A multi-laser coupling photoacoustic device and a method for measuring gas concentration

Abstract

The present invention discloses a multi-laser coupling photoacoustic device, comprising: a resonant cavity, a microphone, a mirror, an air inlet, an air outlet, and at least two sets of laser generation units. The laser generation unit includes a laser light source, a conduction optical fiber, and an optical fiber collimator that are connected in sequence. The air inlet is arranged at the first end of the resonant cavity, and the air outlet is arranged at the second end of the resonant cavity. The mirror and the microphone are arranged at the second end of the resonant cavity. The gas to be measured is input into the resonant cavity through the air inlet and released through the air outlet. The laser emitted by the laser light source in the laser generation unit is incident on the optical fiber collimator through the conduction optical fiber, and the laser collimated by the optical fiber collimator is obliquely incident on the resonant cavity at a preset angle. The laser is incident on the mirror after multiple reflections on the inner sidewall of the resonant cavity. The photoacoustic signal generated by the mirror is detected by the microphone, and based on the photoacoustic signal, the concentration of the gas to be measured is calculated.

Description

Technical Field

[0001] The present invention relates to the technical field of on-line gas monitoring for high-voltage electrical equipment, and more specifically, to a multi-laser coupled photoacoustic device and a method for measuring gas concentration. Background Art

[0002] Currently, oil-filled transformers are commonly used for high-voltage and large-capacity power transformers. When a fault occurs inside the transformer, such as overheating or discharging, the organic polymers in the transformer oil will crack, generating gases such as CH4, C2H4, C2H2, C2H6, CO, and CO2, and the generated gases will gradually dissolve in the transformer oil. By analyzing the components and concentrations of the gases dissolved in the oil, latent faults existing inside the equipment can be detected as early as possible. Gas monitoring technologies mainly include: gas chromatography, Fourier transform infrared spectroscopy, and photoacoustic spectroscopy. Due to the advantages of high sensitivity, good stability, multiple measured components, and no need for carrier gas of the photoacoustic spectroscopy for trace gas monitoring method, photoacoustic spectroscopy has become the preferred technical solution for transformer monitoring.

[0003] Photoacoustic spectroscopy is an indirect spectroscopic technique that detects photoacoustic signals generated in spontaneous emission and is a zero-background detection technique. Photoacoustic spectroscopy is mainly divided into photoacoustic spectroscopy based on mid-infrared thermal radiation light sources and laser photoacoustic spectroscopy according to different photoacoustic excitation light sources. Mid-infrared thermal radiation light sources have a relatively wide spectral emission range, covering the characteristic absorption bands of most polar gas molecules. In 2003, Kleman Company in the UK developed a photoacoustic spectroscopy oil-dissolved gas analysis device based on blackbody radiation infrared broad-spectrum light sources based on photoacoustic spectroscopy technology, which can measure the concentration of multiple gas components in oil at the ppm level. This device can simultaneously measure 8 kinds of fault gases (including C2H2, C2H6, CO, etc.), and can also detect trace water, and is easy to install. However, due to the limitations of the spectrometer structure, problems such as poor anti-interference ability of the detection device in the field have been exposed in recent years during on-site application. The strong electromagnetic interference at the operation site of high-voltage transformers often causes the actual measurement data to deviate seriously from the laboratory calibration results. Due to the advantages of narrow linewidth and high spectral power density of lasers, they have been widely used in the gas detection technology of photoacoustic spectroscopy, and combined with second-harmonic detection technology to reduce low-frequency noise, greatly improving the intensity of the detected photoacoustic signal and simultaneously reducing the influence of multi-component gas spectral line overlap interference. When the acoustic signal is detected, a photoacoustic cell is usually used to amplify the acoustic signal.

[0004] Therefore, designing a multi-laser coupled photoacoustic cell has important application value in on-line gas detection of high-voltage electrical equipment. Summary of the Invention

[0005] The technical solution of the present invention provides a multi-laser coupled photoacoustic device to solve the problem of how to measure the gas concentration based on the multi-laser coupled photoacoustic device.

[0006] To solve the above problems, the present invention provides a multi-laser coupled photoacoustic device, which includes: a resonant cavity, a microphone, a mirror, an air inlet, an air outlet, and at least two groups of laser generation units. The laser generation unit includes a laser light source, a conduction optical fiber, and an optical fiber collimator connected in sequence; the air inlet is arranged at the first end of the resonant cavity, and the air outlet is arranged at the second end of the resonant cavity; the mirror and the microphone are arranged at the second end of the resonant cavity;

[0007] The gas to be measured is input into the resonant cavity through the air inlet and released through the air outlet.

[0008] The laser emitted by the laser light source in the laser generation unit is incident on the optical fiber collimator through the conduction optical fiber. The laser collimated by the optical fiber collimator is obliquely incident on the resonant cavity at a preset angle. The laser is reflected multiple times on the inner side wall of the resonant cavity and then incident on the mirror. The laser reflected back by the mirror continues to be reflected in the resonant cavity to increase the absorption degree of the laser.

[0009] The photoacoustic signal generated by the mirror is detected by the microphone, and based on the photoacoustic signal, the concentration of the gas to be measured is calculated.

[0010] Preferably, the inner diameter of the resonant cavity is 10 mm, and the inner side wall of the resonant cavity is polished and gold-plated. The reflectivity of the processed inner side wall exceeds 98%.

[0011] Preferably, the mirror is a gold-plated plane mirror with a reflectivity exceeding 98%; the diameter and thickness of the mirror are 12.5 mm and 3 mm respectively. A micropore with a pore diameter of 1 mm is opened in the middle of the mirror for the conduction of sound signals and the flow of the gas to be measured.

[0012] Preferably, it includes four groups of laser generation units, where:

[0013] The laser light source of each group of laser generation units is a near-infrared narrow linewidth tunable semiconductor laser;

[0014] The conduction optical fiber of each group of laser generation units is a G652 single-mode quartz optical fiber;

[0015] The wavelength range of the optical fiber collimator of each group of laser generation units is 185 nm - 2500 nm, and the working distance is 80 mm - 100 mm.

[0016] Preferably, where:

[0017] The first fiber collimator in the first group of laser generation units is embedded downward into the resonant cavity at an inclination angle of 30° with respect to the vertical direction;

[0018] The second fiber collimator in the second group of laser generation units is embedded downward into the resonant cavity at an inclination angle of 30° with respect to the horizontal direction;

[0019] The third fiber collimator in the third group of laser generation units is embedded upward into the resonant cavity at an inclination angle of 30° with respect to the horizontal direction;

[0020] The fourth fiber collimator in the fourth group of laser generation units is embedded upward into the resonant cavity at an inclination angle of 30° with respect to the vertical direction.

[0021] Based on another aspect of the present invention, the present invention provides a method for measuring the gas concentration based on a multi-laser coupling type photoacoustic device, the method comprising:

[0022] Establishing a multi-laser coupling type photoacoustic device, the multi-laser coupling type photoacoustic device comprising: a resonant cavity, a microphone, a mirror, an air inlet, an air outlet, and at least two groups of laser generation units, the laser generation units comprising a laser light source, a conduction optical fiber, and a fiber collimator connected in sequence; the air inlet is arranged at the first end of the resonant cavity, the air outlet is arranged at the second end of the resonant cavity; the mirror and the microphone are arranged at the second end of the resonant cavity;

[0023] Inputting the gas to be measured into the resonant cavity via the air inlet, and releasing the gas to be measured via the air outlet;

[0024] The laser emitted by the laser light source in the laser generation unit is incident on the fiber collimator through the conduction optical fiber, and the laser collimated by the fiber collimator is obliquely incident on the resonant cavity at a preset angle. The laser is reflected multiple times on the inner side wall of the resonant cavity and then incident on the mirror. The laser reflected back by the mirror continues to be reflected in the resonant cavity to increase the absorption degree of the laser;

[0025] Detecting the photoacoustic signal generated by the mirror through the microphone, and calculating the concentration of the gas to be measured based on the photoacoustic signal.

[0026] Preferably, the inner diameter of the resonant cavity is 10 mm, and the inner side wall of the resonant cavity is polished and gold-plated. The reflectivity of the processed inner side wall exceeds 98%.

[0027] Preferably, the mirror is a gold-plated plane mirror with a reflectivity exceeding 98%; the diameter and thickness of the mirror are 12.5 mm and 3 mm respectively, and a micropore with a pore diameter of 1 mm is opened in the middle of the mirror for the conduction of sound signals and the flow of the gas to be measured.

[0028] Preferably, the multi-laser coupled photoacoustic device includes four groups of laser generation units, where:

[0029] The laser light source of each group of laser generation units is a near-infrared narrow linewidth tunable semiconductor laser;

[0030] The conduction optical fiber of each group of laser generation units is a G652 single-mode silica optical fiber;

[0031] The wavelength range of the fiber collimator of each group of laser generation units is 185nm - 2500nm, and the working distance is 80mm - 100mm.

[0032] Preferably, where:

[0033] The first fiber collimator in the first group of laser generation units is embedded into the resonant cavity downward at an inclination angle of 30° with respect to the vertical direction;

[0034] The second fiber collimator in the second group of laser generation units is embedded into the resonant cavity downward at an inclination angle of 30° with respect to the horizontal direction;

[0035] The third fiber collimator in the third group of laser generation units is embedded into the resonant cavity upward at an inclination angle of 30° with respect to the horizontal direction;

[0036] The fourth fiber collimator in the fourth group of laser generation units is embedded into the resonant cavity upward at an inclination angle of 30° with respect to the vertical direction.

[0037] The technical solution of the present invention provides a multi-laser coupled photoacoustic device, which includes: a resonant cavity, a microphone, a mirror, an air inlet, an air outlet, and at least two groups of laser generation units. The laser generation unit includes a laser light source, a conduction optical fiber, and a fiber collimator connected in sequence; the air inlet is arranged at the first end of the resonant cavity, and the air outlet is arranged at the second end of the resonant cavity; the mirror and the microphone are arranged at the second end of the resonant cavity; the gas to be measured is input into the resonant cavity through the air inlet and released through the air outlet; the laser emitted by the laser light source in the laser generation unit is incident on the fiber collimator through the conduction optical fiber, and the laser collimated by the fiber collimator is incident on the resonant cavity at a preset angle obliquely. The laser is reflected multiple times on the inner side wall of the resonant cavity and then incident on the mirror. The laser reflected back by the mirror continues to be reflected in the resonant cavity to increase the absorption degree of the laser; the photoacoustic signal generated by the mirror is detected by the microphone, and based on the photoacoustic signal, the concentration of the gas to be measured is calculated. The technical solution of the present invention proposes a multi-laser coupled photoacoustic device, aiming to solve the problems of short light absorption path and difficulty in efficiently coupling multiple lasers into a single photoacoustic device at the same time, and expanding a larger space for the application of photoacoustic spectroscopy technology in on-line gas detection of high-voltage electrical equipment. Description of the Drawings

[0038] The exemplary embodiments of the present invention can be more fully understood by referring to the following drawings:

[0039] Figure 1 It is a diagram of a multi-laser coupled photoacoustic device according to a preferred embodiment of the present invention; and

[0040] Figure 2 It is a flowchart of a method for measuring gas concentration based on a multi-laser coupled photoacoustic device according to a preferred embodiment of the present invention. Detailed Embodiments

[0041] Now, the exemplary embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely, and to fully convey the scope of the present invention to those skilled in the art. The terms in the exemplary embodiments shown in the drawings are not intended to limit the present invention. In the drawings, the same units / components are denoted by the same reference numerals.

[0042] Unless otherwise specified, the terms (including scientific and technical terms) used herein have the ordinary meaning understood by those skilled in the art. Additionally, it can be understood that the terms defined in the commonly used dictionary should be construed to have a meaning consistent with the context of their relevant fields, and should not be construed as idealized or overly formal meanings.

[0043] Figure 1 It is a diagram of a multi-laser coupled photoacoustic device according to a preferred embodiment of the present invention. The present invention provides a multi-laser coupled photoacoustic device to solve the problems of short optical absorption path and difficulty in simultaneously and efficiently coupling multiple lasers into a single photoacoustic cell, thus expanding a larger space for the application of photoacoustic spectroscopy technology in on-line gas detection of high-voltage electrical equipment.

[0044] Figure 1 It is a schematic structural diagram of a multi-laser coupled photoacoustic device provided by the present invention. Figure 1 In the figure: 1 resonance cavity; 2 microphone; 3 mirror; 4 air inlet; 5 air outlet; 6 laser light source 1#; 7 conduction optical fiber 1#; 8 fiber collimator 1#; 9 laser light source 2#; 10 conduction optical fiber 2#; 11 fiber collimator 2#; 12 laser light source 3#; 13 conduction optical fiber 3#; 14 fiber collimator 3#; 15 laser light source 4#; 16 conduction optical fiber 4#; 17 fiber collimator 4#.

[0045] The present invention provides a multi-laser coupling photoacoustic device, which comprises: a resonant cavity, a microphone, a mirror, an air inlet, an air outlet, and at least two groups of laser generating units. Each laser generating unit includes a laser light source, a conducting optical fiber, and an optical fiber collimator connected in sequence; the air inlet is arranged at the first end of the resonant cavity, and the air outlet is arranged at the second end of the resonant cavity; the mirror and the microphone are arranged at the second end of the resonant cavity.

[0046] The gas to be measured is input into the resonant cavity through the air inlet and released through the air outlet.

[0047] The laser emitted by the laser light source in the laser generating unit is incident on the optical fiber collimator through the conducting optical fiber. The laser collimated by the optical fiber collimator is obliquely incident on the resonant cavity at a preset angle. After multiple reflections on the inner sidewall of the resonant cavity, the laser is incident on the mirror, and the laser reflected back by the mirror continues to be reflected in the resonant cavity to increase the absorption degree of the laser.

[0048] The photoacoustic signal generated by the mirror is detected by the microphone, and based on the photoacoustic signal, the concentration of the gas to be measured is calculated.

[0049] Preferably, the inner diameter of the resonant cavity is 10 mm, and the inner sidewall of the resonant cavity is polished and gold-plated. The reflectivity of the processed inner sidewall exceeds 98%.

[0050] Preferably, the mirror is a gold-plated plane mirror with a reflectivity exceeding 98%; the diameter and thickness of the mirror are 12.5 mm and 3 mm respectively, and a micropore with a pore diameter of 1 mm is opened in the middle of the mirror for the conduction of sound signals and the flow of the gas to be measured.

[0051] Preferably, it includes four groups of laser generating units, wherein:

[0052] The laser light source of each group of laser generating units is a near-infrared narrow linewidth tunable semiconductor laser;

[0053] The conducting optical fiber of each group of laser generating units is a G652 single-mode quartz optical fiber;

[0054] The wavelength range of the optical fiber collimator of each group of laser generating units is 185 nm - 2500 nm, and the working distance is 80 mm - 100 mm.

[0055] Preferably, wherein:

[0056] The first optical fiber collimator in the first group of laser generating units is embedded into the resonant cavity downward at an inclination angle of 30° with respect to the vertical direction;

[0057] The second optical fiber collimator in the second group of laser generating units is embedded into the resonant cavity downward at an inclination angle of 30° with respect to the horizontal direction;

[0058] The third fiber collimator in the third group of laser generation units is embedded into the resonant cavity upward at an inclination angle of 30° with respect to the horizontal direction;

[0059] The fourth fiber collimator in the fourth group of laser generation units is embedded into the resonant cavity upward at an inclination angle of 30° with respect to the vertical direction.

[0060] The present invention provides a multi-laser coupled photoacoustic device, including a 1# laser light source 6, a 1# conducting optical fiber 7, a 1# fiber collimator 8, a 2# laser light source 9, a 2# conducting optical fiber 10, a 2# fiber collimator 11, a 3# laser light source 12, a 3# conducting optical fiber 13, a 3# fiber collimator 14, a 4# laser light source 15, a 4# conducting optical fiber 16, and a 4# fiber collimator 17.

[0061] In the present invention, the gas to be measured enters the designed multi-laser coupled photoacoustic cell through the air inlet 4 and is released through the air outlet 5; the laser emitted by the 1# laser light source 6 enters the 1# fiber collimator 8 through the 1# conducting optical fiber 7, and the laser collimated by the 1# fiber collimator 8 is obliquely incident on the resonant cavity 1 at a certain incident angle. After multiple reflections on the side wall of the resonant cavity 1, it is incident on the mirror 3, and the reflected laser continues to reflect in the resonant cavity 1 to increase the optical absorption path length; in the same way, the lasers emitted by the 2# laser light source 9, the 3# laser light source 12, and the 4# laser light source 15 respectively enter the 2# fiber collimator 11, the 3# fiber collimator 14, and the 4# fiber collimator 17 through the 2# conducting optical fiber 10, the 3# conducting optical fiber 13, and the 4# conducting optical fiber 16. The lasers collimated by the fiber collimators are respectively obliquely incident on the resonant cavity 1 at a certain incident angle. After multiple reflections on the side wall of the resonant cavity 1, they are incident on the mirror 3, and the reflected laser continues to reflect in the resonant cavity 1 to increase the optical absorption path length; the microphone 2 detects the generated photoacoustic signal.

[0062] A multi-laser coupled photoacoustic device provided by the present invention collimates multiple laser beams and simultaneously couples them into the photoacoustic cell. After multiple reflections in the resonant cavity of the photoacoustic cell, the photoacoustic signal is enhanced by multi-pass absorption, and the photoacoustic signal generated by the microphone detection is combined. The specific steps are as follows:

[0063] First, the dissolved gas in the transformer oil enters the multi-laser coupled photoacoustic cell through the air inlet 4; the lasers emitted by the 1# laser light source 6, the 2# laser light source 9, the 3# laser light source 12, and the 4# laser light source 15 respectively enter the 1# fiber collimator 8, the 2# fiber collimator 11, the 3# fiber collimator 14, and the 4# fiber collimator 17 through the 1# conducting optical fiber 7, the 2# conducting optical fiber 10, the 3# conducting optical fiber 13, and the 4# conducting optical fiber 16, and the collimated laser beams are respectively incident on the tube wall of the resonant cavity 1 at a certain inclination angle;

[0064] Then, the laser reflected by the side wall of the resonant cavity 1 is finally received by the mirror 3 and reflected back into the resonant cavity 1 again to form multiple reflections; the gas to be measured in the multi-laser coupling photoacoustic cell absorbs the laser energy and generates a photoacoustic signal, and the multiple reflections are used to achieve the effect of multi-pass absorption to enhance the photoacoustic signal.

[0065] Finally, the microphone 2 processes the generated photoacoustic signal, and finally calculates the concentration of the dissolved gas in the oil.

[0066] The inner diameter of the resonant cavity 1 of the present invention is 10 mm. The function of the resonant cavity is, on the one hand, to promote heat exchange, which is beneficial to the generation of the photoacoustic effect; on the other hand, to promote the formation of multiple reflections. The inner wall is polished and gold-plated, and the reflectivity of the treated pipe wall is more than 98%.

[0067] The mirror 3 of the present invention is a gold-plated plane mirror with a high reflectivity, and the reflectivity is more than 98%. It is used to increase the optical path length and improve the absorption optical path of the gas; the diameter and thickness are 12.5 mm and 3 mm respectively, and a micropore with a pore diameter of 1 mm is opened in the middle of the mirror 3 for the conduction of sound signals and the flow of gas.

[0068] The 1# laser light source 6, 2# laser light source 9, 3# laser light source 12, and 4# laser light source 15 of the present invention are near-infrared narrow linewidth tunable semiconductor lasers.

[0069] The 1# conducting optical fiber 7, 2# conducting optical fiber 10, 3# conducting optical fiber 13, and 4# conducting optical fiber of the present invention are all G652 single-mode silica optical fibers.

[0070] The wavelength ranges of the 1# fiber collimator 8, 2# fiber collimator 11, 3# fiber collimator 14, and 4# fiber collimator 17 of the present invention are all in the range of 185 nm - 2500 nm, and the working distance is in the range of 80 mm - 100 mm; the 1# fiber collimator 8 is embedded into the resonant cavity 1 at an inclination angle of 30° with respect to the vertical direction downward, the 2# fiber collimator 11 is embedded into the resonant cavity 1 at an inclination angle of 30° with respect to the horizontal direction downward, the 3# fiber collimator 14 is embedded into the resonant cavity 1 at an inclination angle of 30° with respect to the horizontal direction upward, and the 4# fiber collimator 17 is embedded into the resonant cavity 1 at an inclination angle of 30° with respect to the vertical direction upward.

[0071] The present invention can couple multiple lasers into the photoacoustic device at the same time, without devices such as optical switches, with low loss and low cost. The light beam is reflected multiple times in the resonant cavity, and the mirror is fully utilized to greatly increase the absorption path of light, improving the detection sensitivity. The microphone is used to achieve high-sensitivity detection of the photoacoustic signal. The present invention provides a highly competitive technical solution for on-line gas detection of high-voltage electrical equipment.

[0072] Figure 2A flowchart of a method for measuring gas concentration based on a multi-laser coupled photoacoustic device according to a preferred embodiment of the present invention. As Figure 2 shown, the present invention provides a method for measuring gas concentration based on a multi-laser coupled photoacoustic device, the method comprising:

[0073] Step 201: Establish a multi-laser coupled photoacoustic device, the multi-laser coupled photoacoustic device comprising: a resonant cavity, a microphone, a mirror, an air inlet, an air outlet, and at least two sets of laser generation units, the laser generation units comprising a laser light source, a conducting optical fiber, and an optical fiber collimator connected in sequence; the air inlet is provided at a first end of the resonant cavity, and the air outlet is provided at a second end of the resonant cavity; the mirror and the microphone are provided at the second end of the resonant cavity;

[0074] Step 202: Input the gas to be measured into the resonant cavity via the air inlet, and release the gas to be measured via the air outlet;

[0075] Step 203: The laser emitted by the laser light source in the laser generation unit is incident on the optical fiber collimator through the conducting optical fiber, and the laser collimated by the optical fiber collimator is obliquely incident on the resonant cavity at a preset angle. The laser is reflected multiple times on the inner sidewall of the resonant cavity and then incident on the mirror. The laser reflected back by the mirror continues to be reflected in the resonant cavity to increase the absorption degree of the laser;

[0076] Step 204: Detect the photoacoustic signal generated by the mirror through the microphone, and calculate the concentration of the gas to be measured based on the photoacoustic signal.

[0077] Preferably, the inner diameter of the resonant cavity is 10 mm, and the inner sidewall of the resonant cavity is polished and gold-plated. The reflectivity of the processed inner sidewall exceeds 98%.

[0078] Preferably, the mirror is a gold-plated plane mirror with a reflectivity exceeding 98%; the diameter and thickness of the mirror are 12.5 mm and 3 mm respectively, and a micropore with a pore diameter of 1 mm is opened in the middle of the mirror for the conduction of sound signals and the flow of the gas to be measured.

[0079] Preferably, the multi-laser coupled photoacoustic device comprises four sets of laser generation units, wherein:

[0080] The laser light source of each set of laser generation units is a near-infrared narrow linewidth tunable semiconductor laser;

[0081] The conducting optical fiber of each set of laser generation units is a G652 single-mode quartz optical fiber;

[0082] The wavelength range of the optical fiber collimator of each set of laser generation units is 185 nm - 2500 nm, and the working distance is 80 mm - 100 mm.

[0083] Preferably, wherein:

[0084] The first fiber collimator in the first group of laser generating units is embedded downward into the resonant cavity at an inclination angle of 30° with respect to the vertical direction;

[0085] The second fiber collimator in the second group of laser generating units is embedded downward into the resonant cavity at an inclination angle of 30° with respect to the horizontal direction;

[0086] The third fiber collimator in the third group of laser generating units is embedded upward into the resonant cavity at an inclination angle of 30° with respect to the horizontal direction;

[0087] The fourth fiber collimator in the fourth group of laser generating units is embedded upward into the resonant cavity at an inclination angle of 30° with respect to the vertical direction.

[0088] The present invention has been described by referring to a few embodiments. However, as is well known to those skilled in the art, other embodiments equivalent to those disclosed above of the present invention equally fall within the scope of the present invention as defined by the appended patent claims.

[0089] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless otherwise clearly defined therein. All references to "a / the [device, component, etc.]" are to be interpreted openly as at least one instance of the device, component, etc., unless otherwise explicitly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless explicitly stated.

Claims

1. A multi-laser coupling photoacoustic device, the device comprising: A resonant cavity, a microphone, a mirror, an air inlet, an air outlet, and at least two sets of laser generation units, where the laser generation unit includes a laser light source, a conducting optical fiber, and an optical fiber collimator connected in sequence; the air inlet is arranged at the first end of the resonant cavity, and the air outlet is arranged at the second end of the resonant cavity; the mirror and the microphone are arranged at the second end of the resonant cavity; It includes four sets of laser generation units, where: The laser light source of each set of laser generation units is a near-infrared narrow linewidth tunable semiconductor laser; The conducting optical fiber of each set of laser generation units is a G652 single-mode silica optical fiber; The wavelength range of the optical fiber collimator of each set of laser generation units is 185 nm - 2500 nm, and the working distance is 80 mm - 100 mm; The first optical fiber collimator in the first set of laser generation units is embedded into the resonant cavity downward at an inclination angle of 30° with respect to the vertical direction; The second optical fiber collimator in the second set of laser generation units is embedded into the resonant cavity downward at an inclination angle of 30° with respect to the horizontal direction; The third optical fiber collimator in the third set of laser generation units is embedded into the resonant cavity upward at an inclination angle of 30° with respect to the horizontal direction; The fourth optical fiber collimator in the fourth set of laser generation units is embedded into the resonant cavity upward at an inclination angle of 30° with respect to the vertical direction; The gas to be measured is input into the resonant cavity through the air inlet and released through the air outlet; The laser emitted by the laser light source in the laser generation unit is incident on the optical fiber collimator through the conducting optical fiber, and the laser collimated by the optical fiber collimator is obliquely incident on the resonant cavity at a preset angle. The laser is reflected multiple times on the inner side wall of the resonant cavity and then incident on the mirror. The laser reflected back by the mirror continues to be reflected in the resonant cavity to increase the absorption degree of the laser; The photoacoustic signal generated by the mirror is detected by the microphone, and based on the photoacoustic signal, the concentration of the gas to be measured is calculated.

2. The device according to claim 1, wherein the inner diameter of the resonant cavity is 10 mm, and the inner side wall of the resonant cavity is polished and gold-plated. The reflectivity of the processed inner side wall exceeds 98%.

3. The device according to claim 1, wherein the mirror is a gold-plated plane mirror with a reflectivity exceeding 98%; the diameter and thickness of the mirror are 12.5 mm and 3 mm respectively, and a micropore with a pore diameter of 1 mm is opened in the middle of the mirror for the conduction of sound signals and the flow of the gas to be measured.

4. A method for measuring the concentration of a gas based on a multi-laser coupled photoacoustic device, the method comprising: Establishing a multi-laser coupled photoacoustic device, the multi-laser coupled photoacoustic device including: a resonant cavity, a microphone, a mirror, an air inlet, an air outlet, and at least two sets of laser generation units, where the laser generation unit includes a laser light source, a conducting optical fiber, and an optical fiber collimator connected in sequence; the air inlet is arranged at the first end of the resonant cavity, and the air outlet is arranged at the second end of the resonant cavity; the mirror and the microphone are arranged at the second end of the resonant cavity; the multi-laser coupled photoacoustic device includes four sets of laser generation units, where: The laser light source of each group of laser generation units is a near-infrared narrow linewidth tunable semiconductor laser; The conduction optical fiber of each group of laser generation units is a G652 single-mode silica optical fiber; The wavelength range of the fiber collimator of each group of laser generation units is 185nm - 2500nm, and the working distance is 80mm - 100mm; The first fiber collimator in the first group of laser generation units is embedded into the resonant cavity downward at an inclination angle of 30° with respect to the vertical direction; The second fiber collimator in the second group of laser generation units is embedded into the resonant cavity downward at an inclination angle of 30° with respect to the horizontal direction; The third fiber collimator in the third group of laser generation units is embedded into the resonant cavity upward at an inclination angle of 30° with respect to the horizontal direction; The fourth fiber collimator in the fourth group of laser generation units is embedded into the resonant cavity upward at an inclination angle of 30° with respect to the vertical direction; The gas to be measured is input into the resonant cavity via the air inlet, and the gas to be measured is released via the air outlet; The laser emitted by the laser light source in the laser generation unit is incident on the fiber collimator through the conduction optical fiber, and the laser collimated by the fiber collimator is obliquely incident on the resonant cavity at a preset angle. The laser is reflected multiple times on the inner side wall of the resonant cavity and then incident on the mirror. The laser reflected back by the mirror continues to be reflected in the resonant cavity to increase the absorption degree of the laser; The photoacoustic signal generated by the mirror is detected by the microphone, and based on the photoacoustic signal, the concentration of the gas to be measured is calculated.

5. The method according to claim 4, wherein the inner diameter of the resonant cavity is 10mm, and the inner side wall of the resonant cavity is polished and gold-plated. The reflectivity of the processed inner side wall exceeds 98%.

6. The method according to claim 4, wherein the mirror is a gold-plated plane mirror with a reflectivity exceeding 98%; the diameter and thickness of the mirror are 12.5mm and 3mm respectively, and a micropore with a pore diameter of 1mm is opened in the middle of the mirror for the conduction of sound signals and the flow of the gas to be measured.

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