Calabash-shaped photoacoustic cell based on diffuse reflection integral and process thereof

Abstract

The invention discloses a gourd-shaped photoacoustic cell based on diffuse reflection integration and a process thereof, and relates to the technical field of photoacoustic spectrometry and trace gas detection. The photoacoustic cell comprises an air hole (1), an optical fiber collimator (2), a calabash-shaped buffer chamber (3), a reflecting gold film (4), a girdling curve resonant cavity (5) and an optical microphone (6), a reflecting gold film (4) is arranged on the inner wall of the calabash-shaped buffer chamber (3), and two air holes (1) are formed in the bottom of the calabash-shaped buffer chamber (3); an incident light hole is formed in the lower part of the left side of the gourd-shaped buffer chamber (3) and is used for mounting the optical fiber collimator (2); the optical fiber collimator (2), the gourd-shaped buffer chamber (3), the waist curve resonant cavity (5) and the optical microphone (6) are sequentially connected from left to right. The calabash-shaped body is designed, so that the light-gas phase molecule action path is greatly increased, the intensity of a photoacoustic signal is improved, and the detection lower limit of a photoacoustic spectrum gas detection system is further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photoacoustic spectroscopy and trace gas detection, in particular to a gourd-shaped photoacoustic cell based on diffuse reflection integration and a process thereof. Background Art

[0002] With the rapid progress of society, the demand for high-precision detection of various trace gases is growing in various fields. However, traditional gas detection methods such as semiconductor sensing, electrochemical sensing, and mass spectrometry are generally limited by problems such as poor repeatability, low sensitivity, and cross-interference, making it difficult to meet the current dual challenges of high precision and cost control. Photoacoustic spectroscopy gas detection technology has the advantages of real-time, rapid response, high sensitivity, non-contact detection, and miniaturization. It can be used for real-time detection of multi-component trace gases. It currently has broad application prospects in coal mine toxic gas monitoring and early warning, medical respiratory gas auxiliary diagnosis, and electrical equipment failure gas analysis, and has become the focus of the gas detection industry.

[0003] Photoacoustic spectroscopy, based on the photoacoustic effect, is used to detect gas concentration and composition. It's known that when a laser beam with a wavelength in the absorption band of gas molecules shines on a gas sample, the gas molecules absorb the light energy and transition to an excited state. They then undergo non-relaxation radiation, converting the kinetic energy of intermolecular relaxation collisions into internal energy. When the laser beam is modulated in intensity or wavelength, it interacts with gas-phase molecules, generating periodic thermal fluctuations. This causes the surrounding gas to periodically contract and expand, generating sound waves. After being resonated and amplified by a photoacoustic cell, the sound wave signal is recorded in real time using acoustic sensors such as microphones, and real-time data processing is used to invert the harmonic signal to determine trace gas concentrations.

[0004] The core part of photoacoustic spectroscopy technology, that is, the source of photoacoustic signals - the photoacoustic cell, is directly related to the detection accuracy of trace gases whether its design is reasonable or not. The existing photoacoustic cells are divided into non-resonant photoacoustic cells and resonant photoacoustic cells: non-resonant photoacoustic cells are cheap and have a relatively simple structure, but due to their large size, the sound pressure signal cannot be concentrated, resulting in low detection sensitivity, which is not conducive to the high-precision requirements of future development; resonant photoacoustic cells are based on the principle of acoustic wave resonance and have a strong sound pressure amplification effect and high detection sensitivity. The various resonant photoacoustic cells currently launched, such as H-type, T-type, and sphere, are combined with various Methods such as combining the Herriott gas cell with the White gas cell to increase the interaction path between the pump light and the material molecules and the shape coupling of the cylinder, sphere, and cone for resonant amplification and delaying the airflow noise have all demonstrated high-precision gas detection effects. However, the resonant photoacoustic cell can not only reduce the influence of airflow noise, but also increase the interaction path between light and matter, thereby greatly improving the effective power of the photoacoustic excitation light and improving the detection sensitivity and stability of the system. Miniaturized photoacoustic cells further reflect the future prospects of trace gas detection that are both miniaturized, fast-responding, and more accurate.

[0005] In recent years, the combination of optical sensors and various small resonant photoacoustic cells has become a hot topic. This approach utilizes the resonant state of the photoacoustic cell and combines the path length of light and molecular interaction to improve detection accuracy through two-stage acoustic signal intensity amplification. Based on this paper, Wu Ruiming, Ni Wenjun, Yang Chunyong, et al. (Application of multi-path length reflection enhancement based on a balloon-type photoacoustic unit in trace gas sensing). Photoacoustics, 2024, 41: 100681. A miniaturized special gourd-shaped resonant photoacoustic sensor was designed. The sensor mainly consists of a miniaturized gourd-shaped resonant photoacoustic cell and a fiber-thin film Fabry-Perot photoacoustic interferometer. The gourd-shaped resonant photoacoustic cell primarily consists of a coupled sphere buffer chamber and a waisted, curved resonant cavity. The inner wall of the coupled sphere is coated with a high-reflectivity film, creating diffuse reflection within the cell to extend the interaction path between the pump light and gas molecules, significantly reducing its volume. The gourd-shaped cell also slows airflow, improving noise immunity. The waisted, curved resonant cavity effectively concentrates the sound pressure signal at the gourd's mouth and resonates and amplifies it. The fiber-thin film Fabry-Perot photoacoustic interferometer formed at the end is highly sensitive to sound pressure signals and has a higher detection limit for acoustic signal response, further improving the system's detection performance.

[0006] In terms of acoustic signal detection, from capacitive microphones to quartz tuning forks, and then to fiber optic acoustic sensors with cantilever beams and thin-film Fabry-Perot cavities, photoacoustic spectroscopy trace gas detection systems have always been a trade-off between miniaturization and detection accuracy. In comparison, optical sensors formed by cantilever beams and thin-film Fabry-Perot cavities have advantages such as miniaturization and resistance to electromagnetic interference, and are therefore more commonly used in the construction of miniature photoacoustic spectroscopy systems. Although fiber optic cantilevers measure the displacement of the cantilever tip through optical interference and exhibit high sensitivity during mechanical resonance, their narrow resonant bandwidth also makes it easy to filter out background noise. However, they are susceptible to unstable environmental factors, causing the resonant frequency to drift, thereby affecting the stability of the output PA signal. In contrast, when the film-based Fabry-Perot cavity operates in a non-resonant state, the use of nano-scale films made of materials such as silicon, compounds, metals and graphene can not only increase the sensitivity of the sound pressure response, so that the detection limit reaches the ppb level, but also make the structure more compact. The wide-band response and good adjustability also achieve a significant improvement in acoustic sensitivity. However, high-sensitivity detection is often accompanied by poor immunity to static pressure or airflow disturbances. Therefore, a stable signal demodulation solution is required in practical applications.

[0007] In summary, it can be seen that designing a miniaturized all-optical acousto-optic gas sensor with long action optical path, high sensitivity, high detection accuracy and good system stability has important application value. Summary of the Invention

[0008] The present invention aims to overcome the shortcomings and deficiencies of existing technologies by providing a gourd-shaped photoacoustic cell based on diffuse reflectance integration and its process. This sensor boasts high sensitivity and a compact size. The gourd-shaped cell not only buffers airflow noise but also increases the path length of light-matter interaction. This novel design concept provides an innovative approach for the miniaturization of specialized resonant photoacoustic sensors and holds great promise for their application in photoacoustic spectroscopy trace gas detection.

[0009] To achieve the above object, the technical solution of the present invention is:

[0010] 1. Gourd-shaped photoacoustic cell based on diffuse reflection integration

[0011] The photoacoustic cell includes an air hole, a fiber collimator, a gourd-shaped buffer chamber, a reflective gold film, a waisted curved resonant cavity and an optical microphone.

[0012] A reflective gold film is provided on the inner wall of the gourd-shaped buffer chamber, and two air holes are provided at the bottom of the gourd-shaped buffer chamber;

[0013] An incident light hole is opened at the lower left side of the gourd-shaped buffer chamber for installing a fiber collimator;

[0014] From left to right, the fiber collimator, gourd-shaped buffer chamber, waisted curved resonant cavity and optical microphone are connected in sequence.

[0015] 2. Process of gourd-shaped photoacoustic cell based on diffuse reflection integration

[0016] ① The gourd-shaped photoacoustic cell designed for diffuse reflection integration does not artificially add a buffer chamber like a spherical-cylinder coupled cell or an H-shaped photoacoustic cell. The special feature of the gourd-shaped sphere is that it has a natural double buffer chamber system. The gourd-shaped buffer chamber is formed by coupling spheres of different radii, which greatly slows down the gas flow rate and thus reduces the airflow noise in the detection background.

[0017] ② The inner wall of the gourd-shaped body is coated with a high-reflectivity film. The laser is incident on the inside of the gourd sphere through a fiber collimator, so that the light path forms diffuse reflection throughout the coupling sphere, increasing the interaction path between light and gas phase molecules, improving the intensity of the photoacoustic signal, and greatly improving the detection sensitivity of the system.

[0018] ③ The radii of the coupling spheres are 15 mm and 10 mm respectively, and the distance between the centers of the spheres is 20 mm.

[0019] ④ The waisted curved resonant cavity is 15 mm long, has a cavity opening radius of 1.3 mm, and a volume of approximately 0.148 cubic centimeters.

[0020] The present invention has the following advantages and positive effects:

[0021] ① The present invention provides a gourd-shaped photoacoustic cell based on diffuse reflection integration. Based on the gourd-shaped double-sphere structure, the traditional cylindrical buffer chamber is abandoned. The introduction of a spherical buffer chamber further reduces airflow noise, effectively overcoming the technical challenges faced by current photoacoustic sensors in balancing the pursuit of a small-sized resonant photoacoustic cell with the reduction of gas flow noise.

[0022] ② A gourd-shaped body is designed to form a diffuse reflection light path inside the cavity through a specific entrance and incident angle, which greatly increases the light-gas phase molecule interaction path, improves the intensity of the photoacoustic signal, and reduces the background noise, thereby further improving the detection limit of the photoacoustic spectroscopy gas detection system.

[0023] ③ Compared with the existing H-type photoacoustic sensor based on multi-column buffering, the diffuse reflection integrating gourd-shaped photoacoustic cell has the advantages of miniaturization, low airflow noise, high system stability, and a long path of interaction between light and matter. In addition, a high-precision Fabry-Perot interferometer is formed between the end of the optical fiber and the 100nm gold film, which is more sensitive to sound pressure signals and has a higher response lower limit, which can further improve the detection performance of the system.

[0024] ④ The new design concept of the present invention provides an innovative direction for the miniaturization of special resonant photoacoustic sensors, and will show broad application prospects in the field of photoacoustic spectroscopy trace gas detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the structure of the photoacoustic cell, in which:

[0026] 1—stomata,

[0027] 2—Fiber collimator,

[0028] 3—Gourd-shaped buffer chamber,

[0029] 4—Reflective gold film,

[0030] 5—waisted curved resonant cavity,

[0031] 6—Optical microphone;

[0032] Figure 2-1 This is the main view of the diffuse reflection path inside the gourd-shaped buffer chamber;

[0033] Figure 2-2 This is the left view of the diffuse reflection path inside the gourd-shaped buffer chamber;

[0034] Figure 3 is the sound pressure signal curve excited by the photoacoustic cell at different frequencies. DETAILED DESCRIPTION

[0035] The following is a detailed description with reference to the accompanying drawings and embodiments.

[0036] 1. Structure of the gourd-shaped photoacoustic cell (referred to as the photoacoustic cell) based on diffuse reflection integration

[0037] 1. Overall

[0038] like Figure 1 The photoacoustic cell includes an air hole 1, a fiber collimator 2, a gourd-shaped buffer chamber 3, a reflective gold film 4, a waisted curved resonant cavity 5 and an optical microphone 6;

[0039] A reflective gold film 4 is provided on the inner wall of the gourd-shaped buffer chamber 3, and two air holes 1 are provided at the bottom of the gourd-shaped buffer chamber 3;

[0040] An incident light hole is opened at the lower left side of the gourd-shaped buffer chamber 3 for installing the optical fiber collimator 2;

[0041] From left to right, the optical fiber collimator 2, the gourd-shaped buffer chamber 3, the waisted curved resonant cavity 5 and the optical microphone 6 are connected in sequence.

[0042] 2. Functional components

[0043] 1) Stoma 1

[0044] The air hole 1 is located at the bottom of the gourd-shaped buffer chamber 3, allowing the gas to be measured in the specific air chamber to enter the interior of the photoacoustic cell through free diffusion between molecules, thereby ensuring measurement accuracy and stability;

[0045] Pore ​​1 plays a crucial role in the photoacoustic spectroscopic gas detection system, controlling the properties of the gas surrounding the sample to be tested to ensure detection accuracy. Pore 1 is responsible for gas exchange and pressure regulation, thereby affecting the photoacoustic signal response of the sample to be tested inside the photoacoustic cell. The design of pore 1 optimizes the acoustic properties and improves the weak signal detection capability to enhance the response strength and sensitivity of the detection signal. At the same time, the same device can be used to adapt to the detection of multiple gases, thereby improving the versatility and flexibility of the photoacoustic cell.

[0046] 2) Fiber collimator 2

[0047] The fiber collimator 2 is a passive optical device, which is an integrated cylindrical structure of optical fiber and lens. It converts the divergent light in the optical fiber into collimated light through a self-focusing lens.

[0048] The fiber collimator 2 is located at the lower left side of the gourd-shaped buffer chamber 3 to ensure the correct alignment and focusing of the light beam; it is used to guide the laser beam into the photoacoustic pool for transmission, ensuring the stability and collimation of the light spot for accurate photoacoustic gas excitation; through correct alignment, the collimated light is focused on the center of the light hole, ensuring that the first reflected light beam guiding the incident light is located in the second spherical buffer chamber, thereby forming diffuse reflection, thereby increasing the reflected light path and further improving the acoustic signal intensity and detection sensitivity.

[0049] 3) Gourd-shaped buffer chamber 3

[0050] The gourd-shaped buffer chamber 3 is the part with the smallest sound pressure signal inside the photoacoustic cell, which can improve the flow field distribution in the photoacoustic cell, reduce the airflow noise and thus improve the signal-to-noise ratio;

[0051] The gourd-shaped buffer chamber 3 provides an environment to ensure the stable position of the sample, thereby reducing the impact of external environmental interference and vibration on the accuracy of the experimental results; in addition, the biggest highlight of the gourd-shaped buffer chamber 3 is that it can also form a diffuse reflection light path to increase the interaction path between light and matter, thereby enhancing the intensity of the photoacoustic signal, enabling the photoacoustic pool to detect and analyze the target gas more efficiently and accurately.

[0052] 4) Reflective gold film 4

[0053] The reflective gold film 4 coated on the inner wall of the gourd-shaped photoacoustic cell plays a decisive role in the detection of photoacoustic signals. The high-reflectivity gold film improves the utilization rate of light energy, causes light to be diffusely reflected in the cell, and increases the interaction time with the gas, thereby increasing the intensity of the photoacoustic effect, and then improving the detection sensitivity and signal-to-noise ratio, optimizing the overall performance of the photoacoustic detection system.

[0054] 5) Waisted curved resonator 5

[0055] The waisted curved resonant cavity 5 is a key component in the photoacoustic spectroscopy system. It uses the waisted curved body to perform waist-shaped focusing of phonon energy, concentrate the sound pressure signal at the center of the resonant cavity and resonate and amplify it. This structure can improve the signal-to-noise ratio and enhance the accuracy of the all-optical photoacoustic spectroscopy trace gas detection system.

[0056] 6) Optical microphone 6

[0057] Optical microphone 6 is a sensor used to detect photoacoustic signals. The sound pressure signal generated by the interaction between light and gas molecules causes the nanoscale thin film to form periodic vibrations, which modulates the optical path of the Fabry-Perot interferometer formed by the single-mode optical fiber, allowing the sound pressure signal to be reflected in the optical signal for high-precision data processing. The characteristics and design of optical microphone 6 are crucial in the detection of photoacoustic signals.

[0058] In summary, the above components are indispensable in the photoacoustic cell, and each performs its function to achieve high sensitivity, high precision, and fast and real-time trace gas detection.

[0059] In the photoacoustic cell, the modulated pump light is incident on the lower left side of the gourd-shaped photoacoustic cell through the fiber collimator 2. The light is diffusely reflected by the high-reflectivity internally plated reflective gold film 4 and interacts with the trace gas to be measured. The sound pressure signal generated by the photoacoustic effect resonates and strengthens in the waisted curved resonant cavity 5, causing the metal film in the optical microphone 6 to form periodic vibrations and modulate the optical path of the Fabry-Perot interferometer formed with the single-mode optical fiber, converting the sound pressure signal into an optical signal.

[0060] In this photoacoustic cell, the sound pressure sensitivity of the gourd-shaped buffer chamber 3, the waisted curved resonant cavity 5, and the optical microphone 6 determines comprehensive indicators such as measurement accuracy, minimum detection limit, anti-interference, sensitivity, and signal-to-noise ratio in the photoacoustic cell. By using a high-reflectivity gold film 4 coated on the inner wall of the gourd-shaped buffer chamber 3, the incident light is diffusely reflected, thereby greatly improving the utilization rate of light energy and increasing the interaction time with the gas, thereby increasing the intensity of the photoacoustic effect and enhancing the measurement accuracy of the entire system.

[0061] 2. Photoacoustic cell technology

[0062] Based on the gourd-shaped structure, the interior is coated with a high reflectivity film, which uses a specific angle to form diffuse reflection to increase the distance between light and matter;

[0063] The gourd-shaped structure abandons the traditional cylindrical buffer chamber and provides a natural double-sphere buffer chamber to reduce airflow noise and improve the signal-to-noise ratio.

[0064] The waisted curved resonant cavity provides an eccentricity e as an optimized angle to further amplify the sound pressure signal, and concentrates the sound pressure signal at the mouth of the gourd-shaped photoacoustic cell and combines it with a thin film Fabry-Perot photoacoustic interferometer, thereby improving the lower limit of the detection response by utilizing the sensitivity measurement of the optical microphone.

[0065] 3. Examples

[0066] Figure 1 It is a schematic diagram of the structure of the photoacoustic cell.

[0067] The gourd-shaped buffer chamber 3 is plated with a reflective gold film 4 and is connected to the fiber collimator 2 through a reserved mechanical hole. The end part of the waisted curved resonant cavity 5 is the location where sound pressure is concentrated. Therefore, the optical microphone 6 is placed at the end of the waisted curved resonant cavity 5 for connection. Through a specific hole, the acoustic signal modulates the film vibration of the optical microphone 6, thereby enabling high-sensitivity acquisition of the photoacoustic signal. The air hole 1 is used for gas exchange and regulates the air pressure inside the gourd-shaped photoacoustic cell. The double air hole design also increases the diffusion rate of the gas, further reducing the system response time. The pump light source collimates the pump light through the fiber collimator 2 and injects it into the photoacoustic cell composed of the gourd-shaped buffer chamber 3, the reflective gold film 4 and the waisted curved resonant cavity 5. After diffuse reflection, the action path with the gas is extended, thereby generating a high-intensity photoacoustic signal and forming the maximum amplitude sound pressure at the end part of the waisted curved resonant cavity 5. Therefore, the optical microphone 6 collects the maximum sound pressure signal and transmits it to the phase-locked amplifier for signal processing to obtain the second harmonic signal, thereby inverting the trace gas concentration information to be measured.

[0068] Figure 2-1 、 2-2 They are the main view and left view of the 50ns reflection path in the diffuse reflection integrating gourd-shaped photoacoustic cell. Multiple reflections will greatly increase the effective optical power and the sound pressure amplitude by nearly 1.1mPa, further reducing the detection limit of the system.

[0069] Figure 3 Figure 2 shows the acoustic pressure signal curves of a gourd-shaped photoacoustic cell excited at different modulation frequencies. Curve A represents the frequency response of the integrated gourd-shaped photoacoustic cell under diffuse light reflection, while Curve B represents the frequency response of the integrated gourd-shaped photoacoustic cell under direct light reflection. It can be seen that diffuse reflection significantly improves the acoustic signal intensity compared to direct light reflection, further increasing the detection limit. This structural feature demonstrates the advantages of miniaturization, high precision, high sensitivity, and stable performance in photoacoustic spectroscopy trace gas detection systems.

[0070] 4. Application of Gourd-Shaped Photoacoustic Cell Based on Diffuse Reflection Integration

[0071] 1. Structure

[0072] exist Figure 1On the basis of the above, the following functional components are added to form a detection system.

[0073] A. 1532nm laser source: acts as pump light to interact with gas molecules;

[0074] B. 1550nm detection light: good coherence, used as detection light source;

[0075] C. Isolator: prevents reflected light from entering the light source and damaging the light source equipment;

[0076] D. Filter: Set a certain wavelength limit so that the light source in this band can be transmitted;

[0077] E. Circulator: prevents signal reflection and echo interference, thereby isolating the signal;

[0078] F. Erbium-doped fiber amplifier: improves the effective power of laser;

[0079] G. Fiber coupler: splits the light source into two paths to facilitate observation and control of the pump light source;

[0080] H. Signal generator: output sine wave and triangle wave to perform high frequency modulation and low frequency scanning on 1532nm laser;

[0081] I. Lock-in amplifier: extracts weak signals from strong noise background and amplifies them to meet the accuracy requirements for gas detection;

[0082] J. Photodetector: converts light signals into electrical signals;

[0083] K. Computer terminal: Process and display the second harmonic signal in real time;

[0084] L. Spectrometer: Connects to the reference signal to directly observe whether the pump light source is in the gas absorption peak band.

[0085] 2. Parameters of each functional component

[0086] a. 1532nm laser source: distributed feedback laser chip DFB-D23024010003, equipped with butterfly laser driver ORLD PRO series - ORLD-1200S;

[0087] b. 1550 nm probe light: Koheras-BASIK–E15 erbium fiber laser, 1535-1580 nm, 40 mW;

[0088] c. Isolator: IOT-H-1550A-dual-stage fiber optic isolator, 1550nm, single mode, FC / APC connector;

[0089] d. Filter: Bandpass fiber filter, 1310-1550nm;

[0090] e. Circulator: 3-port insensitive circulator, 1520-1580nm;

[0091] f. Erbium-doped fiber amplifier: HPEDFA-C-BA37-FA-B high-power fiber laser amplifier, 1535-1565nm;

[0092] g. Fiber coupler: TW1550R2F1-1×2 broadband fiber coupler, 1550 + 100nm, 90:10 split ratio, FC / APC;

[0093] h. Signal generator: SIGLENT-SDG2122X arbitrary waveform generator, dual-channel output, 1.2GSa / s sampling rate, 16-bit vertical resolution;

[0094] i. Lock-in amplifier: Saintech E1022-102kHz digital lock-in amplifier, DC to 102kHz measurement range, time constant 10us-3ks, dynamic storage up to 130dB, with FFT spectrum analysis function;

[0095] j. Photodetector: APD130C-InGaAs avalanche photodetector, temperature compensated, 900-1700nm, 8-32 taps;

[0096] k. Computer: DELL precision 3490 workstation;

[0097] 1. Spectrometer: AE8600E high-performance optical spectrum analyzer, 600nm-1700nm, 75dB dynamic range, ±0.01nm high wavelength accuracy.

[0098] 3. Experimental process

[0099] In the trace acetylene gas detection experiment, the trace acetylene gas to be measured first enters and exits the gourd-shaped photoacoustic cell through the air hole. A 1532nm laser source is used as pump light. After passing through a fiber isolator, it enters an erbium-doped fiber amplifier to amplify the power to 200mW. After being filtered by a 1532nm filter, it enters the fiber coupler. One beam enters the spectrometer as reference light to facilitate adjustment of the pump light peak to the acetylene gas absorption peak. Another beam enters the fiber collimator and is collimated and incident on the gourd-shaped photoacoustic cell for diffuse reflection.

[0100] After the interaction between light and gas molecules, the gas molecules absorb light energy and transition to an excited state. They then undergo a non-relaxation radiation effect, and the kinetic energy of the relaxation collisions between molecules is converted into internal energy. Then, when the laser beam is modulated, periodic heat changes are formed, causing the surrounding gas to be periodically compressed and expanded, thereby forming sound waves. The sound wave signal enters the waisted curved resonant cavity for resonant amplification. An optical microphone is placed at the mouth of the resonant cavity where the sound pressure amplitude is maximum to detect the sound wave signal, causing the metal film inside the optical microphone to vibrate, and its vibration frequency is close to the sound wave signal frequency.

[0101] After a beam of 1550nm detection light enters the circulator, the outlet is connected to an optical microphone. After the detection light is reflected by the metal film, the vibration on the film will modulate the optical path of the detection light in the Fabry-Perot interferometer, so that the detection light source carries the acoustic wave signal information and returns to the photodetector through the circulator. The optical signal is converted into an electrical signal and enters the phase-locked amplifier. After signal noise reduction and amplification, it is transmitted to the computer for data processing to obtain the second harmonic signal of the acoustic wave signal, thereby inverting the concentration information of the trace acetylene gas to be measured.

[0102] 4. Experimental results

[0103] The results show that when the detection signal duration reaches 100s integration time, the gourd-shaped photoacoustic cell's detection limit for trace acetylene gas reaches the ppb (parts per billion) level, and can even reach lower levels. This shows that the gourd-shaped photoacoustic cell achieves the required detection accuracy for the target detection gas. At the same time, its advantages of miniaturization, fast response, and high sensitivity provide innovative directions for the miniaturization of special resonant photoacoustic sensors, and will show broad application prospects in the field of photoacoustic spectroscopy trace gas detection.

[0104] The present invention is provided as a preferred embodiment only and is not intended to limit the application of the present invention. Those skilled in the art will appreciate that the present invention is susceptible to numerous modifications and adjustments. As long as such modifications, equivalent substitutions, or improvements conform to the core spirit and basic principles of the present invention, they shall be deemed to fall within the scope of protection of the present invention.

Claims

1. A gourd-shaped photoacoustic cell based on diffuse reflection integration, characterized in that: It includes an air hole (1), an optical fiber collimator (2), a gourd-shaped buffer chamber (3), a reflective gold film (4), a waisted curved resonant cavity (5) and an optical microphone (6); A reflective gold film (4) is provided on the inner wall of the gourd-shaped buffer chamber (3), and two air holes (1) are provided at the bottom of the gourd-shaped buffer chamber (3); An incident light hole is provided at the lower left side of the gourd-shaped buffer chamber (3) for installing a fiber collimator (2); From left to right, the optical fiber collimator (2), the gourd-shaped buffer chamber (3), the waisted curved resonant cavity (5) and the optical microphone (6) are connected in sequence.

2. The process of the gourd-shaped photoacoustic cell based on diffuse reflection integration according to claim 1, characterized in that: ① The gourd-shaped photoacoustic cell for diffuse reflection integration is designed. It is not like the spherical-cylinder coupling or H-type photoacoustic cell that artificially adds a buffer chamber. The special feature of the gourd sphere is that it has a natural double buffer chamber system. The gourd-shaped buffer chamber (3) is formed by coupling spheres with different radii, which greatly slows down the gas flow rate and thus reduces the airflow noise in the detection background. ② The inner wall of the gourd-shaped body is plated with a high-reflectivity gold film, and the laser is incident on the inside of the gourd sphere through the optical fiber collimator (2), so that the light path forms diffuse reflection all over the coupling sphere, increasing the interaction path between light and gas phase molecules, improving the intensity of the photoacoustic signal, and greatly improving the detection sensitivity of the system; ③ The radii of the coupling spheres are 15 mm and 10 mm respectively, and the distance between the centers of the spheres is 20 mm; ④ The waisted curved resonant cavity has a length of 15 mm, a cavity opening radius of 1.3 mm, and a volume of approximately 0.148 cubic centimeters.

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