A weak gas concentration detection device and method

Abstract

The application discloses a weak gas concentration detection device and method, which comprises a laser light source module, a light beam collimation shaping isolation module, a light beam pointing beam combination module, a light beam coupling cavity detection module and a light beam receiving conversion module. The laser light source module is used for generating a laser beam of a gas absorption peak to be detected. The light beam collimation shaping isolation module is used for collimating and shaping the laser beam, so that the outgoing light spot presents a circular Gaussian distribution light spot. The light beam pointing beam combination module is used for adjusting the propagation direction of the laser beam and making the laser beam transmit along the same light path to form a light beam combination. The light beam receiving conversion module is used for polarizing and separating the laser light emitted from an optical cavity and converting the optical signal contained in the polarized and separated laser beam into an electrical signal. The light beam coupling cavity detection module comprises a light beam coupling convergence unit and an optical cavity, which realizes synchronous measurement of two or even more weak gas concentrations and multiplexing of a single optical cavity.

Description

Technical Field

[0001] This invention relates to gas concentration detection. More specifically, it relates to a device and method for detecting weak gas concentrations. Background Technology

[0002] There is an urgent need for high-precision and high-sensitivity methods and devices for the detection and concentration assessment of trace substances in various fields such as industrial production, resource exploration, medical diagnosis, environmental monitoring, social security, and scientific research. Based on high-quality optical resonators and combining the advantages of good laser beam monochromaticity and long equivalent optical path of the optical cavity, cavity-enhanced absorption spectroscopy (CEAS) and laser ring-down spectroscopy (CRDS) have been developed, offering advantages such as high resolution, high sensitivity, and self-calibration. By achieving spectral resonance between a high-precision optical cavity, the characteristic absorption wavelength of the gas to be detected, and the incident laser, the equivalent absorption optical path is significantly extended to hundreds of meters or even tens of kilometers, thus becoming a powerful means of high-sensitivity in-situ detection.

[0003] Optical cavity-based spectroscopic instruments can choose either broadband or narrowband lasers as the spectral absorption laser source. Due to the high precision of optical cavities, broadband light source spectral measurement, while offering multi-gas absorption spectral coverage and enabling simultaneous monitoring of multiple gas concentrations through careful design, suffers from low energy efficiency and requires the introduction of structures such as grating spectrometers or spectrophotometers, significantly increasing instrument complexity and maintenance costs. Continuous wave cavity enhanced absorption spectroscopy (CWB-LD) using distributed feedback semiconductor lasers (DFB-LD) or external cavity semiconductor lasers (ECDL) offers structural simplicity, but suffers from a narrow emission spectral range, typically in the MHz range. Even with temperature, cavity length, or current adjustments, it can only measure the concentration of a single gas. Simultaneous monitoring of two or more gas concentrations necessitates the construction of multiple optical cavities, each matched to a specific light source. This not only significantly increases instrument cost, size, and complexity but also severely limits the instrument's applicability, especially in situations requiring understanding the interaction mechanisms and concentration evolution processes of multiple gases within the analyte.

[0004] Therefore, there is a need to provide a device and method for detecting weak gas concentrations. Summary of the Invention

[0005] The purpose of this invention is to provide a device and method for detecting weak gas concentrations.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A weak gas concentration detection device includes: a laser source module, a beam collimation, shaping and isolation module, a beam pointing and combining module, a beam coupling optical cavity detection module, and a beam receiving and conversion module.

[0008] The laser source module is used to generate a laser beam that produces the absorption peak value of the gas to be measured.

[0009] The beam collimation and shaping isolation module is used to collimate and shape the laser beam so that the emitted light spot presents a circular Gaussian distribution.

[0010] The beam pointing and beam combining module is used to adjust the propagation direction of the laser beam and make the laser beam propagate along the same optical path to form a beam combining module.

[0011] The beam receiving and conversion module is used to perform polarization separation on the laser emitted from the optical cavity and convert the optical signal contained in the polarization-separated laser beam into an electrical signal.

[0012] The beam-coupled optical cavity detection module includes a beam-coupled convergence unit and an optical cavity;

[0013] The beam coupling and converging unit is used to perform mode matching between the laser beam output from the beam pointing and beam combining module and the optical cavity.

[0014] The optical cavity is used to enhance the absorption of the laser beam by the gas under test.

[0015] Preferably, the laser source module includes a first laser source module that generates a first laser beam and a second laser source module that generates a second laser beam.

[0016] Preferably, each of the laser source modules includes a tunable laser for generating a laser beam that represents the absorption peak of the gas to be measured.

[0017] A laser driving unit is used to drive and control the tunable laser; and

[0018] A temperature control unit is used to control the temperature of the tunable laser.

[0019] Preferably, the beam collimation and shaping isolation module includes a first beam collimation and shaping isolation module and a second beam collimation and shaping isolation module.

[0020] Preferably, each of the beam collimation and shaping isolation modules includes,

[0021] A beam collimation unit is used to collimate the output beam of the tunable laser.

[0022] A beam shaping unit is used to shape the collimated output beam of the tunable laser into a circular Gaussian-distributed spot; and

[0023] A beam isolation unit is used to isolate the effects of reflected and stray light on the operation of the tunable laser.

[0024] Preferably, the beam pointing and beam combining module includes a beam polarization adjustment unit, a beam pointing adjustment unit, and a beam polarization beam combining unit;

[0025] The beam polarization adjustment unit includes a first beam polarization adjustment unit and a second beam polarization adjustment unit, which are used to make the first laser beam and the second laser beam orthogonal to each other.

[0026] The beam pointing adjustment unit is used to adjust the propagation direction of the first laser beam;

[0027] The beam polarization combining unit is used to combine the two laser beams that have passed through the beam polarization adjustment unit.

[0028] Preferably, the beam receiving and conversion module includes a beam polarization separation unit and a beam receiving and conversion unit.

[0029] The beam polarization separation unit and the beam polarization combining unit correspond to each other and are used to separate different polarization components in the laser output from the optical cavity;

[0030] The beam receiving and conversion unit includes a first beam receiving and conversion unit and a second beam receiving and conversion unit, which are used to convert the optical signals contained in the first laser beam and the second laser beam after polarization separation into electrical signals.

[0031] Preferably, it also includes a data processing and system control module, which is used to store, analyze and process, and transmit the collected test data, and to perform comprehensive control of the entire system.

[0032] Preferably, the device further includes a data display function for displaying the concentration of the gas to be measured, the output power of the laser light source, the operating temperature, and the operating temperature, humidity, and internal gas pressure of the optical cavity of the measuring device.

[0033] A method for detecting weak gas concentrations, comprising the following steps:

[0034] The laser source module emits a laser beam that coincides with the absorption peak of the gas being measured;

[0035] The beam collimation and shaping isolation module collimates and shapes the laser emitted from the laser source module so that the emitted laser spot presents a circular Gaussian distribution.

[0036] The emitted light spot is polarized and combined by the beam pointing and beam combining module to achieve transmission along the same optical path.

[0037] The two wavelength laser beams after beam combining are incident on the same high-precision optical cavity, and after multiple round trips, they exit from the optical cavity.

[0038] The emitted laser beam undergoes polarization separation and is converted into an electrical signal by a beam receiving and conversion module.

[0039] The beneficial effects of this invention are as follows:

[0040] This invention can be applied to situations where simultaneous measurement of the concentrations of two or more weak gases is required. By combining polarization beam combining with spectral beam combining, a single optical cavity can be reused, reducing the number of components used. This not only reduces the cost, size, and complexity of the measuring instrument, but also improves the reliability of the instrument.

[0041] This invention has the advantages of fast detection speed, high detection accuracy, and simultaneous detection of multiple gases, realizing the simultaneous detection of multiple substances in the test object, which is beneficial for correctly analyzing the evolution law of the test object and the interrelationship characteristics of the synchronous changes among the components.

[0042] This invention has the advantage of simple structure and can be applied to various fixed or mobile weak gas concentration detection applications. Attached Figure Description

[0043] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0044] Figure 1 A schematic diagram of the weak gas concentration detection device of the present invention is shown.

[0045] Figure Descriptions: 100 First Laser Source Module; 101 First Tunable Laser; 102 First Laser Driver Unit; 103 First Temperature Control Unit; 200 Second Laser Source Module; 201 Second Tunable Laser; 202 Second Laser Driver Unit; 203 Second Temperature Control Unit; 300 First Beam Collimation, Shaping, and Isolation Module; 301 First Beam Collimation Unit; 302 First Beam Shaping Unit; 303 First Beam Isolation Unit; 400 Second Beam Collimation, Shaping, and Isolation Module; 401 Second Beam Collimation Unit; 402 Second Beam Shaping Unit; 403 Second Beam Isolation Unit; 500 Beam Pointing and Beam Combining Module; 501 First Beam Polarization Adjustment Unit; 502 Second Beam Polarization Adjustment Unit; 503 Beam Pointing Adjustment Unit; 504 Beam Polarization Beam Combining Unit; 600 Beam Coupling Cavity Detection Module; 601 Beam Coupling and Converging Unit; 602 Optical Cavity; 700 Beam Receiving and Conversion Module; 701 First Beam Polarization Separation Unit; 702 First Beam Receiving and Conversion Unit; 703 Second Beam Receiving and Conversion Unit; 800 Data Processing and System Control Module Detailed Implementation

[0046] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further explains the invention. Similar components in the drawings are indicated by the same reference numerals. Those skilled in the art should understand that the specific description below is illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0047] It should be noted that all descriptions using "first" and "second" in the embodiments of the present invention are for the purpose of distinguishing two entities or parameters with the same name but different names. It is clear that "first" and "second" are only for the convenience of expression and should not be construed as limiting the embodiments of the present invention. Subsequent embodiments will not explain this in detail.

[0048] like Figure 1 As shown, one embodiment of the present invention provides a weak gas concentration detection device, including: a laser source module, a beam collimation, shaping and isolation module, a beam pointing and combining module, a beam coupling optical cavity detection module, and a beam receiving and conversion module.

[0049] The laser source module is used to generate a laser beam that produces the absorption peak value of the gas to be measured.

[0050] The beam collimation and shaping isolation module is used to collimate and shape the laser beam so that the emitted light spot presents a circular Gaussian distribution.

[0051] The beam pointing and beam combining module is used to adjust the propagation direction of the laser beam and make the laser beam propagate along the same optical path to form a beam combining module.

[0052] The beam receiving and conversion module is used to perform polarization separation on the laser emitted from the optical cavity and convert the optical signal contained in the polarization-separated laser beam into an electrical signal.

[0053] The beam-coupled optical cavity detection module includes a beam-coupled convergence unit and an optical cavity;

[0054] The beam coupling and converging unit is used to perform mode matching between the laser beam output from the beam pointing and beam combining module and the optical cavity.

[0055] The optical cavity is used to enhance the absorption of the laser beam by the gas under test.

[0056] Specifically, the beam coupling and converging unit achieves mode matching between the dual-wavelength laser beam output from the beam pointing and combining module and the optical cavity through converging processing; the optical cavity is composed of multiple optical reflection components for beam reflection.

[0057] Depending on the design, the reflective assembly consists of one or more optical reflective elements; the optical reflective elements are not limited to high reflectivity lenses, but also include prisms, gratings, microstructured surfaces, etc., to realize optical path refraction and reflection; the laser is reflected multiple times between multiple optical reflective assemblies, which can increase the effective absorption optical path, thereby improving the detection accuracy of gas concentration;

[0058] This invention combines polarization beam combining and spectral beam combining techniques to create an instrument manufacturing method and apparatus for detecting dual-component trace gas concentrations within a single optical cavity. This enables simultaneous online detection of dual-component trace gas concentrations within a single optical cavity, allowing for the reuse of a single optical cavity and reducing the number of components used. This not only lowers the cost, size, and complexity of the measuring instrument but also improves its reliability.

[0059] In one optional embodiment, the laser source module includes a first laser source module that generates a first laser beam and a second laser source module that generates a second laser beam.

[0060] Specifically, the wavelength range of the laser emitted by the laser source module includes ultraviolet, visible, near-infrared, mid-infrared, and far-infrared bands, selected according to the characteristic absorption wavelength of the gas to be measured.

[0061] In one alternative embodiment, each of the laser source modules includes a tunable laser for generating a laser beam that represents the absorption peak of the gas to be measured.

[0062] A laser driving unit is used to drive and control the tunable laser; and

[0063] A temperature control unit is used to control the temperature of the tunable laser.

[0064] Specifically, the tunable laser can be a distributed feedback semiconductor laser, an external cavity semiconductor laser, a spectrally confined dye laser, or a solid-state or gas laser, etc. The selection of the specific laser emission wavelength depends on the absorption spectrum of the different gases being tested. The operating characteristics of the laser source module are determined by the laser driving unit and the temperature control unit, which are used to adjust the output power and spectral characteristics of the laser source module. The laser driving unit is used to drive and control the tunable laser; the temperature control unit is used to control the temperature of the tunable laser, ensuring that the tunable laser operates under specific conditions.

[0065] In one optional embodiment, the beam collimation and shaping isolation module includes a first beam collimation and shaping isolation module and a second beam collimation and shaping isolation module.

[0066] In one alternative embodiment, each of the beam collimation and shaping isolation modules includes,

[0067] A beam collimation unit is used to collimate the output beam of the tunable laser.

[0068] A beam shaping unit is used to shape the collimated output beam of the tunable laser into a circular Gaussian-distributed spot; and

[0069] A beam isolation unit is used to isolate the effects of reflected and stray light on the operation of the tunable laser.

[0070] Specifically, the first beam collimation, shaping, and isolation module is connected to the first laser source module, and the second beam collimation, shaping, and isolation module is connected to the second laser source module. The beam collimation unit collimates the output beam of the tunable laser. The beam shaping unit shapes the collimated output beam of the tunable laser to form a circular Gaussian distribution spot. The beam isolation unit is used to prevent reflected light and stray light from affecting the operation of the tunable laser.

[0071] In one optional embodiment, the beam pointing and beam combining module includes a beam polarization adjustment unit, a beam pointing adjustment unit, and a beam polarization beam combining unit;

[0072] The beam polarization adjustment unit includes a first beam polarization adjustment unit and a second beam polarization adjustment unit, which are used to make the first laser beam and the second laser beam orthogonal to each other.

[0073] The beam pointing adjustment unit is used to adjust the propagation direction of the first laser beam;

[0074] The beam polarization combining unit is used to combine the two laser beams that have passed through the beam polarization adjustment unit.

[0075] Specifically, the first beam polarization adjustment unit is connected to the first beam collimation and shaping isolation module, and the second beam polarization adjustment unit is connected to the second beam collimation and shaping isolation module. The first and second beam polarization adjustment units are used to change the optical wave oscillation polarization planes of the first and second laser beams, respectively, so that they are orthogonal to each other. The beam pointing adjustment unit is used to adjust the propagation direction of the first laser beam. The beam polarization combining unit is used to combine the two laser beams that have passed through the beam polarization adjustment unit. The beam polarization combining unit can be a polarizing prism, a thin-film polarizer, or other polarizing optical elements.

[0076] In one optional embodiment, the beam receiving and conversion module includes a beam polarization separation unit and a beam receiving and conversion unit.

[0077] The beam polarization separation unit and the beam polarization combining unit correspond to each other and are used to separate different polarization components in the laser output from the optical cavity;

[0078] The beam receiving and conversion unit includes a first beam receiving and conversion unit and a second beam receiving and conversion unit, which are used to convert the optical signals contained in the first laser beam and the second laser beam after polarization separation into electrical signals.

[0079] Specifically, the beam polarization separation unit is used to separate different polarization components in the laser output from the optical cavity. The beam polarization separation unit corresponds to the beam polarization combining unit and can be a polarizing prism, a thin-film polarizer, or other polarization optical elements. The first beam receiving and conversion unit and the second beam receiving and conversion unit are used to convert the optical signals contained in the first and second laser beams after polarization separation into electrical signals, respectively. The beam receiving and conversion unit includes, but is not limited to, photodiodes, phototransistors, avalanche photodiodes, charge-coupled devices, complementary metal-oxide-semiconductor (CMOS) devices, and other photoelectric conversion devices.

[0080] In an optional embodiment, the system further includes a data processing and system control module for storing, analyzing, processing, and transmitting the acquired test data, and for comprehensively controlling the entire system.

[0081] Specifically, the data processing and system control module, on the one hand, stores and analyzes the collected detection data and calculates the concentrations of the two analytes; on the other hand, it can also transmit detection data, instrument operating parameters, real-time status parameters, and other information to external interfaces according to a specified protocol. The system control functions include device detection process control, operating parameter setting, operating parameter acquisition, operating log generation, operating protection, and alarms.

[0082] In an optional embodiment, the device further includes a data display function for displaying the concentration of the gas to be measured, the output power of the laser light source, the operating temperature, and the operating temperature, humidity, and internal gas pressure of the optical cavity of the measuring device.

[0083] A second embodiment of the present invention provides a method for detecting weak gas concentrations, the steps of which include:

[0084] The laser source module emits a laser beam that coincides with the absorption peak of the gas being measured;

[0085] The beam collimation and shaping isolation module collimates and shapes the laser emitted from the laser source module so that the emitted laser spot presents a circular Gaussian distribution.

[0086] The emitted light spot is polarized and combined by the beam pointing and beam combining module to achieve transmission along the same optical path.

[0087] The two wavelength laser beams after beam combining are incident on the same high-precision optical cavity, and after multiple round trips, they exit from the optical cavity.

[0088] The emitted laser beam undergoes polarization separation and is converted into an electrical signal by a beam receiving and conversion module.

[0089] Specifically, the multiple round trips of the two laser beams after beam combining within the high-precision optical cavity result in significant absorption and enhancement of the laser beams by the two gases being tested within the cavity.

[0090] In a specific embodiment of the present invention, a method and apparatus for manufacturing an instrument based on a tunable laser source, combined with polarization beam combining and spectral beam combining techniques, is provided to realize the detection of dual-component trace gas concentrations within a single optical cavity. This includes:

[0091] The system comprises a first laser source module, a second laser source module, a first beam collimation, shaping and isolation module, a second beam collimation, shaping and isolation module, a beam pointing and combining module (including a first beam polarization adjustment unit and a second beam polarization adjustment unit), a beam coupling cavity detection module, a beam receiving and conversion module (including a first beam receiving and conversion unit and a second beam receiving and conversion unit), and a data processing and system control module.

[0092] The optical cavity consists of two or more high-reflectivity mirrors and is located inside the beam-coupled optical cavity detection module.

[0093] The first beam receiving and conversion unit and the second beam receiving and conversion unit are electrically connected to the data processing and system control module, and the data processing and system control module is connected to the first laser source module and the second laser source module, respectively.

[0094] The first laser source module, under the action of the first laser driving unit and the first temperature control unit, emits a laser beam located at the absorption peak of the first gas to be detected. After passing through the first beam collimation, shaping, and isolation module, the beam enters the beam pointing and combining module. In the beam pointing and combining module, the laser beam is polarized horizontally by the first beam polarization adjustment unit, and then exits through the polarization combining unit into the beam coupling optical cavity detection module. After passing through the beam coupling and focusing unit, it enters the optical cavity, achieving enhanced absorption of the first gas to be detected. The beam emitted from the optical cavity is horizontally polarized and output to the first beam receiving and conversion unit under the action of the beam polarization separation unit. The concentration data of the first gas to be detected is measured using this laser beam and output under the control of the data processing and system control module.

[0095] The second laser source module, under the action of the second laser driving unit and the second temperature control unit, emits a laser beam located at the absorption peak of the second gas to be detected. After passing through the second beam collimation, shaping, and isolation module, the beam enters the beam pointing and combining module. In the beam pointing and combining module, the laser beam is polarized vertically by the second beam polarization adjustment unit, and then reflected by the beam pointing adjustment unit and polarization combining unit before entering the beam coupling optical cavity detection module. After passing through the beam coupling and focusing unit, it enters the optical cavity, achieving enhanced absorption of the second gas to be detected. The beam emitted from the optical cavity is vertically polarized and output to the second beam receiving and conversion unit under the action of the beam polarization separation unit. The concentration data of the second gas to be detected, measured using this laser beam, is output under the control of the data processing and system control module.

[0096] The present invention provides a method and apparatus for manufacturing a dual-component trace gas concentration detection instrument that combines laser source polarization beam combining and spectral beam combining technologies. This invention enables synchronous online detection of dual-component trace gas concentration within a single optical cavity, allowing for the reuse of a single optical cavity and reducing the number of components used. This not only lowers the cost, size, and complexity of the measuring instrument but also improves its reliability.

[0097] In embodiments of the present invention, the optical cavity can be a linear cavity composed of two cavity mirrors, or a linear cavity or annular cavity composed of three or four cavity mirrors. The cavity mirrors are coated with a high-reflectivity thin film with high reflectivity at the first and second absorption peak wavelengths of the gas to be measured on their reflective surfaces, while an anti-reflection film at the aforementioned wavelengths is coated on their other transmissive surfaces. Furthermore, both the first beam receiving and conversion unit and the second beam receiving and conversion unit have high response rates, and their spectral response ranges respectively cover the first and second characteristic absorption wavelengths of the gas to be measured. Furthermore, the first beam polarization adjustment unit, the second beam polarization adjustment unit, the beam pointing adjustment unit, and the polarization combining unit in the first beam collimation and shaping isolation module, the second beam collimation and shaping isolation module, and the beam pointing and combining module are all coated with anti-reflection films corresponding to the characteristic absorption wavelengths of the gas to be measured.

[0098] The figure shows a schematic diagram of the method and apparatus for detecting two-component trace gas concentrations, which combines tunable laser source polarization beam combining and spectral beam combining technologies according to an embodiment of the present invention.

[0099] As can be seen from the figure, the measurement method and measurement device of this embodiment include a first laser source module 100, a second laser source module 200, a first beam collimation, shaping and isolation module 300, a second beam collimation, shaping and isolation module 400, a beam pointing and beam combining module 500 (including a first beam polarization adjustment unit 501 and a second beam polarization adjustment unit 502), a beam coupling optical cavity detection module 600, a beam receiving and conversion module 700 (including a first beam receiving and conversion unit 702 and a second beam receiving and conversion unit 703), and a data processing and system control module 800.

[0100] In this embodiment, the first laser source module 100 and the second laser source module 200 can be distributed feedback semiconductor lasers, external cavity semiconductor lasers, quantum well lasers, solid-state lasers, dye lasers, etc., and have characteristics such as narrow output spectral range and adjustable output wavelength (adjustable by current control, temperature control, or dispersion control). Using these laser source modules, the visible and infrared characteristic absorption wavelengths of most gases can be provided, and the spectral resolution of gas concentration measurement can be improved by controlling the output linewidth.

[0101] The purpose of the beam coupling and focusing unit 601 in the beam coupling optical cavity detection module 600 is to achieve a good match between the laser beam mode emitted by the first laser source module 100 and the second laser source module 200 and the intrinsic mode of the optical cavity 602. It can adopt the structure of a Galilean optical telescope or a Kepler optical telescope. In the design, aberrations should be minimized and the length shortened as much as possible.

[0102] The optical cavity 602 comprises a series of highly reflective mirrors forming a high-precision, stable resonant cavity. The reflective surfaces of the mirrors are coated with highly reflective films targeting the characteristic absorption wavelengths of the first and second target gases, achieving a reflectivity higher than 99.9%, or even 99.999%. Higher reflectivity of the optical cavity mirrors results in higher sensitivity for measuring the concentration of the target gas. The transmissive surfaces of the mirrors are coated with anti-transmission films targeting the characteristic absorption wavelengths of the first and second target gases. For a linear resonant optical cavity, when the laser beam is incident normally and does not resonate with the cavity, the highly reflective mirrors will prevent the laser beam from entering the cavity and cause it to return along its original path. For a ring-shaped optical cavity composed of multiple highly reflective mirrors, the returned laser beam deviates from the incident direction, thus eliminating the need for an optical isolator.

[0103] In the beam receiving and conversion module 700, the first beam receiving and conversion unit 702 and the second beam receiving and conversion unit 703 adopt fast-response photoelectric conversion devices, which convert the radiation emitted from the optical cavity into electrical signals. These devices can be indium gallium arsenide detectors, silicon detectors, lead selenide, lead sulfide, or avalanche photodiodes, photomultiplier tubes, etc.

[0104] When the laser beam is incident directly into the optical cavity 602, the device is a laser ring-down method and measurement device for detecting the concentration of two-component trace gases. (T) 01 T 02 Let T1 and T2 represent the ring-down times received by the first beam receiving and conversion unit 702 and the second beam receiving and conversion unit 703, respectively, and calculated by the data processing and system control module when the optical cavity is free of the gas to be measured (vacuum and nitrogen-filled cavity), respectively. Let T1 and T2 represent the ring-down times received by the first beam receiving and conversion unit 702 and the second beam receiving and conversion unit 703, respectively, and calculated by the data processing and system control module when the optical cavity contains the gas to be measured, respectively. Then, the concentrations of the first gas to be measured, N1 and N2, calculated using Beer-Lambert's law, are respectively...

[0105]

[0106]

[0107] Where c is the speed of light, σ(λ1) and σ(λ2) are the absorption cross-sections of the first and second gases at the characteristic absorption wavelength, respectively, and time intervals T1, T2, and T3 are also represented. 01 T 02 These are the previously measured oscillation times.

[0108] When the laser beam enters the optical cavity 602 at an oblique angle or without an optical switch, the device is a cavity-enhanced absorption method and measuring device for detecting the concentration of two-component trace gases. (I) 01 I 02 These represent the optical cavity emission intensities received by the first beam receiving and conversion unit 702 and the second beam receiving and conversion unit 703, respectively, and calculated by the data processing and system control module when there is no gas to be measured inside the optical cavity (vacuum and nitrogen-filled cavity), respectively. Let I represent the emission intensity. 01 (ν1(、I 02 (ν2) represents the optical cavity emission intensity received by the first beam receiving and conversion unit 702 and the second beam receiving and conversion unit 703 and calculated by the data processing and system control module when there is no gas to be measured in the optical cavity (vacuum and nitrogen filling), respectively. I1(ν1) and I2(ν2) represent the optical cavity emission intensities received by the first beam receiving and conversion unit 702 and the second beam receiving and conversion unit 703 and calculated by the data processing and system control module when there is the first gas to be measured and the second gas to be measured in the optical cavity, respectively. L1 and L2 represent the total propagation length of the first laser beam and the second laser beam in the optical cavity, respectively. R1 and R2 represent the reflectivity of the high-reflectivity mirror of the optical cavity at the characteristic absorption wavelengths of the first gas to be measured and the second gas to be measured, respectively. Then, the concentrations N1 and N2 of the first gas to be measured, calculated by Lambert-Beer's law, are respectively...

[0109]

[0110]

[0111] Where σ(λ1) and σ(λ2) are the absorption cross-sections of the first and second gases to be tested at the characteristic absorption wavelengths, respectively. In the above equation, the laser intensity I... 01 Both (ν) and I1(ν) were measured when the first detection laser wavelength coincided with the characteristic absorption wavelength of the first gas to be measured. The laser intensity I 02 Both I2(ν) and I2(ν) were measured when the second detection laser wavelength coincided with the characteristic absorption wavelength of the second gas to be tested.

[0112] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is impossible to exhaustively list all the implementation methods here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A device for detecting weak gas concentration, characterized in that, include: The system includes a laser source module, a beam collimation, shaping, and isolation module, a beam pointing and combining module, a beam coupling optical cavity detection module, and a beam receiving and conversion module. The laser source module is used to generate a laser beam that produces the absorption peak value of the gas to be measured. The beam collimation and shaping isolation module includes a first beam collimation and shaping isolation module and a second beam collimation and shaping isolation module, which are used to collimate and shape the laser beam so that the emitted light spot presents a circular Gaussian distribution. The beam pointing and beam combining module is used to adjust the propagation direction of the laser beam and make the laser beam propagate along the same optical path to form a beam combining module. The beam-coupled optical cavity detection module includes a beam-coupled convergence unit and an optical cavity; The beam receiving and conversion module is used to perform polarization separation on the laser emitted from the optical cavity and convert the optical signal contained in the polarization-separated laser beam into an electrical signal. The beam coupling and converging unit is used to perform mode matching between the laser beam output from the beam pointing and beam combining module and the optical cavity. The optical cavity is used to enhance the absorption of the laser beam by the gas under test; The laser source module includes a first laser source module that generates a first laser beam and a second laser source module that generates a second laser beam. The beam pointing and beam combining module includes a beam polarization adjustment unit, a beam pointing adjustment unit, and a beam polarization beam combining unit; The beam polarization adjustment unit includes a first beam polarization adjustment unit and a second beam polarization adjustment unit, which are used to make the first laser beam and the second laser beam orthogonal to each other. The beam pointing adjustment unit is used to adjust the propagation direction of the first laser beam; The beam polarization combining unit is used to combine the two laser beams that have passed through the beam polarization adjustment unit.

2. The weak gas concentration detection device according to claim 1, characterized in that, Each of the laser source modules includes a tunable laser for generating a laser beam that produces the absorption peak of the gas to be measured; A laser driving unit is used to drive and control the tunable laser. and A temperature control unit is used to control the temperature of the tunable laser.

3. The weak gas concentration detection device according to claim 2, characterized in that, Each of the aforementioned beam collimation and shaping isolation modules includes... A beam collimation unit is used to collimate the output beam of the tunable laser. A beam shaping unit is used to shape the collimated output beam of the tunable laser into a circular Gaussian-distributed spot; and A beam isolation unit is used to isolate the effects of reflected and stray light on the operation of the tunable laser.

4. The weak gas concentration detection device according to claim 1, characterized in that, The beam receiving and conversion module includes a beam polarization separation unit and a beam receiving and conversion unit. The beam polarization separation unit and the beam polarization combining unit correspond to each other and are used to separate different polarization components in the laser output from the optical cavity; The beam receiving and conversion unit includes a first beam receiving and conversion unit and a second beam receiving and conversion unit, which are used to convert the optical signals contained in the first laser beam and the second laser beam after polarization separation into electrical signals.

5. The weak gas concentration detection device according to claim 1, characterized in that, It also includes a data processing and system control module, which is used to store, analyze, process and transmit the collected test data, and to perform comprehensive control of the entire system.

6. The weak gas concentration detection device according to claim 5, characterized in that, The device also includes a data display function for displaying the concentration of the gas to be tested, the output power and operating temperature of the laser light source, and the operating temperature, humidity and internal gas pressure of the detection device, as measured by the device.

7. A method for detecting weak gas concentration, characterized in that, The steps include, The laser source module emits a laser beam that coincides with the absorption peak of the gas being measured; The beam collimation and shaping isolation module includes a first beam collimation and shaping isolation module and a second beam collimation and shaping isolation module, which collimates and shapes the laser emitted from the laser source module so that the emitted laser spot presents a circular Gaussian distribution. The emitted light spot is polarized and combined by the beam pointing and beam combining module to achieve transmission along the same optical path. The two wavelength laser beams after beam combining are incident on the same high-precision optical cavity, and after multiple round trips, they exit from the optical cavity. The emitted laser beam undergoes polarization separation and is converted into an electrical signal by a beam receiving and conversion module. The laser source module includes a first laser source module that generates a first laser beam and a second laser source module that generates a second laser beam. The beam pointing and beam combining module includes a beam polarization adjustment unit, a beam pointing adjustment unit, and a beam polarization beam combining unit; The beam polarization adjustment unit includes a first beam polarization adjustment unit and a second beam polarization adjustment unit, which are used to make the first laser beam and the second laser beam orthogonal to each other. The beam pointing adjustment unit is used to adjust the propagation direction of the first laser beam; The beam polarization combining unit is used to combine the two laser beams that have passed through the beam polarization adjustment unit.

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