An optical resonant cavity gas detection system and detection method thereof

Abstract

An optical resonant cavity gas detection system and a detection method thereof, comprising a laser, a resonant cavity infrared detector, a first optical fiber beam splitter, a second optical fiber beam splitter, a hollow optical fiber, an inlet end conversion chamber and an outlet end conversion chamber, the laser emission end is connected to the incident end of the first optical fiber beam splitter, the first optical fiber beam splitter output end is connected to the incident end of the second optical fiber beam splitter, the second optical fiber beam splitter output end is connected to the inlet end conversion chamber, the two ends of the hollow optical fiber are respectively connected to the inlet end conversion chamber and the outlet end conversion chamber, the outlet end conversion chamber is connected to the incident end of the second optical fiber beam splitter, and the output end of the second optical fiber beam splitter is connected to the resonant cavity infrared detector. The present invention is stable and reliable, has high sensitivity, and fast response time, and can be applied to the detection of low trace gas components. Combined with the measurement and control of laser wavelength, sample pressure and temperature, the instrument and equipment of the present invention can achieve sensitivity measurement of ppbv to pptv.

Description

Technical Field

[0001] The invention belongs to the technical field of gas detection, and in particular relates to an optical resonant cavity gas detection system and a detection method thereof. Background Art

[0002] Cavity ring-down spectroscopy (CRDS) is a new type of gas detection method. In principle, it does not require standard gas calibration and is a highly sensitive laser absorption spectroscopy method that can measure trace samples or a large number of weakly converted samples. At present, CRDS has been applied in the measurement of mirror reflectivity, trace gas component detection, and aerosol extinction coefficient measurement. The gas detection method of cavity ring-down absorption spectroscopy has the following disadvantages or shortcomings:

[0003] 1) The resonant cavity is very important in cavity ring-down absorption spectroscopy and is difficult to manufacture.

[0004] Cavity ring-down absorption spectroscopy generally uses two high-reflectivity mirrors to construct a resonant cavity pool. The laser pulse is introduced into the resonant cavity surrounded by two high-reflectivity mirrors. The reflected laser oscillates in the resonant cavity, and a small amount of light is lost with each reflection. The detector placed behind the second mirror measures the weakening intensity of the reflected light. When the measured gas in the resonant cavity cannot absorb, the signal decays slowly; when there is gas absorption in the resonant cavity, the signal decays quickly. By calculating the signal attenuation curve, the concentration of the measured gas in the resonant cavity is calculated.

[0005] The key to CRDS detection technology is the optical resonant cavity, and the key to the resonant cavity is the two highly reflective lenses. The higher the reflectivity of the reflective lens, the longer the ring-down time, and the higher the sensitivity of the equipment. Generally, the reflectivity of the lens is required to be >99.9%. However, due to the limitations of manufacturing processes and materials, it is difficult and costly to produce lenses with ultra-high reflectivity at this stage, so the CRDS spectrum detection method has not been widely promoted.

[0006] 2) In the existing cavity ring-down spectroscopy absorption method, the light source drifts for a long time and the measurement accuracy cannot be guaranteed.

[0007] The CRDS spectral absorption method relies on the absorption of laser by gas, and generally uses semiconductor tunable lasers. The center wavelength of the output laser of semiconductor tunable lasers changes with the ambient temperature and the injected current. Generally, the center wavelength shifts by 0.1nm for every 1°C change in temperature, and the center wavelength changes by 0.01nm for every 1mA change in injected current. The center wavelength of the laser will change slowly and for a long time during use due to the influence of the manufacturing process and the characteristics of the device itself. If there is no effective means to correct the absorption wavelength, the drift of the center wavelength of the laser will cause inaccurate measurement or even make it impossible to measure.

[0008] At present, there is also a spectrum detection method using hollow optical fiber technology, which has the following disadvantages or shortcomings:

[0009] 1) Long reaction time

[0010] At present, there are literatures that combine hollow optical fibers for spectral analysis of gas components. The characteristics of hollow optical fibers that can conduct both lasers and gases are used to detect gas components. However, since the core diameter of hollow optical fibers is very small, only about 100nm, the efficiency of gas replacement is very low when using such a small core diameter to conduct gas, which makes the response time of the entire system longer and cannot give full play to the advantages of efficient and fast optical spectral detection.

[0011] 2) Hollow fiber technology combined with hollow fiber design resonant cavity has poor sensitivity

[0012] Some literature uses a beam splitter combined with a hollow optical fiber to achieve cavity ring-down, but does not design a reasonable adjustment structure to adjust the length of the resonant cavity (i.e., the path length of the light). The present invention adjusts the length of the resonant cavity by designing a fine-tuning mechanism, so that the laser reaches a resonant state, thereby improving the detection sensitivity of the entire system. Summary of the invention

[0013] In order to solve the deficiencies in the prior art, the present invention provides a stable, reliable, highly sensitive and fast-responding optical resonant cavity gas detection system and a detection method thereof.

[0014] In order to solve the above technical problems, the present invention adopts the following technical scheme: an optical resonant cavity gas detection system, comprising a laser, a resonant cavity infrared detector, a first optical fiber beam splitter, a second optical fiber beam splitter, a hollow optical fiber, an air inlet conversion chamber and an air outlet conversion chamber, the emission end of the laser is connected to the incident end of the first optical fiber beam splitter, the output end of the first optical fiber beam splitter is connected to the incident end of the second optical fiber beam splitter through the first incident optical fiber, the output end of the second optical fiber beam splitter is connected to the air inlet conversion chamber through the first output optical fiber, the two ends of the hollow optical fiber are respectively connected to the air inlet conversion chamber and the air outlet conversion chamber, the air outlet conversion chamber is connected to the incident end of the second optical fiber beam splitter through the second incident optical fiber, and the output end of the second optical fiber beam splitter is connected to the resonant cavity infrared detector through the second output optical fiber.

[0015] It also includes a main control unit and an optical fiber length fine-tuning device. The optical fiber length fine-tuning device is a cylindrical reel with a temperature resistor and an electric heating rod inside. The hollow optical fiber is wound around the outer circle of the reel. The temperature resistor, the electric heating rod, the laser and the resonant cavity infrared detector are respectively connected to the main control unit through control lines.

[0016] It also includes a reference gas absorption pool, at both ends of which are respectively provided with a reference gas chamber photoelectric detector and a reference gas chamber collimator. The reference gas chamber photoelectric detector is connected to the main control unit through a reference data line, and the reference gas chamber collimator is connected to the output end of the first optical fiber splitter through a reference optical fiber.

[0017] The structures of the inlet end conversion chamber and the outlet end conversion chamber are the same and are arranged symmetrically on the left and right. The inlet end conversion chamber is located on the left side of the outlet end conversion chamber. The inlet end conversion chamber includes a sensor interface component. A conversion collimator is provided at the upper end of the sensor interface component through a collimator adapter. An interface connected to the hollow optical fiber is provided at the lower end of the sensor interface component. A first connection port is provided on the left side of the sensor interface component, and a second connection port is provided on the right side of the sensor interface component. The first connection port on the left side of the inlet end conversion chamber is the air inlet, and the second connection port on the right side of the outlet end conversion chamber is the air outlet.

[0018] The first connection port of the conversion air chamber at the air inlet end on the left is connected with the first connection port of the conversion air chamber at the air outlet end on the right through a communication air pipe, and a gas circuit solenoid valve is arranged on the communication air pipe.

[0019] A detection method for an optical resonant cavity gas detection system comprises the following steps:

[0020] (1) The gas to be tested is introduced to replace the gas in the conversion chamber at the air inlet end and the conversion chamber at the air outlet end;

[0021] (2) Determine the central wavelength of the laser;

[0022] (3) Start the laser, pass the gas to be tested, and adjust the optical fiber length fine-tuning device to determine the optimal resonance temperature during the test;

[0023] (4) Determination of the concentration of the gas being measured.

[0024] The specific process of step (1) is as follows: the gas circuit solenoid valve is opened, and the gas to be measured passes through the gas inlet, the gas inlet end conversion chamber, the air pipe, the gas circuit solenoid valve, the gas outlet end conversion chamber in sequence, and is finally exhausted from the gas outlet; after the gas in the gas inlet end conversion chamber is fully replaced, the gas circuit solenoid valve is closed, and the gas to be measured passes through the gas inlet, the gas inlet end conversion chamber, the hollow optical fiber, the gas outlet end conversion chamber in sequence, and is finally exhausted through the gas outlet.

[0025] The laser uses a semiconductor tunable laser. The center wavelength of the laser output changes with the ambient temperature and the injected current. In general, the center wavelength shifts by 0.1nm for every 1°C change in temperature, and the center wavelength changes by 0.01nm for every 1mA change in injected current. The laser is affected by the manufacturing process and the characteristics of the device itself. During use, the center wavelength of the laser will change slowly and for a long time. If there is no effective means to correct its absorption wavelength, the drift of the center wavelength of the laser will cause inaccurate measurement or even impossible measurement.

[0026] The specific process of step (2) is as follows: the first optical fiber beam splitter splits part of the light energy, which is introduced into the reference gas absorption cell through the reference optical fiber and the reference gas chamber collimator, and after being absorbed by the measured gas, it is converted into an electrical signal through the photoelectric detector, and then input into the main control unit for processing; the main control unit obtains the electrical signal of the photoelectric detector of the reference gas chamber, combines it with the tunable semiconductor laser absorption spectroscopy (TDALS) technology, and uses the principle that the absorption peak of a certain component gas in the measured gas is relatively constant with the absorption peak of the measured gas, thereby real-time tracking and correcting the change of the laser wavelength so that the laser center wavelength is always at a specific position of the gas absorption peak.

[0027] The specific process of step (3) is as follows: the main control unit controls the laser to emit a laser of a certain wavelength, and more than 95% of the light energy is transmitted to the second optical fiber splitter after passing through the first optical fiber splitter; the second optical fiber splitter has a splitting ratio of 99:1, and emits two beams of light, the first output light contains 99% of the light energy, and the second output light contains 1% of the light energy. The first output light enters the conversion air chamber at the air inlet end, is collimated by the conversion collimator, and then enters the hollow optical fiber. After passing through the circularly wound hollow optical fiber, it enters the conversion air chamber at the air outlet end, is collimated by the conversion collimator in the conversion air chamber at the air outlet end, and is coupled to the second incident optical fiber. The second incident light enters the second optical fiber splitter 2 together with the first incident light again, and enters the hollow optical fiber again.

[0028] During the process of passing the measured gas, the main control unit controls the laser to keep emitting light, and adjusts the temperature of the drum through the electric heating rod and the temperature resistor. The outer circle of the drum expands due to heat or shrinks due to cold, thereby adjusting the length of the hollow optical fiber. When the optical path length in the resonant hollow optical fiber and the optical path length in the auxiliary optical fiber and the structural parts reaches an integer multiple of the laser wavelength, the incident light and the outgoing light reach a resonant state, and the photoelectric signal received at the resonant cavity infrared detector is the strongest.

[0029] The main control unit adjusts the temperature of the optical fiber length fine-tuning device, scans from low to high, and records the temperature when the photoelectric signal received at the resonant cavity infrared detector is the strongest to determine that this temperature is the optimal resonant temperature.

[0030] The specific process of step (4) is as follows: after the photoelectric signal intensity at the infrared detector reaches the maximum, the laser is turned off, and the photoelectric signal at the resonant cavity infrared detector is recorded until the signal returns to zero; by recording the ring-down curve of this process, it is fitted by an algorithm and then the concentration of the measured gas is inverted.

[0031] By adopting the above technical solution, the present invention combines the existing TDLAS technology and cavity ring-down technology and designs a new cavity ring-down gas detection method using hollow optical fiber. It has the characteristics of stability and reliability (using the TDLAS principle and reference gas chamber to correct the laser wavelength), high sensitivity (fine-tuning the length of the hollow optical fiber to make it reach the resonance state, making the ring-down curve longer), and rapid response (designing a bypass gas path to speed up the pipeline gas replacement time).

[0032] The reason for being more stable and reliable: The present invention sets a reference gas chamber bypass in the system. The reference gas absorption cell is filled with an appropriate amount of the measured gas. Combined with the tunable semiconductor laser absorption spectroscopy (TDALS) technology, it can track and correct the change of the laser wavelength in real time, so that the laser center wavelength is always at a specific position of the gas absorption peak. This can solve the drift of the laser center wavelength under long-term use, making the measurement results more stable and reliable.

[0033] Reasons for high sensitivity: The present invention designs a fiber length fine-tuning device, which heats the mechanical structure of the reel that winds the hollow optical fiber, uses the principle of thermal expansion and contraction, controls the temperature of the reel through an electric heating rod, and monitors the temperature value through a temperature resistor. The temperature of the hollow optical fiber changes with the temperature of the reel, and the deformation caused by the temperature change of the reel will stretch the optical fiber wound on it, and then fine-tune the length of the hollow optical fiber. Fine-tune the length of the hollow optical fiber to make it reach a resonant state, and the light intensity of the resonant state reaches the strongest, making the ring-down curve longer, and then making the device achieve better sensitivity.

[0034] Reasons for quick response: Limited by the core diameter of the hollow optical fiber, the gas replacement speed of the spectral detection system using the hollow optical fiber for gas detection is relatively slow. The present invention designs a gas path bypass purge structure (conducting air tube) to speed up the gas replacement speed. Because the aperture of the hollow optical fiber is very fine, its gas resistance is relatively large when the optical path is long. If there is no conducting air tube and gas path solenoid valve to bypass the gas in the early stage, the gas dead corner in the air inlet end conversion chamber and the gas in the pipeline before the conversion chamber can only be removed through the hollow optical fiber, and the replacement time is relatively long. After using the conducting air tube, the replacement speed of useless gas in the early stage can be accelerated, and the response time of the system can be improved. After starting the measurement, it is only necessary to replace the gas in the hollow optical fiber to measure the gas to be measured, which greatly speeds up the measurement speed of the system.

[0035] In summary, the present invention is stable and reliable, has high sensitivity and fast reaction time, and can be applied to the detection of low trace gas components. By combining the measurement and control of laser wavelength, sample pressure and temperature, the instrument and equipment of the present invention can achieve sensitivity measurement of ppbv to pptv. It can be widely used in the fields of power, chemical industry, food safety, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0037] Figure 2 yes Figure 1 Schematic diagram of the internal structure of the conversion chamber at the middle air intake end;

[0038] Figure 3 yes Figure 1 Schematic diagram of the cross section of the optical fiber length fine-tuning device. DETAILED DESCRIPTION

[0039] like Figure 1 , Figure 2 and Figure 3 As shown, an optical resonant cavity gas detection system of the present invention includes a laser 1, a resonant cavity infrared detector 2, a first optical fiber beam splitter 3, a second optical fiber beam splitter 4, a hollow optical fiber 5, an air inlet end conversion chamber 6 and an air outlet end conversion chamber 7, the emitting end of the laser 1 is connected to the incident end of the first optical fiber beam splitter 3, the output end of the first optical fiber beam splitter 3 is connected to the incident end of the second optical fiber beam splitter 4 through a first incident optical fiber 8, the output end of the second optical fiber beam splitter 4 is connected to the air inlet end conversion chamber 6 through a first output optical fiber 9, the two ends of the hollow optical fiber 5 are respectively connected to the air inlet end conversion chamber 6 and the air outlet end conversion chamber 7, the air outlet end conversion chamber 7 is connected to the incident end of the second optical fiber beam splitter 4 through a second incident optical fiber 10, and the output end of the second optical fiber beam splitter 4 is connected to the resonant cavity infrared detector 2 through a second output optical fiber 11.

[0040] It also includes a main control unit 12 and an optical fiber length fine-tuning device 13. The optical fiber length fine-tuning device 13 is a cylindrical reel 14. A temperature resistor 15 and an electric heating rod 16 are arranged inside the reel 14. The hollow optical fiber 5 is wound around the outer circle of the reel 14. The temperature resistor 15, the electric heating rod 16, the laser 1 and the resonant cavity infrared detector 2 are respectively connected to the main control unit 12 through control lines.

[0041] It also includes a reference gas absorption pool 17, at both ends of which are provided with a reference gas chamber photodetector 18 and a reference gas chamber collimator 19, the reference gas chamber photodetector 18 is connected to the main control unit 12 through a reference data line, and the reference gas chamber collimator 19 is connected to the output end of the first optical fiber splitter 3 through a reference optical fiber.

[0042] The structures of the air inlet end conversion chamber 6 and the air outlet end conversion chamber 7 are the same and are arranged symmetrically on the left and right. The air inlet end conversion chamber 6 is located on the left side of the air outlet end conversion chamber 7. The air inlet end conversion chamber 6 includes a sensor interface component 20. The upper end of the sensor interface component 20 is provided with a conversion collimator 22 through a collimator adapter 21. The lower end of the sensor interface component 20 is provided with an interface connected to the hollow optical fiber 5. A first connecting port 23 is provided on the left side of the sensor interface component 20, and a second connecting port 24 is provided on the right side of the sensor interface component 20. The first connecting port 23 on the left side of the air inlet end conversion chamber 6 is an air inlet, and the second connecting port on the right side of the air outlet end conversion chamber 7 is an air outlet.

[0043] The first connection port 23 of the air inlet conversion chamber 6 on the left side is connected to the first connection port 23 of the air outlet conversion chamber 7 on the right side through a communication pipe 25 , and a gas circuit solenoid valve 26 is provided on the communication pipe 25 .

[0044] A detection method for an optical resonant cavity gas detection system comprises the following steps:

[0045] (1) The gas to be measured is introduced to replace the gas in the conversion chamber 6 at the gas inlet end and the conversion chamber 7 at the gas outlet end;

[0046] (2) Determine the central wavelength of laser 1;

[0047] (3) Starting the laser 1, passing the gas to be tested to test the gas, and adjusting the optical fiber length fine-tuning device 13 during the test to determine the optimal resonance temperature;

[0048] (4) Determination of the concentration of the gas being measured.

[0049] The specific process of step (1) is as follows: the gas circuit solenoid valve 26 is opened, and the gas to be measured passes through the air inlet, the air inlet end conversion chamber 6, the air pipe 25, the gas circuit solenoid valve 26, the air outlet end conversion chamber 7 in sequence, and is finally discharged from the air outlet; after the gas in the air inlet end conversion chamber 6 is fully replaced, the gas circuit solenoid valve 26 is closed, and the gas to be measured passes through the air inlet, the air inlet end conversion chamber 6, the hollow optical fiber 5, the air outlet end conversion chamber 7 in sequence, and is finally discharged through the air outlet.

[0050] Laser 1 uses a semiconductor tunable laser 1. The center wavelength of the laser output by laser 1 changes with the ambient temperature and the injected current. Generally, the center wavelength shifts by 0.1nm for every 1°C change in temperature, and the center wavelength changes by 0.01nm for every 1mA change in injected current. Laser 1 is affected by the manufacturing process and the characteristics of the device itself. During use, the center wavelength of laser 1 will change slowly and for a long time. If there is no effective means to correct its absorption wavelength, the drift of the center wavelength of laser 1 will cause inaccurate measurement or even make it impossible to measure.

[0051] The specific process of step (2) is as follows: the first optical fiber beam splitter 3 divides part of the light energy, which is introduced into the reference gas absorption cell 17 through the reference optical fiber and the reference gas chamber collimator 19, and after being absorbed by the measured gas, it is converted into an electrical signal through the photoelectric detector, and then input into the main control unit 12 for processing; the main control unit 12 obtains the electrical signal of the photoelectric detector of the reference gas chamber, combines it with the tunable semiconductor laser 1 absorption spectroscopy (TDALS) technology, and uses the principle that the absorption peak of a certain component gas in the measured gas is relatively constant with the absorption peak of the measured gas, thereby real-time tracking and correcting the change of the wavelength of the laser 1, so that the central wavelength of the laser 1 is always at a specific position of the absorption peak of the measured gas.

[0052] The specific process of step (3) is as follows: the main control unit 12 controls the laser 1 to emit a laser of a certain wavelength, and more than 95% of the light energy is transmitted to the second optical fiber splitter 4 after passing through the first optical fiber splitter 3; the second optical fiber splitter 4 has a splitting ratio of 99:1, and emits two beams of light, the first output light contains 99% of the light energy, and the second output light contains 1% of the light energy. The first output light enters the air inlet conversion chamber 6, is collimated by the conversion collimator 22, and then enters the hollow optical fiber 5. After passing through the circularly wound hollow optical fiber 5, it enters the air outlet conversion chamber 7, is collimated by the conversion collimator 22 in the air outlet conversion chamber 7, and is coupled to the second incident optical fiber 10. The second incident light enters the second optical fiber splitter 42 together with the first incident light again, and enters the hollow optical fiber 5 again.

[0053] During the process of passing the measured gas, the main control unit 12 controls the laser 1 to emit light all the time, and adjusts the temperature of the reel 14 through the electric heating rod 16 and the temperature resistor 15. The outer circle of the reel 14 expands due to heat or shrinks due to cold, thereby adjusting the length of the hollow optical fiber 5. When the optical path length in the resonant hollow optical fiber 5 and the optical path length in the auxiliary optical fiber and the structural member reach an integer multiple of the laser wavelength, the incident light and the outgoing light reach a resonant state, and at this time, the photoelectric signal received at the resonant cavity infrared detector 2 is the strongest.

[0054] The main control unit 12 adjusts the temperature of the optical fiber length fine-tuning device 13, scans from low to high, and records the temperature when the photoelectric signal received at the resonant cavity infrared detector 2 is the strongest to determine that this temperature is the optimal resonant temperature.

[0055] The specific process of step (4) is as follows: after the photoelectric signal intensity at the infrared detector 2 reaches the maximum, turn off the laser 1, and record the photoelectric signal at the resonant cavity infrared detector 2 until the signal returns to zero; by recording the ring-down curve of this process, it is fitted by an algorithm and then the concentration of the measured gas is inverted.

[0056] This embodiment does not impose any formal limitation on the shape, material, structure, etc. of the present invention. Any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A detection method for an optical resonant cavity gas detection system, characterized in that: The optical resonant cavity gas detection system comprises a laser, a resonant cavity infrared detector, a first optical fiber beam splitter, a second optical fiber beam splitter, a hollow optical fiber, an inlet end conversion air chamber and an outlet end conversion air chamber, the emission end of the laser is connected to the incident end of the first optical fiber beam splitter, the output end of the first optical fiber beam splitter is connected to the incident end of the second optical fiber beam splitter through the first incident optical fiber, the output end of the second optical fiber beam splitter is connected to the inlet end conversion air chamber through the first output optical fiber, the two ends of the hollow optical fiber are respectively connected to the inlet end conversion air chamber and the outlet end conversion air chamber, the outlet end conversion air chamber is connected to the incident end of the second optical fiber beam splitter through the second incident optical fiber, and the output end of the second optical fiber beam splitter is connected to the resonant cavity infrared detector through the second output optical fiber; The optical resonant cavity gas detection system also includes a main control unit and an optical fiber length fine-tuning device, the optical fiber length fine-tuning device is a cylindrical reel, a temperature resistor and an electric heating rod are arranged inside the reel, a hollow optical fiber is wound around the outer circle of the reel, and the temperature resistor, the electric heating rod, the laser and the resonant cavity infrared detector are respectively connected to the main control unit through control circuits; The optical resonant cavity gas detection system also includes a reference gas absorption cell, and a reference gas chamber photoelectric detector and a reference gas chamber collimator are respectively provided at both ends of the reference gas absorption cell, the reference gas chamber photoelectric detector is connected to the main control unit through a reference data line, and the reference gas chamber collimator is connected to the output end of the first optical fiber beam splitter through a reference optical fiber; The structures of the air inlet conversion chamber and the air outlet conversion chamber are the same and are arranged symmetrically on the left and right. The air inlet conversion chamber is located on the left side of the air outlet conversion chamber. The air inlet conversion chamber includes a sensor interface component. The upper end of the sensor interface component is provided with a conversion collimator through a collimator adapter. The lower end of the sensor interface component is provided with an interface connected to the hollow optical fiber. The left side of the sensor interface component is provided with a first connection port, and the right side of the sensor interface component is provided with a second connection port. The first connection port on the left side of the air inlet conversion chamber is an air inlet, and the second connection port on the right side of the air outlet conversion chamber is an air outlet. The first connection port of the conversion air chamber at the air inlet end on the left is connected to the first connection port of the conversion air chamber at the air outlet end on the right through a communication air pipe, and a gas circuit solenoid valve is provided on the communication air pipe; The detection method comprises the following steps: (1) The gas to be tested is introduced to replace the gas in the conversion chamber at the air inlet end and the conversion chamber at the air outlet end; (2) Determine the central wavelength of the laser; (3) Start the laser, pass the gas to be tested, and adjust the optical fiber length fine-tuning device to determine the optimal resonance temperature during the test; (4) Determination of the concentration of the gas being measured; The specific process of step (3) is as follows: the main control unit controls the laser to emit a laser of a certain wavelength, and more than 95% of the light energy is transmitted to the second optical fiber splitter after passing through the first optical fiber splitter; the second optical fiber splitter has a splitting ratio of 99:1, and emits two beams of light, the first output light contains 99% of the light energy, and the second output light contains 1% of the light energy. The first output light enters the conversion chamber at the air inlet end, is collimated by the conversion collimator, and then enters the hollow optical fiber. After passing through the circularly wound hollow optical fiber, it enters the conversion chamber at the air outlet end, is collimated by the conversion collimator in the conversion chamber at the air outlet end, and then is coupled to the second incident optical fiber. The second incident light enters the second optical fiber splitter together with the first incident light again, and enters the hollow optical fiber again. During the process of passing the measured gas, the main control unit controls the laser to emit light all the time, and adjusts the temperature of the reel through the electric heating rod and the temperature resistor. The outer circle of the reel expands due to heat or shrinks due to cold, thereby adjusting the length of the hollow optical fiber. When the optical path length in the resonant hollow optical fiber and the optical path length in the auxiliary optical fiber and the structural component reaches an integer multiple of the laser wavelength, the incident light and the outgoing light reach a resonant state, and at this time, the photoelectric signal received at the resonant cavity infrared detector is the strongest; The main control unit adjusts the temperature of the optical fiber length fine-tuning device, scans from low to high, and records the temperature when the photoelectric signal received at the resonant cavity infrared detector is the strongest to determine that this temperature is the optimal resonant temperature.

2. The detection method of an optical resonant cavity gas detection system according to claim 1, characterized in that: The specific process of step (1) is as follows: the gas circuit solenoid valve is opened, and the gas to be measured passes through the gas inlet, the gas inlet end conversion chamber, the air pipe, the gas circuit solenoid valve, the gas outlet end conversion chamber in sequence, and is finally exhausted from the gas outlet; after the gas in the gas inlet end conversion chamber is fully replaced, the gas circuit solenoid valve is closed, and the gas to be measured passes through the gas inlet, the gas inlet end conversion chamber, the hollow optical fiber, the gas outlet end conversion chamber in sequence, and is finally exhausted through the gas outlet.

3. The detection method of an optical resonant cavity gas detection system according to claim 1, characterized in that: The specific process of step (2) is as follows: a first optical fiber beam splitter splits part of the light energy, which is introduced into the reference gas absorption cell through the reference optical fiber and the reference gas chamber collimator, and after being absorbed by the measured gas, it is converted into an electrical signal through the photoelectric detector, and then input into the main control unit for processing; the main control unit obtains the electrical signal of the photoelectric detector of the reference gas chamber, combines it with the tunable semiconductor laser absorption spectroscopy technology, and uses the principle that the absorption peak of a certain component gas in the measured gas is relatively constant with the absorption peak of the measured gas, thereby real-time tracking and correcting the change of the laser wavelength so that the laser center wavelength is always at a specific position of the gas absorption peak.

4. The detection method of an optical resonant cavity gas detection system according to claim 1, characterized in that: The specific process of step (4) is as follows: after the photoelectric signal intensity at the infrared detector reaches the maximum, the laser is turned off, and the photoelectric signal at the resonant cavity infrared detector is recorded until the signal returns to zero; by recording the ring-down curve of this process, it is fitted by an algorithm and then the concentration of the measured gas is inverted.

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