Intermediate infrared continuous laser light source based on phonon spread spectrum and application thereof

Abstract

The invention discloses an intermediate infrared continuous laser light source based on phonon spread spectrum and application thereof, and belongs to the technical field of laser measurement. The device comprises an intermediate infrared continuous laser light source based on phonon spread spectrum, an electro-optical modulation module and a detection module. The intermediate infrared continuous laser light source comprises a pumping source, an isolator, an optical fiber wavelength division multiplexer, a first collimator, a focusing lens, a laser medium, a semiconductor cooler, a second collimator, a high-reflectivity fiber bragg grating and a low-reflectivity fiber bragg grating. The strong electron-phonon coupling effect of the II-VI group compound crystal doped with transition metal ions is utilized, so that phonons absorb energy generated by part of electrons in the transition process, correspondingly, energy originally transmitted to photons is reduced, the wavelength moves towards long waves, and broadening of an output spectrum in a middle-infrared band is achieved. According to the invention, intermediate infrared detection laser can be directly output, introduction of a near-infrared-intermediate infrared nonlinear frequency conversion process is not needed, and improvement of laser efficiency and detection precision is realized.

Description

Technical Field

[0001] The present invention relates to a mid-infrared continuous laser light source based on phonon spectral broadening and its applications, belonging to the technical field of laser measurement. Background Art

[0002] Continuous laser light sources with wavelength coverage in the mid-infrared band play an important role in the field of spectral measurement. The mid-infrared band covers the "fingerprint regions" of common greenhouse gas molecules such as CO 2 , N 2 O. In this band, the absorption line strength of greenhouse gas molecules can reach the order of 10 -19 , which is nearly 4 orders of magnitude higher than that in the near-infrared band. Based on the mid-infrared continuous laser light source, numerous sidebands can be generated around the carrier of the mid-infrared output light through electro-optic modulation. The interval between the sidebands is the frequency of the modulation signal, forming an electro-optically modulated optical frequency comb, simply referred to as an electro-optic comb. The electro-optic comb can accurately and rapidly adjust its repetition frequency by changing the frequency of the driving signal to meet the parameter requirements such as resolution, range, and dynamic range needed in different measurement scenarios. Therefore, the electro-optically modulated optical frequency comb based on the mid-infrared laser light source has wide applications in the field of precision measurement of gas absorption spectra and can provide strong support for greenhouse gas monitoring, atmospheric monitoring, and green agriculture under required conditions.

[0003] Currently, several mainstream technical solutions for realizing mid-infrared optical frequency combs include:

[0004] 1) Based on optical parametric oscillation (OPO) technology

[0005] The optical parametric oscillation technology uses the second-order nonlinear effect to convert near-infrared incident light into mid-infrared signal light and idler light, and then by introducing a resonant cavity, at least one of the two output lights generates resonance, resulting in amplitude gain of the signal light and idler light, which is applicable to the field of laser spectroscopy. The limitation of this technology is that the resonant cavity used will introduce additional optical phase noise, so it is difficult to achieve high signal-to-noise ratio and high-resolution gas molecular spectroscopy measurement.

[0006] 2) Based on difference frequency generation (DFG) technology

[0007] The optical difference frequency generation technology uses two near-infrared lasers with different frequencies to simultaneously enter a nonlinear crystal, and uses the second-order nonlinear effect of the nonlinear crystal to generate mid-infrared difference frequency light. The limitation of this technology is that the mid-infrared laser generation process must satisfy phase matching or quasi-phase matching, and the laser conversion efficiency is limited.

[0008] 3) Based on quantum cascade laser (QCL) technology

[0009] The working principle of quantum cascade laser technology is that electrons jump between sub-bands of the conduction band of semiconductor materials and tunnel with the assistance of phonon resonance to generate light amplification, and its emission wavelength is determined by the energy difference between the sub-bands of the conduction band. This technology is still in the development stage, and it is still difficult to realize broadband mid-infrared optical frequency comb suitable for outdoor use.

[0010] In summary, the mid-infrared optical comb systems currently used for spectral measurement have more or less technical deficiencies and defects in terms of system complexity and conversion efficiency. Summary of the invention

[0011] The purpose of the present invention is to provide a mid-infrared continuous laser light source and an electro-optical modulation optical frequency comb spectrum measurement device based on phonon spectrum expansion, and also to provide a method for measuring gas absorption spectrum based on electro-optical modulation optical frequency comb based on phonon spectrum expansion, which utilizes the strong electron-phonon coupling effect of transition metal ion-doped II-VI compound crystals to make the electrons and phonons in the lattice widen the spectrum through strong coupling during the transition process, and provide a wider gain bandwidth in the mid-infrared region. This method can directly output mid-infrared detection laser without the introduction of nonlinear frequency conversion process, thereby improving laser efficiency and detection accuracy.

[0012] The objective of the present invention is achieved through the following technical solutions:

[0013] The present invention discloses a mid-infrared continuous laser light source based on phonon spectrum expansion, comprising a pump source, an isolator, an optical fiber wavelength division multiplexer, a first collimator, a focusing lens, a laser medium, a semiconductor refrigerator, a second collimator, a high-reflection optical fiber grating and a low-reflection optical fiber grating;

[0014] The pump light emitted by the pump source passes through the isolator and the fiber wavelength division multiplexer in sequence, and is irradiated on the laser medium via the first collimator and the focusing lens. The temperature of the laser medium is regulated by the semiconductor refrigerator. The formed 4-5μm mid-infrared laser is converged and input into the optical fiber via the second collimator. The mid-infrared laser of a specific wavelength oscillates back and forth between the high-reflection fiber grating and the low-reflection fiber grating with frequency selection effect, passes through the laser medium for many times to realize the light amplification of stimulated radiation, and finally outputs high-power 4-5μm mid-infrared laser through the transmission of the low-reflection fiber grating.

[0015] Furthermore, the pump source is a continuous laser light source emitting 2.8 μm; a II-VI compound crystal doped with transition metal ions having a strong electron-phonon coupling effect is selected, Fe 2+ : ZnSe crystal, the two light-transmitting ends of the crystal are plated with 2.8μm and 4-5μm anti-reflection dielectric films;

[0016] The high-reflection fiber grating has a reflectivity of 99% to 4 μm wavelength laser, and the low-reflection fiber grating has a reflectivity of 80% to 4 μm wavelength laser.

[0017] Furthermore, a semiconductor cooler is used to control the temperature of the laser medium. As the lattice constant of the laser medium increases, the electron-phonon coupling strength increases, that is, the number of phonons participating in spectral broadening increases. The central wavelength of the light source output shifts to the long wavelength as the temperature rises, realizing tunable laser output with temperature control.

[0018] Furthermore, according to the multi-phonon transition theory, compared with free atoms, there is an interaction between the electrons of the laser-activated ions in the laser medium and the surrounding lattice. Under the Condon approximation, for the transition process of electrons between two energy levels i and j with energy E j >E i , its transition probability is mainly determined by the overlap integral of the atomic vibration wave functions, that is,

[0019]

[0020] where Av represents the statistical average over the phonon states n of the initial electronic energy level j according to the thermal distribution, M represents the electric dipole moment, the energy conservation of the transition process is ensured by the δ function, χ represents the phonon wave function, n s and n' s are the phonon numbers, Q s is the normal coordinate of each vibration mode, and represent the displacements of the lattice atoms relative to the equilibrium position in different electronic states, W ji represents the energy difference between electrons in different energy levels, is the phonon energy.

[0021] The laser emission spectrum generated by the strong electron-phonon coupling effect should contain a series of spectral lines with energy , p is the net number of phonons changed in the transition process, and the spectral line function is described by the following formula

[0022]

[0023] where S describes the magnitude of the electron-phonon coupling strength and represents the effective number of participating phonons in the coupling process. For laser-activated ions with strong electron-phonon coupling strength, the S factor increases as the distance between lattice atoms increases. Therefore, as the temperature rises, the lattice constant continuously increases, the effective number of participating phonons S in the coupling process increases, and the corresponding laser output wavelength shifts to the long wavelength. Therefore, by controlling the operating temperature of the laser medium with the semiconductor cooler, the output wavelength tuning of the mid-infrared laser source is realized.

[0024] An electro-optic modulation optical frequency comb spectroscopy device based on phonon spectral broadening disclosed by the present invention is realized based on the mid-infrared continuous laser light source based on phonon spectral broadening. An electro-optic modulation optical frequency comb spectroscopy device based on phonon spectral broadening includes a mid-infrared continuous laser light source based on phonon spectral broadening, an electro-optic modulation module, and a detection module.

[0025] The output mid-infrared laser is used as seed light and is divided into two beams by a 1×2 fiber splitter. The first beam of seed light is transmitted along the first path into the first electro-optic modulator, and the second beam of seed light is transmitted along the second path into the second electro-optic modulator to form an electro-optic comb. The modulation signals of the two electro-optic modulators are provided by a radio frequency signal source. By adjusting the radio frequency signal source, the two electro-optic frequency combs are set to have a small repetition frequency difference, which are respectively used as the probe light and the local oscillator light. The two beams of electro-optic frequency combs are combined by a 50:50 fiber coupler and divided into two paths. One path passes through the sample gas cell as the signal to be measured, and the other path serves as the reference signal.

[0026] The gas detection module includes a 2×2 fiber coupler, a sample gas cell, a first photodetector, a second photodetector, and a data acquisition device. The first photodetector and the second photodetector are used to detect the two interference signals, and the data acquisition device is used to record the radio frequency optical comb generated after beat frequency, so as to obtain the detection data.

[0027] Furthermore, the fiber coupler adopts fluoride fiber to reduce the transmission loss of mid-infrared laser.

[0028] A method for measuring gas absorption spectrum by electro-optic modulation optical frequency comb based on phonon spectral broadening disclosed by the present invention is realized based on the electro-optic modulation optical frequency comb spectroscopy device based on phonon spectral broadening. A method for measuring gas absorption spectrum by electro-optic modulation optical frequency comb based on phonon spectral broadening: select the composition of the gas to be measured, determine the central wavelength of the mid-infrared femtosecond laser for measurement, adjust the optical path to obtain the beat frequency measurement signal, and through the spectral down-conversion technology of Fourier transform, convert the measurement signal to the radio frequency spectral region that is easy to detect, so as to obtain the absorption spectrum within the passband of the measurement signal. After verification by comparison with the HITRAN database, calculate the absorbance in the measurement path, and according to Beer's law, combine the traversal algorithm to calculate the concentration of the gas in the path.

[0029] Furthermore, at the detection end, the spectrum is divided into several spectral bands and combined with several detectors for parallel detection. For different absorption spectral regions of the product to be measured, filters with different bandwidths and central wavelengths are selected to reduce the spectral width of the spectrum to be measured and ensure the spectral resolution and sampling rate of the system.

[0030] Beneficial effects:

[0031] 1. A mid-infrared continuous laser source based on phonon spectral broadening and its application disclosed by the present invention utilize the strong electron-phonon coupling characteristic of a laser medium to broaden the intrinsic output wavelength of the laser medium and directly form a 4-5 μm mid-infrared laser output. Compared with the commonly used near-infrared to mid-infrared non-linear frequency conversion method, it can obtain a more efficient laser output and improve the spectral detection efficiency.

[0032] 2. A mid-infrared continuous laser source based on phonon spectral broadening and its application disclosed by the present invention, based on the principle of strong electron-phonon coupling, uses a semiconductor cooler to control the operating temperature of the laser medium and regulate the effective phonon participation number. Compared with the method of replacing non-linear crystals, it can more conveniently achieve wavelength adjustment and reduce the device cost.

[0033] 3. A mid-infrared continuous laser source based on phonon spectral broadening and its application disclosed by the present invention uses an electro-optically modulated continuous laser as a frequency comb light source for spectroscopy. Compared with the frequency comb based on mode-locked pulsed lasers in traditional technologies, it has a simple structure, avoids the introduction of a complicated frequency locking process. More importantly, the electro-optic frequency comb can accurately and quickly adjust the repetition frequency to meet the parameter requirements such as resolution, range, and dynamic range required for measurement.

[0034] 4. A mid-infrared continuous laser source based on phonon spectral broadening and its application disclosed by the present invention uses dual-comb spectroscopy, makes full use of the advantages of the optical comb, can obtain molecular broadband spectral information in real time in a system without mechanical scanning components, and has characteristics such as high signal-to-noise ratio and high resolution, which is conducive to realizing high-resolution and high-signal-to-noise ratio gas absorption spectral measurement.

[0035] 5. A mid-infrared continuous laser source based on phonon spectral broadening and its application disclosed by the present invention, on the basis of achieving the above beneficial effects 1, 2, 3, and 4, obtains gas concentration information by detecting the gas absorption spectrum, and can be used for applications such as greenhouse gas monitoring, atmospheric monitoring, and green agriculture under the required conditions. Description of the Drawings

[0036] Figure 1 It is a schematic diagram of the composition of a mid-infrared continuous laser source based on phonon spectral broadening.

[0037] Among them, 1 - pump source, 2 - isolator, 3 - high-reflection fiber grating, 4 - fiber wavelength division multiplexer, 5 - first collimator, 6 - focusing lens, 7 - laser medium, 8 - semiconductor cooler, 9 - second collimator, 10 - low-reflection fiber grating.

[0038] Figure 2 It is a schematic diagram of the composition of the electro-optic modulation module and the detection module.

[0039] Among them, 11 - 1×2 optical fiber splitter, 12 - first electro-optic modulator, 13 - first pulse generator, 14 - first radio frequency signal source, 15 - second electro-optic modulator, 16 - second pulse generator, 17 - second radio frequency signal source, 18 - 2×2 fiber coupler, 19 - sample gas cell, 20 - first photodetector, 21 - second photodetector, 22 - data acquisition device.

[0040] Figure 3 It is a schematic diagram of an electro-optic frequency comb formed after the mid-infrared continuous laser source is modulated by the electro-optic modulator. Detailed implementation mode

[0041] To better illustrate the purpose and advantages of the present invention, the following further describes the content of the invention in conjunction with the drawings and examples.

[0042] Example 1:

[0043] A mid-infrared continuous laser source based on phonon spectral broadening and its application disclosed in this embodiment include a mid-infrared continuous laser source, an electro-optic modulation module, and a detection module. The mid-infrared continuous laser source is as Figure 1 shown, including a pump source 1, an isolator 2, a high-reflection fiber grating 3, an optical fiber wavelength division multiplexer 4, a first collimator 5, a focusing lens 6, a laser medium 7, a semiconductor refrigerator 8, a second collimator 9, and a low-reflection fiber grating 10. The electro-optic modulation module is as Figure 2 shown, including: 1×2 optical fiber splitter 11, first electro-optic modulator 12, first pulse generator 13, first radio frequency signal source 14, second electro-optic modulator 15, second pulse generator 16, second radio frequency signal source 17, 2×2 fiber coupler 18, sample gas cell 19, first photodetector 20, second photodetector 21, and data acquisition device 22.

[0044] First, select a II-VI group compound crystal doped with transition metal ions with a strong electron-phonon coupling effect. Since the electron arrangement of the 3d orbital energy level on which the transition metal ions depend for luminescence is in the outermost layer, it is easily affected by the surrounding lattice vibration. Therefore, phonons can absorb a part of the energy generated during the electron transition, and the energy transmitted to the photon decreases accordingly, and the wavelength moves towards the long wave, that is, the strong electron-phonon coupling effect will lead to the expansion of the laser gain spectrum, thereby providing a wider laser emission bandwidth in the mid-infrared region. This process avoids the introduction of near-infrared to mid-infrared non-linear frequency conversion, and can achieve the improvement of laser efficiency and the simplification of the optical path.

[0045] According to the multi-phonon transition theory, compared with free atoms, there is an interaction between the electrons of the laser-activated ions in the laser medium and the surrounding lattice. Under the Condon approximation, for the energy E of the electron transition process between the i and j energy levelsj >E i , its transition probability is mainly determined by the overlap integral of atomic vibration wave functions, that is,

[0046]

[0047] where Av represents the statistical average over the phonon states n of the initial electronic energy level j according to the thermal distribution, M represents the electric dipole moment, the energy conservation of the transition process is ensured by the δ function, χ represents the phonon wave function, n s and n' s are the phonon numbers, Q s is the normal coordinate of each vibration mode, and represent the displacements of the lattice atoms relative to the equilibrium position in different electronic states, W ji represents the energy difference between electrons in different energy levels, is the phonon energy.

[0048] The laser emission spectrum generated by the strong electron-phonon coupling effect should contain a series of spectral lines with energy , p is the net number of phonons changed during the transition process, and the spectral line function is described by the following formula

[0049]

[0050] where S describes the magnitude of the electron-phonon coupling strength and represents the effective number of participating phonons in the coupling process. For activator ions with strong electron-phonon coupling strength, the S factor increases as the distance between lattice atoms increases.

[0051] Therefore, by regulating the operating temperature of the laser medium through the semiconductor cooler, when the temperature is increased from 92K to 211K, the lattice constant of the laser medium continuously increases, the S factor of the effective number of participating phonons in the coupling process increases, and the central wavelength of the light source output moves from 4150nm to 4600nm, realizing temperature-tuned mid-infrared laser output.

[0052] A dual-comb system with a small repetition frequency difference is built using an electro-optic modulation module. After the two electro-optic frequency combs are combined, they are divided into two paths: the signal to be measured and the reference signal. An optoelectronic detector is used to detect the interference signals of the two paths, and a data acquisition device is used to obtain the detection data. Since they have different repetition frequencies and adjustable optical paths, stationary pulses and scanning pulses can be formed. Fourier transform of the detected time-domain correlation interferogram can obtain the projection of the spectrum in the frequency domain. The obtained absorption spectrum is compared with the dual-comb beat frequency background map to obtain the absorption peak distribution map; the Voigt line shape function is used to fit the absorption peak distribution map to obtain all absorption peak models; the baseline of the curve is fitted, and the fitted absorption peaks are compared with the spectral baseline, and the area of each absorption peak is calculated to obtain its integrated absorbance. According to the line intensity corresponding to the absorption peak in this band in the HITRAN database, the concentration of the measured gas can be obtained.

[0053] A mid-infrared continuous laser light source based on phonon spectrum broadening and its application device for optical frequency comb spectroscopy disclosed in this embodiment are specifically implemented as follows:

[0054] The resonant cavity of the mid-infrared continuous laser light source is composed of a high-reflection fiber grating 3 with a frequency selection function and a low-reflection fiber grating 10. The high-reflection fiber grating 3 has a reflectivity of 99% for 4-μm wavelength laser, and the low-reflection fiber grating 10 has a reflectivity of 80% for 4-μm wavelength laser. The 2.8-μm pump light emitted by the pump source 1 sequentially passes through the isolator 2 and the fiber wavelength division multiplexer 4, and is irradiated on the laser medium 7 through the first collimator 5 and the focusing lens 6 with a focal length of 50 mm. The temperature of the laser medium is regulated by the semiconductor cooler 8. The formed 4-5-μm mid-infrared laser is converged by the second collimator 9 and input into the fiber. The mid-infrared laser with a specific wavelength oscillates back and forth between the high-reflection fiber grating 3 with a frequency selection function and the low-reflection fiber grating 10, and passes through the laser medium multiple times to realize the optical amplification of stimulated emission. Finally, high-power 4-5-μm mid-infrared laser is transmitted and output through the low-reflection fiber grating.

[0055] Select a group II-VI compound crystal doped with transition metal ions with strong electron-phonon coupling effect, Fe 2+ :ZnSe crystal, Fe 2+ :ZnSe crystal is coated with an anti-reflection medium film of 2.8 μm and 4-5 μm on both light-passing end faces.

[0056] The temperature of the laser medium is regulated by the semiconductor cooler. As the lattice constant of the laser medium increases, the electron-phonon coupling strength increases, that is, the more phonons participate in the spectrum broadening, and the central wavelength of the light source output shifts to the long wave with the increase of temperature, realizing the tunable laser output of temperature regulation.

[0057] The output mid-infrared laser, as the seed light, is split into two beams by a 1×2 fiber optic splitter. The first beam of seed light is transmitted into the first electro-optic modulator through the first path, and the second beam of seed light is transmitted into the second electro-optic modulator through the second path, forming an electro-optic comb( Figure 3 ). The modulation signals of the two electro-optic modulators are provided by a radio frequency signal source. By adjusting the radio frequency signal source, the two electro-optic frequency combs are set to have a small repetition frequency difference, which are respectively used as the probe light and the local oscillator light. The two beams of electro-optic frequency combs are combined by a 50:50 fiber optic coupler and divided into two paths. One path passes through the sample gas cell as the signal to be measured, and the other path serves as the reference signal.

[0058] The component of the gas to be measured is selected, the central wavelength of the mid-infrared femtosecond laser for measurement is determined, the optical path is adjusted to obtain the beat frequency measurement signal, and through the spectral down-conversion technology of Fourier transform, the measurement signal is converted to the radio frequency spectral region that is easy to detect, so as to obtain the absorption spectrum within the passband of the measurement signal. After verification by comparison with the HITRAN database, the absorbance in the measurement path is calculated, and according to Beer's law, the concentration of the gas in the path is calculated by combining the traversal algorithm.

[0059] The above specific description further details the purpose, technical solution and beneficial effects of the invention. It should be understood that the above is only a specific embodiment of the present invention and is not used to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A mid-infrared continuous laser light source based on phonon spectrum expansion, characterized in that: It includes a pump source, an isolator, a fiber wavelength division multiplexer, a first collimator, a focusing lens, a laser medium, a semiconductor refrigerator, a second collimator, a high-reflection fiber Bragg grating and a low-reflection fiber Bragg grating; The pump light emitted by the pump source passes through the isolator and the fiber wavelength division multiplexer in sequence, and is irradiated on the laser medium via the first collimator and the focusing lens. The temperature of the laser medium is regulated by the semiconductor refrigerator. The formed 4-5μm mid-infrared laser is converged and input into the optical fiber via the second collimator. The mid-infrared laser of a specific wavelength oscillates back and forth between the high-reflection fiber grating and the low-reflection fiber grating with frequency selection effect, passes through the laser medium many times, realizes the light amplification of stimulated radiation, and finally outputs high-power 4-5μm mid-infrared laser through the transmission of the low-reflection fiber grating.

2. A mid-infrared continuous laser light source based on phonon spectrum expansion as claimed in claim 1, characterized in that: The pump source is a continuous laser light source emitting 2.8μm laser; the II-VI compound crystal doped with transition metal ions with strong electron-phonon coupling effect is selected, Fe 2+ : ZnSe crystal, the two end surfaces of the crystal through light are plated with 2.8μm and 4-5μm anti-reflection medium films; the high-reflection fiber grating has a reflectivity of 99% for 4μm wavelength laser, and the low-reflection fiber grating has a reflectivity of 80% for 4μm wavelength laser.

3. A mid-infrared continuous laser light source based on phonon spectrum expansion as claimed in claim 1, characterized in that: The temperature of the laser medium is controlled by a semiconductor cooler. The increase in temperature will cause the lattice constant of the laser medium to increase, and the electron-phonon coupling strength to increase. Correspondingly, more phonons will participate in the spectrum expansion, and the central wavelength of the light source output will shift toward a longer wave as the temperature increases, thus obtaining a temperature-controlled tunable laser output.

4. A mid-infrared continuous laser light source based on phonon spectrum expansion as claimed in claim 3, characterized in that: According to the multi-phonon transition theory, compared with free atoms, the electrons of the activated ions in the laser medium interact with the surrounding lattice. Under the Condon approximation, the energy E of the transition process between the i and j energy levels is j >E i , and its transition probability is mainly determined by the overlap integral of the atomic vibration wave function, that is, Among them, Av represents the statistical average of each phonon state n of the initial electronic energy level j according to the thermal distribution, M represents the electric dipole moment, and the energy conservation of the transition process is guaranteed by the δ function, χ represents the wave function of the phonon, and n s and n' s is the number of phonons, Q s are the normal coordinates of each vibration mode, and Represents the displacement of lattice atoms in different electronic states relative to the equilibrium position, W ji represents the energy difference between electrons at different energy levels. is the phonon energy; The laser emission spectrum generated by the strong electron-phonon coupling effect should contain A series of spectral lines, p is the net number of phonons changed during the transition, and the spectral line function is described by the following formula Among them, S describes the magnitude of the electron-phonon coupling strength and represents the number of effective phonons participating in the coupling process. For laser media with strong electron-phonon coupling strength, the S factor increases with the distance between lattice atoms. Therefore, as the temperature increases, the lattice constant continues to increase, the number of effective phonons participating in the coupling process S increases, and the corresponding laser output wavelength moves toward the long wave. Therefore, the operating temperature of the laser medium is regulated by the semiconductor refrigerator to achieve output wavelength tuning of the mid-infrared laser light source.

5. A spectroscopy device based on electro-optical modulation optical frequency comb phonon spreading, which is realized based on a mid-infrared continuous laser light source based on phonon spreading as claimed in claim 1, 2 or 3, characterized in that: It includes a mid-infrared continuous laser light source, an electro-optical modulation module, and a detection module based on phonon spectrum expansion; The output mid-infrared laser is used as seed light and is divided into two beams via a 1×2 fiber beam splitter. The first seed light is transmitted from a first path into a first electro-optic modulator, and the second seed light is transmitted from a second path into a second electro-optic modulator to form an electro-optic comb. The modulation signals of the two electro-optic modulators are provided by a radio frequency signal source. By adjusting the radio frequency signal source, the two electro-optic frequency combs are set to have a small repetition frequency difference, which are used as detection light and local oscillator light respectively; the two electro-optic frequency combs are combined by a 50:50 optical fiber coupler and divided into two paths, one of which passes through the sample gas chamber as the signal to be measured, and the other as the reference signal; The gas detection module includes a 2×2 optical fiber coupler, a sample gas chamber, a first photodetector, a second photodetector, and a data acquisition device; the first photodetector and the second photodetector are used to detect two interference signals, and the data acquisition device is used to record the radio frequency light comb generated after the beat frequency, so as to obtain detection data.

6. The electro-optical modulation optical frequency comb spectrum measurement device based on phonon spectrum spreading according to claim 5, characterized in that: The optical fiber coupler adopts fluoride optical fiber to reduce the transmission loss of mid-infrared laser.

7. A method for measuring gas absorption spectrum by an electro-optical modulation optical frequency comb spectrometer based on phonon spectrum expansion, which is implemented based on an electro-optical modulation optical frequency comb spectrometer based on phonon spectrum expansion as claimed in claim 5 or 6, characterized in that: The gas composition to be measured is selected, the central wavelength of the mid-infrared femtosecond laser used for measurement is determined, the optical path is adjusted to obtain the beat frequency measurement signal, and the measurement signal is converted to an easily detectable radio frequency spectrum band through Fourier transform spectral down-conversion technology, thereby obtaining the absorption spectrum within the passband of the measurement signal; after comparison and verification with the HITRAN database, the absorbance in the measurement path is calculated, and the concentration of the path gas is calculated based on Beer's law combined with the traversal algorithm.

8. The method for measuring gas absorption spectrum using an electro-optical modulation optical frequency comb spectrometer based on phonon spectrum expansion according to claim 7, characterized in that: At the detection end, the spectrum is divided into several spectral segments and combined with several detectors for parallel detection. According to the different absorption spectrum regions of the products to be measured, filters with different bandwidths and central wavelengths are selected to reduce the width of the spectrum to be measured and ensure the spectral resolution and sampling rate of the system.

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