A tuning fork type optical fiber photoacoustic spectrum detection method and device

Abstract

The application discloses a tuning fork type optical fiber photoacoustic spectrum detection method and device, and belongs to the technical field of spectrum detection, which comprises a tuning fork, a first detection optical fiber and a second detection optical fiber, the tuning fork is arranged in a to-be-detected gas environment, and the two detection optical fibers respectively form Fabry-Perot cavities with the outer surfaces of two vibration arms of the tuning fork. The method comprises the following steps: after modulating excitation laser, the modulated excitation laser is incident to the gap between the two vibration arms of the tuning fork, and the to-be-detected gas absorbs the modulated excitation laser to generate a photoacoustic signal; the photoacoustic signal drives the two vibration arms of the tuning fork to generate mechanical vibration, so that the cavity lengths of the two Fabry-Perot cavities change; the change amounts of the corresponding reflected interference spectra of the two Fabry-Perot cavities when the cavity lengths change are detected respectively, the change amounts of the two obtained reflected interference spectra are added, a harmonic signal is extracted, and the concentration information of the to-be-detected gas is inversely calculated through the amplitude of the harmonic signal. The spectrum detection method and device are high in sensitivity, high in accuracy, low in cost, easy to integrate, capable of resisting electromagnetic interference and suitable for long-distance detection.

Description

Technical Field

[0001] This invention belongs to the field of spectral detection technology, and more specifically, relates to a tuning fork fiber photoacoustic spectral detection method and device. Background Technology

[0002] Gas detection has wide applications in numerous fields, including environmental monitoring, aerospace, energy exploration, power systems, and medical diagnostics. Laser absorption spectroscopy-based gas detection technology offers advantages such as high detection sensitivity, strong resistance to cross-interference, and short response time. Compared to traditional direct laser absorption spectroscopy, indirect laser absorption spectroscopy technology is even more advantageous.

[0003] Photoacoustic spectroscopy based on quartz tuning forks, as an indirect laser absorption spectroscopy technique, offers advantages such as small size and strong resistance to external noise. However, existing tuning fork photoacoustic spectroscopy methods generally utilize the piezoelectric effect of quartz to convert the vibration displacement of the tuning fork into a measurable current signal, making them susceptible to electromagnetic interference and unable to achieve long-distance gas detection. Regarding gas detection performance, some methods employ simultaneous detection with two tuning forks to multiply the photoacoustic signal; however, because it is difficult to ensure that the two tuning forks have completely equal resonant frequencies, the enhancement factor of the photoacoustic signal is less than two times. Furthermore, some existing techniques can only detect the displacement of one arm of the tuning fork, thus limiting further improvements in detection sensitivity; simultaneously, this method of detecting only the displacement of one arm cannot suppress noise interference in the detection environment, increasing measurement inaccuracies.

[0004] Furthermore, quartz tuning forks are difficult to integrate with other devices, resulting in low integration and poor stability of gas sensors. Moreover, compared to standard commercial quartz tuning forks, the manufacturing process for custom quartz tuning forks is extremely complex and expensive; while standard commercial quartz tuning forks have a high resonant frequency, making them ineffective for detecting gases with low relaxation rates (such as CO and CH4). Additionally, the 300μm gap between the arms of a standard quartz tuning fork makes it difficult for the beam to pass through the gap without contact when using excitation sources with poor beam quality, such as LEDs, fiber amplifiers, mid-infrared light sources, and terahertz light sources, thus generating significant background noise. Summary of the Invention

[0005] In view of the shortcomings of the existing technology and the need for improvement, the present invention provides a tuning fork fiber photoacoustic spectroscopy detection method and device, the purpose of which is to improve the sensitivity and accuracy of spectral detection.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a tuning fork-type fiber optic photoacoustic spectroscopy detection method is provided, comprising a tuning fork, a first probe fiber, and a second probe fiber. The tuning fork is disposed in a gas environment to be tested. One end face of the first probe fiber and the outer surface of one vibrating arm of the tuning fork form a first Fabry-Perot cavity, and one end face of the second probe fiber and the outer surface of the other vibrating arm of the tuning fork form a second Fabry-Perot cavity. The photoacoustic spectroscopy detection method includes: S1. After the excitation laser is modulated, it is incident on the gap between the two arms of the tuning fork. The gas to be tested absorbs the modulated excitation laser and generates a photoacoustic signal. The photoacoustic signal drives the two arms of the tuning fork to generate mechanical vibration, causing the cavity lengths of the two Fabry-Perot cavities to change. The two Fabry-Perot cavities are the first Fabry-Perot cavity and the second Fabry-Perot cavity. S2. Detect the changes in the reflection interference spectra corresponding to the changes in the cavity length of the two Fabry-Perot cavities from the other ends of the first and second detection fibers, respectively. Add the changes in the two reflection interference spectra, extract the harmonic signal of the added changes, and infer the concentration information of the gas to be measured from the amplitude of the harmonic signal; wherein, the changes in the reflection interference spectra are either intensity changes or phase changes.

[0007] Furthermore, in S1, if the modulation of the excitation laser is wavelength modulation, then the modulation frequency of the excitation laser is half of the resonant frequency of the tuning fork; in S2, the harmonic signal is a second harmonic signal. In S1, if the modulation of the excitation laser is intensity modulation, then the modulation frequency of the excitation laser is consistent with the resonance frequency of the tuning fork; in S2, the harmonic signal is a first harmonic signal.

[0008] Furthermore, if the modulation of the excitation laser is wavelength modulation, it also includes: Under the same gas concentration, the modulation depth of the excitation laser is scanned, and the optimal modulation depth of the excitation laser is obtained when the amplitude of the second harmonic signal is the largest; the excitation laser is modulated using the optimal modulation depth.

[0009] Furthermore, it also includes: Under the same gas concentration, by changing the excitation position of the excitation laser, the optimal excitation position of the excitation laser is obtained when the amplitude of the harmonic signal is at its maximum; the tuning fork is then excited using the optimal excitation position.

[0010] According to a second aspect of the present invention, a tuning fork-type fiber optic photoacoustic spectroscopy detection device is provided, characterized in that it is used to perform the spectral detection method according to any one of the first aspects, wherein the spectral detection device comprises: a tuning fork, a first detection fiber, a second detection fiber, an excitation laser modulation module, and a fiber optic interferometry detection module. The tuning fork is placed in the gas environment to be tested. One end face of the first detection optical fiber and the outer surface of one arm of the tuning fork form a first Fabry-Perot cavity, and one end face of the second detection optical fiber and the outer surface of the other arm of the tuning fork form a second Fabry-Perot cavity. The excitation laser modulation module is used to modulate the excitation laser and incident it into the gap between the two arms of the tuning fork. The gas to be tested absorbs the modulated excitation laser and generates a photoacoustic signal. The photoacoustic signal drives the two arms of the tuning fork to produce mechanical vibration, causing the cavity lengths of the two Fabry-Perot cavities to change. The two Fabry-Perot cavities are the first Fabry-Perot cavity and the second Fabry-Perot cavity. The fiber optic interferometric detection module is used to detect the changes in the reflected interference spectra corresponding to the changes in the cavity lengths of the two Fabry-Perot cavities from the other ends of the first and second detection fibers, respectively. After adding the changes in the two reflected interference spectra, the harmonic signal of the added changes is extracted, and the concentration information of the gas to be measured is inferred from the amplitude of the harmonic signal. The changes in the reflected interference spectra are either changes in intensity or changes in phase.

[0011] Furthermore, it also includes a fixing structure; the fixing structure includes a housing, a first ceramic ferrule, and a second ceramic ferrule; The outer shell is integrated with the tuning fork; the outer shell has through holes, the centers of which are respectively aligned with the two arms of the tuning fork; the first ceramic insert and the second ceramic insert pass through the through holes and are fixed to the outer shell. One end of the first detection optical fiber passes through the first ceramic ferrule and forms a first Fabry-Perot cavity with the outer surface of one vibrating arm of the tuning fork, and the other end is connected to the optical fiber interferometric detection module. One end of the second detection optical fiber passes through the second ceramic ferrule and forms a second Fabry-Perot cavity with the outer surface of the other vibrating arm of the tuning fork, and the other end is connected to the optical fiber interferometric detection module.

[0012] Furthermore, the fixing structure also includes a first ceramic sleeve and a second ceramic sleeve fixed to the outer casing through the through hole; The first ceramic insert is inserted into the first ceramic sleeve, and the second ceramic insert is inserted into the second ceramic sleeve.

[0013] Furthermore, the center of the through hole is aligned with the top of the two arms of the tuning fork.

[0014] Furthermore, the tuning fork is made of metal and manufactured using machining.

[0015] Furthermore, it also includes a collimator for collimating the modulated excitation laser.

[0016] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: (1) The tuning fork-type fiber photoacoustic spectroscopy detection method of the present invention forms two Fabry-Perot cavities by connecting the first and second detection fibers to the outer surfaces of the two arms of the tuning fork, respectively. Since the photoacoustic signal is generated in the middle of the arms of the tuning fork, it drives the two arms of the tuning fork to vibrate in opposite directions, causing the cavity lengths of the two Fabry-Perot cavities to change, producing the same amount of change. Meanwhile, the noise in the outside world that is consistent with the resonance frequency of the tuning fork causes the two arms of the tuning fork to vibrate in the same direction, causing the changes in the cavity lengths of the two Fabry-Perot cavities to increase and decrease respectively. At this time, the intensity change or phase change of the reflection interference spectrum corresponding to the change in the cavity length of the two Fabry-Perot cavities is detected, and the changes are added together. In this way, a multiplied harmonic signal can be obtained using only a single tuning fork. When the gas to be tested is detected based on the multiplied harmonic signal, the detection sensitivity can be improved, and the noise interference in the detection environment can be suppressed, thereby improving the detection accuracy.

[0017] Meanwhile, this invention uses a tuning fork as a photoacoustic transducer and employs fiber optic Fabry-Perot interferometry to measure the vibration of the tuning fork, avoiding the traditional electrical detection method that relies on the piezoelectric effect of quartz. It has extremely strong anti-electromagnetic interference capability and long-distance detection capability.

[0018] (2) Furthermore, using the optimal modulation depth to modulate the excitation laser, or using the optimal excitation position to excite the tuning fork, can further improve the measurement sensitivity.

[0019] (3) Furthermore, unlike a single tuning fork assembly in a quartz tuning fork, the tuning fork of this invention is made of metal and is machined to allow for the design of the tuning fork's dimensional parameters based on the gas to be tested and the excitation light source. This allows for the modification of the tuning fork's resonant frequency and the gap between the two arms, overcoming the limitations of commercially available standard quartz tuning forks in detecting gases with low relaxation rates and the difficulty in pairing them with excitation light sources of poor beam quality. Simultaneously, it reduces the cost and complexity of tuning fork manufacturing and increases the flexibility of tuning fork design.

[0020] (4) Furthermore, through the design of the fixed structure, the tuning fork and the shell can be integrated into one piece, which facilitates the adjustment of the optical fiber and the integration of the sensor, as well as increases the stability and shock resistance of the sensor.

[0021] (5) Furthermore, the stability of the optical fiber during detection is further tested by fixing the ceramic ferrule with a designed ceramic sleeve.

[0022] (6) Preferably, the center of the through hole is aligned with the top of the two arms of the tuning fork to obtain the maximum cavity length change and further improve the detection sensitivity.

[0023] (7) The spectral detection device of the present invention includes only an excitation laser generation module, a collimator, a tuning fork and an optical fiber interference detection module. It has few components, is simple, has high sensitivity and good confidentiality. Attached Figure Description

[0024] Figure 1 This is a flowchart of the tuning fork-type fiber photoacoustic spectroscopy detection method of the present invention.

[0025] Figure 2 This is a schematic diagram of the structure of the tuning fork-type fiber optic photoacoustic spectroscopy detection device of the present invention.

[0026] Figure 3 This is a schematic diagram of the shape of the tuning fork of the present invention.

[0027] Figure 4 This is a schematic diagram of the combination of the tuning fork, the probe fiber, and the fixing structure of the present invention.

[0028] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-Tuning fork, 2-Outer shell, 3-First ceramic sleeve, 4-First ceramic ferrule, 5-First detection fiber, 6-Second ceramic sleeve, 7-Second ceramic ferrule, 8-Second detection fiber, 9-Laser control unit, 10-Excitation light source, 11-Collimator, 12-Fixed structure, 13-Fiber interferometric detection module. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] In this invention, the terms "first," "second," etc., used in the invention and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0031] Example 1 like Figure 1As shown, the tuning fork-type fiber optic photoacoustic spectroscopy detection method of the present invention includes a tuning fork 1, a first detection fiber 5, and a second detection fiber 8. The tuning fork 1 is placed in the gas environment to be tested. One end face of the first detection fiber 5 and the outer surface of one vibrating arm of the tuning fork form a first Fabry-Perot cavity. One end face of the second detection fiber 8 and the outer surface of the other vibrating arm of the tuning fork form a second Fabry-Perot cavity. The detection method includes: S1. The excitation laser is modulated and incident on the gap between the two arms of the tuning fork 1; the gas to be tested absorbs the modulated excitation laser energy and generates sound waves through the photoacoustic effect, that is, generates a photoacoustic signal; wherein, the center wavelength of the modulated excitation laser is consistent with the absorption wavelength of the gas to be tested. The photoacoustic signal drives the two arms of the tuning fork to produce mechanical vibration. This mechanical vibration causes the cavity lengths of the two Fabry-Perot cavities to change by the same amount. The two Fabry-Perot cavities are the first Fabry-Perot cavity and the second Fabry-Perot cavity. Since the two arms of the tuning fork have the same size and mass and are coupled together, the displacements produced by the two arms are the same. Therefore, the cavity lengths of the two Fabry-Perot cavities change by the same amount.

[0032] S2. The changes in the reflected interference spectra corresponding to the changes in the cavity length of the two Fabry-Perot cavities are detected from the other end faces of the first detection fiber 5 and the second detection fiber 8, respectively. The changes in the two reflected interference spectra are added together, and the harmonic signal of the added change is extracted. The amplitude of the harmonic signal is proportional to the concentration of the gas to be measured. The concentration information of the gas to be measured is inferred from the magnitude of the amplitude of the harmonic signal. The change in the reflected interference spectrum is either an intensity change or a phase change. The reflected light from the outer surface of the tuning fork arm interferes with the reflected light from the end face of the optical fiber to form the aforementioned reflected interference light.

[0033] Specifically, before S1, it also includes: generating an excitation laser.

[0034] Specifically, in S1, the center wavelength of the excitation laser is aligned with the absorption line of the gas to be measured. When the modulation of the excitation laser is wavelength modulation, the modulation frequency of the excitation laser is half of the tuning fork resonance frequency. Correspondingly, in S2, the extracted harmonic signal is the second harmonic signal of intensity or phase change. When the modulation of the excitation laser is intensity modulation, the modulation frequency of the excitation laser is consistent with the tuning fork resonance frequency. Correspondingly, in S2, the extracted harmonic signal is the first harmonic signal of intensity or phase change.

[0035] If wavelength modulation is used to excite the laser, the steps preceding S1 include: Under the same gas concentration, the modulation depth of the excitation laser is scanned, and the optimal modulation depth of the excitation laser is obtained when the amplitude of the second harmonic signal in the harmonic signal is the largest. Using this optimal modulation depth to modulate the excitation laser can further improve the measurement sensitivity.

[0036] Preferably, the method of the present invention further includes: obtaining the optimal excitation position of the excitation laser on the tuning fork, including: Under the same gas concentration, by changing the excitation position of the laser, the optimal excitation position for the excitation laser is obtained when the amplitude of the harmonic signal is at its maximum. Using this optimal excitation position to excite the tuning fork can further improve the measurement sensitivity.

[0037] Preferably, in step S1, before the modulated excitation laser is incident on the gap between the two arms of the tuning fork, the modulated excitation laser is collimated before being incident on the gap between the two arms of the tuning fork.

[0038] Specifically, in S2, intensity demodulation or phase demodulation is used to obtain the intensity change or phase change of the corresponding reflected interference spectrum. Intensity demodulation includes orthogonal operating point demodulation, and phase demodulation includes white light phase demodulation, dual-wavelength phase demodulation, etc.

[0039] Example 2 like Figure 2 As shown, this embodiment of the invention provides a tuning fork-type fiber photoacoustic spectroscopy detection device, including: a tuning fork 1, a first detection fiber 5, a second detection fiber 8, an excitation laser modulation module, and a fiber interferometric detection module 13; The tuning fork 1 is placed in the gas environment to be tested. One end face of the first detection fiber 5 and the outer surface of one vibrating arm of the tuning fork form a first Fabry-Perot cavity, and one end face of the second detection fiber 8 and the outer surface of the other vibrating arm of the tuning fork form a second Fabry-Perot cavity. The excitation laser modulation module is used to modulate the excitation laser and incident it into the gap between the two arms of the tuning fork 1; the gas to be tested absorbs the modulated excitation laser energy and generates a photoacoustic signal; wherein, the center wavelength of the modulated excitation laser is consistent with the absorption wavelength of the gas to be tested; The photoacoustic signal drives the two arms of the tuning fork to produce mechanical vibration, which causes the cavity lengths of the two Fabry-Perot cavities to change by the same amount. The fiber optic interferometric detection module 13 is used to detect the changes in the reflected interference spectrum corresponding to the changes in the cavity length of the two Fabry-Perot cavities from the other end faces of the first detection fiber 5 and the second detection fiber 8, respectively. After adding the changes in the two reflected interference spectra, the harmonic signal of the added changes is extracted. The amplitude of the harmonic signal is proportional to the concentration of the gas to be measured. The concentration information of the gas to be measured is inferred from the magnitude of the amplitude of the harmonic signal. The change in the reflected interference spectrum is either an intensity change or a phase change.

[0040] In this embodiment of the invention, the tuning fork 1 is made of metal, which can provide sufficient reflectivity to construct a Fabry-Perot cavity between the end face of the probe fiber; the material of the tuning fork 1 includes, but is not limited to, aluminum alloy and stainless steel.

[0041] Preferably, the tuning fork 1 is manufactured by machining, and the resonant frequency of the tuning fork can be arbitrarily designed according to the gas to be tested and the excitation light source. And the gap between the vibrating arms, g.

[0042] The shape and size parameters of the tuning fork are as follows: Figure 3 As shown, the resonance frequency of the tuning fork The relationship between it and its dimensional parameters can be expressed as:

[0043] In the formula, and These represent the width and length of each arm of the tuning fork. E and ρ These are Young's modulus and density of the tuning fork material, respectively. ν 0 is a constant for the fundamental frequency vibration mode. ν 0 is 1.194. Figure 3 In this context, T represents the thickness of each arm of the tuning fork.

[0044] Preferably, to facilitate the adjustment of the detection light 4 and the integration of the sensor, as well as to increase the stability and shock resistance of the sensor, such as Figure 4 As shown, the tuning fork fiber photoacoustic spectroscopy detection device in this embodiment of the invention also includes a fixing structure 12; The fixing structure 12 includes: a housing 2, a first ceramic insert 4, and a second ceramic insert 7; wherein, the housing 2 is integrated with the tuning fork 1; the housing 2 is provided with a through hole, and the first ceramic insert 4 and the second ceramic insert 7 pass through the through hole and are fixed on the housing 2; the center of the through hole is respectively aligned with the two arms of the tuning fork; One end of the first detection fiber 5 passes through the first ceramic ferrule 4 and forms a first Fabry-Perot cavity with the outer surface of a vibrating arm of a tuning fork, and the other end is connected to the fiber interferometric detection module 13. One end of the second detection fiber 8 passes through the second ceramic ferrule 7 and forms a second Fabry-Perot cavity with the outer surface of the other vibrating arm of the tuning fork, while the other end is connected to the fiber interferometric detection module 13.

[0045] Preferably, the fixing structure 12 further includes a first ceramic sleeve 3 and a second ceramic sleeve 6 fixed to the outer shell 2 through a through hole; the first ceramic insert 4 is fixed to the outer shell 2 by being inserted into the first ceramic sleeve 3; and the second ceramic insert 7 is fixed to the outer shell 2 by being inserted into the second ceramic sleeve 6.

[0046] Specifically, the outer shell 2 is integrally integrated with the tuning fork 1 through machining. In this embodiment of the invention, the resonant frequency range of the tuning fork is 2~30kHz, and the quality factor is not less than 2000.

[0047] Preferably, the center of the through hole is aligned with the top of the two arms of the tuning fork to obtain the maximum change in cavity length and further improve the detection sensitivity.

[0048] Specifically, the excitation laser modulation module includes a laser control unit 9 and an excitation light source 10. The laser control unit 9 is used to adjust the temperature and current of the excitation light source 10 so that the center wavelength of the excitation laser emitted by the excitation light source 10 is aligned with the absorption line of the gas to be measured.

[0049] Preferably, the tuning fork-type fiber photoacoustic spectroscopy detection device of the present invention further includes a collimator 11 for collimating the modulated excitation laser.

[0050] The tuning fork-type fiber optic photoacoustic spectroscopy detection method of the present invention forms two Fabry-Perot cavities by connecting a first probe fiber and a second probe fiber to the outer surfaces of the two arms of a tuning fork, respectively. Since a photoacoustic signal is generated in the middle of the tuning fork arms, it drives the two arms to vibrate in opposite directions, causing changes in the cavity lengths of the two Fabry-Perot cavities by the same amount. Meanwhile, external noise with the same resonant frequency as the tuning fork causes the two arms to vibrate in the same direction, resulting in one cavity length increasing and the other decreasing. At this point, the intensity or phase change of the reflected interference spectrum corresponding to the changes in cavity length of the two Fabry-Perot cavities is detected. Adding these changes yields a multiplied harmonic signal. When detecting the gas to be tested based on this multiplied harmonic signal, the detection sensitivity can be improved, while noise interference in the detection environment can be suppressed, thus improving the detection accuracy. Meanwhile, this invention uses a tuning fork as a photoacoustic transducer and employs fiber optic Fabry-Perot interferometry to measure the vibration of the tuning fork, avoiding the traditional electrical detection method that relies on the piezoelectric effect of quartz. It has extremely strong anti-electromagnetic interference capability and long-distance detection capability.

[0051] This invention uses a single tuning fork and two vibrating arms to construct two Fabry-Perot cavities, which achieves harmonic signal multiplication while also canceling out external noise.

[0052] Unlike individual tuning fork components of a quartz tuning fork, this invention uses machining to integrate the tuning fork and housing into a single unit, facilitating fiber optic adjustment and sensor integration, as well as increasing sensor stability and shock resistance.

[0053] The tuning fork in this invention is made of metal and can be manufactured by machining. The resonant frequency and arm gap of the tuning fork can be arbitrarily designed according to the gas to be tested and the excitation light source, which reduces the cost and complexity of tuning fork manufacturing and increases the flexibility of tuning fork design.

[0054] In summary, this invention addresses the problems of high manufacturing costs and complex processes associated with custom quartz tuning forks in existing technologies, difficulties in integrating quartz tuning forks, low sensor stability, susceptibility to electromagnetic interference, and inability to perform long-distance detection based on the electrical measurement methods of quartz tuning forks. It further improves gas detection performance by employing a scheme that uses two vibrating arms for simultaneous detection. The invention utilizes machining to manufacture the tuning forks and a fully fiber-optic detection scheme, fully leveraging the advantages of low machining costs and high flexibility, as well as the small size, light weight, low long-distance transmission loss, electromagnetic interference resistance, good confidentiality, intrinsic security, high temperature resistance, easy networking, and easy reuse of optical fibers. This invention can be widely applied in various fields such as energy and chemical engineering, power systems, environmental monitoring, and national defense.

[0055] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A tuning fork-type fiber optic photoacoustic spectroscopy detection method, characterized in that, It includes a tuning fork, a first detection fiber, and a second detection fiber. The tuning fork is placed in the gas environment to be tested. One end face of the first detection fiber and the outer surface of one vibrating arm of the tuning fork form a first Fabry-Perot cavity. One end face of the second detection fiber and the outer surface of the other vibrating arm of the tuning fork form a second Fabry-Perot cavity. The photoacoustic spectroscopy detection method includes: S1. After the excitation laser is modulated, it is incident on the gap between the two arms of the tuning fork. The gas to be tested absorbs the modulated excitation laser and generates a photoacoustic signal. The photoacoustic signal drives the two arms of the tuning fork to generate mechanical vibration, causing the cavity lengths of the two Fabry-Perot cavities to change. The two Fabry-Perot cavities are the first Fabry-Perot cavity and the second Fabry-Perot cavity. S2. Detect the changes in the reflection interference spectra corresponding to the changes in the cavity length of the two Fabry-Perot cavities from the other ends of the first and second detection fibers, respectively. Add the changes in the two reflection interference spectra, extract the harmonic signal of the added changes, and infer the concentration information of the gas to be measured from the amplitude of the harmonic signal; wherein, the changes in the reflection interference spectra are either intensity changes or phase changes.

2. The tuning fork-type fiber optic photoacoustic spectroscopy detection method according to claim 1, characterized in that, In S1, if the modulation of the excitation laser is wavelength modulation, then the modulation frequency of the excitation laser is half of the resonant frequency of the tuning fork; in S2, the harmonic signal is a second harmonic signal. In S1, if the modulation of the excitation laser is intensity modulation, then the modulation frequency of the excitation laser is consistent with the resonance frequency of the tuning fork; in S2, the harmonic signal is a first harmonic signal.

3. The tuning fork-type fiber optic photoacoustic spectroscopy detection method according to claim 2, characterized in that, If the modulation of the excitation laser is wavelength modulation, it also includes: Under the same gas concentration, the modulation depth of the excitation laser is scanned, and the optimal modulation depth of the excitation laser is obtained when the amplitude of the second harmonic signal is the largest; the excitation laser is modulated using the optimal modulation depth.

4. The tuning fork fiber photoacoustic spectroscopy detection method according to claim 1 or 2, characterized in that, Also includes: Under the same gas concentration, by changing the excitation position of the excitation laser, the optimal excitation position of the excitation laser is obtained when the amplitude of the harmonic signal is at its maximum; the tuning fork is then excited using the optimal excitation position.

5. A tuning fork-type fiber optic photoacoustic spectroscopy detection device, characterized in that, The tuning fork fiber photoacoustic spectroscopy detection device is used to perform the tuning fork fiber photoacoustic spectroscopy detection method according to any one of claims 1-4, and the tuning fork fiber photoacoustic spectroscopy detection device includes: a tuning fork, a first detection fiber, a second detection fiber, an excitation laser modulation module, and a fiber interferometric detection module. The tuning fork is placed in the gas environment to be tested. One end face of the first detection optical fiber and the outer surface of one arm of the tuning fork form a first Fabry-Perot cavity, and one end face of the second detection optical fiber and the outer surface of the other arm of the tuning fork form a second Fabry-Perot cavity. The excitation laser modulation module is used to modulate the excitation laser and incident it into the gap between the two arms of the tuning fork. The gas to be tested absorbs the modulated excitation laser and generates a photoacoustic signal. The photoacoustic signal drives the two arms of the tuning fork to produce mechanical vibration, causing the cavity lengths of the two Fabry-Perot cavities to change. The two Fabry-Perot cavities are the first Fabry-Perot cavity and the second Fabry-Perot cavity. The fiber optic interferometric detection module is used to detect the changes in the reflected interference spectra corresponding to the changes in the cavity lengths of the two Fabry-Perot cavities from the other ends of the first and second detection fibers, respectively. After adding the changes in the two reflected interference spectra, the harmonic signal of the added changes is extracted, and the concentration information of the gas to be measured is inferred from the amplitude of the harmonic signal. The changes in the reflected interference spectra are either changes in intensity or changes in phase.

6. The tuning fork-type fiber optic photoacoustic spectroscopy detection device according to claim 5, characterized in that, It also includes a fixing structure; the fixing structure includes a housing, a first ceramic ferrule, and a second ceramic ferrule. The outer shell is integrated with the tuning fork; the outer shell has through holes, the centers of which are respectively aligned with the two arms of the tuning fork; the first ceramic insert and the second ceramic insert pass through the through holes and are fixed to the outer shell. One end of the first detection optical fiber passes through the first ceramic ferrule and forms a first Fabry-Perot cavity with the outer surface of one vibrating arm of the tuning fork, and the other end is connected to the optical fiber interferometric detection module. One end of the second detection optical fiber passes through the second ceramic ferrule and forms a second Fabry-Perot cavity with the outer surface of the other vibrating arm of the tuning fork, and the other end is connected to the optical fiber interferometric detection module.

7. The tuning fork-type fiber optic photoacoustic spectroscopy detection device according to claim 6, characterized in that, The fixing structure also includes a first ceramic sleeve and a second ceramic sleeve fixed to the outer shell through the through hole; The first ceramic insert is inserted into the first ceramic sleeve, and the second ceramic insert is inserted into the second ceramic sleeve.

8. The tuning fork-type fiber optic photoacoustic spectroscopy detection device according to claim 6 or 7, characterized in that, The center of the through hole is aligned with the top of the two arms of the tuning fork.

9. The tuning fork-type fiber optic photoacoustic spectroscopy detection device according to claim 5, characterized in that, The tuning fork is made of metal and is manufactured using machining.

10. The tuning fork-type fiber optic photoacoustic spectroscopy detection device according to claim 5, characterized in that, It also includes a collimator for collimating the modulated excitation laser.

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