CRDS-based small high-precision gas detection device and method

Abstract

The invention relates to the technical field of gas concentration detection, and provides a CRDS-based small high-precision gas detection device, which comprises an integrating tube and two groups of endoscope assemblies respectively arranged in an incident end cavity and an emergent end cavity of the integrating tube, and each endoscope assembly comprises a high-reflectivity mirror and an adjusting frame for mounting the high-reflectivity mirror, and each adjusting frame is used for adjusting the angle of the corresponding high-reflectivity mirror, so that the high-reflectivity mirror in the incident end cavity and the high-reflectivity mirror in the emergent end cavity are arranged in parallel. The invention further provides a CRDS-based small high-precision gas detection method. The adjusting frame is arranged in the tube to adjust the angle of the high-reflectivity mirror, and compared with an existing detection device which is large in size and troublesome in cavity mirror adjustment, accuracy and operability of parallelism adjustment of the high-reflectivity mirror can be guaranteed on the premise that miniaturization of a resonant cavity space is achieved; actual detection operation is more convenient, the use conditions of special occasions are met, and the situation that the detection precision of the device is affected by contamination of the lens placed outside can be avoided.

Description

Technical Field

[0001] The present invention relates to the technical field of gas concentration detection, and in particular to a small-sized high-precision gas detection device and method based on CRDS. Background Art

[0002] In cavity ring-down spectroscopy (CRDS), the light source is reflected back and forth in the optical resonant cavity and then emitted from the cavity mirror. The concentration of the gas to be measured can be obtained by detecting the ring-down time of the emitted light. Cavity ring-down spectroscopy usually uses a pulsed laser or a continuous laser as the light source. The laser is incident into the optical resonant cavity at an angle perpendicular to the high-reflection mirror and reflects back and forth inside. When the laser frequency resonates with the cavity mode frequency of the resonant cavity, the light intensity in the resonant cavity will increase rapidly. Breaking the resonance state at this time, the transmitted light will gradually decay with the characteristics of an e-exponential curve. The higher the concentration of the gas to be measured, the shorter the ring-down time. This ring-down time can be obtained by fitting the attenuated e-exponential curve. The wavelength modulation method scans the laser frequency point by point according to different cavity mode frequencies to obtain discrete absorption spectrum signals. The horizontal coordinate of the absorption spectrum signal is obtained through the free spectrum range of the optical resonant cavity, which is the laser or cavity mode frequency value. Finally, the spectrum signal is inverted to obtain the concentration of the gas to be measured.

[0003] In order to achieve mode matching, the existing CRDS gas detection device has a very complex overall structure and a large size. At the same time, the adjustment of the cavity mirror is very troublesome and unstable. In addition, in order to achieve the laser beam waist position and spot diameter matching the fundamental mode position and spot size of the optical resonant cavity, two groups of aspheric lenses are used for precision adjustment, which is very complicated to operate. The final gas detection device is very large and difficult to meet the needs of portability and special environment detection. Summary of the invention

[0004] The object of the present invention is to provide a small-sized high-precision gas detection device and method based on CRDS, which can at least solve some of the defects in the prior art.

[0005] To achieve the above-mentioned purpose, an embodiment of the present invention provides the following technical solution: a small-scale high-precision gas detection device based on CRDS, comprising an integrating tube, and also comprising two groups of cavity mirror assemblies respectively arranged in the incident end cavity and the output end cavity of the integrating tube, each of the cavity mirror assemblies comprises a high-reflection mirror and an adjustment frame for mounting the high-reflection mirror, and each of the adjustment frames is used to adjust the angle of the corresponding high-reflection mirror so that the high-reflection mirror in the incident end cavity is arranged in parallel with the high-reflection mirror in the output end cavity.

[0006] Furthermore, an adjustment hole is provided on the contact surface where the adjustment frame cooperates with the high-reflection mirror, and a spring top screw capable of pushing and pulling the adjustment frame and the high-reflection mirror is installed in the adjustment hole.

[0007] Furthermore, a fixing hole which can be fixed to the integrating tube is provided on the contact surface where the adjusting frame cooperates with the high-reflection mirror, and the adjusting frame and the high-reflection mirror are fixed to the integrating tube by screws.

[0008] Furthermore, an adjustable focus collimator and a plane mirror adjustment frame for mode matching are provided outside the incident end and the output end of the integrating tube.

[0009] Furthermore, it also includes a laser for inputting laser into the integrating tube.

[0010] Furthermore, it also includes a driving and signal processing circuit for controlling the operation of the laser and / or receiving and processing a laser feedback signal.

[0011] Furthermore, the driving and signal processing circuit provides the laser with a low-frequency sawtooth wave scanning signal and a high-frequency sine wave modulation signal.

[0012] Furthermore, the driving and signal processing circuit receives an electrical signal converted from the laser output from the output end of the integrating tube, and obtains a cavity ring-down signal after processing the electrical signal. The concentration of the gas to be measured is determined by analyzing the ring-down time of the cavity ring-down signal.

[0013] Furthermore, it also includes a gas access unit for supplying gas into the integrating tube and monitoring the gas.

[0014] The embodiment of the present invention provides another technical solution: a small-scale high-precision gas detection method based on CRDS, using the above-mentioned device, comprising the following steps:

[0015] S1, using the integrating tube and two groups of cavity mirror components to construct an optical resonant cavity and introducing a gas to be measured into the optical resonant cavity;

[0016] S2, using the adjustment frame to adjust the angle of the corresponding high-reflection mirror, so as to adjust the Newton rings generated by the high-reflection mirror in the incident end cavity and the Newton rings generated by the high-reflection mirror in the output end cavity in the optical resonant cavity to overlap;

[0017] S3, inputting laser light from the incident end of the optical resonant cavity;

[0018] S4, adjust the two plane mirror adjustment frames at the incident end to collimate the laser through the center of the resonant cavity, and adjust the position of the aspheric lens inside the collimator to match the laser with the resonant cavity mode;

[0019] S5, the laser is reflected multiple times in the optical resonant cavity to achieve gas absorption, and two plane mirrors are adjusted at the output end to collimate the transmitted laser into a collimator and transmit it into a photodetector using an optical fiber;

[0020] S6, performing photoelectric conversion by the photodetector;

[0021] S7, analyzing the converted electrical signal and calculating the concentration of the gas to be measured.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. By setting an adjustment frame inside the tube to adjust the angle of the high-reflection mirror, compared with the existing detection device with a large volume and troublesome cavity mirror adjustment, it can ensure the accuracy and ease of operation of the parallelism adjustment of the high-reflection mirror while realizing miniaturization of the resonant cavity space. The actual detection operation is more convenient and meets the conditions for use in special occasions. It can also prevent the lens from being placed outside and being contaminated, affecting the detection accuracy of the device.

[0024] 2. Two sets of cavity mirror components are placed on both sides of the resonant cavity and their relative positions are consistent to ensure the ease and high precision of light path collimation and coupling into the photodetector, thereby achieving more accurate mode matching with the optical resonant cavity.

[0025] 3. Brewster windows are installed on both sides of the integrating tube, which not only seals the integrating tube but also does not affect the incidence and emission of the light path in the resonant cavity, ensuring accurate and high-precision detection of the gas detection device.

[0026] 4. The driving and signal processing circuit can not only drive the normal operation of the laser, but also provide the laser with low-frequency sawtooth scanning signal and high-frequency sine wave modulation signal.

[0027] 5. The resonant cavity constructed by the integrating tube and two sets of cavity mirror components can allow the laser to reach an effective optical path of kilometers after multiple reflections, thereby improving the detection sensitivity of the device.

[0028] 6. The gas access unit uses a gas flow meter and a gas molecular pump to draw the gas in the test environment into the optical resonant cavity to detect the concentration of the gas to be tested. The gas flow meter controls the flow rate to ensure the stability of the gas flow and controls the pressure change inside the optical resonant cavity. A pressure sensor and a filter are used. The pressure controller is used to monitor the gas pressure change inside the optical resonant cavity. The filter is used to filter out substances in the environment that may contaminate the high-reflection mirror or interfere with the detection.

[0029] 7. Through the coordination of multiple focusing collimators and multiple plane mirrors, the adjustable part is increased while the difficulty of fine adjustment of mode matching is greatly reduced. The relative optical path distance between the adjustable focusing collimator and the optical resonant cavity and the distance between the internal aspheric lens and the optical fiber light output position are adjusted, and the laser output laser spot waist position is adjusted to the center position of the optical resonant cavity to achieve mode matching, maximize the suppression of high-order modes in the cavity mode signal, and the laser output light is incident into the adjustable focusing collimator through the plane mirror to focus into the optical fiber and then connected to the photodetector, reducing the high-order transverse mode in the cavity mode signal to improve the signal-to-noise ratio. The high-order mode signal is reduced as much as possible without affecting the size of the fundamental mode signal in the cavity mode signal, ensuring that the high signal-to-noise ratio is maintained when the spot size does not achieve mode matching to achieve low-concentration gas detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of a small-sized high-precision gas detection device based on CRDS provided in an embodiment of the present invention;

[0031] In the accompanying drawings: 1-driving and signal processing circuit; 2-laser; 3-optical isolator; 4-first adjustable-focus collimator; 5-first plane reflector; 6-second plane reflector; 7-first Brewster window; 8-first adjustment frame; 9-first high-reflection mirror; 10-integrating tube; 11-second high-reflection mirror; 12-second adjustment frame; 13-second Brewster window; 14-third plane reflector; 15-fourth plane reflector; 16-second adjustable-focus collimator; 17-photodetector; 18-filter; 19-pressure sensor; 20-temperature control module; 21-gas flow meter; 22-gas molecular pump. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention.

[0033] See also Figure 1The embodiment of the present invention provides a small high-precision gas detection device based on CRDS, including an integrating tube 10, and also including two groups of cavity mirror components respectively arranged in the incident end cavity and the exit end cavity of the integrating tube 10, each of the cavity mirror components includes a high-reflection mirror and an adjustment frame for installing the high-reflection mirror, and each of the adjustment frames is used to adjust the angle of the corresponding high-reflection mirror so that the high-reflection mirror in the incident end cavity and the high-reflection mirror in the exit end cavity are arranged in parallel. In the existing detection device, the lens is arranged outside the integrating tube 10, which can neither reduce the size of the device nor easily contaminate the lens, resulting in a decrease in detection accuracy. In this embodiment, by arranging an adjustment frame in the tube to adjust the angle of the high-reflection mirror, the device can be miniaturized, and the accuracy and ease of operation of the parallelism adjustment of the high-reflection mirror can be guaranteed. The actual detection operation is more convenient and meets the conditions for use in special occasions. It can also avoid the lens being placed outside and being contaminated to affect the detection accuracy of the device. Compared with the existing CRDS gas detection device, the overall volume of this device is smaller, and the optical path adjustment and pattern matching adjustment are more precise and simple. The actual detection sensitivity is not affected by the small and simple structure, and the high-precision detection of low-concentration gas is still maintained.

[0034] See also Figure 1 The contact surface of the adjustment frame and the high reflective mirror is provided with an adjustment hole, and a spring top screw is installed in the adjustment hole to push and pull the adjustment frame and the high reflective mirror. In this embodiment, the adjustment is made through the adjustment hole, which can be a threaded hole. When the high reflective mirror and the adjustment frame are both cylindrical, the adjustment hole can be set on the circumferential surface of the lens and the adjustment frame, and the adjustment frame can be pulled with the spring top screw, so as to achieve the requirements of simple angle adjustment and ensuring that the lens is placed inside the gas pool.

[0035] See also Figure 1 The contact surface where the adjustment frame cooperates with the high-reflection mirror is provided with a fixing hole that can be fixed to the integrating tube 10, and the adjustment frame and the high-reflection mirror are fixed to the integrating tube 10 by screws. In this embodiment, the function of the fixing hole is to fix the cavity mirror assembly on the integrating tube 10, and the fixing hole can be designed as a truncated cone-shaped through hole, and the adjustment frame can be embedded and fixed on the inner wall of the integrating tube 10 with screws, and the inner wall of the integrating tube 10 is also provided with corresponding holes. Preferably, there can be three threaded holes, which can be designed to be consistent with the number of fixing holes, and the adjustment holes and the fixing holes can be evenly and spaced apart, wherein the three fixing holes are not adjacent, and the three adjustment holes are not adjacent. Because the present device is designed with two groups of cavity mirror assemblies, in order to facilitate the illustration of the various components in the figure, the two high-reflection mirrors are respectively defined as the first high-reflection mirror 9 and the second high-reflection mirror 11, and the two adjustment frames are respectively defined as the first adjustment frame 8 and the second adjustment frame 12, wherein the first adjustment frame 8 is for the installation of the first high-reflection mirror 9, both of which are arranged in the incident end cavity, and the second adjustment frame 12 is for the installation of the second high-reflection mirror 11, both of which are arranged in the output end cavity.

[0036] See also Figure 1 , the incident end and the exit end of the integrating tube 10 are both provided with Brewster windows. Brewster windows are provided on both sides of the integrating tube 10, and preferably the inclination angles of the two are both 56.4°, which not only seals the integrating tube 10 but also does not affect the incident and exit of the optical path in the resonant cavity, ensures the accurate and high-precision detection of the gas detection device, and also ensures that the laser of the laser 2 will not deflect at an angle during the incident and exit processes. The sealing of the integrating tube 10 also realizes the sealing treatment of the gas absorption cell. For the convenience of description, the two Brewster windows are respectively defined as the first Brewster window 7 and the second Brewster window 13, wherein the first Brewster window 7 is at the incident end, and the second Brewster window 13 is at the exit end.

[0037] See also Figure 1The device further comprises a laser 2 for inputting laser light into the integrator tube 10, and a driving and signal processing circuit 1 for controlling the operation of the laser 2 and / or receiving and processing a signal fed back by the laser. In this embodiment, the laser 2 is a tunable semiconductor laser 2, and the driving and signal processing circuit 1 drives the tunable semiconductor laser 2 to work normally, and provides the laser 2 with a low-frequency sawtooth wave scanning signal and a high-frequency sine wave modulation signal. The driving and signal processing circuit 1 receives the electrical signal converted from the laser output from the output end of the integrating tube 10. The electrical signal is processed to obtain a cavity ring-down signal. The concentration of the gas to be measured is determined by analyzing the ring-down time of the cavity ring-down signal. Specifically, the signal processing system is implemented by the driving and signal processing circuit 1. The electrical signal of the photodetector 17 is received, and the fundamental mode signal will reach the trigger threshold in a short time. At this time, the comparison circuit part in the circuit is converted from a high level to a low level output, that is, when the trigger threshold comes, the circuit output drops to 0V within ns level time and maintains a low level time of 500μs. At this time, the signal collected is the cavity ring-down signal. The concentration of the gas to be measured can be determined by analyzing the ring-down time of the cavity ring-down signal, thereby realizing the detection of low-concentration gas. The outgoing light of the laser 2 passes through the optical isolator 3 to prevent the reflected light from the first high-reflection mirror 9 from hitting the laser 2 and causing damage, and then the outgoing light is collimated by the first adjustable-focus collimator 4. The collimated light adjusts the optical path through the first plane reflector 5 and the second plane reflector 6, and enters the resonant cavity at an angle perpendicular to the first high-reflection mirror 9 and the second high-reflection mirror 11. Then, the mode matching with the resonant cavity is achieved by adjusting the distance between the aspheric lens with a focal length of 11 mm inside the first adjustable-focus collimator 4 and the light output position of the optical fiber. In addition, in the present device, the tunable semiconductor laser 2 is used to emit a laser in the wavelength band where the absorption spectrum of the gas to be measured is located; the optical isolator 3 is used to prevent part of the laser from being reflected back to the laser 2 when it is incident into the resonant cavity and causing damage; the adjustable focus collimator is used to collimate the light spot of the tunable semiconductor laser 2 and perform mode matching adjustment with the resonant cavity, and couple the output light into the single-mode optical fiber; the plane reflector is used to adjust the incident and output light paths; the optical resonant cavity is used to seal and contain the gas to be measured and allow the incident laser of the tunable semiconductor laser 2 to be reflected multiple times inside it to achieve gas absorption; the photodetector 17 is used to receive the laser emitted from the optical resonant cavity and coupled into the single-mode optical fiber, and convert the optical signal into an electrical signal; the driving and signal processing circuit 1 includes a comparison circuit that provides a low-frequency sawtooth wave scanning signal and a high-frequency sine wave modulation signal to the tunable semiconductor laser 2, receives the output signal of the photodetector 17 and cuts off the signal to attenuate it when the signal reaches the trigger threshold, and fits analysis and calculation to obtain the concentration information of the gas to be measured online.The light is reflected multiple times in the resonant cavity and transmits weak light. The third plane reflector 14 and the fourth plane reflector 15 adjust the outgoing light to enter the second adjustable focus collimator 16 to converge the outgoing light into the photodetector 17 for signal detection. The photodetector 17 converts the detected optical signal into an electrical signal and transmits it to the driving and signal processing circuit 1 for subsequent processing. Specifically, the mode matching of CRDS is realized by the first adjustable focus collimator 4, the second adjustable focus collimator 16 and the first plane reflector 5, the second plane reflector 6, the third plane reflector 14, and the fourth plane reflector 15. The adjustable part is increased but the difficulty of fine adjustment of the mode matching is greatly reduced. The first plane reflector 5 and the second plane reflector 6 accurately adjust the incident light to ensure that the optical path is perpendicular to the first high-reflection mirror 9 and the second high-reflection mirror 11, adjust the relative optical path distance between the first adjustable focus collimator 4 and the optical resonant cavity, and the distance between the internal aspheric lens and the optical fiber light output position, and adjust the outgoing laser spot waist position of the laser 2 to the center position of the optical resonant cavity. The laser light is incident into the second adjustable focus collimator 16 through the third plane reflector 14 and the fourth plane reflector 15 to adjust the angle, focus into the optical fiber and then connect to the photodetector 17, so as to reduce the high-order transverse mode in the cavity mode signal to improve the signal-to-noise ratio. In the above optical path, four plane reflectors on both sides of the optical resonant cavity are used to replace the five-dimensional adjustment frame to realize the angle adjustment of the incident and emitted light path, so as to ensure that the light path is incident under coaxial conditions and enters the photodetector 17 after emission. Although this increases the distance of the light path before entering the resonant cavity, it greatly improves the accuracy and simplicity of the light path adjustment. At the same time, the adjustable focus collimator at the output end is used to couple the light into the single-mode optical fiber to connect the photodetector 17 for detection, so that only the waist position of the light spot needs to be considered during the mode matching process, and there is no need to ensure that the size of the light spot is completely consistent with the size of the fundamental mode light spot of the optical resonant cavity, which greatly simplifies the operation during the actual light path adjustment. The method of coupling the emitted light into the single-mode optical fiber using the adjustable focus collimator can reduce the high-order mode signal as much as possible without affecting the size of the fundamental mode signal in the cavity mode signal, thereby ensuring that the high signal-to-noise ratio is maintained when the light spot size does not achieve mode matching, thereby realizing the detection of low-concentration gas.

[0038] See also Figure 1, the device also includes a gas access unit for supplying gas into the integrating tube 10 and monitoring the gas. The gas access unit includes a temperature control module 20, a gas control module, and a pressure sensor 19, wherein the temperature control module 20 is arranged on the side wall of the optical resonant cavity, with the heating end facing the inside of the optical resonant cavity, and is used to heat the gas to be measured inside the optical resonant cavity to maintain a constant temperature, the gas control module includes a gas flow meter 21 and a gas molecular pump 22, which are arranged at the second gas interface of the optical resonant cavity, and the gas to be measured is passed into the optical resonant cavity at a desired flow rate by controlling the pumping speed, and the pressure sensor 19 is arranged on one side of the first gas interface of the optical resonant cavity, and is used to detect the pressure value of the gas to be measured inside the optical resonant cavity. The second gas interface is used to use the gas flow meter 21 and the gas molecular pump 22 to pump the gas in the environment to be measured into the optical resonant cavity through the first gas interface to detect the concentration of the gas to be measured, and the gas flow meter 21 controls the flow rate to ensure the stability of gas flow and control the pressure change inside the optical resonant cavity. The first gas interface is connected to a pressure sensor 19 and a filter 18. The pressure controller is used to monitor the changes in gas pressure inside the optical resonant cavity. The filter 18 is used to filter out substances in the environment that may contaminate the high-reflective mirror or interfere with the detection. Specifically, the air drawn by the gas molecular pump 22 is filtered through the filter 18 before entering the optical resonant cavity to avoid the entry of gases that contaminate the first high-reflective mirror 9, the second high-reflective mirror 11 and other gases that may affect the detection results.

[0039] See also Figure 1The embodiment of the present invention provides a small-scale high-precision gas detection method based on CRDS, which adopts the above-mentioned device and includes the following steps: S1, using the integrating tube and two groups of the cavity mirror components to construct an optical resonant cavity and introduce the gas to be measured into the optical resonant cavity; S2, using the adjustment frame to adjust the angle of the corresponding high-reflection mirror, so as to adjust the Newton rings generated by the high-reflection mirror in the incident end cavity in the optical resonant cavity to coincide with the Newton rings generated by the high-reflection mirror in the exit end cavity; S3, inputting laser from the incident end of the optical resonant cavity; S4, adjusting two plane mirror adjustment frames at the incident end to collimate the laser through the center of the resonant cavity, and adjusting the position of the aspheric lens inside the collimator to match the laser with the resonant cavity mode; S5, the laser is reflected multiple times in the optical resonant cavity to achieve gas absorption, and adjusting two plane mirror reflectors at the exit end to collimate the transmitted laser into the collimator and transmit it into the photodetector using optical fiber; S6, performing photoelectric conversion through the photodetector; S7, analyzing the converted electrical signal and calculating the concentration of the gas to be measured. In this embodiment, the laser light collimated by the laser 2 can reach the effective optical path of kilometers after multiple reflections in the optical resonant cavity, thereby improving the detection sensitivity of the device. In order to ensure the relative parallelism of the two sets of cavity mirror components, the parallelism is adjusted by passing the visible red light of the helium-neon laser 2 through the Newton rings generated by the center of the first high-reflection mirror 9 and the second high-reflection mirror 11, and the angles of the first high-reflection mirror 9 and the second high-reflection mirror 11 are finely adjusted by pulling the spring top screws and screws on the circumference of the first adjustment frame 8 and the second adjustment frame 12. While improving the measurement accuracy, the embedded design also reduces the volume of the detection device as much as possible, making the actual measurement more convenient, and finally making the Newton rings generated by the first high-reflection mirror 9 and the Newton rings generated by the second high-reflection mirror 11 highly overlap.

[0040] See also Figure 1 The tunable semiconductor laser 2 is connected to the optical isolator 3 through an optical fiber and then fixed to the first adjustable focus collimator 4. The collimated laser is incident into the optical resonant cavity through the adjustment of the first plane reflector 5 and the second plane reflector 6 and is reflected multiple times inside. The output light enters the second adjustable focus collimator 16 through the adjustment of the third plane reflector 14 and the fourth plane reflector 15. The internal lens of the second adjustable focus collimator 16 couples the output light into the single-mode optical fiber, and the laser coupled into the optical fiber is transmitted to the photodetector 17.

[0041] See also Figure 1The method can adjust the parallelism of the high-reflection mirror of the optical resonant cavity more simply and accurately, and the design that the high-reflection mirror adjustment frame is embedded in the integrating tube 10 makes it possible to miniaturize the structure; four plane reflectors on both sides of the optical resonant cavity replace the five-dimensional adjustment frame to realize the angle adjustment of the incident and emitted light path, ensure that the light path enters the optical resonant cavity under the coaxial condition at the incident end, and realize higher-precision light path adjustment to ensure the best effect, and at the output end, it is completely coupled into the single-mode optical fiber through the adjustable focus collimator to connect to the photodetector 17 for detection; the output laser is connected to the photodetector 17 through the single-mode optical fiber, which simplifies the mode matching. The waist position and size of the beam must match the requirements of the optical resonant cavity, and only the spot waist position needs to be adjusted to the center of the optical resonant cavity; while not affecting the size of the fundamental mode signal in the cavity mode signal, the high-order mode signal is reduced as much as possible, ensuring that the high signal-to-noise ratio is maintained when the spot size does not achieve mode matching to achieve low-concentration gas detection.

[0042] See also Figure 1 , the ambient gas to be measured is drawn into the optical resonant cavity. Specifically, the wavelength of the tunable semiconductor laser 22 is scanned by the driving and signal processing circuit 11 with a low-frequency sawtooth wave to make it resonate with the optical resonant cavity. At the same time, a high-frequency sine wave is superimposed on the sawtooth wave to increase the resonance frequency of the light and the cavity. The position where no resonance occurs is used as the adjacent longitudinal mode distinction point to obtain a discrete optical spectrum. The multiple ring-down events at each position are averaged to improve the signal-to-noise ratio and the e index is fitted to obtain the signal spectrum. Finally, the integral absorbance A, the absorption line intensity S(T) of the spectral database, and the temperature and pressure information collected in real time are obtained by fitting, and the gas concentration is inverted using the formula X=A / PS(T).

[0043] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A small high-precision gas detection device based on CRDS, including an integrating tube, characterized in that: It also includes two groups of cavity mirror assemblies respectively arranged in the incident end cavity and the output end cavity of the integrating tube, each of the cavity mirror assemblies includes a high-reflection mirror and an adjustment frame for mounting the high-reflection mirror, and each of the adjustment frames is used to adjust the angle of the corresponding high-reflection mirror so that the high-reflection mirror in the incident end cavity is arranged in parallel with the high-reflection mirror in the output end cavity.

2. The small-sized high-precision gas detection device based on CRDS as claimed in claim 1, characterized in that: An adjustment hole is arranged on the contact surface where the adjustment frame and the high-reflection mirror cooperate, and a spring top screw which can push and pull the adjustment frame and the high-reflection mirror is arranged in the adjustment hole.

3. The small-sized high-precision gas detection device based on CRDS as claimed in claim 1, characterized in that: The contact surface where the adjustment frame cooperates with the high-reflection mirror is provided with a fixing hole which can be fixed to the integrating tube, and the adjustment frame and the high-reflection mirror are fixed to the integrating tube by screws.

4. The small-sized high-precision gas detection device based on CRDS as claimed in claim 1, characterized in that: An adjustable focus collimator and a plane mirror adjustment frame for mode matching are arranged outside the incident end and the exit end of the integrating tube.

5. The small-sized high-precision gas detection device based on CRDS as claimed in claim 1, characterized in that: Also included is a laser for inputting laser light into the integrating tube.

6. The small-sized high-precision gas detection device based on CRDS as claimed in claim 5, characterized in that: It also includes a driving and signal processing circuit for controlling the operation of the laser and / or receiving and processing a laser feedback signal.

7. The small-sized high-precision gas detection device based on CRDS as claimed in claim 6, characterized in that: The driving and signal processing circuit provides the laser with a low-frequency sawtooth wave scanning signal and a high-frequency sine wave modulation signal.

8. The small-sized high-precision gas detection device based on CRDS as claimed in claim 6, characterized in that: The driving and signal processing circuit receives the electrical signal converted from the laser output from the output end of the integrating tube, and obtains the cavity ring-down signal after processing the electrical signal. The concentration of the gas to be measured is determined by analyzing the ring-down time of the cavity ring-down signal.

9. The small-sized high-precision gas detection device based on CRDS as claimed in claim 1, characterized in that: Also included is a gas access unit for supplying gas into the integrating tube and monitoring the gas.

10. A small-scale high-precision gas detection method based on CRDS, characterized in that: The device according to any one of claims 1 to 9 comprises the following steps: S1, using the integrating tube and two groups of cavity mirror components to construct an optical resonant cavity and introducing a gas to be measured into the optical resonant cavity; S2, using the adjustment frame to adjust the angle of the corresponding high-reflection mirror, so as to adjust the Newton rings generated by the high-reflection mirror in the incident end cavity and the Newton rings generated by the high-reflection mirror in the output end cavity in the optical resonant cavity to overlap; S3, inputting laser light from the incident end of the optical resonant cavity; S4, adjust the two plane mirror adjustment frames at the incident end to collimate the laser through the center of the resonant cavity, and adjust the position of the aspheric lens inside the collimator to match the laser with the resonant cavity mode; S5, the laser is reflected multiple times in the optical resonant cavity to achieve gas absorption, and two plane mirrors are adjusted at the output end to collimate the transmitted laser into a collimator and transmit it into a photodetector using an optical fiber; S6, performing photoelectric conversion by the photodetector; S7, analyzing the converted electrical signal and calculating the concentration of the gas to be measured.

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