High-power and high-mutual dryness double-optical comb spectrum system based on Raman gain modulation

Abstract

The invention discloses a high-power and high-mutual dryness double-optical comb spectrum technology based on Raman gain modulation. The method can be used for rapid spectrum detection and multi-component atmosphere remote sensing. The system comprises a mode-locked laser, a rare earth doped optical fiber amplifier, a coupler, a Raman gain optical fiber, an optical splitter, a single-frequency laser, an acoustic optical modulator, a to-be-measured target, a photoelectric detector and sampling equipment. The two mode-locked lasers output ultrafast pulses, the ultrafast pulses are amplified through the rare earth doped optical fiber amplifiers respectively and coupled with the same single-frequency laser respectively to enter the Raman gain optical fiber, Raman gain modulation is provided for the single-frequency laser, the single-frequency laser is shaped into a high-power and high-mutual-dryness double-optical-frequency comb, and the double-optical-frequency comb is combined with the single-frequency laser. The repetition frequency is equal to the repetition frequency of the pump pulse. The two paths of output optical frequency combs have high mutual dryness and high output power, and high-speed and high-signal-to-noise-ratio double-optical-comb spectrum gas absorption detection is realized at the millisecond magnitude under the condition of no feedback locking and correction algorithm.

Description

Technical Field

[0001] The present invention relates to the technical fields of ultrafast fiber lasers, optical frequency combs, and spectroscopic detection technologies, and specifically to a high-power, high mutual coherence dual-comb spectroscopy system based on Raman gain modulation. Background Art

[0002] Dual-comb spectroscopy technology is an active coherent spectroscopy detection technology that can achieve the detection of multi-component gas absorption spectra. It has fast detection time, does not require mechanical scanning, has a wide spectral range and high spectral resolution at the same time, and is insensitive to environmental disturbances. It is an ideal spectroscopic detection technology. It can be widely applied in various fields such as high-precision gas concentration detection, atmospheric multi-component gas remote sensing, high-precision ranging, exhaust flame temperature sensing, spaceborne or airborne remote sensing, etc.

[0003] However, currently, dual-comb spectroscopy technology has not been able to be practically applied. This is mainly because the realization of dual-comb spectroscopy technology depends on the good mutual coherence of the two combs. Currently, the method to achieve the mutual coherence of the two combs is to lock the two combs to an ultra-stable laser cavity through complex electrical feedback locking, which will bring unacceptable costs and extremely high complexity in practical applications, and can only work in a stable environment in the laboratory. Another method is to use various post-processing correction algorithms to restore the mutual coherence of the two combs by calculating and compensating for jitter, but the correction algorithm can only restore the coherence time to the millisecond level, and lacks real-time performance and robustness, and is also limited to laboratory research applications. Another problem that restricts dual-comb spectroscopy technology is that the optical frequency comb optical power output by a mode-locked laser is only a few milliwatts, and the spectral width covers dozens of nanometers, so that the optical power of each longitudinal mode is only on the order of nanowatts. In applications such as atmospheric remote sensing or other high optical loss scenarios, such weak comb tooth energy will be submerged in noise and difficult to distinguish. When using a mature rare-earth doped fiber amplifier for amplification, amplified spontaneous emission and additional noise will be introduced, destroying the mutual coherence and making the locking and post-processing correction algorithms more unstable. Therefore, how to enable the dual-comb spectroscopy system to achieve a coherence time of dozens of seconds without active feedback locking and post-processing correction algorithms, and reach sufficient energy for long-distance atmospheric remote sensing or non-cooperative target atmospheric remote sensing is still a difficult problem in this field. Summary of the Invention

[0004] To solve the problems faced by the current application of dual-comb spectroscopy technology, such as extremely high costs, the need for extremely complex feedback locking, non-robust and non-real-time calibration algorithms, low optical power, and low spectral energy density, the present invention provides a novel method for generating high-power and highly mutually coherent dual optical frequency combs. Based on the Raman gain modulation caused by stimulated Raman scattering, the present invention generates an optical frequency comb centered on a single-frequency laser. The central optical frequencies of the two optical frequency combs are traced back to the same single-frequency laser, having excellent mutual coherence. Compared with traditional technologies such as active feedback locking control and post-data calibration algorithm processing, this method can achieve passive spontaneous locking of the dual-comb phase, thus greatly simplifying the system complexity and cost, and improving the spectral detection rate and quality. In addition, due to the high conversion efficiency of stimulated Raman scattering, the two generated optical frequency combs each have an average power on the order of several watts, and are also applicable to long-distance atmospheric remote sensing and non-cooperative target remote sensing. In summary, this system uses an all-fiber structure, with low cost, simple system, and does not require any electrical feedback locking and calibration algorithms. It can achieve wide spectral range, high spectral resolution, fast, multi-component gas spectral detection, and atmospheric multi-component remote sensing.

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

[0006] A high-power and highly mutually coherent dual-comb spectroscopy system based on Raman gain modulation, comprising a first mode-locked laser, a second mode-locked laser, a first rare-earth doped fiber amplifier, a second rare-earth doped fiber amplifier, a first coupler, a second coupler, a third coupler, a first Raman gain fiber, a second Raman gain fiber, a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a first photodetector, a second photodetector, a single-frequency laser, an acousto-optic modulator, a target to be measured, and a sampling device;

[0007] The first mode-locked laser and the second mode-locked laser respectively generate ultrafast pulsed lasers with different repetition frequencies. After the two pulsed lasers are respectively subjected to chirped pulse amplification by the first rare-earth doped fiber amplifier and the second rare-earth doped fiber amplifier, the two continuous lasers output by the single-frequency laser and split by the first optical splitter are respectively coupled into the first Raman gain fiber and the second Raman gain fiber through the first coupler and the second coupler; in the first Raman gain fiber and the second Raman gain fiber, the amplified pulsed laser serves as the pump light, and the pump light energy is transferred to the continuous laser wavelength through the stimulated Raman scattering effect to form Raman light, thereby respectively converting the two continuous lasers into two high-power and highly coherent optical frequency combs with the same repetition frequencies as the corresponding first mode-locked laser and the second mode-locked laser; after separating the two remaining pump lights from the second optical splitter and the third optical splitter and outputting them through the first output port and the second output port, in the two optical frequency combs, one is subjected to frequency shift processing by an acousto-optic modulator, and the other is transmitted at the original frequency to avoid spectral aliasing of the two optical frequency combs; then the two optical frequency combs are combined by the third coupler and divided into two groups by the fourth optical splitter. One group of optical paths passing through the target to be measured is received by the first photodetector to obtain the interference signal carrying the sample absorption information as the signal path; the other group of optical paths not passing through the target to be measured is directly received by the second photodetector to obtain the original interference signal as the reference path, and the interference signals of the signal path and the reference path are synchronously collected and processed by the sampling device; all fiber devices in the system are polarization-maintaining devices.

[0008] The first mode-locked laser and the second mode-locked laser are rare-earth doped mode-locked lasers, generating ultrafast pulsed lasers with a repetition frequency difference of 200 Hz to 10 kHz.

[0009] The first rare-earth doped fiber amplifier and the second rare-earth doped fiber amplifier are erbium-doped fiber amplifiers, ytterbium-doped fiber amplifiers, thulium-doped fiber amplifiers, holmium-doped fiber amplifiers or other rare-earth doped fiber amplifiers. After performing chirped pulse amplification processing on the input pump pulsed laser, the average power of the single-channel output pump pulsed laser is 2 to 15 W, and the pulse width is 1 to 100 ps.

[0010] The first coupler, the second coupler, the third coupler, the first optical splitter, the second optical splitter, the third optical splitter, and the fourth optical splitter are wavelength division multiplexers or optical couplers.

[0011] The first Raman gain fiber and the second Raman gain fiber are silicon-based fibers with a small core design, and their lengths are 1 to 20 meters. In each Raman gain fiber, the pump light transfers energy to the Stokes light through stimulated Raman scattering, and the conversion efficiency can reach more than 60%. The average power of the generated optical frequency comb per channel is 1 to 10 W, and its pulse width is 0.9 to 1 times that of the pump pulse width. The high mutual coherence of the two optical frequency combs is manifested as the comb line width in the radio frequency domain of the interference signal being on the order of mHz and the coherence time being greater than 30 seconds. The high mutual coherence of the two optical frequency combs can be achieved without an active locking control unit, and the repetition frequency difference of the two optical frequency combs is also correspondingly in the range of 200 Hz to 10 kHz.

[0012] The line width of the single-frequency laser ≤ 10 MHz, the wavelength tuning range ≥ 5 nm, and the output power ≥ 10 mW.

[0013] The frequency shift amount generated by the acousto-optic modulator is 10 MHz to 300 MHz, and after frequency shift, it is used to avoid radio frequency spectrum information aliasing.

[0014] The first photodetector and the second photodetector are indium gallium arsenide detectors with a bandwidth ≥ 500 MHz.

[0015] The sampling device is an oscilloscope or a data acquisition card, and the sampling rate ≥ 20 MHz.

[0016] Compared with the prior art, the technical effects of the present invention are:

[0017] 1) The present invention generates a high-power optical frequency comb through Raman gain modulation, with a conversion efficiency of more than 60%, and outputs an optical frequency comb in the order of several watts, which can be applied to long-distance, non-cooperative target atmospheric remote sensing and other spectral detections with large optical losses.

[0018] 2) The present invention generates a high-power optical frequency comb through Raman gain modulation. During the amplification process by stimulated Raman scattering, no additional noise is introduced. On the contrary, this process makes the coherence of the generated optical frequency comb originate from the single-frequency laser, improving the output coherence.

[0019] 3) The present invention generates a high-power optical frequency comb through Raman gain modulation. Its repetition frequency is exactly equal to the repetition frequency of the pump pulse. Therefore, by adjusting the repetition frequency of the mode-locked laser, the repetition frequency of the output high-power optical frequency comb can be adjusted. Correspondingly, the repetition frequency difference of the output high-power and highly mutually coherent dual optical frequency combs can also be synchronously adjusted, so as to achieve a balance between avoiding aliasing and fast detection.

[0020] 4) The present invention generates a high-power dual optical frequency comb through Raman gain modulation. The frequency of the signal after beat frequency in the radio frequency spectrum can be continuously adjusted by adjusting the frequency shift amount of the acousto-optic modulator.

[0021] 5) The present invention generates high-power dual optical frequency combs through Raman gain modulation. Its spectrum can be continuously translated by tuning a single-frequency laser while maintaining the spectral shape, enabling flexible tracking of the absorption lines of different gases or different absorption lines of the same gas.

[0022] 6) The present invention generates high-power dual optical frequency combs through Raman gain modulation. Its spectral width can be optimized by adjusting the pump power and the length of the Raman gain fiber, and can be accurately predicted through simulation based on the nonlinear Schrödinger equation.

[0023] 7) The present invention generates high-power dual optical frequency combs through Raman gain modulation. The two combs originate from the same single-frequency laser. The jitter of the single-frequency laser has no effect on the radio frequency spectrum after the beat frequency of the two combs, and the repetition frequency jitter of the two combs is transmitted from the position of the single-frequency laser to both sides, reducing the repetition frequency jitter by six orders of magnitude compared to a free-running mode-locked laser.

[0024] 8) The dual optical combs generated by the present invention through Raman gain modulation have high mutual coherence between the two optical combs without any feedback locking or correction algorithms, enabling spectral detection with a wide spectral range, high spectral resolution, fast high signal-to-noise ratio.

[0025] 9) Compared with other technical means that can restore the mutual coherence of dual optical combs to the level of dozens of seconds, the present invention uses an all-fiber structure, significantly reducing costs and complexity, significantly increasing output power, significantly enhancing robustness and stability, and being easy to integrate, meeting the conditions for practical application development. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic structural diagram of a high-power, high-mutual-coherence dual optical comb spectroscopy system based on Raman gain modulation of the present invention.

[0027] Figure 2 is the time-domain 500 ms data and the interferogram after averaging the 500 ms data collected by a high-power, high-mutual-coherence dual optical comb spectroscopy system based on Raman gain modulation of the present invention.

[0028] Figure 3 is the radio frequency domain spectral information obtained by directly performing a Fourier transform on the time-domain 500 ms raw data collected by a high-power, high-mutual-coherence dual optical comb spectroscopy system based on Raman gain modulation of the present invention, as well as the detailed comb teeth after amplification.

[0029] Figure 4 is the spectral result after averaging the 500 ms data collected by a high-power, high-mutual-coherence dual optical comb spectroscopy system based on Raman gain modulation of the present invention, as well as the comparison between the experimentally measured gas absorption information and the simulation results of the HITRAN database.

[0030] Description of reference numerals:

[0031] 101-first mode-locked laser, 102-second mode-locked laser, 201-first rare-earth-doped fiber amplifier, 202-second rare-earth-doped fiber amplifier, 301-first coupler, 302-second coupler, 303-third coupler, 401-first Raman gain fiber, 402-second Raman gain fiber, 501-first optical splitter, 502-second optical splitter, 503-third optical splitter, 504-fourth optical splitter, 601-first photodetector, 602-second photodetector, 7-single-frequency laser, 8-acoustic-optic modulator, 9-target to be measured, 10-sampling device, A1-first output port, A2-second output port. DETAILED DESCRIPTION

[0032] The present invention is further described below with reference to an example and accompanying drawings, but this should not limit the protection scope of the present invention.

[0033] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0034] It should be noted that the terms used herein are intended only to describe specific embodiments and are not intended to be limiting. It should be understood that when a unit is referred to herein as being "connected" or "coupled" to another unit, it may be directly connected or coupled to the other unit, or an intermediate unit may exist. Conversely, when a unit is referred to herein as being "directly connected" or "directly coupled" to another unit, it indicates that there is no intermediate unit.

[0035] This example provides a high-power, high mutual coherence dual-comb spectroscopy system based on Raman gain modulation. The system structure is similar to Figure 1The same. The first mode-locked laser 101 and the second mode-locked laser 102 generate ultrafast pulses with different repetition frequencies, which are respectively coupled into the first rare-earth-doped fiber amplifier 201 and the second rare-earth-doped fiber amplifier 202 for chirped pulse amplification; the output laser of the single-frequency laser 7 is divided into two paths by the first optical splitter 501, and is respectively coupled with the two amplified ultrafast pulses into the first Raman gain fiber 401 and the second Raman gain fiber 402 through the first coupler 301 and the second coupler 302; in the first Raman gain fiber 401 and the second Raman gain fiber 402, due to the Raman gain modulation caused by stimulated Raman scattering, the single-frequency laser 7 is shaped into two high-power and highly coherent optical frequency combs; the second optical splitter 502 and the third optical splitter 503 are respectively used to separate the optical frequency combs generated by shaping from the remaining pump light, and the two remaining pump lights are respectively output from the first output port A1 and the second output port A2; in the separated dual optical comb optical path, one path is frequency-shifted by the acousto-optic modulator 8, and the other path maintains the original frequency transmission to avoid spectral aliasing of the dual optical combs; the third coupler 303 is used to combine the two dual optical combs, and the fourth optical splitter 504 is used to divide the combined dual combs into two groups, one group passes through the target under test 9, and after carrying the gas absorption information, it is detected by the first photodetector 601 as the signal path; the other group is directly detected by the second photodetector 602 as the reference path. Finally, the signal path and the reference path simultaneously use the sampling device 10 to collect data.

[0036] The first mode-locked laser 101 and the second mode-locked laser 102 with different repetition frequencies used are both erbium-doped mode-locked lasers, with repetition frequencies of about 102.3 MHz, center wavelengths of 1550 nm, and a repetition frequency difference of 2.2 kHz.

[0037] The first rare-earth-doped fiber amplifier 201 and the second rare-earth-doped fiber amplifier 202 used are both erbium-doped fiber amplifiers. They can amplify the ultrafast pulses output by the first mode-locked laser 101 and the second mode-locked laser 102 to an average power of 2 - 15 W.

[0038] The first coupler 301, the second coupler 302, and the third coupler 303 used are respectively a 1550 / 1645 nm wavelength division multiplexer, a 1550 / 1645 nm wavelength division multiplexer, and a 1645 nm optical coupler produced by LightPath Technologies.

[0039] The first Raman gain fiber 401 and the second Raman gain fiber 402 used are both small-core design silica-based fibers produced by OFS, with a length of 10 meters each.

[0040] The first optical splitter 501, the second optical splitter 502, the third optical splitter 503, and the fourth optical splitter 504 used are a 1550 / 1645 nm wavelength division multiplexer, a 1645 nm optical coupler, a 1550 / 1645 nm wavelength division multiplexer, and a 1645 nm optical coupler produced by LightBank Corporation respectively.

[0041] The single-frequency laser 7 used is a continuous laser with a central wavelength of 1645 nm and a line width of 200 kHz produced by LD-PD Corporation. The output power is 50 mW, and the tuning range is 5 nm.

[0042] The acousto-optic modulator 8 used is an acousto-optic modulator with an optimal frequency shift of 110 MHz produced by Gooch&Housego Corporation. When the frequency shift amount is adjusted within 90 - 130 MHz, the optical loss is less than 3 dB.

[0043] The target to be measured 9 used is a carbon dioxide hollow fiber absorption cell made by Fudan University and a methane spatial absorption cell produced by Futai Technology Corporation.

[0044] The first photodetector 601 and the second photodetector 602 used are DET01CFC indium gallium arsenide photodetectors produced by THORLABS.

[0045] The sampling device 10 used is a DSO-S254A oscilloscope produced by KEYSIGHT Corporation, which can provide a maximum sampling depth of 500 ms at a sampling rate of 200 MHz, or average up to 65536 times for a single interferogram.

[0046] The 1550 nm pulsed lasers output by the first mode-locked laser 101 and the second mode-locked laser 102 are amplified to 4 W by the first rare-earth doped fiber amplifier 201 and the second rare-earth doped fiber amplifier 202 respectively, and then are combined with the two beams of laser light output by the single-frequency laser 7 and split by the first optical splitter 501 and injected into the first Raman gain fiber 401 and the second Raman gain fiber 402 through the first coupler 301 and the second coupler 302. Through the gain modulation effect of stimulated Raman scattering, the single-frequency laser is shaped into an optical frequency comb centered at 1645 nm, with an output power of 2.2 W, a repetition frequency the same as that of the pump pulse at 102.3 MHz, and a repetition frequency difference also of 2.2 kHz. Considering the 15% fusion loss of the tails of the first Raman gain fiber 401, the second Raman gain fiber 402, the first coupler 301, and the second coupler 302, the conversion efficiency reaches 64.7%. The two remaining pump beams are separated by the second optical splitter 502 and the third optical splitter 503. In the separated two-frequency comb optical path, one path is frequency-shifted by the acousto-optic modulator 8, and the other path is transmitted at the original frequency. The third coupler 303 is used to combine the two two-frequency combs, and then the fourth optical splitter 504 is used to divide the combined double comb into two groups. One group passes through the target under test 9, and the double comb carrying the spectral absorption information of the target under test 9 is detected by the first photodetector 601 as the signal path; the other group is directly detected by the second photodetector 602 as the reference path; the sampling device 10 is used to collect and process the signal path and the reference path simultaneously, with a sampling rate of 200 MHz, collecting 500 ms of raw data, including 1090 interferogram information. After averaging the interferograms, a high signal-to-noise ratio interferogram is obtained, as Figure 2 shown. The raw data is directly Fourier-transformed to obtain radio frequency data. After amplification, the radio frequency comb teeth are obvious, as Figure 3 shown. The obtained radio frequency comb tooth linewidth is 2 Hz, corresponding to the resolution limit of 500 ms, indicating that the two-frequency comb of this system has high mutual coherence. After Fourier-transforming and averaging the radio frequency spectra of each interferogram and inverting back to the wavelength coordinate through the gas absorption line, the obtained spectral absorption information is as Figure 4As shown, the methane gas absorption rate can reach up to 80%, and the absorption width is as high as about 20 GHz; the absorption rates of multiple carbon dioxide gas absorption information are about 10%, and the absorption width is less than 2 GHz. The strong absorption information of methane at 1640.2 nm and 1642.9 nm and the weak absorption information of carbon dioxide at more than ten places such as 1642.2 nm are clearly visible, the spectral profile is smooth, and the signal-to-noise ratio reaches more than 30 dB. Compared with the simulation data of the HITRAN database for the absorption lines of methane and carbon dioxide gases, the absorption rate residual is lower than 0.8%. It is proved that the high-power and high mutual coherence dual optical frequency comb spectroscopy system based on Raman gain modulation of the present invention can generate high-power and high mutual coherence dual optical frequency combs, and can achieve fast multi-component gas spectroscopy detection with a wide spectral range, high spectral resolution, and on the order of hundreds of milliseconds without any feedback locking and correction algorithms.

Claims

1. A high-power and high mutual coherence dual optical comb spectroscopy system based on Raman gain modulation, characterized in that, Including a first mode-locked laser (101), a second mode-locked laser (102), a first rare-earth doped fiber amplifier (201), a second rare-earth doped fiber amplifier (202), a first coupler (301), a second coupler (302), a third coupler (303), a first Raman gain fiber (401), a second Raman gain fiber (402), a first optical splitter (501), a second optical splitter (502), a third optical splitter (503), a fourth optical splitter (504), a first photodetector (601), a second photodetector (602), a single-frequency laser (7), an acousto-optic modulator (8), a target to be measured (9), and a sampling device (10); The first mode-locked laser (101) and the second mode-locked laser (102) respectively generate ultrafast pulsed lasers with different repetition frequencies. After the two pulsed lasers are respectively chirped pulse amplified by the first rare-earth doped fiber amplifier (201) and the second rare-earth doped fiber amplifier (202), they are respectively coupled into the first Raman gain fiber (401) and the second Raman gain fiber (402) through the first coupler (301) and the second coupler (302) together with two continuous lasers output by the single-frequency laser (7) and split by the first optical splitter (501). In the first Raman gain fiber (401) and the second Raman gain fiber (402), the amplified pulsed laser serves as the pump light, and the pump light energy is transferred to the continuous laser wavelength through the stimulated Raman scattering effect to form Raman light, so that the two continuous lasers are respectively converted into two high-power and highly coherent optical frequency combs with the same repetition frequencies as the corresponding first mode-locked laser (101) and second mode-locked laser (102). After separating the two remaining pump lights from the second optical splitter (502) and the third optical splitter (503) and outputting them through the first output port and the second output port, in the two optical frequency combs, one is frequency-shifted by the acousto-optic modulator (8), and the other is transmitted at the original frequency to avoid spectral aliasing of the two optical frequency combs. Subsequently, the two optical frequency combs are combined by the third coupler (303) and divided into two groups by the fourth optical splitter (504). One group of optical paths passing through the target to be measured (9) is received by the first photodetector (601) to obtain the interference signal carrying the sample absorption information as the signal path; the other group of optical paths not passing through the target to be measured (9) is directly received by the second photodetector (602) to obtain the original interference signal as the reference path, and the interference signals of the signal path and the reference path are synchronously collected and processed by the sampling device (10).

2. The high-power, high mutual coherence dual optical comb spectroscopy system based on Raman gain modulation according to claim 1, wherein The first mode-locked laser (101) and the second mode-locked laser (102) are rare-earth doped mode-locked lasers. The first mode-locked laser (101) and the second mode-locked laser (102) respectively generate ultrafast pulsed lasers with different repetition frequencies, and the repetition frequency difference is 200 Hz to 10 kHz.

3. The high-power, high mutual coherence dual optical comb spectroscopy system based on Raman gain modulation according to claim 1, characterized in that, After the first rare-earth doped fiber amplifier (201) and the second rare-earth doped fiber amplifier (202) perform chirped pulse amplification processing on the input pump pulsed laser, the average power of the single-channel output pump pulsed laser is 2-15 W, and the pulse width is 1-100 ps.

4. The high-power, high mutual coherence dual optical comb spectroscopy system based on Raman gain modulation according to claim 1, characterized in that, The first coupler (301), the second coupler (302), the third coupler (303), the first optical splitter (501), the second optical splitter (502), the third optical splitter (503), and the fourth optical splitter (504) are wavelength division multiplexers or optical couplers.

5. The high-power, high mutual coherence dual optical comb spectroscopy system based on Raman gain modulation according to claim 1, wherein The first Raman gain fiber (401) and the second Raman gain fiber (402) are silicon-based fibers with a small core design, with a length of 1-20 meters. The pump light transfers energy to the Stokes light through stimulated Raman scattering, and the conversion efficiency can reach more than 60%. The single-channel average power of the generated optical frequency comb is 1-10 W, and its pulse width is 0.9-1 times that of the pump pulse width. The mutual coherence of the two optical frequency combs is manifested as the comb line width in the radio frequency domain of the interference signal being on the order of mHz, and the coherence time is greater than 30 seconds. High mutual coherence of the two optical frequency combs can be achieved without an active locking control unit.

6. The high-power, high mutual coherence dual optical comb spectroscopy system based on Raman gain modulation according to claim 1, wherein The line width of the single-frequency laser (7) ≤ 10 MHz, the wavelength tuning range ≥ 5 nm, and the output power ≥ 10 mW.

7. The high-power, high mutual coherence dual optical comb spectroscopy system based on Raman gain modulation according to claim 1, wherein The frequency shift amount generated by the acousto-optic modulator (8) is 10 MHz - 300 MHz, and it is used to avoid radio frequency spectrum information aliasing after frequency shifting.

8. The high-power, high mutual coherence dual optical comb spectroscopy system based on Raman gain modulation according to claim 1, characterized in that, The first photodetector (601) and the second photodetector (602) are indium gallium arsenide detectors with a bandwidth ≥ 500 MHz.

9. The high-power, high mutual coherence dual optical comb spectroscopy system based on Raman gain modulation according to claim 1, wherein The sampling device (10) is an oscilloscope or a data acquisition card, and the sampling rate ≥ 20 MHz.

10. The high-power and high mutual coherence dual optical comb spectroscopy system based on Raman gain modulation according to claim 1, characterized in that, All fiber devices in the system are polarization-maintaining devices.

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