Annular multi-pass absorption cell and detection method thereof

Abstract

The invention relates to the technical field of gas sensing and optical detection, in particular to an annular multi-pass absorption cell and a detection method thereof.The annular multi-pass absorption cell comprises a reflecting mirror, the reflecting mirror is a cylinder with the two ends open, and a reflecting film is arranged on the inner wall of the reflecting mirror to form a continuous annular optical reflecting surface; the end cover assemblies are arranged at the openings in the two ends of the reflecting mirror, and a closed gas cavity is defined by the end cover assemblies and the reflecting mirror; an incident light hole and an emergent light hole are formed in the cylinder wall of the reflecting mirror and are respectively used for guiding a detection light beam to enter and exit from the gas chamber. The cylindrical reflector with two open ends is adopted, and an annular optical reflecting surface is formed on the inner wall of the cylindrical reflector, so that complex optical paths of discrete components in a traditional absorption cell are integrated in a single structure, the innovative design remarkably improves the system integration level, effectively compresses the size, can realize a longer absorption optical path in a limited space, and improves the absorption efficiency. The sensitivity of gas detection is greatly improved.

Description

Technical Field

[0001] This invention relates to the fields of gas sensing technology and optical detection technology, specifically to a ring-shaped multi-pass absorption cell and its detection method. Background Technology

[0002] Natural gas, as an important clean energy source, poses a serious threat to public safety, the ecological environment, and human health if leaks occur during its production, transportation, and use. Methane and ethane, as major trace components of natural gas, have always been a focus of industry attention for rapid and accurate monitoring. In recent years, with the development of sensing technology and optical analysis methods, tunable semiconductor laser absorption spectroscopy (TDLAS) has gradually become one of the mainstream methods in the field of gas detection. This technology utilizes the characteristic absorption lines of gas molecules in the infrared band and analyzes the intensity attenuation of the laser beam after passing through the gas medium to achieve accurate inversion of gas concentration. Due to its high selectivity, fast response, and good reliability, TDLAS has been widely used in industrial safety and environmental monitoring.

[0003] However, in the actual deployment of TDLAS systems, the multi-pass absorption cell, as a core sensitivity enhancement component, still faces significant technical bottlenecks. Traditional multi-pass cells typically employ two or more spherical mirrors to construct multiple reflection optical paths, resulting in complex system structures, low integration, and bulky size. Furthermore, it is difficult to effectively extend the optical path within a limited space, thus limiting further improvements in detection sensitivity. Summary of the Invention

[0004] To address the above technical problems, this invention provides a technical solution for an annular multi-pass absorption cell and its detection method.

[0005] The technical problem solved by this invention can be achieved by the following technical solution: an annular multi-pass absorption cell, comprising: a reflector, the reflector being a cylindrical tube open at both ends, the inner wall of the reflector being provided with a reflective film to form a continuous annular optical reflecting surface; an end cap assembly, disposed at the two end openings of the reflector, and together with the reflector forming a closed gas chamber; the cylindrical wall of the reflector being provided with an incident light hole and an exit light hole, respectively used to guide the detection beam into and out of the gas chamber.

[0006] Preferably, the end cap assembly includes: a first end plate covering a first end of the reflector; and a second end plate covering a second end of the reflector.

[0007] Preferably, the first end plate is provided with an air inlet pipe, and the second end plate is provided with an air outlet pipe; both the air inlet pipe and the air outlet pipe protrude in a direction away from the reflector.

[0008] Preferably, it further includes a sealing ring, and the first end plate and the second end plate are respectively sealed to both ends of the reflector through the sealing ring.

[0009] Preferably, it further includes a housing, which is annular and fitted around the periphery of the reflector; a through hole is formed on the side wall of the housing at the position corresponding to the incident light aperture and the exit light aperture for the detection beam to pass through.

[0010] Preferably, the reflector is made of K9 glass.

[0011] Preferably, the reflective film has a reflectivity of not less than 98% in the infrared band.

[0012] Preferably, the incident light aperture and the exit light aperture are located on the same generatrix of the reflector and are distributed along the axial direction of the reflector.

[0013] Preferably, the diameters of the incident light aperture and the exit light aperture are 120%-130% of the collimated spot diameter of the probe beam.

[0014] The method also includes a gas detection method using a ring-shaped multi-pass absorption cell, implemented as described above. The method comprises: introducing a gas to be tested into a gas chamber through the inlet pipe; projecting a collimated probe beam into the gas chamber through the incident aperture, wherein the probe beam contains at least two wavelengths, each matching a characteristic absorption peak of a different component in the gas to be tested; the probe beam undergoes multiple reflections between optical reflective surfaces to form a long effective optical path absorption path before exiting through the exit aperture; detecting the intensity of the emitted beam using a detector, and analyzing the component concentration of the gas to be tested based on the absorption spectrum.

[0015] The beneficial effects of this invention are as follows: By using a cylindrical reflector with openings at both ends, a continuous annular optical reflecting surface is formed on its inner wall, thereby integrating the complex optical path of discrete elements in a traditional absorption cell into a single structure. This innovative design significantly improves the system integration, effectively compresses the volume, and can achieve a longer absorption optical path in a limited space. Ultimately, while ensuring structural compactness and mechanical stability, it greatly improves the sensitivity of gas detection. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the reflector structure of the present invention; Figure 2 This is a simulation diagram of the light transmission path in the reflector according to the present invention; Figure 3 This is a schematic diagram of the annular multi-channel absorption cell structure of the present invention; Figure 4 This is an exploded view of the annular multi-channel absorption cell structure of the present invention.

[0017] Explanation of reference numerals in the attached drawings: 1. Reflector; 2. Outer shell; 3. First end plate; 4. Second end plate; 5. Sealing ring; 11. Reflective film; 12. Entrance aperture; 13. Exit aperture; 21. Through hole; 31. Air inlet pipe; 41. Air outlet pipe. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0021] Reference Figure 1 This invention provides an annular multi-channel absorption cell for monitoring trace gases in natural gas, comprising: a reflector 1, which is a cylindrical tube open at both ends, and a reflective film 11 is provided on the inner wall of the reflector 1 to form a continuous annular optical reflective surface; an end cap assembly, which is disposed at the two ends of the reflector 1 and together with the reflector 1 to form a closed gas chamber; and an entrance light hole 12 and an exit light hole 13 are provided on the cylindrical wall of the reflector 1 to guide the detection beam into and out of the gas chamber, respectively.

[0022] Specifically, in this embodiment of the invention, the technical problems of traditional multi-pass absorption cells, which are characterized by complex system structure, bulky size, low integration, and difficulty in effectively extending the optical path in a limited space due to the use of multiple discrete spherical reflectors, are addressed by employing a cylindrical reflector 1 with openings at both ends and a continuous annular reflective surface on its inner wall. This integrates the traditional discrete reflection optical path into a single structure, avoiding the inherent bottlenecks of multi-mirror alignment, poor mechanical stability, and low space utilization. It enables the construction of a stable, long-path absorption path in a compact physical space, significantly improving system integration and detection sensitivity, while also enhancing the overall structural robustness and environmental adaptability.

[0023] Specifically, such as Figure 2As shown, after the probe laser enters from the incident aperture 12 at a specific angle, it does not propagate in a simple spiral within the continuous annular reflective surface formed by the reflective film 11. Instead, it undergoes multiple reflections following a stable closed optical path determined by the geometry of the annular cavity. This controlled reflection mechanism strictly confines the beam to repeatedly pass through the gas within the annular region, thereby achieving a significantly extended absorption optical path with a physical size much smaller than that of a conventional multipass cell.

[0024] Taking an embodiment of the present invention as an example, the inner diameter of the cylindrical reflector 1 is designed to be 120 mm, the outer diameter to be 130 mm, and the length to be 40 mm, resulting in a total volume of 452.16 mL for the multi-pass cell. When the laser is incident with a direction vector (1, 0.0087, 0.0005), it can complete 540 reflections within the annular reflective surface, achieving a total effective optical path of 64.8 m. In contrast, traditional multi-pass cells rely on two or more spherical reflectors to construct the optical path, resulting in a complex structure, large volume, and sparse distribution of light spots on the mirror surface, thus limiting space utilization and optical path extension capabilities. The present invention integrates the reflective surface into the inner wall of the cylinder through an integrated annular structure. By simply adjusting the incident angle, a dense light spot distribution can be formed on the reflective surface, thereby achieving an ultra-long optical path within a compact volume, significantly improving mirror utilization and system integration.

[0025] More specifically, the end cap assembly is located at both ends of the reflector 1, forming a closed gas chamber together with the reflector 1, providing a sealed environment for gas detection.

[0026] In a preferred embodiment of the present invention, the end cap assembly includes: a first end plate 3 covering a first end of the reflector 1; and a second end plate 4 covering a second end of the reflector 1.

[0027] Specifically, considering that the optical cavity needs to simultaneously meet multiple requirements such as structural sealing, mechanical stability, and optical path integrity, in this embodiment of the invention, reference is made to... Figure 3 and Figure 4 The first end plate 3 and the second end plate 4 are symmetrically arranged metal plates with a thickness of 3 mm at the openings at both ends of the reflector 1. The metal plate is a circular plate with a diameter of 130 mm, which matches the outer diameter of the reflector 1. This size matching design ensures that the end plates can completely cover the end face of the reflector, providing a uniform pressing surface for the sealing structure.

[0028] In terms of structural design, the thickness of the end plate was optimized through mechanical simulation to ensure sufficient structural rigidity to prevent deformation while controlling the overall weight. The assembly of the end plate and the reflector 1 adopts a precision axial pressing method. By precisely controlling the parallelism and surface flatness of the end face of the end plate and the reflector 1, a uniform, stable, and tight fit is ensured between the two contact surfaces.

[0029] This design achieves complex optical sealing requirements through a simple planar contact structure, avoiding the uneven assembly stress caused by the multiple bolts in traditional flange connections, and achieving optimal sealing performance with the fewest interfaces and the simplest assembly process.

[0030] In a preferred embodiment of the present invention, the first end plate 3 is provided with an air inlet pipe 31 and the second end plate 4 is provided with an air outlet pipe 41; both the air inlet pipe 31 and the air outlet pipe 41 protrude in a direction away from the reflector 1.

[0031] Specifically, in the embodiments of the present invention, reference is made to... Figure 3 and Figure 4 The inlet pipe 31 and outlet pipe 41 are manufactured using an integrated molding process with the first end plate 3 and the second end plate 4, respectively, ensuring the structural integrity and sealing reliability of the connection. The two pipes extend outward along the axis of the reflector 1. Their extension length has been carefully designed to ensure sufficient installation and operation space for external gas path connectors while minimizing cantilever length, thereby improving the overall structural rigidity and suppressing vibrations or deformations that may be caused by excessive pipe length. This layout ensures that the gas inlet and outlet are always outside the effective optical path area, completely eliminating potential interference from the pipe components to the beam propagation path. It also creates favorable conditions for the gas to form a stable and directional flow pattern within the chamber, effectively improving gas replacement efficiency and detection response speed.

[0032] In a preferred embodiment of the present invention, a sealing ring 5 is also included, wherein the first end plate 3 and the second end plate 4 are respectively sealed to both ends of the reflector 1 through the sealing ring 5.

[0033] Specifically, considering that the optical cavity needs to maintain a long-term stable high airtightness to ensure detection accuracy, in this embodiment of the invention, an O-ring made of high-performance elastic rubber material is preferred as the sealing ring 5. The end faces of both ends of the reflector 1 and the contact surfaces of the first end plate 3, the second end plate 4 and the sealing ring 5 are all precision machined and treated to have low surface roughness, so as to form a flat and reliable sealing interface.

[0034] During assembly, the tight fit between the annular outer shell 2 and the first end plate 3 and the second end plate 4 directly applies axial pressure to the end plates, causing the sealing ring 5 placed between them to undergo controllable elastic deformation and remain within an optimized compression ratio range. This forms a stable and continuous sealing band between the end plates and the end faces of the reflector 1. This design combines planar sealing with axial pressure, eliminating the need for additional fasteners such as bolts. This not only makes the overall structure simple and compact but also significantly simplifies the assembly process.

[0035] Meanwhile, the installation position of the sealing ring 5 is precisely designed to be located on the outer edge of the end face of the reflector 1, ensuring that it is completely outside the effective optical path area, thus fundamentally avoiding any interference from the sealing assembly to the transmission and reflection of the light beam within the annular reflective surface.

[0036] Thanks to the excellent resilience and compressibility of the O-ring, as well as the good environmental adaptability and long-term stability of the selected elastic material, this sealing structure can maintain excellent sealing performance under complex field conditions, effectively preventing gas leakage, providing a reliable guarantee for high-precision measurement of gas concentration, and ensuring the reliability of the system's long-term operation.

[0037] In a preferred embodiment of the present invention, the reflector 1 is made of K9 glass.

[0038] Specifically, in this embodiment of the invention, since the optical path stability of the annular multi-pass cell is closely related to the optical uniformity and thermal stability of the substrate of the reflector 1, K9 glass is used as the substrate material of the reflector 1. Its excellent optical uniformity enables low absorption and low scattering transmission of infrared detection laser, ensuring the stability of the light spot shape in multiple reflections. In addition, the low coefficient of thermal expansion of K9 glass gives it excellent surface shape retention capability, effectively suppressing cavity length drift caused by environmental temperature changes, providing a fundamental guarantee for the long-term reliable operation of the long-path absorption cell.

[0039] More specifically, in this embodiment of the invention, in addition to using K9 glass, fused silica can also be used, which has a lower coefficient of thermal expansion (approximately 5.5 × 10⁻⁶). -7 With its higher thermal stability (6℃) and superior optical path stability under conditions of large ambient temperature fluctuations, it also exhibits lower absorption loss in the infrared band, making it suitable for precision monitoring applications with extremely high requirements for long-term stability.

[0040] In a preferred embodiment of the present invention, the reflective film 11 has a reflectivity of not less than 98% in the infrared band.

[0041] Specifically, since the light intensity loss from a single reflection accumulates sharply with the number of reflections, directly limiting the system's maximum usable optical path and detection limit, this embodiment of the invention employs a high-performance reflective film 11 with a reflectivity of not less than 98% in the infrared band. This ensures that after the incident laser undergoes hundreds of reflections within the annular cavity, its signal intensity remains at a level that can be accurately identified by the detector, thus providing a crucial guarantee for the accuracy of concentration inversion. Simultaneously, the high-reflectivity film layer and the optimized annular optical path work synergistically to effectively suppress mode interference and stray light noise caused by multiple reflections, further reducing the system's minimum detection limit for trace gases such as methane and ethane.

[0042] More specifically, considering that the performance of the reflective film 11 directly determines the optical path capability and signal-to-noise ratio of the system, this invention preferably employs a high-precision optical coating process to prepare the infrared high-reflectivity film 11 on a glass substrate. This film system is composed of alternating layers of optical medium materials with high and low refractive index contrasts in a periodic structure. The film layer structure is optimized to achieve extremely high reflectivity within the target infrared band. The selected coating process effectively enhances the compactness and bonding strength of the film layers, giving it good mechanical durability and environmental adaptability. It can withstand long-term laser irradiation and fluctuations in external temperature and humidity, thus ensuring that the annular reflective surface maintains excellent and stable optical performance in various application scenarios.

[0043] In a preferred embodiment of the present invention, the incident light aperture 12 and the exit light aperture 13 are located on the same generatrix of the reflector 1 and are distributed along the axial direction of the reflector 1.

[0044] Specifically, considering the need to achieve the longest possible effective absorption optical path within a limited cavity length, while ensuring spatial separation and non-interference between the incident and outgoing optical paths, in this embodiment of the invention, the cylindrical structure of the reflector 1 is laid flat, such as... Figure 1 As shown, an xyz coordinate system is established with the center of the left side of the cylindrical tube as the origin, and the left side is the xy plane. Both the incident aperture 12 and the exit aperture 13 are located on a specific generatrix with the same x and y coordinates (130, 0) on the outer wall of the cylindrical tube, and are strictly distributed along the z-axis (i.e., the axis of the reflector 1). The coordinates of the incident aperture 12 and the exit aperture 13 are (130, 0, 4.8) and (130, 0, 35.2), respectively. This arrangement ensures that the two apertures are completely collinear in space along a single generatrix, thus physically isolating the incident and exit light paths and fundamentally avoiding crosstalk between beams. Simultaneously, this design fully utilizes the axial space of the cylindrical tube. By precisely controlling the axial distance between the two apertures, it lays the optimal geometric foundation for the formation of a stable, long-range closed reflection light path within the annular cavity, which is one of the core structural guarantees for the system to achieve high-sensitivity detection. Those skilled in the art can determine the appropriate axial position and incident angle of the aperture through ray tracing simulation based on the cavity length and the desired number of reflections. This design is a conventional implementation of the present invention.

[0045] More specifically, to ensure precise aperture dimensions, smooth inner walls, and minimal damage to the K9 glass substrate, this embodiment of the invention employs a combination of ultrasonic processing and laser finishing for aperture fabrication. First, ultrasonic drilling is performed using a diamond grinding head for initial shaping, effectively reducing the risk of edge chipping in the K9 glass. Subsequently, a pulsed laser is used to scan and finish the aperture walls, eliminating microcracks and minimizing light scattering loss caused by aperture wall roughness.

[0046] In a preferred embodiment of the present invention, the diameters of the incident light aperture 12 and the exit light aperture 13 are 120%-130% of the collimated spot diameter of the probe beam.

[0047] Specifically, in this embodiment of the invention, the diameters of the incident aperture 12 and the exit aperture 13 are set to 3.6 mm. This diameter value is determined based on the spot diameter (not greater than 3 mm) with sufficient safety margin. This design makes the aperture slightly larger than the spot diameter, which provides sufficient space for the light beam to enter and exit the absorption cell, effectively avoiding diffraction effects and light intensity loss caused by the aperture wall blocking, thereby ensuring the transmission quality and integrity of the light beam. At the same time, it controls the aperture size as much as possible to suppress the entry of external stray light and maintain the structural strength and sealing performance of the gas chamber. This carefully optimized aperture parameter is one of the key design elements for achieving a stable, long optical path absorption path in a compact volume.

[0048] As a preferred embodiment of the present invention, it further includes a housing 2, which is annular and sleeved around the periphery of the reflector 1; a through hole 21 for the detection beam to pass through is formed on the side wall of the housing 2 at the position corresponding to the incident light hole 12 and the exit light hole 13.

[0049] Specifically, the reflector 1, as a precision optical element made of K9 glass, is susceptible to damage from mechanical stress, dust contamination, and fluctuations in ambient temperature and humidity due to its surface accuracy and high reflectivity film. Therefore, in this embodiment of the invention, referring to... Figure 3 and Figure 4 A ring-shaped metal outer shell 2 is tightly fitted around the reflector 1 via an interference fit. This outer shell 2, through its rigid structure, provides uniform radial support to the brittle glass reflector tube, effectively resisting external mechanical impacts and assembly stresses, preventing damage or deformation during transportation, installation, and use. Simultaneously, this outer shell structure constitutes a physical isolation barrier, significantly reducing the impact of environmental factors such as dust and moisture on the core optical components.

[0050] More specifically, two through holes 21 are precision-machined (such as precision milling or laser drilling) on ​​the sidewall of the outer casing 2. These two through holes 21 are spatially aligned precisely with the incident light aperture 12 and the exit light aperture 13 on the reflector 1. Their aperture diameters are precisely calculated to be as small as possible while ensuring unobstructed passage of the detection beam to limit stray light incidence. The inner walls of the through holes 21 can be chamfered or polished to further reduce beam obstruction and scattering. This design provides a robust, sealed physical protection environment for the core optical components without compromising their optical function, thereby significantly improving the mechanical strength, long-term stability, and environmental adaptability of the entire absorption cell.

[0051] As a preferred embodiment of the present invention, a gas detection method for an annular multi-pass absorption cell is also included, applied to an annular multi-pass absorption cell as described above, comprising: introducing a gas to be tested into a gas chamber through the inlet pipe 31; injecting a collimated probe beam into the gas chamber through the incident light aperture 12, wherein the probe beam contains at least two wavelengths, which respectively match the characteristic absorption peaks of different components in the gas to be tested; the probe beam undergoes multiple reflections between optical reflective surfaces to form a long effective optical path absorption path, and then exits from the exit light aperture 13; detecting the intensity of the emitted beam with a detector, and analyzing the component concentration of the gas to be tested based on the absorption spectrum.

[0052] Specifically, in this embodiment of the invention, the configuration includes a laser emitting unit located at the front end of the annular multi-pass absorption cell, a signal detection unit located at the rear end of the annular multi-pass absorption cell, and a gas circulation unit connecting the inlet pipe 31 and the outlet pipe 41. The laser emitting unit includes two tunable semiconductor lasers with center wavelengths corresponding to the absorption peaks of methane (1653nm) and ethane (1684nm), respectively, a laser beam combiner, and a collimation system. The beams output from the two lasers are combined by the beam combiner and then shaped into a parallel beam with a diameter of less than 1mm by the collimation system. The detection beam is precisely aligned with the incident light aperture 12 and enters the gas chamber with a direction vector of (1, 0.0087, 0.0005).

[0053] Within the gas chamber, the probe beam propagates along a stable closed optical path within a continuous annular reflective surface formed by the reflective film 11, forming an ultra-long absorption path after hundreds of reflections. The gas circulation unit includes a vacuum pump and a gas flow control valve, continuously pumping the gas to be tested into the chamber through the inlet pipe 31 and simultaneously expelling it through the outlet pipe 41, ensuring continuous gas renewal within the chamber. After completing the absorption path, the beam exits from the exit aperture 13 and is received by a detector located directly behind it. This detector can be a high-sensitivity InGaAs photodetector, whose output signal is transmitted to a signal processing system. The system utilizes wavelength modulation spectroscopy to simultaneously analyze the characteristic absorption signals corresponding to methane and ethane in the beam, thereby directly retrieving their respective gas concentrations, ultimately achieving rapid and accurate determination of natural gas leaks.

[0054] In summary, this invention provides a ring-shaped multi-pass absorption cell and its detection method. By employing a cylindrical mirror 1 with openings at both ends and a continuous ring-shaped reflective surface on its inner wall, the discrete multi-mirror reflection structure of traditional multi-pass cells is innovatively integrated into a single optical element, successfully constructing a stable and compact ring-shaped long optical path absorption cavity. This design not only fundamentally solves the technical bottlenecks of traditional multi-pass cells, such as complex system structure, bulky size, difficult assembly and adjustment, and poor mechanical stability caused by the discrete multiple mirrors, but also achieves an ultra-long effective optical path of up to 64.8 m within an extremely small volume of only 452.16 mL, significantly improving the sensitivity of gas detection and mirror utilization. Its integrated structure combines excellent stability and portability, providing core hardware support for the field-based, high-precision application of tunable semiconductor laser absorption spectroscopy technology in industrial safety and environmental monitoring.

[0055] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A ring-shaped multi-channel absorption cell, characterized in that, include: A reflector (1), which is a cylindrical tube open at both ends, has a reflective film (11) on its inner wall to form a continuous annular optical reflective surface; an end cap assembly, which is disposed at the two ends of the reflector (1) and together with the reflector (1) forms a closed gas chamber; the cylindrical wall of the reflector (1) has an entrance light hole (12) and an exit light hole (13) for guiding the probe beam into and out of the gas chamber, respectively; the end cap assembly includes: a first end plate ( 3), covering the first end of the reflector (1); second end plate (4), covering the second end of the reflector (1); the first end plate (3) is provided with an air inlet pipe (31), and the second end plate (4) is provided with an air outlet pipe (41); the air inlet pipe (31) and the air outlet pipe (41) are both protruding in a direction away from the reflector (1); the incident light hole (12) and the outgoing light hole (13) are located on the same generatrix of the reflector (1) and are distributed along the axial direction of the reflector (1).

2. The annular multi-channel absorption cell according to claim 1, characterized in that, It also includes a sealing ring (5), and the first end plate (3) and the second end plate (4) are respectively sealed to both ends of the reflector (1) through the sealing ring (5).

3. The annular multi-channel absorption cell according to claim 1, characterized in that, It also includes a housing (2), which is annular and fitted around the outer periphery of the reflector (1); a through hole (21) is formed on the side wall of the housing (2) at the position corresponding to the incident light hole (12) and the exit light hole (13) for the detection beam to pass through.

4. The annular multi-channel absorption cell according to claim 1, characterized in that, The reflector (1) is made of K9 glass.

5. The annular multi-channel absorption cell according to claim 1, characterized in that, The reflective film (11) has a reflectivity of not less than 98% in the infrared band.

6. The annular multi-channel absorption cell according to claim 1, characterized in that, The diameters of the incident aperture (12) and the exit aperture (13) are 120%-130% of the collimated spot diameter of the probe beam.

7. A gas detection method using an annular multi-pass absorption cell, characterized in that, The application is implemented in a ring-shaped multi-pass absorption cell as described in any one of claims 1-6, comprising: introducing a gas to be tested into a gas chamber through the inlet pipe (31); injecting a collimated probe beam into the gas chamber through the incident light aperture (12), wherein the probe beam contains at least two wavelengths, which are respectively matched with the characteristic absorption peaks of different components in the gas to be tested; the probe beam undergoes multiple reflections between optical reflective surfaces to form an absorption path with a long effective optical path, and then exits from the exit light aperture (13); detecting the intensity of the emitted beam through a detector, and analyzing the component concentration of the gas to be tested based on the absorption spectrum.

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