Photoacoustic Spectroscopy Gas Detection System Based on Open Differential Resonant Cavity Optical Path Enhancement

Abstract

The present invention relates to a photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement, comprising: a tunable laser light source module, a first optical path extension module, an open differential T-shaped photoacoustic resonator, a second optical path extension module, and a photoacoustic signal acquisition and central processing module. The tunable laser light source module is used to generate incident light with main path wavelength modulation. The first optical path extension module is arranged on the optical path of the tunable laser light source module and on one side of the open differential T-shaped photoacoustic resonator. The second optical path extension module is arranged on the other side of the open differential T-shaped photoacoustic resonator. The photoacoustic signal acquisition and central processing module is connected to the open differential T-shaped photoacoustic resonator. In this detection system, the open differential T-shaped photoacoustic resonator realizes multiple reuse of optical energy, resonance enhancement, and differential noise elimination, making the detection system have the advantages of no need for sampling, small loss, high Q value, strong structure, long-distance operation, and safe use.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical nondestructive detection of trace gases, and in particular relates to a photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement. Background Art

[0002] Nondestructive online detection of trace gases holds significant research value and application significance in fields such as atmospheric monitoring, industrial safety, and medical diagnostics. Industrial production activities have already caused significant damage to the natural environment, most notably through the greenhouse effect. CO2 and CH4 are the primary greenhouse gases. Monitoring changes in atmospheric greenhouse gas composition can be used for climate change research. Furthermore, monitoring the emission concentrations of pollutants such as nitrogen oxides, sulfides, and carbon monoxide is a powerful tool for atmospheric environmental protection. Detection of toxic and hazardous gases primarily targets industrial waste gas emissions and industrial process leaks, such as hydrogen sulfide, hydrogen chloride, and hydrogen cyanide. While these gases typically occur at extremely low levels, a leak can have devastating consequences. Monitoring volatile organic compounds (VOCs) has long garnered significant attention. VOCs encompass hundreds of volatile organic compounds, many of which are harmful to human health and the environment. The sampling characteristics of traditional chromatographic methods result in lengthy detection times, making continuous online monitoring impossible. To improve the atmospheric environment, scientific monitoring and accurate assessment of emissions and reduction effectiveness across various regions and industries within China are necessary.

[0003] Traditional gas detection methods, primarily chemical, require sample collection and processing, are susceptible to cross-interference from other gases, and are no longer able to meet the demands of on-site measurements in terms of sensitivity, range, and response time. Currently, photoacoustic detection technology is widely used for trace gas detection due to its high sensitivity and fast detection speed.

[0004] To improve detection sensitivity, existing photoacoustic detection devices often use multi-channel cells to increase the absorption pathlength, such as White and Herriott cells, to replace single-channel cells. However, these multi-channel cells are typically large and difficult to calibrate, making them difficult to miniaturize. Furthermore, existing closed photoacoustic cells require gas sampling and flow control. The aeration and purification steps are cumbersome and require additional equipment, making them costly and inconvenient to operate. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, the present invention provides a photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0006] The embodiment of the present invention provides a photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement, comprising: a tunable laser light source module, a first optical range extension module, an open differential T-type photoacoustic resonant cavity, a second optical range extension module, and a photoacoustic signal acquisition and central processing module, wherein:

[0007] The tunable laser light source module is used to generate incident light with a main wavelength modulated;

[0008] The first optical range extender module is disposed on the optical path of the tunable laser light source module and on one side of the open differential T-type photoacoustic resonant cavity, and is used to make the incident light enter the open differential T-type photoacoustic resonant cavity at a certain longitudinal deflection angle, and is used to generate the first reflected light multiple times;

[0009] The second optical range-extending module is disposed on the other side of the open differential T-type photoacoustic resonant cavity, and is used to generate the second reflected light multiple times;

[0010] The open differential T-type photoacoustic resonator is used to resonate enhance and differentially amplify the photoacoustic signal generated by the gas to be measured entering the cavity absorbing the incident light, the first reflected light, and the second reflected light, to obtain an output photoacoustic signal;

[0011] The photoacoustic signal acquisition and central processing module is connected to the open differential T-type photoacoustic resonant cavity, and is used to receive the output photoacoustic signal and process the output photoacoustic signal to achieve qualitative and quantitative detection of the gas to be measured.

[0012] In one embodiment of the present invention, the tunable laser light source module includes a tunable laser diode light source and a signal generator, wherein:

[0013] The tunable laser diode light source is used to generate incident laser light;

[0014] The signal generator is connected to the tunable laser diode light source and is used to modulate the wavelength of the incident laser using a current formed by superimposing a sine wave and a triangular wave to generate the incident light for exciting the gas to be measured.

[0015] In one embodiment of the present invention, the first optical range-extending module includes a plane mirror and a collimating mirror, wherein:

[0016] The collimating mirror is embedded in the plane mirror and is arranged on the optical path of the tuned laser light source module;

[0017] The collimating mirror is used to make the incident light enter the open differential T-type photoacoustic resonant cavity at a certain longitudinal deflection angle, and the plane mirror is used to generate the first reflected light multiple times.

[0018] In one embodiment of the present invention, the second optical range extender module includes a concave mirror, and the concave mirror is used to generate the second reflected light multiple times.

[0019] In one embodiment of the present invention, the plane mirror is made of BK7 glass, with a semi-aperture of 2.9 - 3.1 mm and a thickness of 1.9 - 2.1 mm;

[0020] The collimating mirror is made of BK7 glass, with a semi-aperture of 0.05 - 0.25 mm and a deflection angle of 27 - 31 degrees of x-axis deflection;

[0021] The collimating mirror is located 1.9 - 2.1 mm above the center y-axis of the plane mirror;

[0022] The concave mirror is made of BK7 glass, with a semi-aperture of 2.9 - 3.1 mm, a thickness of 1.9 - 2.1 mm, and a radius of curvature of 49.9 - 50.1 mm;

[0023] The distance between the concave mirror and the plane mirror is 21.9 - 22.1 mm.

[0024] In one embodiment of the present invention, the open differential T-type photoacoustic resonator includes a first buffer cavity, a second buffer cavity, an absorption cavity, a first resonance cavity, and a second resonance cavity. Among them,

[0025] The first buffer cavity is located at one end of the absorption cavity, the second buffer cavity is located at the other end of the absorption cavity. The sides of the first buffer cavity and the second buffer cavity both adopt an open structure, and the first buffer cavity and the second buffer cavity are symmetrically distributed left and right;

[0026] The first resonance cavity and the second resonance cavity are vertically symmetrically placed above the absorption cavity, forming a differential dual-resonance T-type structure with the absorption cavity, and are connected to the photoacoustic signal acquisition and central processing module;

[0027] The first buffer cavity and the second buffer cavity are used to allow the gas to be measured to enter the absorption cavity and change the resonance conditions of the acoustic boundary;

[0028] The absorption cavity is used to allow the gas to be measured to absorb the incident light, the first reflected light, and the second reflected light to generate the photoacoustic signal;

[0029] The first resonance cavity and the second resonance cavity are used to form standing wave acoustic signals with the same amplitude and opposite phases, so that the photoacoustic signal is resonance enhanced and differentially amplified to obtain the output photoacoustic signal.

[0030] In one embodiment of the present invention, the first buffer cavity, the second buffer cavity, the absorption cavity, the first resonance cavity, and the second resonance cavity all adopt a cylindrical structure.

[0031] In one embodiment of the present invention, the diameters of the first buffer cavity and the second buffer cavity are larger than the diameters of the absorption cavity, the first resonance cavity, and the second resonance cavity.

[0032] In one embodiment of the present invention, the diameters of the first resonance cavity and the second resonance cavity are smaller than the diameter of the absorption cavity.

[0033] In one embodiment of the present invention, the photoacoustic signal acquisition and central processing module includes a sound wave detection and acquisition module, a lock-in amplifier, and a signal processor. Among them,

[0034] The sound wave detection and acquisition module is connected to the open differential T-shaped photoacoustic resonator for converting the output photoacoustic signal into an electrical signal;

[0035] The lock-in amplifier is connected to the tunable laser light source module and the sound wave detection and acquisition module for processing the electrical signal to modulate a second harmonic signal having the same resonance frequency as that of the open differential T-shaped photoacoustic resonator, and obtaining a processed electrical signal;

[0036] The signal processor is connected to the lock-in amplifier for storing and signal analyzing the processed electrical signal to achieve qualitative and quantitative detection of the gas to be measured.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1. The gas detection system of the present invention can change the direction of light propagation and increase the optical path length by respectively arranging a first optical path extension module and a second optical path extension module on both sides of the open differential T-shaped photoacoustic resonator to generate reflected light multiple times, thereby improving the gas detection sensitivity and being beneficial to the miniaturization of the detection system.

[0039] 2. The gas detection system of the present invention adopts the structure of an open photoacoustic resonator, without using an optical lens as a window, greatly reducing the optical power loss. At the same time, there is no need for a gas sampling and gas flow control device, eliminating the complex procedures of inflating / purifying the traditional closed-type sensor, reducing the instrument cost and operation difficulty, and being more conducive to long-term high-precision online detection of trace gases.

[0040] 3. In the gas detection system of the present invention, the ends of the first buffer cavity and the second buffer cavity adopt an open structure. On the one hand, the buffer cavity does not need to place optical windows made of materials such as calcium fluoride and zinc selenide, greatly reducing the optical power loss. On the other hand, there is no acoustic wall boundary on its side. Combined with the mirror combination, it realizes the enhancement of the absorption optical path, does not generate an optical window background signal, avoids the problem of coherent noise generated by the interaction between the optical window and the modulated laser beam in the existing closed photoacoustic cell, and changes the acoustic boundary conditions, improving the sensitivity and accuracy of gas detection.

[0041] 4. In the gas detection system of the present invention, differential processing is performed on the anti-phase photoacoustic signals generated by the first resonance cavity and the second resonance cavity, which can eliminate the background noise of the same phase and amplify the photoacoustic signals of the different phase by 2 times, improving the sensitivity and accuracy of gas detection.

[0042] 5. In the detection system of the present invention, the open differential T-shaped photoacoustic resonator realizes the multiple reuse of optical energy, resonance enhancement and differential noise cancellation, making the detection system have the advantages of no need for sampling, small loss, high Q value, strong structure, long-distance operation and safe use. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic structural diagram of a photoacoustic spectroscopy gas detection system based on the optical path enhancement of an open differential resonator provided by an embodiment of the present invention;

[0044] Figure 2 It is a schematic structural diagram of another photoacoustic spectroscopy gas detection system based on the optical path enhancement of an open differential resonator provided by an embodiment of the present invention;

[0045] Figure 3 It is a schematic diagram of an optimized combination structure of a concave mirror and a plane mirror and a ray tracing diagram provided by an embodiment of the present invention;

[0046] Figures 4a - 4b It is a schematic diagram of the irradiance of the reflected light on the inner surface of a concave mirror and a plane mirror provided by an embodiment of the present invention;

[0047] Figure 5 It is a schematic structural diagram of an open differential T-shaped photoacoustic resonator provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] The following further describes the present invention in detail with specific embodiments, but the implementation manners of the present invention are not limited thereto.

[0049] Embodiment 1

[0050] Please refer to Figure 1 , Figure 1This is a schematic structural diagram of a photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement, provided by an embodiment of the present invention. The gas detection system includes a tunable laser light source module 1, a first optical range extension module 2, an open differential T-type photoacoustic resonant cavity 3, a second optical range extension module 4, and a photoacoustic signal acquisition and central processing module 5. The tunable laser light source module 1 is used to generate incident light with a main wavelength modulated. The first optical range extension module 2 is connected to the tunable laser light source module 1 and is disposed on one side of the open differential T-type photoacoustic resonant cavity 3. It is used to cause the incident light to enter the open differential T-type photoacoustic resonant cavity 3 at a certain longitudinal deflection angle and generate a first reflected light multiple times. The second optical range extension module 4 is disposed on the other side of the open differential T-type photoacoustic resonant cavity 3 and is used to generate a second reflected light multiple times. The open differential T-type photoacoustic resonant cavity 3 is used to resonantly enhance and differentially amplify the photoacoustic signals generated by the gas to be detected entering the cavity absorbing the first and second reflected lights, thereby obtaining an output photoacoustic signal. The photoacoustic signal acquisition and central processing module 5 is connected to the open differential T-type photoacoustic resonant cavity 3 and is used to receive the output photoacoustic signal and process the output photoacoustic signal to achieve qualitative and quantitative detection of the gas to be tested.

[0051] Specifically, the first optical range extender module 2 and the second optical range extender module 4 together form an optical range extender assembly for generating reflected light multiple times to increase the absorption optical path. As the optical path increases, the acoustic signal generated by the light absorption intensity of the gas to be measured is enhanced.

[0052] The gas detection system of this embodiment provides a first optical range-extending module and a second optical range-extending module on either side of an open differential T-type photoacoustic resonator for generating reflected light multiple times. This can change the direction of light propagation and increase the length of the optical path, thereby improving gas detection sensitivity and facilitating miniaturization of the detection system.

[0053] Specifically, the open differential T-type photoacoustic resonant cavity 3 has a ventilation window to allow the gas to be measured to enter the cavity, and then the gas to be measured in the cavity is irradiated with a light beam including incident light, first reflected light, and second reflected light to generate a photoacoustic signal, and the photoacoustic signal is resonantly enhanced and differentially amplified to obtain an output photoacoustic signal.

[0054] The gas detection system of this embodiment adopts an open photoacoustic resonant cavity structure, which does not require an optical lens as a window, greatly reducing the optical power loss. At the same time, it does not require gas sampling and airflow control devices, eliminating the complex inflation / purification procedures of traditional closed sensors, reducing instrument costs and operating difficulty, and is more conducive to long-term, high-precision online detection of trace gases.

[0055] Specifically, the signal processing module 5 is used to convert the output photoacoustic signal into an electrical signal, and process the electrical signal to complete the detection of the gas to be detected.

[0056] See Figure 2 , Figure 2 A schematic diagram of the structure of another photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement provided by an embodiment of the present invention. In one specific embodiment, a tunable laser light source module 1 includes a tunable laser diode light source 11 and a signal generator 12. The tunable laser diode light source 11 is used to generate incident laser light. The signal generator 12 is connected to the tunable laser diode light source 11 and is used to wavelength-modulate the incident laser light using a current composed of a superposition of a sine wave and a triangular wave to generate incident light that excites the gas to be detected.

[0057] Specifically, the tunable laser diode light source 11 is primarily used to provide a wavelength-tunable laser. The wavelength of the laser can be adjusted according to the main absorption peak of the gas to be measured. In other words, the wavelength of the laser must correspond to the main absorption peak of the gas to be measured. The signal generator 12 modulates the wavelength of the laser generated by the tunable laser diode light source 11 at a certain frequency. The modulation frequency should be half the eigenmode frequency of the open differential T-type photoacoustic resonator. After the modulation is completed, the incident light can be directly incident on the interior of the open differential T-type photoacoustic resonator 3.

[0058] See Figure 3 and Figures 4a - 4b , Figure 3 A schematic diagram of an optimized reflector combination structure of a concave mirror and a plane mirror and ray tracing provided by an embodiment of the present invention, Figures 4a - 4b A schematic diagram of the irradiance of reflected light on the inner surface of a concave mirror and a plane mirror provided in an embodiment of the present invention, Figure 4a The spot is the surface reflected light irradiance diagram of the concave mirror, Figure 4b The light spot is the irradiation intention of the reflected light on the inner surface of the plane mirror. Figure 4a and Figure 4b The number of spots of the mid-surface irradiance indicates the number of times the incident laser is reflected between the two reflectors. In a specific embodiment, the first optical range-extending module 2 includes a plane mirror 21 and a collimating mirror 22. The collimating mirror 22 is embedded in the plane mirror 21 and is arranged on the optical path of the tunable laser light source module 1, and is connected to the tunable laser light source module 1 through an optical fiber; the collimating mirror 22 is used to make the incident light enter the open differential T-type photoacoustic resonator 3 at a certain longitudinal deflection angle, and the plane mirror 21 is used to generate the first reflected light multiple times. The second optical range-extending module 4 includes a concave mirror 41, which is used to generate the second reflected light multiple times.

[0059] Specifically, the plane mirror can be a plane mirror with a gold-plated film, and the concave mirror can also be a concave mirror with a gold-plated film. The plane mirror and the collimator mirror together with the concave mirror form a mirror combination for generating reflected light multiple times. The collimator mirror 22 is used to make the incident light enter the open differential T-shaped photoacoustic resonator 3 at a certain longitudinal deflection angle, and this longitudinal deflection angle is the same as the deflection angle of the collimator mirror 22. By optimizing the diameters of the concave mirror and the plane mirror, the focal length of the concave mirror, and the deflection angle of the collimator, the light beam can be reflected multiple times on the plane mirror and the concave mirror, as Figure 3 shown, so as to enhance the absorption optical path. Moreover, multiple reflections only occur in the open differential T-shaped photoacoustic resonator, that is, the buffer cavity and the absorption cavity, which can effectively suppress sidewall absorption and eliminate the influence of coherent noise.

[0060] In a specific embodiment, the plane mirror 21 is made of BK7 glass, with a semi-aperture of 2.9 - 3.1 mm and a thickness of 1.9 - 2.1 mm. The collimator mirror 22 is made of BK7 glass, with a semi-aperture of 0.05 - 0.25 mm and a deflection angle of 27 - 31 degrees of deflection about the x-axis. The collimator mirror 22 is located 1.9 - 2.1 mm above the center y-axis of the plane mirror 21. The concave mirror 41 is made of BK7 glass, with a semi-aperture of 2.9 - 3.1 mm, a thickness of 1.9 - 2.1 mm, and a radius of curvature of 49.9 - 50.1 mm. The distance between the concave mirror 41 and the plane mirror 21 is 21.9 - 22.1 mm.

[0061] Preferably, by optimizing the parameter combinations such as the diameters of the concave mirror and the plane mirror, the focal length of the concave mirror, the deflection angle of the collimator mirror, and the spacing distance between the mirrors, after optimization, the plane mirror 21 is made of BK7 glass, with a semi-aperture of 3 mm and a thickness of 2 mm; the collimator mirror 22 is made of BK7 glass, with a semi-aperture of 0.15 mm and a deflection angle of 29 degrees of deflection about the x-axis; the collimator mirror 22 is located 2 mm above the center y-axis of the plane mirror 21; the concave mirror 41 is made of BK7 glass, with a semi-aperture of 3 mm, a thickness of 2 mm, and a radius of curvature of 50 mm; the distance between the concave mirror 41 and the plane mirror 21 is 22 mm. Under this parameter combination, the detection system reaches the maximum optical path increment, achieving an enhanced effect of 31 reflections on the plane mirror and 32 reflections on the concave mirror, as Figures 4a - 4b shown, Figure 4a and Figure 4b the multiple light spots of

[0062] indicate that the light has been reflected multiple times between the plane mirror and the concave mirror.

[0063] Please refer to Figure 5 , Figure 5 which is a schematic structural diagram of an open differential T-shaped photoacoustic resonator provided by an embodiment of the present invention. In a specific embodiment, the open differential T-shaped photoacoustic resonator 3 is a double-resonance differential T-shaped photoacoustic resonator, including a first buffer cavity 31, a second buffer cavity 32, an absorption cavity 33, a first resonance cavity 34 and a second resonance cavity 35. Among them, the first buffer cavity 31 is located at one end of the absorption cavity 33, the second buffer cavity 32 is located at the other end of the absorption cavity 33, the sides of the first buffer cavity 31 and the second buffer cavity 32 both adopt an open structure, and the first buffer cavity 31 and the second buffer cavity 32 are symmetrically distributed left and right. The first resonance cavity 34 and the second resonance cavity 35 are vertically symmetrically placed above the absorption cavity 33, forming a differential double-resonance T-shaped structure with the absorption cavity 33, and are connected to the photoacoustic signal acquisition and central processing module 5. The first buffer cavity 31 and the second buffer cavity 32 are used to allow the gas to be measured to enter the absorption cavity 33 and change the resonance conditions of the acoustic boundary; the absorption cavity 33 is used to absorb the incident light, the first reflected light and the second reflected light by the gas to be measured to generate a photoacoustic signal; the first resonance cavity 34 and the second resonance cavity 35 are used to form standing wave acoustic signals with the same amplitude and opposite phases, so that the photoacoustic signal is resonance enhanced and differentially amplified to obtain an output photoacoustic signal.

[0064] Specifically, the first buffer cavity 31 and the second buffer cavity 32 are arranged at both ends of the absorption cavity 33. The sides of the first buffer cavity 31 and the second buffer cavity 32 adopt an open structure, without using an optical lens as an incident window, and ventilation windows are provided at both ends to communicate with the external gas environment, so that the gas to be measured can enter the resonator; and the first buffer cavity 31 and the second buffer cavity 32 are symmetrically distributed left and right. The first buffer cavity 31 and the second buffer cavity 32 are used to change the resonance conditions of the acoustic boundary.

[0065] The absorption cavity 33 is located in the middle of the lower part of the open photoacoustic resonator, and is used to absorb the incident light and generate a photoacoustic effect, and can also be used as a cavity for multiple reflected lights.

[0066] The first resonance cavity 34 and the second resonance cavity 35 are located above the absorption cavity 33, and are symmetrically distributed left and right, forming a T-shaped structure with the absorption cavity 33. The first resonance cavity 34 and the second resonance cavity 35 are used to generate standing wave photoacoustic signals with equal amplitudes and opposite phases, and output after resonance enhancement and differential amplification of the photoacoustic signal.

[0067] Specifically, place the gas detection system with the open differential T-shaped photoacoustic resonator 3 in the environment of the gas to be measured. The gas to be measured can enter the photoacoustic resonator through the ventilation windows at both ends of the absorption cavity, making the inside of the open differential T-shaped photoacoustic resonator 3 filled with ambient gas. The incident light enters the absorption cavity 33 of the photoacoustic resonator at a certain longitudinal deflection angle and is reflected multiple times in the absorption cavity 33, the first buffer cavity 31, and the second buffer cavity 32, causing the gas to be measured to periodically absorb light and generate relaxation, thereby generating a photoacoustic signal. The magnitude of the photoacoustic signal is linearly related to the concentration of the gas to be measured, and as the optical path increases, the sound signal generated by the absorption of light by the gas in the open T-shaped photoacoustic resonator 33 is enhanced. Further, the double resonance cavity resonantly increases and differentially amplifies the photoacoustic signal generated by the absorption cavity, and then outputs the processed photoacoustic signal to the signal processing module to demodulate the second harmonic signal.

[0068] In this embodiment, an open differential T-shaped photoacoustic resonator is adopted. On the one hand, due to the addition of an open buffer cavity, the structure of an open resonant photoacoustic cell is formed, eliminating the need to place optical windows made of materials such as calcium fluoride and zinc selenide, greatly reducing the optical power loss. On the other hand, there is no acoustic wall boundary on the side of the buffer cavity. Combined with a mirror combination, the absorption optical path is enhanced, and no photo-window background signal is generated. There is no need for an optical lens as a window, avoiding the problem of coherent noise generated by the interaction between the optical window and the modulated laser beam in the existing closed photoacoustic cell. Moreover, the acoustic boundary conditions are changed, isolating external noise, and improving the sensitivity and accuracy of gas detection.

[0069] In this embodiment, a double resonance cavity is used to generate photoacoustic signals with the same amplitude and opposite phases. After differential processing, the in-phase ambient noise is eliminated, and the anti-phase photoacoustic signal of the target gas is amplified by 2 times, improving the sensitivity and accuracy of gas detection and enhancing the detection signal-to-noise ratio.

[0070] In this embodiment, an open differential T-shaped photoacoustic resonator is used as the resonant photoacoustic cell, realizing multiple reuse of light energy, resonance enhancement, and differential noise cancellation, making the detection system have the advantages of no need for sampling, small loss, high Q value, strong structure, long-distance operation, and safe use.

[0071] In a specific embodiment, the first buffer cavity 31, the second buffer cavity 32, the absorption cavity 33, the first resonance cavity 34, and the second resonance cavity 35 all adopt a cylindrical structure. The diameters of the first buffer cavity 31 and the second buffer cavity 32 are larger than those of the absorption cavity 33, the first resonance cavity 34, and the second resonance cavity 35. The diameters of the first resonance cavity 34 and the second resonance cavity 35 are smaller than that of the absorption cavity 33.

[0072] In a specific embodiment, the photoacoustic signal acquisition and central processing module 5 is arranged on the top of the open differential T-shaped photoacoustic resonator 3, and includes a sound wave detection and acquisition module 51, a lock-in amplifier 52 and a signal processor 53. Among them, the sound wave detection and acquisition module 51 is connected to the open differential T-shaped photoacoustic resonator 3, specifically connected to the tops of the first resonator 34 and the second resonator 35, and is used to convert the output photoacoustic signal into an electrical signal. The lock-in amplifier 52 is connected to the tunable laser light source module 1 and the sound wave detection and acquisition module 51, and is used to process the electrical signal to modulate the second harmonic signal with the same resonance frequency as the open differential T-shaped photoacoustic resonator 3 to obtain the processed electrical signal. Specifically, the lock-in amplifier 52 is connected to the signal generator 12 and the sound wave detection and acquisition module 51, and the signal generator 12 is used to provide a reference signal. The signal processor 53 is connected to the lock-in amplifier 52, and is used to store and analyze the processed electrical signal to realize the qualitative and quantitative detection of the gas to be measured.

[0073] The detection method of the above photoacoustic spectroscopy gas detection system based on open differential resonator optical path enhancement is as follows: Place the open differential T-shaped photoacoustic resonator 3 in the measurement environment to make the ambient gas fill the open differential T-shaped photoacoustic resonator 3. The tunable laser diode light source 11 generates laser light with a wavelength corresponding to the main absorption peak of the trace gas to be measured, and then uses the signal generator 12 to modulate the laser light intensity at a certain frequency. The modulation frequency should be half of the eigenmode frequency of the open differential T-shaped photoacoustic resonator 3. The modulated laser light is incident on the absorption cavity of the open differential T-shaped photoacoustic resonator 3 at a certain longitudinal deflection angle and is reflected multiple times in the absorption cavity, causing the periodic absorption of light by the gas to be measured and generating relaxation, thereby generating a photoacoustic signal. The magnitude of the photoacoustic signal is linearly related to the concentration of the gas to be measured. The photoacoustic signal is detected by the sound wave detection and acquisition module 51 located at the antinode of the photoacoustic signal wave after resonance amplification and differential processing by the first resonator 34 and the second resonator 35 and is converted into an electrical signal. The lock-in amplifier 52 performs cross-correlation operation and low-pass filtering on the electrical signal to filter out interference signals with different frequencies from the photoacoustic signal. The electrical signal processed by the lock-in amplifier 52 is transmitted to the signal processor 53 and is stored and analyzed by the signal processor 53 to complete the high-precision online detection of trace gases.

[0074] The gas detection system based on the open differential T-shaped photoacoustic resonator with enhanced multiple reflection light provided in this embodiment does not require a gas flow control device, eliminates the complex procedures of inflating / purifying traditional closed sensors, reduces the instrument cost and operation difficulty, and is more conducive to the long-term high-precision online detection of trace gases.

[0075] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement, characterized in that: include: A tunable laser light source module (1), a first optical range-extending module (2), an open differential T-type photoacoustic resonant cavity (3), a second optical range-extending module (4), and a photoacoustic signal acquisition and central processing module (5), wherein: The tunable laser light source module (1) is used to generate incident light with a main wavelength modulated; The first optical range-extending module (2) is arranged on the optical path of the tunable laser light source module (1) and on one side of the open differential T-type photoacoustic resonant cavity (3), and is used to make the incident light enter the open differential T-type photoacoustic resonant cavity (3) at a certain longitudinal deflection angle, and is used to generate the first reflected light multiple times; The second optical range-extending module (4) is arranged on the other side of the open differential T-type photoacoustic resonant cavity (3) and is used to generate second reflected light multiple times; The open differential T-type photoacoustic resonant cavity (3) is used to resonate enhance and differentially amplify the photoacoustic signal generated by the gas to be measured entering the cavity absorbing the incident light, the first reflected light and the second reflected light, so as to obtain an output photoacoustic signal; the open differential T-type photoacoustic resonant cavity (3) comprises a first buffer cavity (31), a second buffer cavity (32), an absorption cavity (33), a first resonant cavity (34) and a second resonant cavity (35), wherein the first buffer cavity (31) is located at one end of the absorption cavity (33), and the second buffer cavity (32) is located at the other end of the absorption cavity (33); the side surfaces of the first buffer cavity (31) and the second buffer cavity (32) both adopt an open structure, and the first buffer cavity (31) and the second buffer cavity (32) are symmetrically distributed on the left and right; The first resonant cavity (34) and the second resonant cavity (35) are vertically symmetrically placed above the absorption cavity (33), forming a differential double-resonance T-shaped structure with the absorption cavity (33), and are connected to the photoacoustic signal acquisition and central processing module (5); the first buffer cavity (31) and the second buffer cavity (32) are used to allow the gas to be measured to enter the absorption cavity (33) and change the resonance condition of the acoustic boundary; the absorption cavity (33) is used to allow the gas to be measured to absorb the incident light, the first reflected light and the second reflected light to generate the photoacoustic signal; the first resonant cavity (34) and the second resonant cavity (35) are used to form a standing wave acoustic signal with the same amplitude and opposite phase, so that the photoacoustic signal is resonantly enhanced and differentially amplified to obtain the output photoacoustic signal; The photoacoustic signal acquisition and central processing module (5) is connected to the open differential T-type photoacoustic resonant cavity (3) and is used for receiving the output photoacoustic signal and processing the output photoacoustic signal to achieve qualitative and quantitative detection of the gas to be detected.

2. The photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement according to claim 1 is characterized in that: The tunable laser light source module (1) comprises a tunable laser diode light source (11) and a signal generator (12), wherein: The tunable laser diode light source (11) is used to generate incident laser light; The signal generator (12) is connected to the tunable laser diode light source (11) and is used to perform wavelength modulation on the incident laser using a current formed by superimposing a sine wave and a triangle wave to generate the incident light that excites the gas to be measured.

3. The photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement according to claim 1 is characterized in that: The first optical range-extending module (2) comprises a plane mirror (21) and a collimating mirror (22), wherein: The collimating mirror (22) is embedded in the plane mirror (21) and is arranged on the optical path of the tuned laser light source module (1); The collimating mirror (22) is used to make the incident light enter the open differential T-type photoacoustic resonant cavity (3) at a certain longitudinal deflection angle, and the plane mirror (21) is used to generate the first reflected light multiple times.

4. The photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement according to claim 3 is characterized in that: The second optical range-extending module (4) comprises a concave mirror (41), and the concave mirror (41) is used to generate the second reflected light multiple times.

5. The photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement according to claim 4 is characterized in that: The plane mirror (21) is made of BK7 glass with a semi-aperture of 2.9-3.1 mm and a thickness of 1.9-2.1 mm; The collimating mirror (22) is made of BK7 glass, has a semi-aperture of 0.05-0.25 mm, and a deflection angle of 27-31 degrees about the x-axis; The collimating mirror (22) is located 1.9-2.1 mm above the center y-axis of the plane mirror (21); The concave mirror (41) is made of BK7 glass, with a semi-aperture of 2.9-3.1 mm, a thickness of 1.9-2.1 mm, and a curvature radius of 49.9-50.1 mm; The distance between the concave mirror (41) and the plane mirror (21) is 21.9-22.1 mm.

6. The photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement according to claim 1 is characterized in that: The first buffer cavity (31), the second buffer cavity (32), the absorption cavity (33), the first resonance cavity (34) and the second resonance cavity (35) all adopt cylindrical structures.

7. The photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement according to claim 1 is characterized in that: The diameters of the first buffer cavity (31) and the second buffer cavity (32) are larger than the diameters of the absorption cavity (33), the first resonance cavity (34), and the second resonance cavity (35).

8. The photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement according to claim 1 is characterized in that: The diameters of the first resonance cavity (34) and the second resonance cavity (35) are smaller than the diameter of the absorption cavity (33).

9. The photoacoustic spectroscopy gas detection system based on open differential resonant cavity optical path enhancement according to claim 1, characterized in that: The photoacoustic signal acquisition and central processing module (5) includes an acoustic wave detection and acquisition module (51), a phase-locked amplifier (52) and a signal processor (53), wherein: The acoustic wave detection and acquisition module (51) is connected to the open differential T-type photoacoustic resonant cavity (3) and is used to convert the output photoacoustic signal into an electrical signal; The lock-in amplifier (52) is connected to the tunable laser light source module (1) and the acoustic wave detection and acquisition module (51), and is used to process the electrical signal to adjust the second harmonic signal having the same resonance frequency as the open differential T-type photoacoustic resonant cavity (3), thereby obtaining a processed electrical signal; The signal processor (53) is connected to the lock-in amplifier (52) and is used for storing and analyzing the processed electrical signal to achieve qualitative and quantitative detection of the gas to be detected.

Images