 26. According to the known spectral peak Raman shift ( Figure 4 ), use the method as shown in Figure 2 to fit the transformation function of the delay and the Raman shift wave number ( Figure 5 ). At the same time, the transmitted beam of the depolarizing beam splitter 11 acts on the sample in the sample detection module, and the sample transverse axis delay spectrum signal as shown in Figure 3 is obtained. Use the transformation function of the delay and the Raman shift wave number to process it, and finally obtain the online calibrated coherent Raman spectrum of the spectral peak, as shown in Figure 4 .

[0059] The content not described in detail in the specification of the present invention belongs to the prior art well-known to those skilled in the art. It is hereby indicated that the above description helps those skilled in the art to understand the present invention, but does not limit the protection scope of the present invention. Any implementation that is an equivalent replacement, modification and improvement, and / or simplification of the above description without departing from the essence of the present invention falls within the protection scope of the present invention.

Claims

1. A spectrum peak online calibration system for dual-comb coherent Raman spectroscopy measurement, characterized in that: It comprises an optical comb light source module, a dispersion control module, a spectrum peak calibration module and a sample detection module connected in sequence, wherein the optical comb light source module generates pump light and Stokes light with different frequencies and perpendicular polarizations, the dispersion control module applies equal amounts of dispersion to the pump light and the Stokes light and compensates for their delay difference to form a combined light beam, the spectrum peak calibration module divides the combined light beam into transmitted light and reflected light, the reflected light acts on a calibration sample to generate a calibration spectrum signal, the transmitted light is injected into the sample detection module to act on the sample to measure the coherent Raman spectrum signal of the sample, and is recorded by a high-speed data acquisition system together with the calibration spectrum signal and input into a host computer for processing to realize online calibration of the spectrum peak of the sample coherent Raman spectrum; The spectrum peak calibration module comprises a first photomultiplier tube, the output side of the first photomultiplier tube is connected to the high-speed data acquisition system in the sample detection module, the input side of the first photomultiplier tube is connected to the reflection side of the depolarizing beam splitter through the first focusing lens, the first filter, the second objective lens, the calibration sample and the first objective lens in sequence, and the transmission side of the depolarizing beam splitter is connected to the second reflector in the sample detection module; The online calibration of the spectrum peaks includes: observing the spectrum signal of the calibration sample in the host computer, selecting 5 spectrum peaks, recording the Raman shift wavenumbers w1, w2, w3, w4 and w5 corresponding to the spectrum peaks, and the delays d1, d2, d3, d4 and d5 on the time axis; Use the formula to fit the transformation function of delay x and Raman shift wave number y, the formula is: ， where w i 、w j is the recorded Raman shift wave number, d i d j Delay for recording; The coherent Raman spectrum signal of the sample is recorded using a host computer, and the delay on the time axis is converted into wavenumber using the above formula, thereby completing the online wavenumber calibration.

2. The online peak calibration system for dual-comb coherent Raman spectroscopy measurement according to claim 1, characterized in that: The optical comb light source module includes a first optical frequency comb and a second optical frequency comb respectively connected to a reference source, the output side of the first optical frequency comb is connected to the first grating pair in the dispersion control module, and the output side of the second optical frequency comb is connected to the second grating pair in the dispersion control module through a 1 / 2 wave plate.

3. The online peak calibration system for dual-comb coherent Raman spectroscopy measurement according to claim 1, characterized in that: The dispersion control module includes a polarization beam splitter prism, the output side of the polarization beam splitter prism is connected to the depolarization beam splitter in the spectrum peak calibration module, the first input side of the polarization beam splitter prism is connected to the second grating pair, and the second input side of the polarization beam splitter prism is connected to the first grating pair through an aspheric lens pair, a first reflector and a retroreflective mirror in sequence.

4. The online peak calibration system for dual-comb coherent Raman spectroscopy measurement according to claim 1, characterized in that: The sample detection module includes a sample stage, the input side of the sample stage is connected to the second reflector through the third objective lens, and the output side of the sample stage is connected to the host computer through the fourth objective lens, the second filter, the second focusing lens, the second photomultiplier tube and the high-speed data acquisition system in sequence.

5. The online spectral peak calibration system for dual-comb coherent Raman spectroscopy measurement according to claim 2, characterized in that: The reference signal frequency provided by the reference source is 100 MHz, the center frequency repetition frequency of the first optical frequency comb is 100 MHz, the repetition frequency of the second optical frequency comb is 100 MHz, the repetition frequency difference between the first optical frequency comb and the second optical frequency comb is adjustable, and the adjustable range of the repetition frequency difference is 0 to 100 Hz. The output spectrum range of the first optical frequency comb is λ 1-min To 1-max ,λ 1-min is the minimum value of the first wavelength λ1, λ 1-max is the maximum value of the first wavelength λ1, and the output spectrum range of the second optical frequency comb is λ 2-min To 2-max ,λ 2-min is the minimum value of the second wavelength λ2, λ 2-max is the maximum value of the second wavelength λ2, where λ 1-max <λ 2-min .

6. The online peak calibration system for dual-comb coherent Raman spectroscopy measurement according to claim 3, characterized in that: The gratings in the first grating pair and the second grating pair are blazed gratings, the blazing wavelength of the gratings in the first grating pair is near λ1, and the blazing wavelength of the gratings in the second grating pair is near λ2.

7. The online peak calibration system for dual-comb coherent Raman spectroscopy measurement according to claim 5, characterized in that: The transmission and reflection ratio of the depolarizing beam splitter is 7:3, and the Raman spectrum of the calibration sample is to There are at least 5 Raman peaks with known peak positions within the wavenumber range.

8. The online spectral peak calibration system for dual-comb coherent Raman spectroscopy measurement according to claim 5, characterized in that: The first filter and the second filter are both low-pass filters with a cut-off wavelength of .

9. A method for online calibration of spectrum peaks in dual-comb coherent Raman spectroscopy measurement, characterized in that: The online calibration system for spectrum peaks of dual-comb coherent Raman spectroscopy measurement according to any one of claims 1 to 8 is used to perform online calibration of spectrum peaks of a dual-comb coherent Raman spectroscopy measurement system, comprising the following steps: Step 1, turn on the first optical frequency comb and the second optical frequency comb, lock their repetition frequency difference, adjust the position of the retroreflector, and observe the spectral signal of the calibration sample in the host computer until the signal is maximum and near the center of the time axis; Step 2, observe the spectral signal of the calibration sample in the host computer, select 5 spectral peaks, and record the Raman shift wavenumbers w1, w2, w3, w4 and w5 corresponding to the spectral peaks, as well as their delays d1, d2, d3, d4 and d5 on the time axis; Step 3, use the formula to fit the transformation function of delay x and Raman shift wave number y, the formula is: ； where w i 、w j is the recorded Raman shift wave number, d i d j Delay for recording; Step 4: Use the host computer to record the coherent Raman spectrum signal of the sample, and use the formula in step 3 to convert its delay on the time axis into wave number, thereby completing the online wave number calibration.

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