A gas detection device and method based on optical feedback cavity enhanced raman spectroscopy

Abstract

This invention discloses a gas detection device and method based on optical feedback cavity enhanced Raman spectroscopy, belonging to the field of optical detection technology. Addressing the shortcomings of existing gas detection technologies in terms of sensitivity, selectivity, anti-interference capability, engineering applicability, and Raman scattering light collection efficiency, this invention provides a novel gas detection technology based on optical feedback cavity enhanced Raman spectroscopy. A specially designed irregularly shaped resonant cavity structure is used to improve Raman scattering light collection efficiency. Without relying on precious metal nanomaterial substrates or requiring complex coherent light sources, it achieves high sensitivity (detection limit down to ppm~ppb), high selectivity, and in-situ real-time detection of mine gas, characteristic gases from oil and gas fields, and trace atmospheric pollutants. It also possesses excellent vibration and temperature drift resistance, meeting the practical application needs of complex scenarios such as underground coal mines, field oil and gas fields, and atmospheric environmental monitoring.

Description

Technical Field

[0001] This invention belongs to the field of optical detection technology, specifically relating to a gas detection device and method based on optical feedback cavity enhanced Raman spectroscopy. It is applicable to fields such as real-time monitoring of hazardous gases like mine methane, detection of leaked gases in oil and gas fields, monitoring of trace atmospheric pollutants, and analysis of industrial process gases. Background Technology

[0002] Mine gas (mainly methane), associated / leaked gases from oil and gas fields (methane, hydrogen sulfide, volatile organic compounds, etc.), and air pollutants (NOx) x Rapid, sensitive, and in-situ detection of substances such as SO2, VOCs, and greenhouse gases is a key technological requirement for ensuring safe production and preventing environmental pollution.

[0003] Existing gas detection technologies mainly include:

[0004] 1) Electrochemical sensors: They have a fast response speed but are susceptible to poisoning, have a short lifespan, and suffer from severe cross-interference, making them unsuitable for long-term reliable operation in complex mining environments;

[0005] 2) Infrared absorption spectroscopy: It has good selectivity for specific gases and the detection limit can be in the ppm~ppb range. However, one laser wavelength can only detect 1 to 2 substances. Multi-gas detection requires multiple sets of equipment, which are expensive and complicated, and cannot meet the needs of atmospheric trace pollutants and early warning in mines.

[0006] 3) Gas chromatography: It has high detection sensitivity, but it has two obvious disadvantages: first, the response speed is slow and cannot meet the needs of real-time monitoring; second, the instrument maintenance cost is high and it is not conducive to large-scale promotion.

[0007] 4) Traditional Raman spectroscopy: This belongs to molecular fingerprint spectroscopy and has unique advantages such as simultaneous identification of multiple components, no need for sample pretreatment, and resistance to water vapor interference. However, it is limited by the extremely small Raman scattering cross section (10). -30 cm 2 (on the order of / sr), conventional Raman signals are extremely weak, making it difficult to achieve high-sensitivity detection in industrial settings.

[0008] To enhance Raman signal intensity, existing technologies have developed surface-enhanced Raman (SERS), coherent anti-Stokes Raman (CARS), and stimulated Raman spectroscopy. However, SERS requires substrate contact and is not suitable for remote / in-situ gas detection. CARS systems are complex, costly, and subject to non-resonant background interference, making them difficult to engineer.

[0009] In recent years, cavity-enhanced Raman spectroscopy (CERS) has emerged, which can increase the excitation light power density by hundreds to tens of thousands of times through a high-precision optical resonant cavity, effectively enhancing the Raman signal. However, most existing cavity-enhanced Raman schemes use passive cavities (without active optical feedback), which have key defects such as difficulty in mode matching and poor vibration resistance, making it difficult to work stably in harsh environments such as mine vibration, oil and gas field fields, and atmospheric monitoring platforms.

[0010] Currently, existing gas detection technologies still have significant shortcomings in terms of overall performance: they cannot simultaneously meet core requirements such as ultra-high sensitivity (ppm~ppb), multi-component fingerprint recognition, strong resistance to interference from harsh environments, and structural simplification and engineering adaptation. This bottleneck severely restricts their large-scale application in key areas such as coal mine safety, oil and gas safety, and atmospheric environmental governance. Summary of the Invention

[0011] To address the shortcomings of existing gas detection technologies in terms of sensitivity, selectivity, anti-interference ability, engineering applicability, and Raman scattering light collection efficiency, this invention provides a novel gas detection technology based on optical feedback cavity-enhanced Raman spectroscopy. A specially designed irregularly shaped resonant cavity structure is used to improve Raman scattering light collection efficiency. Without relying on precious metal nanomaterial substrates or complex coherent light sources, this technology achieves high sensitivity (detection limit down to ppm~ppb), high selectivity, and in-situ real-time detection of mine gas, characteristic gases from oil and gas fields, and trace atmospheric pollutants. It also possesses excellent vibration and temperature drift resistance, meeting the practical application needs of complex scenarios such as underground coal mines, field oil and gas fields, and atmospheric environmental monitoring.

[0012] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0013] A gas detection device based on optical feedback cavity enhanced Raman spectroscopy, the gas detection device comprising: a laser, a feedback rate control system, a matching lens, a reflector and a beam splitter sequentially passed by the laser emitted from the laser, and entering an ultra-stable irregular optical feedback cavity; the laser is loaded with a modulation signal generated by a function generator;

[0014] The function generator produces a local reference signal of the same frequency, which enters the mixer of the PID control system and mixes with the modulation signal in the reflected light. The demodulated error signal enters the PID module in the PID control system, and then the output voltage controls the length of the PZT to adjust the phase of the feedback light, thereby achieving laser linewidth narrowing and frequency locking.

[0015] The ultra-stable irregular optical feedback cavity has an internal horn-shaped opening, with the horn inlet serving as the laser inlet and the horn outlet serving as the laser outlet. Furthermore, the ultra-stable irregular optical feedback cavity is also equipped with an air inlet and an air outlet.

[0016] The front mirror of the ultra-stable irregular optical feedback cavity generates reflected light. After passing through the beam splitter, the reflected light enters the photodetector in sequence and is transmitted to the PID control system. After modulation and demodulation, the length of the piezoelectric ceramic set at the reflector is controlled to control the feedback phase.

[0017] The emitted light from the ultra-stable irregular optical feedback cavity passes sequentially through a focusing lens, a bandpass filter, and a spectrometer.

[0018] Furthermore, the laser is a semiconductor laser; the output wavelength uses the visible light band and has a wide linewidth.

[0019] Furthermore, the piezoelectric ceramic is lead zirconate titanate ceramic.

[0020] Furthermore, the ultra-stable irregular optical feedback cavity is cuboid in shape.

[0021] Furthermore, the inner wall of the ultra-stable irregular optical feedback cavity is smooth or coated with a high-reflectivity film.

[0022] A gas detection method based on optical feedback cavity enhanced Raman spectroscopy based on the aforementioned device, wherein a modulated signal generated by a function generator is loaded onto a laser, and the laser emitted from the laser passes through a feedback rate control system, a matching lens, a mirror and a beam splitter, and is then coupled into an ultra-stable irregular optical feedback cavity.

[0023] The intracavity resonant leakage light output from the cavity front mirror of the ultra-stable irregular optical feedback cavity returns to the laser along the original path, forming weak optical feedback that narrows the laser linewidth. The intensity of the feedback light is controlled by the feedback rate control system.

[0024] The direct reflected light from the front mirror of the ultra-stable irregular optical feedback cavity is received by a photodetector via a beam splitter. The radio frequency component is sent to the PID control system. After modulation and demodulation, the length of the piezoelectric ceramic is adjusted in real time to control the feedback phase, thereby obtaining a narrow linewidth and frequency-stable laser.

[0025] After the gas to be tested enters the optical path inside the ultra-stable irregular optical feedback cavity, it undergoes Raman scattering with the enhanced laser inside the cavity. The scattered light strikes the inner wall of the cavity and undergoes multiple reflections. After exiting, the scattered light passes through a focusing lens and a bandpass filter, and is then subjected to spectral separation and detection by a spectrometer and a photodetector. Finally, the data processing unit performs qualitative and quantitative analysis of the gas based on the Raman characteristic peaks.

[0026] Furthermore, the output of the intracavity resonant leakage light is approximately 0.01%.

[0027] Furthermore, the length of the piezoelectric ceramic is adjusted to ensure that the feedback phase is always an integer multiple of 2π.

[0028] Furthermore, the gas to be tested includes any one of the following: mine gas, hydrogen sulfide, alkanes, alkenes and alkynes, volatile organic compounds, greenhouse gases, and air pollutants.

[0029] Furthermore, the direct reflected light from the front mirror of the optical resonant cavity is received by a photodetector. This signal is transmitted to the laser by a modulation frequency generated by a function generator, thereby achieving optical feedback locking between the laser and the ultra-stable irregular optical feedback cavity, ensuring the narrow linewidth and high power density characteristics of the laser within the cavity.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1) By using an optical feedback mechanism, the laser linewidth is reduced, the self-locking is narrowed, and the intracavity power is synchronized and significantly improved. This improves the vibration resistance by 2 to 3 orders of magnitude compared to the traditional passive cavity Raman enhancement scheme, enabling stable operation in the vibration environment of a mine. At the same time, the design of a cuboid and an internal frustum-shaped horn-shaped resonant cavity with smooth inner walls or high-reflectivity coating ensures efficient coupling and feedback locking between the laser and the cavity, increases the interaction length between the target gas and the laser, and significantly improves the collection efficiency of Raman scattered light, further reducing the detection limit.

[0032] 2) The inherent molecular fingerprint characteristics of Raman spectroscopy, combined with the enhanced effective path gain of the optical feedback cavity, achieve ultra-high sensitivity in the ppm~ppb range, without the need for a substrate, high pressure, or liquid nitrogen cooling.

[0033] 3) It can simultaneously detect multiple gases (CH4, C2H2, H2S, CO, NO2, SO2, VOCs, etc.), obtaining full spectrum information in a single measurement;

[0034] 4) The system has a relatively simple structure and strong optical path robustness, making it easy to implement a safety-oriented design in the fields of mining or natural gas detection. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 Diagram of a gas detection system for Raman spectroscopy;

[0037] Figure 2 This is a structural diagram of an ultra-stable irregular optical feedback cavity;

[0038] Figure 3 This is a schematic diagram of the transmission cavity mode amplitude;

[0039] Figure 4 This is a schematic diagram of the power spectral density.

[0040] The components include: 1. Laser; 2. Feedback rate control system; 3. Matching lens; 4. Mirror; 5. Piezoelectric ceramic; 6. Beam splitter; 7. Ultra-stable irregular optical feedback cavity; 8. Focusing lens; 9. Bandpass filter; 10. Spectrometer; 11. Photodetector; 12. PID control system; 13. Air inlet; 14. Air outlet; 15. Function generator; 17. Laser inlet; 18. Laser outlet. Detailed Implementation

[0041] To gain a deeper understanding of this invention, we will provide a comprehensive and detailed description. However, this invention has various implementations and is not limited to the specific examples listed herein. These examples are presented to enhance a full understanding of the disclosure of this invention.

[0042] This solution can detect a variety of gases, including: mine gas, hydrogen sulfide, alkanes, alkenes and alkynes, volatile organic compounds, greenhouse gases, and air pollutants.

[0043] This invention provides a gas detection device based on optical feedback cavity enhanced Raman spectroscopy, comprising: a laser, a feedback rate control system, a matching lens, a reflector and a beam splitter that the laser emitted from the laser passes through in sequence before entering an ultra-stable irregular optical feedback cavity; and a modulation signal generated by a function generator is loaded onto the laser.

[0044] The function generator produces a local reference signal of the same frequency, which enters the mixer of the PID control system and mixes with the modulation signal in the reflected light. The demodulated error signal enters the PID module in the PID control system, and then the output voltage controls the length of the PZT to adjust the phase of the feedback light, thereby achieving laser linewidth narrowing and frequency locking.

[0045] The ultra-stable irregular optical feedback cavity is rectangular in shape with an internal horn-shaped opening. The horn-shaped inlet is the laser input port, and the horn-shaped outlet is the laser output port. The ultra-stable irregular optical feedback cavity also has an air inlet and an air outlet. The inner wall of the ultra-stable irregular optical feedback cavity is smooth or coated with a high-reflectivity film.

[0046] The front mirror of the ultra-stable irregular optical feedback cavity generates reflected light. After passing through the beam splitter, the reflected light enters the photodetector in sequence and is transmitted to the PID control system. After modulation and demodulation, the length of the piezoelectric ceramic set at the reflector is controlled to control the feedback phase.

[0047] The emitted light from the ultra-stable irregular optical feedback cavity passes sequentially through a focusing lens, a bandpass filter, and a spectrometer.

[0048] The laser is a semiconductor laser; the output wavelength uses the visible light band and has a wide linewidth. The piezoelectric ceramic is lead zirconate titanate (PZT).

[0049] Example 1

[0050] Based on the above-described apparatus, the present invention provides a gas detection method based on optical feedback cavity enhanced Raman spectroscopy; the details are as follows:

[0051] The laser is loaded with a modulation signal generated by a function generator. After the laser is emitted from the laser, the laser passes through a feedback rate control system, a matching lens, a mirror, and a beam splitter, and is then coupled into an ultra-stable irregular optical feedback cavity.

[0052] The cavity mirror of the ultra-stable irregular optical feedback cavity outputs 0.01% of the cavity resonant leakage light, which returns to the laser along the original path, forming weak optical feedback to narrow the laser linewidth. The intensity of the feedback light is controlled by the feedback rate control system.

[0053] The direct reflected light from the front mirror of the ultra-stable irregular optical feedback cavity is received by a photodetector via a beam splitter. The radio frequency component is sent to the PID control system. After modulation and demodulation, the length of the piezoelectric ceramic is adjusted in real time to control the feedback phase, so that the feedback phase is always an integer multiple of 2π, thereby obtaining a narrow linewidth and frequency-stable laser.

[0054] After the gas to be tested enters the optical path inside the ultra-stable irregular optical feedback cavity, it undergoes Raman scattering with the enhanced laser inside the cavity. The scattered light strikes the inner wall of the cavity (smooth / high-reflection film) and undergoes multiple reflections. The scattered light after exiting passes through a focusing lens and a bandpass filter, and is then subjected to spectral separation and detection by a spectrometer and a photodetector. Finally, the data processing unit performs qualitative and quantitative analysis of the gas based on the Raman characteristic peaks.

[0055] Example 2

[0056] The optical feedback mechanism significantly improves the laser's linewidth reduction, narrow self-locking, and intracavity power synchronization, resulting in a 2-3 order of magnitude improvement in vibration resistance compared to the traditional passive cavity enhanced Raman scheme, enabling stable operation in mine vibration environments.

[0057] This embodiment employs optical feedback combined with Pound-Drever-Hall (PDH) locking technology. By optimizing the optical path design, it achieves an effective increase in optical path gain and enhances the system's anti-interference performance, effectively suppressing the impact of external environmental interference on laser locking and power stability. Specific test verification is as follows:

[0058] Test environment: standard laboratory environment, temperature controlled at 25±0.2℃, humidity 50±5%RH; simulating common external vibration interference.

[0059] Test equipment: The laser system in this embodiment.

[0060] Test principle: Example 1 above.

[0061] Test duration: The test lasts for 4 hours under each condition, and the test is repeated for 3 sets. The average value is taken to ensure the reliability of the test data. During the test, the lock status, optical path gain and power spectral density are recorded in real time.

[0062] The laser output power is 150mW. After cavity enhancement and amplification, the amplitude at the transmission end of the resonant cavity is approximately 3V, and the calculated cavity power is approximately 300W, representing a 2000-fold amplification compared to the laser output power. The amplification factor fluctuates by ≤ ±1% over 4 hours, indicating stable amplification. Figure 3 Meanwhile, the optimized resonant cavity structure effectively ensures the uniformity of the amplified beam, avoiding local power distortion from affecting the detection effect. In contrast, the cavity-less enhancement design offers no amplification effect.

[0063] The frequency stability is achieved through the synergistic effect of cavity enhancement technology and closed-loop frequency control mechanism: by real-time monitoring of the matching state between the laser frequency and the cavity mode, frequency drift is compensated in a timely manner, and the influence of external environmental fluctuations on the frequency is suppressed. The frequency noise power spectral density is significantly suppressed from the low frequency band to 2kHz. Figure 4 This effectively resists external low-frequency noise, ensuring the stability of optical amplification and providing a stable optical signal foundation for subsequent high-sensitivity detection.

[0064] Example 3

[0065] This embodiment, based on the cavity-enhanced optical amplification and frequency stabilization design of Embodiment 2, constructs a high-sensitivity detection system. Utilizing the high-intensity optical signal after cavity enhancement and amplification, combined with signal noise reduction processing, it achieves ultra-high sensitivity detection of target substances at the ppm level. Specific test verification is as follows:

[0066] Test environment: standard laboratory environment, temperature 25±0.2℃, humidity 50±5%RH, no electromagnetic interference, no stray light.

[0067] Test equipment: In this embodiment, a laser system, some target detection substances (methane, ethane, acetylene, ethylene, hydrogen, carbon monoxide, carbon dioxide), standard samples (concentration of 5000 ppm), and a high-sensitivity spectrometer (detection accuracy of 0.07 nm).

[0068] Test principle: The high-intensity light signal amplified by cavity enhancement technology interacts with the target material (Raman scattering) to generate a characteristic signal. Background noise is suppressed by the signal denoising module, and signal fluctuation is reduced by the frequency stabilization mechanism. The signal-to-noise ratio (SNR) is calculated by comparing the concentration of the standard sample with the intensity of the detected signal. An SNR ≥ 3 indicates that the sample can be effectively detected, thus verifying the detection sensitivity range, accuracy and stability.

[0069] Table 1

[0070]

[0071] Test data shows that the detection sensitivity of this embodiment can reach ppm (Table 1), with high detection accuracy and good repeatability. Under normal environmental fluctuations, the sensitivity can remain stable without significant attenuation, achieving optical amplification and frequency stability, thereby achieving the beneficial effect of ultra-high "detection sensitivity". If the laser power is increased, the detection limit can reach the ppb level, which is suitable for various trace substance detection scenarios and has strong practicality.

[0072] Contents not described in detail in this specification are prior art known to those skilled in the art. Although illustrative specific embodiments of the invention have been described above to facilitate understanding by those skilled in the art, it should be understood that the invention is not limited to the scope of the specific embodiments. Various modifications are readily apparent to those skilled in the art as long as they fall within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of this invention are protected.

Claims

1. A gas detection device based on optical feedback cavity enhanced Raman spectroscopy, characterized in that: The gas detection device includes: a laser, a feedback rate control system, a matching lens, a reflector and a beam splitter that the laser emitted from the laser passes through in sequence before entering an ultra-stable irregular optical feedback cavity; and a modulation signal generated by a function generator is loaded onto the laser. The function generator produces a local reference signal of the same frequency, which enters the mixer of the PID control system and mixes with the modulation signal in the reflected light. The demodulated error signal enters the PID module in the PID control system, and then the output voltage controls the length of the piezoelectric ceramic to adjust the phase of the feedback light, thereby achieving laser linewidth narrowing and frequency locking. The ultra-stable irregular optical feedback cavity has an internal horn-shaped opening, with the horn inlet serving as the laser inlet and the horn outlet serving as the laser outlet. Furthermore, the ultra-stable irregular optical feedback cavity is also equipped with an air inlet and an air outlet. The front mirror of the ultra-stable irregular optical feedback cavity generates reflected light. After passing through the beam splitter, the reflected light enters the photodetector in sequence and is transmitted to the PID control system. After modulation and demodulation, the length of the piezoelectric ceramic set at the reflector is controlled to control the feedback phase. The emitted light from the ultra-stable irregular optical feedback cavity passes sequentially through a focusing lens, a bandpass filter, and a spectrometer.

2. The gas detection device based on optical feedback cavity enhanced Raman spectroscopy according to claim 1, characterized in that: The laser is a semiconductor laser; the output wavelength uses the visible light band and has a wide linewidth.

3. The gas detection device based on optical feedback cavity enhanced Raman spectroscopy according to claim 1, characterized in that: The piezoelectric ceramic is lead zirconate titanate ceramic.

4. The gas detection device based on optical feedback cavity enhanced Raman spectroscopy according to claim 1, characterized in that: The ultra-stable irregular optical feedback cavity is rectangular.

5. A gas detection device based on optical feedback cavity enhanced Raman spectroscopy according to claim 1, characterized in that: The inner wall of the ultra-stable irregular optical feedback cavity is smooth or coated with a high-reflectivity film.

6. A gas detection method based on optical feedback cavity enhanced Raman spectroscopy using the apparatus described in any one of claims 1 to 5, characterized in that: The laser is loaded with a modulation signal generated by a function generator. After the laser is emitted from the laser, the laser passes through a feedback rate control system, a matching lens, a mirror, and a beam splitter, and is then coupled into an ultra-stable irregular optical feedback cavity. The intracavity resonant leakage light output from the cavity front mirror of the ultra-stable irregular optical feedback cavity returns to the laser along the original path, forming weak optical feedback that narrows the laser linewidth. The intensity of the feedback light is controlled by the feedback rate control system. The direct reflected light from the front mirror of the ultra-stable irregular optical feedback cavity is received by a photodetector via a beam splitter. The radio frequency component is sent to the PID control system. After modulation and demodulation, the length of the piezoelectric ceramic is adjusted in real time to control the feedback phase, thereby obtaining a narrow linewidth and frequency-stable laser. After the gas to be tested enters the optical path inside the ultra-stable irregular optical feedback cavity, it undergoes Raman scattering with the enhanced laser inside the cavity. The scattered light strikes the inner wall of the cavity and undergoes multiple reflections. After exiting, the scattered light passes through a focusing lens and a bandpass filter, and is then subjected to spectral separation and detection by a spectrometer and a photodetector. Finally, the data processing unit performs qualitative and quantitative analysis of the gas based on the Raman characteristic peaks.

7. The gas detection method based on optical feedback cavity enhanced Raman spectroscopy according to claim 6, characterized in that: The output of the intracavity resonant leakage light is 0.01%.

8. The gas detection method based on optical feedback cavity enhanced Raman spectroscopy according to claim 1, characterized in that: The length of the piezoelectric ceramic is adjusted to ensure that the feedback phase is always an integer multiple of 2π.

9. The gas detection method based on optical feedback cavity enhanced Raman spectroscopy according to claim 1, characterized in that: The gas to be tested includes any one of the following: mine gas, hydrogen sulfide, alkanes, alkenes and alkynes, volatile organic compounds, greenhouse gases, and air pollutants.

Images