A dual-fiber space-decoupled small-size photoacoustic gas probe

Abstract

This invention discloses a small-sized photoacoustic gas probe with dual-fiber spatial decoupling, belonging to the fields of photoacoustic spectroscopy gas detection and fiber optic sensing technology. The probe comprises an acoustically sensitive diaphragm, a sleeve, a dual-hole positioning element, and parallel excitation and detection fibers. The excitation fiber is radially offset from the center of the diaphragm, while the detection fiber is located at the center of the sleeve. The axial distance between the light-emitting end face of the excitation fiber and the diaphragm is greater than the axial distance between the end face of the detection fiber and the diaphragm. In this structure, the excitation and detection optical paths are radially eccentrically separated, preventing the excitation light from directly irradiating the center of the diaphragm and effectively reducing the solid-state photothermal background of the diaphragm. The unequal spacing design in the axial direction allows the gas photoacoustic interaction region and the Fabry-Perot interferometer cavity to be spatially optimized independently, thus balancing gas absorption optical path length and interference detection sensitivity. The probe as a whole has the advantages of compact structure, good insulation, and high integration.

Description

Technical Field

[0001] This invention belongs to the field of photoacoustic spectroscopy gas detection and fiber optic sensing technology, and specifically relates to a dual-fiber spatially decoupled small-size photoacoustic gas probe. Background Technology

[0002] During long-term operation, gas-insulated equipment may generate characteristic decomposition gases due to partial discharge, overheating, or insulation defects. By detecting the type and concentration of these characteristic gases, the operating status and fault type of the equipment can be determined. Existing detection methods typically require depressurization, gas sampling, testing, and recharging of the equipment, which is complex, time-consuming, and the sampled gas may differ from the actual gas state inside the equipment. Therefore, achieving in-situ detection of characteristic gases inside the equipment is of great significance.

[0003] Photoacoustic spectroscopy utilizes the selective absorption of modulated light of a specific wavelength by a gas to generate sound pressure signals, exhibiting characteristics such as high selectivity and high sensitivity. Employing optical fiber to transmit excitation and detection light, and using a Fabry-Perot fiber optic acoustic sensor to detect the photoacoustic signal, helps to reduce probe size and improve its insulation performance and electromagnetic interference resistance.

[0004] However, in small-sized all-fiber photoacoustic gas probes, gas photoacoustic excitation and Fabry-Perot detection have different requirements for structural dimensions. Gas photoacoustic excitation requires a certain photo-gas interaction distance to ensure sufficient interaction between the modulated excitation light and the gas under test; while a small cavity length needs to be maintained between the end face of the detection fiber and the acoustically sensitive diaphragm to obtain a Fabry-Perot interference cavity suitable for interference demodulation. If the two optical paths use the same axial position, it is difficult to simultaneously achieve good gas absorption optical path length and interference detection sensitivity.

[0005] Furthermore, after the excitation light propagates to the acoustically sensitive diaphragm, the diaphragm absorbs part of the excitation light, generating a solid-state photothermal response. If the excitation light path and the detection light path coincide radially, the solid-state photothermal vibration generated by the excitation light directly irradiating the detection area at the center of the diaphragm is easily read by the detection light path, thus forming a background signal with the same frequency as the gas photoacoustic signal, affecting the detection of weak gas photoacoustic signals. Therefore, it is necessary to coordinate the radial and axial end-face positions of the excitation and detection light paths. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a dual-fiber spatially decoupled small-size photoacoustic gas probe. This probe achieves functional separation of photoacoustic excitation and optical detection by coordinating the radial and axial end-face positions of the excitation and detection optical paths within the same sleeve, establishing a gas photoacoustic excitation region and a diaphragm interference detection region respectively. It can be used for in-situ detection of insulating gases and their decomposition products inside power equipment.

[0007] This invention discloses a dual-fiber spatially decoupled small-size photoacoustic gas probe, which includes an acoustically sensitive diaphragm, a sleeve, a dual-hole positioning element, an excitation fiber, and a detection fiber.

[0008] The acoustically sensitive diaphragm is sealed and fixed to the front end of the sleeve, and the double-hole positioning component is embedded in the rear end of the sleeve; the double-hole positioning component is provided with an eccentric through hole and a central through hole along the radial direction of the sleeve, and the axes of the eccentric through hole and the central through hole are parallel to each other, the axis of the central through hole coincides with the central axis of the sleeve, and there is a radial distance between the axis of the eccentric through hole and the central axis of the sleeve.

[0009] The excitation fiber is inserted into an eccentric through-hole to deliver modulated excitation light corresponding to the absorption spectrum of the gas to be measured into the sleeve, and to form a gas photoacoustic interaction zone between the light-emitting end face of the excitation fiber and the acoustic sensitive diaphragm; the optical axis of the excitation fiber is parallel to the central axis of the sleeve so that the emitted light irradiates the acoustic sensitive diaphragm and is deviated from the geometric center of the acoustic sensitive diaphragm.

[0010] The detection optical fiber is inserted into the central through hole and is used to detect the vibration of the acoustic sensitive diaphragm under the action of photoacoustic signal. The optical axis of the detection optical fiber extends along the central axis of the sleeve, and the emitted light is aligned with the geometric center of the acoustic sensitive diaphragm so that the fiber end face of the detection optical fiber and the acoustic sensitive diaphragm form a Fabry-Perot interferometer cavity.

[0011] As can be seen from the above technical solutions, the present invention has the following beneficial effects:

[0012] This invention utilizes a dual-hole positioning device to place the excitation fiber within an eccentric through-hole and the detection fiber within a central through-hole, achieving radial spatial separation between the excitation and detection optical paths. The excitation optical path is offset from the interference detection region at the center of the diaphragm, effectively avoiding the solid-state photothermal background generated by direct excitation light irradiating the central region of the diaphragm, thus significantly reducing the floor noise in the photoacoustic signal. Simultaneously, the light-emitting end face of the excitation fiber is far from the acoustic-sensitive diaphragm, while the detection end face of the detection fiber is close to the acoustic-sensitive diaphragm, forming a longer gas photoacoustic interaction region and a shorter Fabry-Perot interference cavity within the same sleeve. Axially, they are decoupled, eliminating the need to sacrifice readout sensitivity to extend the absorption path or compress the absorption space to improve sensitivity. Furthermore, the all-fiber transmission and optical readout method ensures the probe itself is uncharged and immune to electromagnetic interference, possessing excellent insulation and intrinsic safety characteristics, making it particularly suitable for online gas monitoring in harsh environments such as flammable and explosive environments and those with strong electromagnetic interference.

[0013] In summary, this invention achieves a comprehensive performance improvement in terms of high sensitivity, low noise, compactness, and high reliability by decoupling the excitation optical path and the detection optical path in both the radial and axial directions. This is achieved by unifying the requirements of gas photoacoustic excitation, signal optical readout, and background suppression into a small-sized probe. Attached Figure Description

[0014] Figure 1 A schematic diagram of the discrete component structure of a dual-fiber spatially decoupled small-size photoacoustic gas probe provided by the present invention;

[0015] Among them, 1 is an acoustic sensitive diaphragm; 2 is a sleeve; 21 is a vent hole; 22 is a gas photoacoustic cavity / Fabry-Perot interference cavity; 3 is a double-hole positioning component; 31 is an eccentric through hole; 32 is a central through hole; 4 is a tapered open fiber optic protective sleeve; 5 is an excitation fiber; and 6 is a detection fiber. Detailed Implementation

[0016] To make the objectives, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present invention will be thorough and complete.

[0017] The terms “first,” “second,” “third,” “fourth,” etc. (if present) in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a particular order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms “comprising” and “having,” and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0018] It should be noted that when an element is referred to as being "fixed to" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," "up," "down," and similar expressions used herein are for illustrative purposes only and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0019] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances. The term "and / or" as used herein includes any and all combinations of one or more of the related listed items.

[0020] To achieve the above objectives, this invention provides a small-sized photoacoustic gas probe with dual-fiber spatial decoupling, comprising an acoustically sensitive diaphragm 1, a sleeve 2, a dual-hole positioning element 3, a tapered open fiber optic protective sleeve 4, an excitation fiber 5, and a detection fiber 6. The acoustically sensitive diaphragm 1 is sealed and fixed to the front end of the sleeve 2 and forms the response interface for the photoacoustic signal. The dual-hole positioning element 3 is embedded in the rear part of the sleeve 2 and is used to define the spatial position of the two fibers. A vent hole 21 communicating with the inner cavity is provided on the side wall of the sleeve 2, allowing the gas to be measured to diffuse into the interior of the sleeve 2 and participate in the photoacoustic interaction.

[0021] The double-hole positioning component 3 has an eccentric through hole 31 and a central through hole 32 radially along the sleeve 2, with the axes of the two through holes parallel to each other. The axis of the central through hole 32 coincides with the central axis of the sleeve 2 and is used to determine the detection optical path; the axis of the eccentric through hole 31 is radially offset relative to the central axis of the sleeve 2 and is used to determine the excitation optical path. Thus, the excitation optical path and the detection optical path form a stable radial position difference within the cross-section of the sleeve 2.

[0022] The excitation fiber 5 is inserted into the eccentric through-hole 31, with its optical axis parallel to the central axis of the sleeve 2, and its projection onto the plane of the acoustically sensitive diaphragm 1 deviates from the geometric center of the diaphragm. Modulated excitation light corresponding to the absorption spectral lines of the gas to be measured is input through the excitation fiber 5 and propagates between the light-emitting end face of the excitation fiber 5 and the acoustically sensitive diaphragm 1. After selective absorption of the modulated excitation light by the gas to be measured, the absorbed energy is converted into periodic heat through non-radiative relaxation, causing periodic thermal expansion of the gas and forming a photoacoustic signal corresponding to the modulation frequency.

[0023] The detection fiber 6 is inserted into the central through-hole 32, with its optical axis extending along the central axis of the sleeve 2 and its detection end face facing the geometric center of the acoustically sensitive diaphragm 1. The end face of the detection fiber 6 and the acoustically sensitive diaphragm 1 form an eigenvalue-Perot interference cavity, and the detection light interferes between the fiber end face and the diaphragm surface. After the photoacoustic signal acts on the acoustically sensitive diaphragm 1, it causes the diaphragm to vibrate periodically, causing the cavity length and the intensity of the reflected interference light to change over time. By detecting and demodulating this interference light signal, the frequency and amplitude information of the photoacoustic signal can be obtained.

[0024] The gas photoacoustic cavity / Fabry-Perot interferometer cavity 22 is formed between the end face of the detection fiber 6 and the acoustic sensitive diaphragm 1, and between the light-emitting end face of the excitation fiber 5 and the acoustic sensitive diaphragm 1.

[0025] For the peripherally fixed circular acoustic-sensitive diaphragm 1, its low-order vibration modes exhibit a large displacement response in the central region. Therefore, aligning the detection optical path with the geometric center of the diaphragm is beneficial for improving the optical detection sensitivity of the diaphragm vibration. The axial distance from the light-emitting end face of the excitation fiber 5 to the acoustic-sensitive diaphragm 1 is greater than the axial distance from the detection end face of the detection fiber 6 to the acoustic-sensitive diaphragm 1, resulting in a longer gas photoacoustic interaction region between the excitation fiber 5 and the acoustic-sensitive diaphragm 1, while a shorter Fabry-Perot interference cavity is formed between the detection fiber 6 and the acoustic-sensitive diaphragm 1. Thus, the excitation optical path and the detection optical path form both a radial positional difference within the cross-section of the sleeve 2 and an end face positional difference along the axial direction of the sleeve 2, achieving spatial decoupling of the two optical paths.

[0026] Furthermore, tapered opening fiber optic protective sleeves 4 are respectively installed in the eccentric through-hole 31 and the central through-hole 32. The excitation fiber 5 and the detection fiber 6 are respectively inserted and fixed in the corresponding tapered opening fiber optic protective sleeves 4. The outer diameter of the tapered opening fiber optic protective sleeve 4 matches the inner diameter of the corresponding through-hole, and the inner diameter matches the outer diameter of the corresponding fiber, which is used to protect the fiber and maintain the radial position and axial end face position of the two fibers.

[0027] Furthermore, the acoustic sensitive diaphragm 1, sleeve 2, double-hole positioning component 3, and tapered open optical fiber protective sleeve 4 are all made of quartz glass, and the excitation optical fiber 5 and detection optical fiber 6 are both made of quartz optical fiber. The components are bonded, fixed, and sealed with low refractive index UV-curable adhesive.

[0028] When the probe is working, the gas to be tested diffuses into the inner cavity of the sleeve 2 through the vent 21; the modulated excitation light is input by the excitation fiber 5 and first interacts with the gas to be tested in the gas photoacoustic interaction zone. The gas to be tested selectively absorbs the excitation light and generates a periodic photoacoustic signal; the photoacoustic signal acts on the acoustic sensitive diaphragm 1 and causes it to vibrate. Subsequently, the optical detection of the vibration information is completed by the Fabry-Perot interferometer cavity composed of the detection fiber 6 and the acoustic sensitive diaphragm 1.

[0029] The following will refer to Figure 1 The exemplary embodiments of the present invention are described in more detail below. While exemplary embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0030] like Figure 1As shown, the dual-fiber spatially decoupled small-size photoacoustic gas probe of this embodiment includes an acoustically sensitive diaphragm 1, a sleeve 2, a dual-hole positioning element 3, a tapered open fiber optic protective sleeve 4, an excitation fiber 5, and a detection fiber 6. The end where the acoustically sensitive diaphragm 1 is located is used as the front end of the sleeve 2, and the end where the dual-hole positioning element 3 is located is used as the rear end of the sleeve 2.

[0031] The acoustic-sensitive diaphragm 1 is a circular quartz glass film, optionally with a diameter of 10 mm and a thickness of 50 μm. The periphery of the acoustic-sensitive diaphragm 1 is bonded and fixed to the annular end face of the sleeve 2, while the center of the diaphragm remains suspended, forming a peripherally fixed acoustic-sensitive structure. The sleeve 2 is a quartz glass cylinder, optionally with an outer diameter of 10 mm, an inner diameter of 8 mm, and an axial length of 8 mm. The inner cavity of the sleeve 2 constitutes the space for containing the gas to be measured and for photoacoustic interaction.

[0032] A vent hole 21 is provided on the side wall of the sleeve 2. The radius of the vent hole 21 is 0.20 mm, that is, the diameter is 0.40 mm. Optionally, the center of the vent hole is about 2 mm away from the front end of the sleeve 2. The vent hole 21 is connected to the inner cavity of the sleeve 2, so that the external gas to be measured can enter the probe through diffusion, while avoiding the need to set up additional metal gas passage components inside the probe.

[0033] The double-hole positioning component 3 is a quartz glass cylinder. Optionally, the outer diameter of the double-hole positioning component 3 is 8mm and the axial length is 4mm, matching the inner diameter of the sleeve 2, and it is embedded in the rear of the sleeve 2. The double-hole positioning component 3 has an eccentric through hole 31 and a central through hole 32 along the axial direction. Optionally, the diameter of both through holes is 1.80mm, and the hole axes are parallel to each other. The axis of the central through hole 32 coincides with the central axis of the double-hole positioning component 3 and the sleeve 2, and the axis of the eccentric through hole 31 is radially offset by 2.80mm relative to the axis of the central through hole 32. The minimum wall thickness between the eccentric through hole 31 and the outer circle of the double-hole positioning component 3 is approximately 0.30mm, and the minimum wall thickness between the two through holes is approximately 1.00mm.

[0034] A tapered optical fiber protective sleeve 4 is provided in both the eccentric through hole 31 and the central through hole 32. The outer diameter of each tapered optical fiber protective sleeve 4 matches the inner diameter of the corresponding through hole, and the inner diameter matches the outer diameter of the optical fiber. The tapered opening of the protective sleeve is used to guide the insertion of the optical fiber and reduce the possibility of optical fiber bending or end face damage during assembly.

[0035] The excitation fiber 5 and the detection fiber 6 pass through their respective tapered opening fiber optic protective sleeves 4 and are fixed after being adjusted to the predetermined axial position. The excitation fiber 5 is inserted into the eccentric through-hole 31, with its optical axis parallel to the central axis of the sleeve 2 and radially offset by approximately 2.80 mm relative to the geometric center of the acoustically sensitive diaphragm 1. Thus, the excitation light propagates along a position offset from the center of the sleeve 2, and its optical axis projection on the plane of the acoustically sensitive diaphragm 1 is located outside the central region of the diaphragm. The excitation fiber 5 is a single-mode silica fiber, and its transmission wavelength is selected according to the absorption spectrum of the gas to be measured.

[0036] The detection fiber 6 is inserted into the central through-hole 32, with its optical axis coinciding with the central axis of the sleeve 2, and its detection end face facing the geometric center of the acoustic sensitive diaphragm 1. The end face of the detection fiber 6 and the inner surface of the acoustic sensitive diaphragm 1 form an eigentype Fabry-Perot interference cavity. After the detection light is input through the detection fiber 6, multi-beam interference occurs between the fiber end face and the acoustic sensitive diaphragm 1.

[0037] During assembly, the light-emitting end face of the excitation fiber 5 is positioned approximately 6 mm from the acoustic-sensitive diaphragm 1, and the detection end face of the detection fiber 6 is positioned approximately 300 μm from the acoustic-sensitive diaphragm 1. This creates a gas photoacoustic interaction region with an axial length of approximately 6 mm between the light-emitting end face of the excitation fiber 5 and the acoustic-sensitive diaphragm 1, and a Fabry-Perot interferometer cavity with a cavity length of approximately 300 μm between the detection end face of the detection fiber 6 and the acoustic-sensitive diaphragm 1. The axial positional difference between the two fiber end faces is approximately 7.7 mm.

[0038] In this embodiment, the acoustic-sensitive diaphragm 1, sleeve 2, dual-hole positioning element 3, and tapered optical fiber protective sleeve 4 are all made of quartz glass, and the excitation optical fiber 5 and detection optical fiber 6 are both made of quartz optical fiber. The acoustic-sensitive diaphragm 1 is bonded to the front end of the sleeve 2, the dual-hole positioning element 3 to the rear end of the sleeve 2, the tapered optical fiber protective sleeve 4 to the dual-hole positioning element 3, and the optical fiber to the tapered optical fiber protective sleeve 4, all using low-refractive-index UV-curable adhesive. During bonding, the adhesive is controlled to distribute only at the corresponding mating interfaces, and UV curing is performed after the optical fiber end face position is adjusted to keep the probe cavity and vent 21 unobstructed.

[0039] When the probe is working, the gas to be tested diffuses into the inner cavity of the sleeve 2 through the vent 21. Modulated excitation light corresponding to the absorption spectrum of the gas to be tested is input through the excitation fiber 5, propagates within a 6mm long gas photoacoustic interaction region, and is selectively absorbed by the gas. The gas undergoes periodic thermal expansion, generating a photoacoustic signal. This photoacoustic signal acts on the acoustically sensitive diaphragm 1, causing it to vibrate periodically, thereby changing the cavity length of the Fabry-Perot interferometer. The detection light transmitted through the detection fiber 6 optically characterizes the change in cavity length. By demodulating the interference light signal, the frequency and amplitude information of the photoacoustic signal can be obtained.

[0040] In the above structure, the excitation fiber 5 is radially offset relative to the detection fiber 6, causing the excitation beam axis to deviate from the central detection region of the acoustically sensitive diaphragm 1. Furthermore, the end face of the excitation fiber 5 is axially shifted backward relative to the end face of the detection fiber 6, making the length of the gas photoacoustic interaction region much greater than the cavity length of the Fabry-Perot interferometer. These radial and axial positional relationships complement each other, achieving spatial decoupling of the photoacoustic excitation and interferometric detection functions without adding an independent gas chamber or external reflecting optical elements.

[0041] It should also be noted that this invention employs axial and radial misalignment. The radial misalignment aims to deflect the excitation light away from the diaphragm center, reducing the intensity of the excitation light absorbed by the diaphragm and thus reducing the solid-state photoacoustic effect and increasing the system's background noise. The detection light is constrained by the Fabry-Perot interference principle and therefore needs to be positioned centrally. Thus, the radial difference is determined by the position of the excitation fiber 5, and in principle, the farther from the center, the better. However, for the probe, the operating frequency requirement in the initial design limits the diameter of the acoustically sensitive diaphragm 1. Therefore, the size of the diaphragm and the processing limits of the positioning components restrict the radial difference between the central through-hole 32 and the eccentric through-hole 31. Without exceeding the size of the acoustically sensitive diaphragm 1 and the processing limits of the positioning components, the eccentric through-hole 31 is positioned as far away from the center as possible.

[0042] Furthermore, the axial misalignment is mainly due to the distance between the detection fiber 6 and the acoustic sensitive diaphragm 1 being the Fabry-Perot cavity length. This is related to the demodulation module settings. For different demodulation techniques, there is no fixed requirement for the cavity length; therefore, this invention does not impose specific limitations. This embodiment uses orthogonal operating point demodulation, so the cavity length is set to 300 μm. The distance between the excitation fiber 5 and the acoustic sensitive diaphragm 1 is to increase the absorption optical path. This is limited by the currently achievable sleeve length; theoretically, longer is not always better, and there should be a reasonable value, generally obtained through extensive experimentation. This embodiment provides a reference value under currently achievable sleeve lengths.

[0043] The specific dimensions given in this embodiment are used to illustrate a feasible structural scheme. Under the premise that the detection fiber is positioned along the central axis of the sleeve, the excitation fiber is offset relative to the central axis of the sleeve, the two fibers are parallel to each other, and the distance from the end face of the excitation fiber to the diaphragm is greater than the distance from the end face of the detection fiber to the diaphragm, the sleeve dimensions, vent dimensions, eccentricity, length of the gas photoacoustic interaction zone, and Fabry-Perot interferometer cavity length can be adjusted accordingly based on the type of gas to be measured, the excitation wavelength, the diaphragm material properties, and the installation space.

[0044] Obviously, the above embodiments are merely illustrative examples and are not intended to limit the implementation. Those skilled in the art can make other variations or modifications based on the above description, and such variations or modifications are still within the scope of protection of this invention.

[0045] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

[0046] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not describe the various possible combinations separately.

[0047] Furthermore, various different implementations of the present invention can be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed in the present invention.

Claims

1. A dual-fiber spatially decoupled small size photoacoustic gas probe, characterized by, The photoacoustic gas probe includes an acoustically sensitive diaphragm (1), a sleeve (2), a dual-hole positioning element (3), an excitation fiber (5), and a detection fiber (6): The acoustic sensitive diaphragm (1) is sealed and fixed to the front end of the sleeve (2), and the double-hole positioning component (3) is embedded in the rear end of the sleeve (2); the double-hole positioning component (3) is provided with an eccentric through hole (31) and a central through hole (32) along the radial direction of the sleeve (2), and the axes of the eccentric through hole (31) and the central through hole (32) are parallel to each other, the axis of the central through hole (32) coincides with the central axis of the sleeve (2), and there is a radial distance between the axis of the eccentric through hole (31) and the central axis of the sleeve (2); The excitation fiber (5) is inserted into the eccentric through hole (31) to deliver modulated excitation light corresponding to the absorption spectrum of the gas to be measured into the sleeve (2), and to form a gas photoacoustic interaction zone between the light-emitting end face of the excitation fiber (5) and the acoustic sensitive diaphragm (1); the optical axis of the excitation fiber (5) is parallel to the central axis of the sleeve (2) so that the emitted light irradiates the acoustic sensitive diaphragm (1) and deviates from the geometric center of the acoustic sensitive diaphragm (1); The detection fiber (6) is inserted into the central through hole (32) and is used to detect the vibration generated by the acoustic sensitive diaphragm (1) under the action of photoacoustic signal. The optical axis of the detection fiber (6) extends along the central axis of the sleeve (2) and the emitted light is aligned with the geometric center of the acoustic sensitive diaphragm (1) so that the fiber end face of the detection fiber (6) and the acoustic sensitive diaphragm (1) form a Fabry-Perot interference cavity.

2. The dual-fiber spatially decoupled small-size photoacoustic gas sensor probe according to claim 1, characterized in that, The axial distance from the light-emitting end face of the excitation fiber (5) to the acoustic sensitive diaphragm (1) is greater than the axial distance from the end face of the detection fiber (6) to the acoustic sensitive diaphragm (1).

3. The dual-fiber spatially decoupled small size photoacoustic gas sensor probe according to claim 1, wherein, The sleeve (2) has a vent hole (21) on its side wall that communicates with the inner cavity of the sleeve (2) to realize the diffusion and exchange of the gas to be tested inside and outside the sleeve (2).

4. The dual-fiber spatially decoupled small-size photoacoustic gas probe according to claim 1, characterized in that, The outer diameter of the double-hole positioning component (3) matches the inner diameter of the sleeve (2).

5. A dual-fiber spatially decoupled small-size photoacoustic gas probe according to claim 1, characterized in that, The photoacoustic gas probe also includes a tapered open optical fiber protective sleeve (4). The tapered opening fiber optic protective sleeve (4) is disposed in the eccentric through hole (31) and the central through hole (32) of the dual-hole positioning component (3). The excitation fiber (5) and the detection fiber (6) are respectively inserted and fixed in the corresponding tapered opening fiber optic protective sleeve (4) to maintain the axial position difference between the light-emitting end face of the excitation fiber (5) and the detection end face of the detection fiber (6).

6. A dual-fiber spatially decoupled small-size photoacoustic gas probe according to claim 5, characterized in that, The outer diameter of the tapered opening optical fiber protective sleeve (4) matches the inner diameter of the corresponding through hole, and the inner diameter of the tapered opening optical fiber protective sleeve (4) matches the outer diameter of the optical fiber.

7. A dual-fiber spatially decoupled small-size photoacoustic gas probe according to claim 1, characterized in that, The acoustic sensitive diaphragm (1), sleeve (2), double-hole positioning component (3), and tapered open fiber optic protective sleeve (4) are all made of quartz glass.

8. A dual-fiber spatially decoupled small-size photoacoustic gas probe according to claim 1, characterized in that, Both the excitation fiber (5) and the detection fiber (6) are quartz optical fibers, and the transmission wavelengths of the excitation fiber (5) and the detection fiber (6) are selected according to the absorption spectrum of the gas to be tested.

9. A dual-fiber spatially decoupled small-size photoacoustic gas probe according to claim 5, characterized in that, The acoustic sensitive diaphragm (1) and the sleeve (2), the double-hole positioning component (3) and the sleeve (2), the tapered open optical fiber protective sleeve (4) and the double-hole positioning component (3), and the optical fiber and the tapered open optical fiber protective sleeve (4) are all bonded, fixed and sealed with ultraviolet glue.

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