Hollow circular-truncated-cone-shaped multi-pass absorption cell

Abstract

The invention provides a hollow circular-truncated-cone-shaped multi-pass absorption cell, and relates to the technical field of gas measurement, the hollow circular-truncated-cone-shaped multi-pass absorption cell comprises a hollow circular plane mirror, a hollow circular concave spherical mirror, a hard plastic pipe, two tripod frames, three supporting rods, two window sheets, two pressing sheets and a rubber ring, the hard plastic pipe comprises an inner circumferential surface and an outer circumferential surface, and the hollow circular plane mirror and the hollow circular concave spherical mirror are respectively nested and fixed between the inner peripheral surface and the outer peripheral surface of the two ends of the hard plastic pipe and are sealed by rubber rings. According to the hollow circular-truncated-cone-shaped multi-pass absorption cell provided by the invention, the inner diameter and the outer diameter of the hollow circular plane mirror obtained through a special cutting mode are smaller than the inner diameter and the outer diameter of the hollow circular concave spherical mirror, the mirror surface is utilized to a high degree, and meanwhile, a hollow circular-truncated-cone-shaped absorption cell structure is formed by combining a specific hollow circular-truncated-cone-shaped hard plastic pipe; therefore, stable light field distribution is formed in the absorption cell, and the mirror surface utilization rate and the gas exchange rate are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of gas measurement, and more specifically, to a hollow frustum-shaped multi-pass absorption cell. Background Art

[0002] An optical multi-pass absorption cell makes a light beam reflect multiple times in the absorption cell through a mirror or other optical elements, thereby increasing the interaction path length between light and a gas sample, that is, the effective optical path. By increasing the optical path, the detection sensitivity is improved, especially for the detection of trace gases. Common types of absorption cells include Herriott cells, White cells, Chernin cells, ring cells, etc. Different optical path structures generate various different spot distribution types, that is, the curvature, coating quality, and arrangement combination of the core element mirror directly affect the detection performance of the multi-pass cell. By precisely adjusting the position and angle of the mirror, the reflection path and spot distribution of the light beam in the multi-pass absorption cell are controlled. During the detection process, the detection light inside the absorption cell needs to be in full contact with the gas sample to ensure full absorption. Therefore, the design of the gas flow path is very important for improving the detection sensitivity. Currently, the design of absorption cells is gradually moving towards miniaturization and integration to meet the requirements of portable detection devices.

[0003] There are still some problems to be solved in the existing absorption cells. Among them, due to the limitation of the reflectivity of the highly reflective mirror used, the light spot energy will be gradually consumed as the light reflects back and forth between the mirrors, resulting in the inability to complete the subsequent reflection and thus unable to reach the ideal optical path. The traditional absorption cell structure mostly increases the base length of the cell itself to extend the single light transmission distance, and further extends the optical path by accumulating the single distances. This method will, on the one hand, increase the volume of the absorption cell and make it inconvenient to further integrate with the system, and on the other hand, increase the ineffective interaction space between the light and the gas during ventilation detection, thereby reducing the response rate of the absorption cell. In addition, due to the use of concave spherical highly reflective mirrors with the same parameters in the traditional optical path structure, the light follows a symmetric round-trip transmission equation when reflecting back and forth, resulting in the distortion of the subsequent light spots, increasing the difficulty of the exit hole design and reducing the accuracy of the detection of the exit light spot, thereby affecting the entire subsequent gas concentration inversion part.

[0004] Therefore, there is an urgent need for a new type of multi-pass absorption cell structure to effectively solve problems such as the accuracy of light spot detection, ensuring the reaction rate between the gas and the light, and the weakening and distortion of the light spot energy due to multiple transmissions, thereby improving the accuracy, stability, and efficiency. Summary of the Invention

[0005] In view of the problems in the background art, the present invention provides a hollow frustum-shaped multi-pass absorption cell to solve the defects existing in the multi-pass absorption cell in the prior art.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: A hollow frustum-shaped multi-pass absorption cell, comprising: A hollow circular plane mirror, a hollow circular concave spherical mirror, a hard plastic tube, two three-legged mirror mounts, two window pieces, two pressing pieces, and a rubber ring, The hard plastic tube includes an inner peripheral surface and an outer peripheral surface. The hollow circular plane mirror and the hollow circular concave spherical mirror are respectively nested and fixed between the inner peripheral surface and the outer peripheral surface at both ends of the hard plastic tube and are sealed with the rubber ring; grooves are provided on three sides of the two three-legged mirror mounts, and three tangent points of the hollow circular plane mirror and the hollow circular concave spherical mirror are respectively fixed in the corresponding grooves through the outer peripheral surface of the hard plastic tube, and the two pressing pieces respectively fix the two window pieces on the two three-legged mirror mounts; Wherein, the hard plastic tube is a hollow frustum shape, and an air inlet and an air outlet are provided on the outer peripheral surface of the hard plastic tube; the hollow circular plane mirror and the hollow circular concave spherical mirror are respectively obtained by cutting a circular plane mirror and a circular concave spherical mirror, the inner diameter of the hollow circular plane mirror is smaller than the inner diameter of the hollow circular concave spherical mirror, and the outer diameter of the hollow circular plane mirror is smaller than the outer diameter of the hollow circular concave spherical mirror.

[0007] Preferably, the multi-pass absorption cell further includes three support rods, threaded holes are provided at three vertex positions of the two three-legged mirror mounts, and the three support rods are connected to the two three-legged mirror mounts through the threaded holes.

[0008] Preferably, an exit hole is provided on the hollow circular plane mirror, and an entrance hole is provided on the hollow circular concave spherical mirror.

[0009] Preferably, the design steps of the multi-pass absorption cell are as follows: Step S1: Determine the incident parameters according to the asymmetric optical path reflected light transmission law matrix, and the asymmetric optical path reflected light transmission law matrix is: , where R is the radius of curvature of the circular concave spherical mirror, and d is the distance between the circular plane mirror and the circular concave spherical mirror; perform simulations of the concentric circular ring spot distribution types under multiple groups of incident parameters, and save multiple groups of incident parameters and simulation diagrams that meet the requirements of subsequent experimental debugging. The incident parameters include the incident angle, the incident position relative to the mirror center, and the mirror spacing; Step S2: Perform actual concentric circular ring spot debugging on the cage structure according to the multiple groups of incident angles, incident positions relative to the mirror center, and mirror spacings determined by the simulation; Step S3: Compare the concentric circular ring spot distribution quality of the circular plane mirror and the circular concave spherical mirror under multiple groups of concentric circular ring spot distributions, and determine whether there is spot overlap or occlusion; Step S4: Compare the number of reflections under the distribution of multiple concentric circular ring light spots, and determine whether the number of reflections meets the expected optical path; Step S5: Determine the optimal incident angle, the optimal incident position, and the optimal mirror spacing for constructing the multipass absorption cell according to the light spot state and the optical path situation of the light beam emitted from the circular plane mirror; Step S6: Cut the circular plane mirror and the circular concave spherical mirror according to the concentric circular ring light spot distribution of the circular plane mirror and the circular concave spherical mirror, determine the mirror cutting dimensions of the circular plane mirror and the circular concave spherical mirror, and remove the largest mirror surface range of the circular plane mirror and the circular concave spherical mirror to obtain the inner diameter and the outer diameter of the hollow circular plane mirror, and the inner diameter and the outer diameter of the hollow circular concave spherical mirror while ensuring that the light transmission and the inner edge light spot distribution are not affected; Step S7: Design the multipass absorption cell according to the optimal incident angle, the optimal incident position, the optimal mirror spacing, and the mirror cutting dimensions of the circular plane mirror and the circular concave spherical mirror.

[0010] Preferably, the specific steps of cutting the circular plane mirror and the circular concave spherical mirror according to the concentric circular ring light spot distribution of the circular plane mirror and the circular concave spherical mirror are as follows: Step S61: Calculate the total energy of each light spot according to the concentric circular ring light spots from the innermost circle to the outermost circle on the circular plane mirror and the circular concave spherical mirror respectively, and compare the light spots with strong energy; Step S62: Record the polar coordinates of all the light spots with strong energy on the circular plane mirror with respect to the mirror surface distribution points. The polar coordinates corresponding to the m-th light spot with strong energy are denoted as (r, θ m ), where the radial distance r in the polar coordinates is a fixed value, and θ m represents the polar angle of the m-th light spot with strong energy with respect to the mirror surface distribution point. m is a positive integer greater than or equal to 1. The polar coordinates of the first fixed reference point are set as (0, θ0), and calculate the distribution distance L m , ; Step S63: Record the polar coordinates (r i , θ i ) of all the light spots with strong energy on the circular concave spherical mirror with respect to the mirror surface distribution points, where i is a positive integer greater than or equal to 1, r i represents the radial distance of the i-th light spot with strong energy with respect to the mirror surface distribution point, and θ iDenote the polar angle of the i-th strong energy light spot relative to the mirror surface distribution point position. The polar coordinates of the second fixed reference point are set as (r0, θ0), and the distribution distance L between all the strong energy light spots on the circular concave spherical mirror relative to the second fixed reference point is calculated. i , ; Step S64: Compare and sort the distribution distance L m and the distribution distance L i according to the distribution positions of the innermost circle and the outermost circle, and respectively screen out the minimum value L m of the distribution distance L m-min , the minimum value L i of the distribution distance L i-min and the maximum value L m of the distribution distance L m-max , the maximum value L i of the distribution distance L i-max ; Step S65: Determine L m-min as the inner diameter of the hollow circular plane mirror, and L m-max as the outer diameter of the hollow circular plane mirror. Determine L i-min as the inner diameter of the hollow circular concave spherical mirror, and L i-max as the outer diameter of the hollow circular concave spherical mirror.

[0011] The beneficial effects of the present invention are as follows: (1) The concave spherical mirror and the plane mirror cooperate to form an asymmetric optical path structure. A complete round trip of the optical path in the multi-pass absorption cell includes: from the concave spherical mirror to the plane mirror, and then to the concave spherical mirror, so that the light spot produces a special converging effect on the plane mirror after being reflected by the concave spherical mirror, thereby increasing the light spot energy and enhancing the optical path. (2) The special asymmetric optical path structure makes the converging light spots with inconsistent light spot distribution ranges generated by each independent light spot on the plane mirror and the concave spherical mirror. Through the different types of concentric circular ring light spot distributions on the plane mirror and the concave spherical mirror, using the particularity of the reflection light ray trajectory, the range where there is no light spot distribution at the centers of the two mirrors and that does not affect the reflection light ray trajectory is cut, removing the ineffective interaction space between the light rays and the gas, and enabling the reflection light rays to fully interact with the gas to be measured, thereby improving the response rate of the absorption cell. (3) Through the special cutting method, the inner diameter and the outer diameter of the hollow circular plane mirror are both smaller than the inner diameter and the outer diameter of the hollow circular concave spherical mirror, highly utilizing the mirror surface. At the same time, combined with a specific hollow frustum-shaped hard plastic tube to form a hollow frustum-shaped multi-pass absorption cell structure, a stable light field distribution is formed inside the multi-pass absorption cell, improving the mirror surface utilization rate and the gas exchange rate. (4) The hollow circular plane mirror and the hollow circular concave spherical mirror are respectively nested and fixed between the inner peripheral surface and the outer peripheral surface at both ends of the hard plastic tube and sealed with rubber rings, improving the sealing effect and sensitivity; (5) Two different fixed reference points are set, and the distribution distances between multiple groups of strong energy light spots from the innermost circle to the outermost circle on the circular plane mirror and the circular concave spherical mirror and the two different fixed reference points are calculated respectively. The minimum distance value is determined as the inner diameter, and the maximum distance value is determined as the outer diameter. Under the condition of not affecting the emission range of the selected strong energy light spots, the mirror surface is cut invalid to the greatest extent, improving the cutting accuracy and efficiency. Description of the Drawings

[0012] To better understand the present invention, the present invention will be described in more detail by referring to the specific embodiments shown in the drawings. These drawings only depict the typical embodiments of the present invention and should not be considered as limiting the protection scope of the present invention.

[0013] Figure 1 It is a schematic structural diagram of a hollow frustum-shaped multi-pass absorption cell provided by an embodiment of the present invention.

[0014] Reference Signs: 1 - hollow circular plane mirror, 2 - hollow circular concave spherical mirror, 3 - incident hole, 4 - exit hole, 5 - hard plastic tube, 6 - air inlet, 7 - air outlet, 8 - rubber ring, 9 - triangular mirror holder, 10 - support rod, 11 - groove, 12 - window piece, 13 - pressing piece, 14 - threaded hole. Detailed Embodiments

[0015] The following describes the embodiments of the present invention with reference to the drawings, so that those skilled in the art can better understand the present invention and implement it. However, the listed embodiments are not intended to limit the present invention. Without conflict, the following embodiments and the technical features in the embodiments can be combined with each other, and the same components are denoted by the same reference signs. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0016] The present invention provides a hollow frustum-shaped multi-pass absorption cell. Please refer to Figure 1 , Figure 1 It is a schematic structural diagram of a hollow frustum-shaped multi-pass absorption cell provided by an embodiment of the present invention.

[0017] Refer to Figure 1 , in the embodiment of the present invention, the hollow frustum-shaped multi-pass absorption cell includes: a hollow circular plane mirror 1, a hollow circular concave spherical mirror 2, a hard plastic tube 5, two triangular mirror holders 9, three support rods 10, two window pieces 12, two pressing pieces 13, and a rubber ring 8, The hard plastic tube 5 includes an inner peripheral surface and an outer peripheral surface. The hollow circular plane mirror 1 and the hollow circular concave spherical mirror 2 are respectively nested and fixed between the inner peripheral surface and the outer peripheral surface at both ends of the hard plastic tube 5 and sealed with rubber rings 8; grooves 11 are provided on the three sides of the two tripod mounts 9. The contact parts of the outer peripheral surface of the hard plastic tube 5 with the hollow circular plane mirror 1 and the hollow circular concave spherical mirror 2 are respectively fixed in the corresponding grooves 11 along the tangent direction. Threaded holes 14 are provided at the three vertex positions of the two tripod mounts 9, and the three support rods 10 are connected to the two tripod mounts 9 through the threaded holes; two pressing plates 13 respectively fix the two window plates 12 on the two tripod mounts 9; Among them, the hard plastic tube 5 is a hollow frustum of a cone, and an air inlet 6 and an air outlet 7 are provided on the outer peripheral surface of the hard plastic tube 5; the hollow circular plane mirror 1 and the hollow circular concave spherical mirror 2 are respectively obtained by cutting a circular plane mirror and a circular concave spherical mirror. The inner diameter of the hollow circular plane mirror 1 is smaller than the inner diameter of the hollow circular concave spherical mirror 2, and the outer diameter of the hollow circular plane mirror 1 is smaller than the outer diameter of the hollow circular concave spherical mirror 2.

[0018] The tripod mount 9 and the support rod 10 are used to fix the entire absorption cell structure to ensure the stability of the absorption cell optical path. The window plate 12 is placed outside the two mirrors and forms a specific angle with the two mirrors to ensure that the light is not affected by the reflection of the window plate 12 when entering the optical path. A number of threaded holes 14 are provided on the pressing plate 13 to fix the window plate 12 on the tripod mount 9 to further ensure the sealing performance.

[0019] It should be noted that most of the existing multi-pass absorption cells are cylindrical structures, and the gas exchange rate is relatively low; in the embodiments of the present invention, the multi-pass absorption cell is a hollow frustum of a cone. The hollow circular plane mirror and the hollow circular concave spherical mirror are respectively nested and fixed between the inner peripheral surface and the outer peripheral surface at both ends of the hard plastic tube and sealed with rubber rings. The inner diameter and outer diameter of the hollow circular plane mirror are both smaller than the inner diameter and outer diameter of the hollow circular concave spherical mirror obtained by a special cutting method, making high use of the mirror surface. At the same time, combined with the specific hollow frustum-shaped hard plastic tube to form a hollow frustum-shaped multi-pass absorption cell structure, so that a stable light field distribution is formed inside the absorption cell, improving the mirror surface utilization rate and the gas exchange rate.

[0020] In another embodiment of the present invention, the design steps of the multi-pass absorption cell are as follows: Step S1: Determine the incident parameters according to the matrix of the transmission law of reflected light in the asymmetric optical path. The matrix of the transmission law of reflected light in the asymmetric optical path is: , where R is the radius of curvature of the circular concave spherical mirror, and d is the distance between the circular plane mirror and the circular concave spherical mirror; perform simulations of the concentric circular ring spot distribution types under multiple sets of incident parameters, and save multiple sets of incident parameters and simulation diagrams that meet the needs of subsequent experimental debugging. The incident parameters include the incident angle, the incident point position relative to the center of the mirror, and the mirror spacing; In step S1, the derivation process of the transmission matrix equation for the reflected light in the asymmetric optical path is as follows: Assume that the radius of curvature of the circular concave spherical mirror is R, and its vertex, i.e., the center point of the mirror surface, is located at a certain point on the optical axis. The circular plane mirror can be regarded as a mirror with an infinite radius of curvature, and its focal length is infinite. Assume that the circular plane mirror and the circular concave spherical mirror are placed parallel to each other, and the distance between them is d. For the propagation from the circular concave spherical mirror to the circular plane mirror, the light starts from the circular concave spherical mirror and propagates a distance d to the circular plane mirror. The reflection matrix of the circular plane mirror can be regarded as a "plane" reflection. A complete round trip includes: from the concave spherical mirror to the plane mirror and then back to the concave spherical mirror. Thus, the total transmission rule matrix can be obtained.

[0021] Step S2: According to multiple groups of incident angles, incident positions relative to the mirror center, and mirror spacings determined by simulation, perform actual concentric circular spot debugging on the cage structure; Step S3: Compare the quality of the concentric circular spot distributions of the circular plane mirror and the circular concave spherical mirror under multiple groups of concentric circular spot distributions, and determine whether there is spot overlap or occlusion; Step S4: Compare the number of reflections under multiple groups of concentric circular spot distributions and determine whether the number of reflections meets the expected optical path; Step S5: According to the spot state and optical path of the light emitted from the circular plane mirror, determine the optimal incident angle, optimal incident position, and optimal mirror spacing for constructing the absorption cell; Step S6: Cut the circular plane mirror and the circular concave spherical mirror according to the concentric circular spot distributions of the circular plane mirror and the circular concave spherical mirror, determine the mirror cutting sizes of the circular plane mirror and the circular concave spherical mirror. Without affecting the light transmission and the spot distribution at the inner edge, remove the largest mirror surface range of the circular plane mirror and the circular concave spherical mirror to obtain the inner and outer diameters of the hollow circular plane mirror 1 and the inner and outer diameters of the hollow circular concave spherical mirror 2; Step S7: Design a multi-pass absorption cell according to the optimal incident angle, optimal incident position, optimal mirror spacing, and the mirror cutting sizes of the circular plane mirror and the circular concave spherical mirror.

[0022] Among them, the specific steps for cutting the circular plane mirror and the circular concave spherical mirror according to the concentric circular spot distributions of the circular plane mirror and the circular concave spherical mirror are as follows: Step S61: Calculate the total energy of each light spot respectively according to the concentric circular spots from the innermost circle to the outermost circle on the circular plane mirror and the circular concave spherical mirror, and compare to find out the light spots with strong energy; Among them, there are multiple strong energy light spots from the innermost circle to the outermost circle of the concentric circular ring light spot. The total energy of each light spot is calculated according to the light spot radius and the initial light spot intensity or the peak intensity at the center of the light spot. The initial light spot intensity or the peak intensity at the center of the light spot can be measured by a power meter. By setting an energy threshold, strong energy light spots are obtained. For example, more than 50% of the peak energy is used as a strong energy light spot. Obtaining strong energy light spots based on the total energy of each light spot belongs to the prior art and will not be elaborated here.

[0023] Step S62: Record the polar coordinates of all the strong energy light spots on the circular plane mirror with respect to the distribution positions on the mirror surface. The polar coordinates corresponding to the m-th strong energy light spot are denoted as (r, θ m ), where the radial distance r in the polar coordinates is a fixed value, and θ m represents the polar angle of the m-th strong energy light spot with respect to the distribution position on the mirror surface. m is a positive integer greater than or equal to 1, m = 1, 2, 3..., and the polar coordinates of the first fixed reference point are set as (0, θ0). Calculate the distribution distance L m , ; Step S63: Record the polar coordinates (r i , θ i ) of all the strong energy light spots on the circular concave spherical mirror with respect to the distribution positions on the mirror surface, where i is a positive integer greater than or equal to 1, i = 1, 2, 3..., r i represents the radial distance of the i-th strong energy light spot with respect to the distribution position on the mirror surface, and θ i represents the polar angle of the i-th strong energy light spot with respect to the distribution position on the mirror surface. The polar coordinates of the second fixed reference point are set as (r0, θ0). Calculate the distribution distance L i , ; Step S64: Compare and sort the distribution distance L m and the distribution distance L i according to the distribution positions from the innermost circle to the outermost circle, and respectively select the minimum value L m of the distribution distance L m-min , the minimum value L i of the distribution distance L i-min , the maximum value L m of the distribution distance L m-max , and the maximum value L i of the distribution distance L i-max ; Step S65: Determine L m-min as the inner diameter of the hollow circular plane mirror 1, and L m-max as the outer diameter of the hollow circular plane mirror 1. Set Li-min Determine the inner diameter and L of the hollow circular concave spherical mirror 2 i-max Determine the outer diameter of the hollow circular concave spherical mirror 2

[0024] In another embodiment of the present invention, the mirror surface size of the circular concave spherical mirror before cutting of the hollow circular concave spherical mirror 2 is a diameter of 50.8 mm, the focal length is 100, and the mirror surface size of the circular plane mirror before cutting of the hollow circular plane mirror 1 is a diameter of 50.8 mm. An incident hole 3 is provided on the hollow circular concave spherical mirror 2, with a size of 1.5 mm and a position 18 mm away from the center of the mirror. An exit hole 4 is provided on the hollow circular plane mirror 1

[0025] The present invention uses a combination of a concave spherical mirror and a plane mirror to form an asymmetric optical path structure. A complete round trip of the optical path in the absorption cell includes: from the concave spherical mirror to the plane mirror, and then to the concave spherical mirror, so that the light spot produces a special converging effect on the plane mirror after being reflected by the concave spherical mirror, thereby increasing the light spot energy and enhancing the optical path; the special asymmetric optical path structure makes the converging light spots with inconsistent light spot distribution ranges generated by each independent light spot on the plane mirror and the concave spherical mirror. Through different types of concentric circular ring light spot distributions on the plane mirror and the concave spherical mirror, using the particularity of the reflection light ray trajectory, the range where there is no light spot distribution at the centers of the two mirrors and that does not affect the path of the reflection light ray trajectory is cut, removing the ineffective interaction space between the light ray and the gas, enabling the reflection light ray to fully interact with the gas to be measured, thereby improving the response rate of the absorption cell; particularly, the present invention sets two different fixed reference points, calculates the distribution distances between multiple groups of strong energy light spots from the innermost circle to the outermost circle on the circular plane mirror and the circular concave spherical mirror and the two different fixed reference points respectively, determines the minimum distance value as the inner diameter and the maximum distance value as the outer diameter respectively, and performs the maximum degree of ineffective mirror cutting under the condition of not affecting the emission range of the selected strong energy light spots, improving the cutting accuracy and efficiency

[0026] The various embodiments in the present invention are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description in the method part

[0027] The above-described embodiments are only relatively preferred specific implementation manners of the present invention. The present specification uses phrases such as "in one embodiment", "in another embodiment", "in yet another embodiment", or "in other embodiments", which can all refer to one or more of the same or different embodiments according to the present disclosure. The ordinary variations and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included in the protection scope of the present invention

Claims

1. A hollow frustum-shaped multi-pass absorption cell, characterized in that, Comprising: A hollow circular plane mirror, a hollow circular concave spherical mirror, a hard plastic tube, two three-legged mirror mounts, two window pieces, two pressing pieces, and a rubber ring. The hard plastic tube includes an inner peripheral surface and an outer peripheral surface. The hollow circular plane mirror and the hollow circular concave spherical mirror are respectively nested and fixed between the inner peripheral surface and the outer peripheral surface at both ends of the hard plastic tube and sealed with the rubber ring. Grooves are provided on the three sides of the two three-legged mirror mounts. The three tangent points of the hollow circular plane mirror and the hollow circular concave spherical mirror are respectively fixed in the corresponding grooves through the outer peripheral surface of the hard plastic tube. The two pressing pieces respectively fix the two window pieces on the two three-legged mirror mounts. Among them, the hard plastic tube is a hollow frustum of a cone, and an air inlet and an air outlet are provided on the outer peripheral surface of the hard plastic tube. The hollow circular plane mirror and the hollow circular concave spherical mirror are respectively obtained by cutting a circular plane mirror and a circular concave spherical mirror. The inner diameter of the hollow circular plane mirror is smaller than the inner diameter of the hollow circular concave spherical mirror, and the outer diameter of the hollow circular plane mirror is smaller than the outer diameter of the hollow circular concave spherical mirror.

2. The hollow frustum-shaped multi-pass absorption cell according to claim 1, wherein The multi-pass absorption cell further includes three support rods. Threaded holes are provided at the three vertex positions of the two three-legged mirror mounts. The three support rods are connected to the two three-legged mirror mounts through the threaded holes.

3. The hollow frustum-shaped multi-pass absorption cell according to claim 2, characterized in that, An exit hole is provided on the hollow circular plane mirror, and an entrance hole is provided on the hollow circular concave spherical mirror.

4. The hollow frustum-shaped multi-pass absorption cell according to any one of claims 1 to 3, characterized in that, The design steps of the multi-pass absorption cell are as follows: Step S1: Determine the incident parameters according to the matrix of the transmission law of reflected light in the asymmetric optical path. The matrix of the transmission law of reflected light in the asymmetric optical path is as follows: , where R is the radius of curvature of the circular concave spherical mirror, and d is the distance between the circular plane mirror and the circular concave spherical mirror; perform simulations on the distribution types of concentric ring spotlights under multiple sets of incident parameters, and save multiple sets of incident parameters and simulation diagrams that meet the requirements of subsequent experimental debugging. The incident parameters include the incident angle, the incident position relative to the mirror center, and the mirror spacing; Step S2: Perform actual concentric circular ring spot debugging on the cage structure according to multiple groups of incident angles, incident point positions relative to the mirror center, and mirror spacings determined by simulation. Step S3: Compare the concentric circular ring spot distribution quality of the circular plane mirror and the circular concave spherical mirror under multiple groups of concentric circular ring spot distributions to determine whether there is spot overlap or occlusion. Step S4: Compare the number of reflections under multiple groups of concentric circular ring spot distributions to determine whether the number of reflections meets the expected optical path. Step S5: Determine the optimal incident angle, optimal incident point position, and optimal mirror spacing for constructing the multi-pass absorption cell according to the spot state and optical path of the light spot emitted by the circular plane mirror. Step S6: Cut the circular plane mirror and the circular concave spherical mirror according to the concentric circular ring spot distribution of the circular plane mirror and the circular concave spherical mirror to determine the mirror surface cutting dimensions of the circular plane mirror and the circular concave spherical mirror. Without affecting the light transmission and the inner edge spot distribution, remove the largest mirror surface range of the circular plane mirror and the circular concave spherical mirror to obtain the inner diameter and outer diameter of the hollow circular plane mirror, and the inner diameter and outer diameter of the hollow circular concave spherical mirror. Step S7: Design the multi-pass absorption cell according to the optimal incident angle, the optimal incident point position, the optimal mirror spacing, and the mirror surface cutting dimensions of the circular plane mirror and the circular concave spherical mirror.

5. The hollow frustum-shaped multi-pass absorption cell according to claim 4, characterized in that, The specific steps for cutting the circular plane mirror and the circular concave spherical mirror according to the concentric circular ring spot distribution of the circular plane mirror and the circular concave spherical mirror are as follows: Step S61: Calculate the total energy of each light spot respectively according to the concentric circular ring light spots from the innermost circle to the outermost circle on the circular plane mirror and the circular concave spherical mirror, and compare the light spots with strong energy; Step S62: Record the polar coordinates of all strong energy light spots on the circular plane mirror with respect to the mirror surface distribution points. The polar coordinates corresponding to the m-th strong energy light spot are denoted as (r, θ m ), where the radial distance r in the polar coordinates is a fixed value, and θ m represents the polar angle of the m-th strong energy light spot with respect to the mirror surface distribution point. m is a positive integer greater than or equal to 1. The polar coordinates of the first fixed reference point are set as (0, θ0), and calculate the distribution distance L between all strong energy light spots on the circular plane mirror and the first fixed reference point m , ; Step S63: Record the polar coordinates (r i , θ i ) of all the strong energy light spots on the circular concave spherical mirror with respect to the mirror surface distribution points, where i is a positive integer greater than or equal to 1, r i represents the radial distance of the i-th strong energy light spot with respect to the mirror surface distribution point, and θ i represents the polar angle of the i-th strong energy light spot with respect to the mirror surface distribution point. The polar coordinates of the second fixed reference point are set as (r0, θ0), and calculate the distribution distance L i , ; Step S64: Take the distribution distance L m and the distribution distance L i Compare and sort them according to the distribution positions of the innermost circle and the outermost circle, and respectively screen out the minimum value L m of the distribution distance L m-min , the minimum value L i of the distribution distance L i-min and the maximum value L m of the distribution distance L m-max , the maximum value L i of the distribution distance L i-max ; Step S65: Take L m-min as the inner diameter of the hollow circular plane mirror, and take L m-max as the outer diameter of the hollow circular plane mirror. Take L i-min as the inner diameter of the hollow circular concave spherical mirror, and take L i-max as the outer diameter of the hollow circular concave spherical mirror.

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