Enhanced photoacoustic spectroscopy gas detection device based on Bessel beam shaping

Abstract

The present invention relates to the field of gas detection technology, and in particular to an enhanced photoacoustic spectroscopy gas detection device based on Bessel beam shaping, comprising: a light source, a beam modulation module and a photoacoustic cell; the beam modulation module modulates the output light generated by the light source to form a Bessel beam; the output end of the beam modulation module is connected to the input end of the photoacoustic cell to input the Bessel beam into the photoacoustic cell and excite the gas to be detected. In view of the problem that the Gaussian beam generated by the light source of the photoacoustic spectroscopy system in the prior art has poor uniformity and cannot be uniformly excited in the photoacoustic cell, in this solution, a group of beam modulation modules are added to the front stage of the photoacoustic cell, and the beam modulation module can phase-modulate the Gaussian beam generated by the laser source and convert it into a Bessel beam with non-diffraction characteristics and relatively concentrated beam, thereby achieving uniform excitation of the gas to be detected in the photoacoustic cell, making the photoacoustic effect more stable, and facilitating the realization of a higher-precision detection effect.

Description

Technical Field

[0001] The present invention relates to the technical field of gas detection, and in particular to an enhanced photoacoustic spectroscopy gas detection device based on Bessel beam shaping. Background Art

[0002] Photoacoustic spectroscopy (PAS) is a highly sensitive analytical method based on the photoacoustic effect, widely used in gas analysis, environmental monitoring, and pollutant detection. Its basic principle is that when light (usually laser light) strikes gas molecules or solid surfaces, the light energy is absorbed and converted into heat, causing local temperature changes that further stimulate acoustic waves. By detecting these acoustic waves, signals related to the intensity and frequency of the light source can be obtained, enabling analysis of the sample.

[0003] For example, Chinese patent CN202122197036.1 discloses a photoacoustic cell, including a photoacoustic cell body, wherein a first buffer chamber, a second buffer chamber and a resonant cavity are provided in the photoacoustic cell body, the first buffer chamber and the second buffer chamber are connected through the resonant cavity, the first buffer chamber is provided with an air inlet and a first window, the second buffer chamber is provided with an air outlet and a second window, the first window is provided with a first window piece, and the incident light through the first window piece passes through the first buffer chamber, the resonant cavity and the second buffer chamber in sequence, and is reflected from the inner wall of the second window back to the inner wall of the resonant cavity and the second buffer chamber, or is directly emitted from the second window; a microphone is provided on the resonant cavity; the interior of the photoacoustic cell body is a sealed cavity; a pressure sensor is provided at the first buffer chamber, and a thermocouple is provided at the second buffer chamber. This photoacoustic cell structure can ensure the same experimental conditions, monitor the pressure and temperature parameters in the photoacoustic cell in real time, and facilitate the analysis of the influence of pressure and temperature on the photoacoustic detection characteristics.

[0004] However, in actual implementation, in traditional PAS systems, Gaussian beams are usually used as excitation light sources. However, the energy distribution of Gaussian beams is uneven, with high energy density at the center and rapid attenuation at the edges. This may lead to local oversaturation of the sample, non-uniform energy distribution, and short depth of focus, limiting the excitation range and uniformity of the photoacoustic signal. Summary of the Invention

[0005] In view of the above problems existing in the prior art, an enhanced photoacoustic spectroscopy gas detection device based on Bessel beam shaping is provided.

[0006] The specific technical solution is as follows: an enhanced photoacoustic spectroscopy gas detection device based on Bessel beam shaping, comprising a light source, a beam modulation module and a photoacoustic cell; the beam modulation module modulates the output light generated by the light source to form a Bessel beam; the output end of the beam modulation module is connected to the input end of the photoacoustic cell to input the Bessel beam into the photoacoustic cell and excite the gas to be detected.

[0007] On the other hand, the input end and the output end of the beam modulation module are arranged in a straight line; the light source, the beam modulation module and the resonant cavity of the photoacoustic cell are arranged coaxially.

[0008] On the other hand, a microphone is provided in the middle of the resonance cavity; the installation depth of the microphone and the total length of the resonance cavity are matched with the focal depth of the Bessel beam respectively.

[0009] On the other hand, the total length of the resonant cavity is 200 mm; the focal depth of the Bessel beam is 50-200 mm; and the adjustment accuracy of the central spot diameter of the Bessel beam is ±10 μm.

[0010] On the other hand, the beam modulation module is sequentially arranged along the optical axis direction: a liquid crystal phase modulator, which forms the Bessel beam by loading a dynamic phase pattern; a nonlinear optical crystal unit, which adjusts the light intensity distribution of the Bessel beam through the photorefractive effect to change the focal depth and spot diameter; and a collimating lens, which performs collimation control on the Bessel beam.

[0011] On the other hand, a microphone is provided in the photoacoustic cell; the enhanced photoacoustic spectroscopy gas detection device also includes: a signal processing circuit, which is connected to the microphone; the signal processing circuit processes the original audio signal output by the microphone to form a preprocessed signal; a processing device, which is connected to the signal processing circuit; the processing device analyzes the preprocessed signal to obtain a measurement result.

[0012] On the other hand, the signal processing circuit includes: a phase-locked amplifier circuit, which processes the original audio signal according to a preset resonant frequency to separate the noise signal and form a denoised signal; an adaptive filtering circuit, which is connected to the phase-locked amplifier circuit; the adaptive filtering circuit samples the denoised signal to obtain the preprocessed signal and outputs it.

[0013] On the other hand, the beam modulation module also includes a piezoelectric control circuit and a temperature control circuit; the temperature control circuit is connected to the nonlinear optical crystal unit and the piezoelectric control circuit; the temperature control circuit measures the crystal temperature of the nonlinear optical crystal unit and generates a first control signal; the piezoelectric control circuit is connected to the nonlinear optical crystal unit; the piezoelectric control circuit changes the voltage applied to the nonlinear optical crystal unit according to the first control signal and the second control signal output by the processing device to adjust the focal depth and spot diameter of the Bessel beam; on the other hand, the light source is a tunable laser, which excites a Gaussian beam of corresponding central wavelength according to the gas to be detected in the photoacoustic cell.

[0014] On the other hand, the photoacoustic cell includes: a first buffer cavity, which is located at the first end of the photoacoustic cell; a resonance cavity, which is located behind the first buffer cavity; and a second buffer cavity, which is located at the second end of the photoacoustic cell; and the second buffer cavity is connected to the resonance cavity.

[0015] The above technical solution has the following advantages or beneficial effects: In response to the problem that the Gaussian beam generated by the light source of the photoacoustic spectroscopy system in the prior art has poor uniformity and cannot be uniformly excited in the photoacoustic cell, in this solution, a group of beam modulation modules are added to the front stage of the photoacoustic cell. The beam modulation module can phase-modulate the Gaussian beam generated by the laser source and convert it into a Bessel beam with non-diffraction characteristics and relatively concentrated beam, thereby achieving uniform excitation of the gas to be detected in the photoacoustic cell, making the photoacoustic effect more stable, and facilitating the realization of higher-precision detection effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The embodiments of the present invention will be described more fully with reference to the accompanying drawings, which are provided for illustration and description only and are not intended to limit the scope of the present invention.

[0017] Figure 1 is an overall schematic diagram of an embodiment of the present invention;

[0018] Figure 2 Schematic diagram of a beam modulation module according to an embodiment of the present invention;

[0019] Figure 3 This is a schematic diagram of a processing module in an embodiment of the present invention;

[0020] Figure 4 Schematic diagram of a signal processing module in an embodiment of the present invention;

[0021] Figure 5 Schematic diagram of a piezoelectric control circuit in an embodiment of the present invention;

[0022] Figure 6Schematic diagram of the photoacoustic cell in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0024] In this specification, unless otherwise specified or limited, terms such as "disposed," "installed," "connected," "connected," and "fixed" should be understood broadly. For example, they may refer to fixed or detachable connections, mechanical connections, direct connections, or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of these terms in this specification based on specific circumstances.

[0025] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0027] The present invention includes: an enhanced photoacoustic spectroscopy gas detection device based on Bessel beam shaping, such as Figure 1-3 As shown, it includes a light source 1, a beam modulation module 2 and a photoacoustic cell 3; the beam modulation module 2 modulates the output light generated by the light source to form a Bessel beam; the output end of the beam modulation module 2 is connected to the input end of the photoacoustic cell 3 to input the Bessel beam into the photoacoustic cell 3 and excite the gas to be detected.

[0028] Specifically, in order to address the problem that the Gaussian beam generated by the light source of the photoacoustic spectroscopy system in the prior art has poor uniformity and cannot be uniformly excited in the photoacoustic cell, in this solution, a group of beam modulation modules are added to the front stage of the photoacoustic cell. The beam modulation module can phase-modulate the Gaussian beam generated by the laser source and convert it into a Bessel beam with non-diffraction characteristics and relatively concentrated beam, thereby achieving uniform excitation of the gas to be detected in the photoacoustic cell, making the photoacoustic effect more stable, and facilitating the realization of higher-precision detection effects.

[0029] Specifically, the enhanced photoacoustic spectroscopy gas detection device in this solution mainly includes the following devices according to the signal transmission direction: light source 1, beam modulation module 2, photoacoustic cell 3, microphone 4, and processing module 5.

[0030] Among them, the light source 1 is a laser source, which generates a laser beam of a specific wavelength under the control of a driving circuit. The laser beam is a Gaussian beam when not modulated, and its energy distribution is uneven, decays rapidly, and has a short focal depth.

[0031] The beam modulation module 2 is a group of optical elements with a phase control function, which can realize phase modulation of the incident light beam to change the phase and energy distribution of the incident light beam.

[0032] In this embodiment, in order to achieve uniform excitation of the gas to be detected, the beam modulation module 2 modulates the Gaussian beam into a Bessel beam (also called a Gaussian-Bessel beam) by loading a phase pattern. The Bessel beam has the characteristics of no diffraction compared to the Gaussian beam, and has a longer focal depth and uniform excitation of the central area compared to the Gaussian beam. Therefore, it helps to improve the accuracy of the subsequent acoustic signal generated by the acousto-optic effect.

[0033] The photoacoustic cell 3 is a device used to excite the gas to be detected. It is typically hollow, with two buffer chambers at either end: a first buffer chamber 31 and a second buffer chamber 32. These are connected by a long cylindrical resonant cavity 33, which houses a microphone 4. End caps are provided on the outside of the first and second buffer chambers at either end of the photoacoustic cell 3, each with an optical window.

[0034] Generally speaking, the photoacoustic cell 3 is used to contain the gas to be detected. The incident light enters the photoacoustic cell 3 through the optical window at one end, enters the resonance cavity through the first buffer cavity, excites the gas to be detected, and thus forms a photoacoustic effect. The sound signal is amplified to a certain extent in the resonance cavity and captured by the microphone 4. The gas can be measured by analyzing the sound signal.

[0035] However, in the traditional technical solution, the incident light is a Gaussian beam with uneven energy distribution, which results in the inability of the incident light to control the effective excitation site of the gas to be detected after entering the photoacoustic pool 3, thereby causing the amplitude of the audio signal captured by the microphone 4 to shift, thereby reducing the accuracy and being insufficient for application in high-precision detection scenarios.

[0036] To address this problem, this application adds a beam modulation module 2 in the front stage of the photoacoustic cell 3. The beam modulation module 2 is a group of optical elements with phase control function, which can realize phase modulation of the incident light beam to change the phase and energy distribution of the incident light beam.

[0037] The beam modulation module 2 modulates the Gaussian beam into a Bessel beam by loading a phase pattern.

[0038] The Bessel beam maintains uniform light intensity over a long distance, avoiding the problem of a Gaussian beam with excessive concentration at the center and insufficient light intensity at the edges, and achieving uniform excitation of the gas throughout the photoacoustic cell. The long focal depth of the Bessel beam ensures a larger excitation area in the photoacoustic cell with a resonant cavity structure, thereby improving the signal strength of the system. Uniform excitation and reduced local heat accumulation reduce the noise component of the photoacoustic signal and improve the overall signal-to-noise ratio. The device is suitable for photoacoustic detection of a variety of gases and has broad application prospects.

[0039] In one embodiment, the input end and the output end of the light beam modulation module 2 are arranged in a straight line; the light source 1, the light beam modulation module 2 and the resonant cavity of the photoacoustic cell 3 are arranged coaxially.

[0040] Specifically, in order to achieve better transmission efficiency, a linear system configuration is set up in this embodiment, wherein the beam modulation module 2 is distributed in a linear shape. After the light source 1 forms a Gaussian beam and emits it, it is input into the linear beam modulation module 2 for phase pattern loading, thereby modulating it to obtain a Bessel beam.

[0041] Subsequently, the Bessel beam is emitted in a straight line to the photoacoustic cell 3, directly coupled into the photoacoustic cell cavity, and coaxially aligned with the cavity axis to ensure that the light energy is evenly distributed in the photoacoustic cell.

[0042] In one embodiment, a microphone is provided in the middle of the resonance cavity 33 ; the installation depth of the microphone 4 and the total length of the resonance cavity 33 are matched with the focal depth of the Bessel beam respectively.

[0043] Specifically, in order to achieve a more uniform excitation effect, in this embodiment, the focal depth of the modulated Bessel light beam is first determined, and then the installation depth of the microphone 4 and the total length of the resonance cavity 33 are adjusted based on the focal depth of the Bessel light beam, so that the microphone 4 can collect the sound signal after uniform excitation by the Bessel light beam.

[0044] In one embodiment, the total length of the resonant cavity is 200 mm; the focal depth of the Bessel beam is 50-200 mm; and the adjustment accuracy of the central spot diameter of the Bessel beam is ±10 μm.

[0045] Specifically, to achieve a more uniform excitation effect, in this embodiment, the focal depth of the modulated Bessel beam is first determined. Taking the detection of acetylene gas as an example, when a distributed feedback (DFB) semiconductor laser is used as the laser light source, the wavelength is set to 1531 nm, and the output power of the laser is 10 mW, the converted Bessel beam has a central area diameter of approximately 300 μm, and the focal depth is adjustable between 50-200 mm.

[0046] On this basis, by determining the total length of the resonant cavity to be 200 mm, the diameter to be 6 mm, and the buffer cavity length to be 20 mm, the Bessel beam can be stably excited, thereby achieving higher acquisition accuracy. At the same time, the resonant cavity can match the full length of the Bessel beam.

[0047] In one embodiment, Figure 2 As shown, the beam modulation module 2 is sequentially provided along the optical axis direction with: a liquid crystal phase modulator 21, which forms a Bessel beam by loading a dynamic phase pattern; a nonlinear optical crystal unit 22, which adjusts the light intensity distribution of the Bessel beam through the photorefractive effect to change the focal depth and the spot diameter; and a collimating lens 23, which performs collimation control on the Bessel beam.

[0048] Specifically, in order to achieve a better modulation effect on the outgoing light, in this embodiment, a nonlinear optical crystal unit 22 and a collimating lens 23 are sequentially provided at the subsequent stage of the liquid crystal phase modulator 21 .

[0049] Specifically, in the process of modulating the Bessel beam, the liquid crystal phase modulator 21 can convert the Gaussian beam into a Bessel beam by loading a phase pattern calculated in real time based on the target focal depth and spot diameter, but the focal depth and spot diameter of the Bessel beam may not be ideal, and a stable excitation effect cannot be achieved in a specific area of ​​the resonant cavity.

[0050] Taking this issue into consideration, in this embodiment, a nonlinear optical crystal unit 22 is introduced at the subsequent stage of the liquid crystal phase modulator 21. The nonlinear optical crystal unit is implemented using a crystal with nonlinear optical properties, such as a lithium niobate crystal. The piezoelectric effect can change its refractive index gradient, thereby forming a specific photorefractive effect to change the light intensity distribution of the Bessel light beam, thereby changing the focal depth and spot diameter, so that the Bessel light beam can stably excite the gas to be detected after entering a specific position of the resonant cavity.

[0051] At the same time, considering that the nonlinear optical crystal unit 22 further modulates the light beam, in order to stabilize the convergence of the light beam, the light beam is further calibrated through the collimating lens 23 and then input into the photoacoustic cell 3 .

[0052] In one embodiment, a microphone 4 is provided in the photoacoustic pool 3; Figure 3 As shown, the processing module 5 in the enhanced photoacoustic spectroscopy gas detection device also includes: a signal processing circuit 51, which is connected to the microphone 4; the signal processing circuit 51 processes the original audio signal output by the microphone to form a preprocessed signal; a processing device 52, which is connected to the signal processing circuit 51; the processing device 52 analyzes the preprocessed signal to obtain a measurement result.

[0053] Specifically, in order to achieve a more accurate measurement effect, in this embodiment, a signal processing circuit 51 is first set in the processing module. The signal processing circuit 51 is connected to the microphone 4. The signal processing circuit 51 processes the original audio signal output by the microphone, including amplification, filtering, etc., thereby forming a preprocessed signal.

[0054] Subsequently, the processing device 52 analyzes the preprocessed signal to obtain a measurement result. The processing device 52 is provided with corresponding processing software, which can implement Fourier transform, bandpass filtering and other processing to finally measure the signal amplitude at a specific frequency and measure the gas concentration in combination with pre-calibrated related parameters.

[0055] In one embodiment, Figure 4 As shown, the signal processing circuit 51 includes: a phase-locked amplifier circuit 511, which processes the original audio signal according to a preset resonant frequency to separate the noise signal and form a denoised signal; an adaptive filtering circuit 512, which is connected to the phase-locked amplifier circuit 511; the adaptive filtering circuit 512 processes the denoised signal according to environmental parameters to obtain a preprocessed signal and outputs it.

[0056] Specifically, to achieve better signal processing, this embodiment first provides a lock-in amplifier circuit 511. This circuit processes the original audio signal according to a preset resonant frequency to separate the noise signal and generate a denoised signal. Microphone 4 is a highly sensitive electret microphone that outputs a full-band analog signal.

[0057] By setting a preset resonant frequency for the phase-locked amplifier circuit 511, the phase-locked amplifier circuit 511 can phase-lock and amplify only that portion of the audio signal and discard noise signals at other frequencies, thereby effectively improving the signal-to-noise ratio of the signal.

[0058] Subsequently, the adaptive filtering circuit 512 processes the denoised signal according to the environmental parameters to obtain a preprocessed signal and outputs the preprocessed signal.

[0059] Among them, the environmental parameters mainly include the ambient temperature, ambient humidity and ambient noise at the time of current acquisition. After obtaining the ambient noise, the denoised signal is first processed by Fourier transform, and then the amplitude of the ambient noise is subtracted in a specific frequency domain for filtering. Then, the filtered signal is compensated based on the ambient temperature and ambient humidity to form a preprocessed signal output.

[0060] In one embodiment, Figure 5As shown, the beam modulation module 2 also includes a piezoelectric control circuit 24 and a temperature control circuit 25; the temperature control circuit 25 is connected to the nonlinear optical crystal unit 22 and the piezoelectric control circuit 24; the temperature control circuit 25 measures the crystal temperature of the nonlinear optical crystal unit 22 and generates a first control signal; the piezoelectric control circuit 25 is connected to the nonlinear optical crystal unit 22; the piezoelectric control circuit 25 changes the voltage applied to the nonlinear optical crystal unit 22 according to the first control signal and the second control signal output by the processing device 52, so as to adjust the focal depth and spot diameter of the Bessel beam.

[0061] Specifically, to achieve better stability of the Bessel beam, this embodiment also adds a piezoelectric control circuit 24 and a temperature control circuit 25. Specifically, the piezoelectric control circuit 24 serves as the driving circuit for the nonlinear optical crystal unit 22. While generating a continuously adjustable voltage signal between 0 and 100 V to change the piezoelectric effect intensity of the nonlinear optical crystal unit 22, an additional control loop is introduced to adjust the driving voltage, thereby ensuring that the refractive index gradient of the nonlinear optical crystal unit 22 meets actual requirements.

[0062] The control loop consists of two parts: a temperature loop and a beam compensation loop.

[0063] The temperature loop consists of a temperature control circuit 25 and a piezoelectric control circuit 24. When the nonlinear optical crystal unit 22 continuously modulates the Bessel beam, the crystal experiences temperature changes due to exposure to the laser light source, which in turn affects the intensity and refractive index of the piezoelectric effect. The temperature control circuit 25 uses a temperature sensor to detect temperature changes on the crystal, generating a temperature signal. It then uses a table lookup to determine the drive voltage adjustment parameters required for the current temperature offset. This signal is then generated and sent to the piezoelectric control circuit 25, which adjusts the drive signal intensity based on the first control signal to compensate for temperature changes and maintain wavelength stability within ±0.1 nm.

[0064] For example, when the ambient temperature fluctuates by ±5°C, the processing device dynamically adjusts the piezoelectric driver voltage through the temperature sensor feedback signal to compensate for the refractive index change of the lithium niobate crystal, ensuring the stability of the light intensity distribution of the Bessel beam.

[0065] The beam compensation ring consists of a processing device 52 and a piezoelectric control circuit 25.

[0066] The processing device 52 collects the intensity of the incident Bessel light beam and the edge distribution through multiple light intensity sensors set at the entrance of the photoacoustic pool, so as to determine whether the Bessel light beam conforms to the expected distribution. If there is a focal depth or spot diameter offset, the compensation parameters of the piezoelectric effect are determined by measuring the offset and looking up the table, forming a second control signal and sending it to the piezoelectric control circuit 25. The piezoelectric control circuit 25 can further adjust the light beam by adjusting the driving signal intensity according to the second control signal.

[0067] When the first control signal and the second control signal exist at the same time, the first control signal is generally used for adjustment first, and then the second control signal is used for adjustment. This is because the crystal itself has a slow and linear temperature rise and does not change much in a short period of time, thus improving the adjustment efficiency.

[0068] In one embodiment, Figure 6 As shown, the photoacoustic pool 3 includes: a first buffer cavity 31, which is located at the first end of the photoacoustic pool 3; a resonance cavity 33, which is located behind the first buffer cavity 31; a second buffer cavity 32, which is located at the second end of the photoacoustic pool 3; and the second buffer cavity 32 is connected to the resonance cavity 31.

[0069] The photoacoustic cell 3 is hollow, with two buffer chambers at each end: a first buffer chamber 31 and a second buffer chamber 32. The first and second buffer chambers 31 and 32 are connected by an elongated cylindrical resonance chamber 33, in which a microphone 4 is placed. End caps are provided outside the first and second buffer chambers at each end of the photoacoustic cell 3, each with an optical window.

[0070] Experimental results show that compared to traditional Gaussian beam solutions, the photoacoustic signal intensity under dynamic Bessel beam excitation increases by 25%, the signal-to-noise ratio improves to 30% of the traditional solution, the detection linear range increases by 45%, from 1230 μL / L to 1780 μL / L, and the signal stability improves by 40% when the temperature fluctuates by ±5°C. The device's dynamic parameter adjustment capability significantly enhances its adaptability to complex working conditions, providing a reliable solution for high-sensitivity gas detection in industrial sites.

[0071] Although the present application includes many specific implementation details, these should not be interpreted as limiting the scope of any disclosure or the scope of protection claimed, but are mainly used to describe the features of the specific disclosed embodiments. Certain features described in multiple embodiments of the present application can also be implemented in combination in a single embodiment. On the other hand, the various features described in a single embodiment can also be implemented separately in multiple embodiments or implemented in any suitable sub-combination. In addition, although features can work in some combinations as described and even initially claim protection, one or more features from the claimed combination can be removed from the combination in some cases, and the claimed combination can point to a variation of a sub-combination or a sub-combination.

[0072] Similarly, although configurations are depicted in a particular order in the accompanying drawings, this should not be understood as requiring that these configurations be performed in the particular order shown or sequentially, or that all illustrated configurations be performed to achieve the desired results. In some cases, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system modules and components in the described embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product, or packaged into multiple software products.

[0073] The above are only preferred embodiments of the present invention and do not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. An enhanced photoacoustic spectroscopy gas detection device based on Bessel beam shaping, characterized in that: It includes a light source, a beam modulation module and a photoacoustic cell; The beam modulation module modulates the outgoing light generated by the light source to form a Bessel beam; The output end of the beam modulation module is connected to the input end of the photoacoustic cell to input the Bessel beam into the photoacoustic cell and excite the gas to be detected; The beam modulation module is sequentially provided along the optical axis direction: A liquid crystal phase modulator, wherein the liquid crystal phase modulator forms the Bessel beam by loading a dynamic phase pattern; a nonlinear optical crystal unit, wherein the nonlinear optical crystal unit adjusts the light intensity distribution of the Bessel beam through a photorefractive effect to change the focal depth and the spot diameter; A collimating lens, configured to collimate the Bessel light beam; A microphone is provided in the photoacoustic pool; The enhanced photoacoustic spectroscopy gas detection device further includes: a signal processing circuit connected to the microphone; The signal processing circuit processes the original audio signal output by the microphone to form a preprocessed signal; a processing device connected to the signal processing circuit; The processing device analyzes the preprocessed signal to obtain a measurement result; The beam modulation module further includes a piezoelectric control circuit and a temperature control circuit; The temperature control circuit is connected to the nonlinear optical crystal unit and the piezoelectric control circuit; The temperature control circuit measures the crystal temperature of the nonlinear optical crystal unit and generates a first control signal; The piezoelectric control circuit is connected to the nonlinear optical crystal unit; The entrance of the photoacoustic cell is provided with a plurality of light intensity sensors, and the processing device collects the intensity and edge distribution of the incident Bessel light beam through the plurality of light intensity sensors provided at the entrance of the photoacoustic cell, thereby determining whether the Bessel light beam conforms to the expected distribution; If there is a focus depth or spot diameter offset, the compensation parameter of the piezoelectric effect is determined by measuring the offset and looking up the table, and a second control signal is generated and sent to the piezoelectric control circuit; The piezoelectric control circuit changes the voltage applied to the nonlinear optical crystal unit according to the first control signal and the second control signal output by the processing device, so as to adjust the focal depth and spot diameter of the Bessel beam; A microphone is provided in the middle of the resonance cavity of the photoacoustic pool; The installation depth of the microphone and the total length of the resonance cavity are respectively matched with the focal depth of the Bessel beam; In order to achieve a more uniform excitation effect, the focal depth of the modulated Bessel beam is first determined, and then the installation depth of the microphone and the total length of the resonance cavity are adjusted based on the focal depth of the Bessel beam, so that the microphone can collect the acoustic signal after uniform excitation by the Bessel beam.

2. The enhanced photoacoustic spectroscopy gas detection device according to claim 1, characterized in that: The input end and the output end of the beam modulation module are arranged in a straight line; The light source, the light beam modulation module and the resonant cavity of the photoacoustic cell are coaxially arranged.

3. The enhanced photoacoustic spectroscopy gas detection device according to claim 1, characterized in that: The total length of the resonant cavity is 200 mm; The focal depth of the Bessel beam is 50-200 mm; The adjustment accuracy of the central spot diameter of the Bessel beam is ±10 μm.

4. The enhanced photoacoustic spectroscopy gas detection device according to claim 1, characterized in that: The signal processing circuit includes: a phase-locked amplifier circuit, wherein the phase-locked amplifier circuit processes the original audio signal according to a preset resonant frequency to separate the noise signal and form a denoised signal; an adaptive filtering circuit, the adaptive filtering circuit being connected to the phase-locked amplifier circuit; The adaptive filtering circuit processes the denoised signal according to environmental parameters to obtain the preprocessed signal and outputs the preprocessed signal.

5. The enhanced photoacoustic spectroscopy gas detection device according to claim 1, characterized in that: The light source is a tunable laser, and the light source excites a Gaussian beam of a corresponding central wavelength according to the gas to be detected in the photoacoustic cell.

6. The enhanced photoacoustic spectroscopy gas detection device according to claim 1, characterized in that: The photoacoustic cell comprises: a first buffer cavity, the first buffer cavity being located at a first end of the photoacoustic cell; a resonant cavity, the resonant cavity being located behind the first buffer cavity; a second buffer cavity, the second buffer cavity being located at a second end of the photoacoustic cell; The second buffer cavity is connected to the resonant cavity.

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