Athermalization intensive multi-reflector cavity based on off-axis mirror and light spot control method

Abstract

The invention discloses an athermalization intensive type multi-reflector cavity based on an off-axis mirror and a light spot control method, the multi-reflector cavity comprises a main reflector and a secondary reflector, a first off-axis reflector is nested in a local area of the main reflector, a second off-axis reflector is nested in a local area of the secondary reflector, and the first off-axis reflector and the second off-axis reflector are arranged in parallel. An incident hole or an emergent hole is formed in the primary reflector or the secondary reflector; a light beam enters from the incidence hole and is reflected back and forth between the primary reflector and the secondary reflector so as to form a plurality of light spots on the primary reflector and the secondary reflector, same-stage concentric rings are formed among the light spots, and the second off-axis reflector can reflect the light beam in the first-stage concentric ring to the second-stage concentric ring. The first off-axis reflector receives the light beam reflected by the second off-axis reflector and reflects the light beam to the second-stage concentric ring of the secondary reflector, and the light beam forms a multi-stage concentric ring after being reflected for multiple times and is emitted from the emitting hole. According to the invention, the utilization rate of the mirror surface can be improved, and the positions and number of light spots can be accurately controlled.

Description

Technical Field

[0001] The present application relates to the field of gas analysis, and in particular to an athermalized intensive multi-reverse cavity and a spot control method based on an off-axis mirror. Background Art

[0002] Laser gas analysis technology is widely used in industrial process monitoring and control, combustion process diagnosis and analysis, engine efficiency and motor vehicle exhaust measurement, explosion detection, atmospheric environment gas monitoring and other fields. In the field of laser gas analysis, the gas measurement cell is mainly used for gas sampling and measurement. It is installed in a cabinet or analysis room to extract the gas from the on-site industrial pipeline and pass it into the gas measurement cell after filtering. The laser gas analyzer is installed at both ends of the gas measurement cell to measure the content of the target gas in the flue gas.

[0003] According to Beer-Lambert's theorem, the longer the effective optical path of the gas measurement cell, the higher its detection sensitivity. With the continuous development of gas measurement technology, many fields have higher and higher requirements for measuring instruments, and high precision and miniaturization have become the main development trends. Miniaturization can be achieved by realizing multiple reflections in a limited volume through an optical long-path absorption cell. The Herriott cell is a commonly used type of gas cell due to its simple structure and easy installation. Patents CN115081038A and CN 114065321 A propose that a specific angle of incident light can be obtained according to an algorithm, so that dense spot patterns of different shapes can be presented on the spherical reflector, which improves the utilization rate of the reflector surface and reduces its volume.

[0004] The current gas measurement cell can already utilize the mirror surface to a large extent and achieve a higher optical path. However, due to the optimization nature of the algorithm, it is easy to fall into a local optimal solution. It takes a long time to obtain the appropriate parameters. In addition, the number of reflections and the position of the light spot are not completely controllable and there is a large degree of randomness. Summary of the invention

[0005] In order to improve the utilization rate of the mirror surface and to accurately control the position and number of light spots, the present application provides an athermalized intensive multi-reverse cavity and light spot control method based on an off-axis mirror.

[0006] The first aspect of the present application provides an athermalized intensive multi-reflector cavity based on an off-axis mirror, which adopts the following technical solution: an athermalized intensive multi-reflector cavity based on an off-axis mirror, comprising a primary reflector and a secondary reflector coaxially arranged opposite to each other, a first off-axis reflector being nested in a local area of ​​the primary reflector, a second off-axis reflector being nested in a local area of ​​the secondary reflector, and an entrance hole or an exit hole being opened on the primary reflector or the secondary reflector; Among them, the light beam is incident from the incident hole, and is reflected back and forth between the primary reflector and the secondary reflector to form multiple light spots on the primary reflector and the secondary reflector, and concentric rings of the same level are formed between the multiple light spots. The second off-axis reflector can reflect the light beam in the primary concentric ring to the secondary concentric ring. The first off-axis reflector receives the light beam reflected from the second off-axis reflector and reflects the light beam to the secondary concentric ring of the secondary reflector. After multiple reflections, the light beam forms multiple levels of concentric rings and is emitted from the exit hole.

[0007] By adopting the above technical solution, multiple concentric rings of light spot distribution can be formed on the primary reflector and the secondary reflector. The number, radius and number of light spots of each level of concentric rings are controllable, which improves the surface utilization of the reflector and enhances the flexibility and controllability of the optical path length, thereby improving the measurement accuracy and stability. At the same time, through the design of off-axis reflectors, multiple precise reflections of the light beam on the reflector can be achieved, avoiding the problems of randomness of light spot position and uncontrollable number of reflections caused by insufficient algorithm optimization in traditional methods.

[0008] Optionally, the surface parameters of the first off-axis reflector and the second off-axis reflector are adjustable so as to adjust the number and radius of concentric rings and the number of light spots of a single concentric ring.

[0009] By adopting the above technical solution, the surface parameters of the first off-axis reflector and the second off-axis reflector are adjustable, and the number and radius of each concentric ring can be accurately controlled. This not only improves the surface utilization of the reflector, but also makes the optical path and spot distribution more flexible and controllable, thereby improving the measurement accuracy and reliability.

[0010] Optionally, the relative positions of the first off-axis reflector and the second off-axis reflector are adjustable so as to adjust the number of light spots in a single concentric ring.

[0011] By adopting the above technical solution, the spot distribution can be dynamically adjusted according to the needs of the actual application scenario, thereby optimizing the measurement accuracy and optical path stability.

[0012] Optionally, the multi-reflection cavity also includes a thermal compensation structure, which includes a base, an optical housing, a thermal compensation rod and a reflector seat, wherein both ends of the optical housing are installed on the base, and the optical housing and the base together form an optical absorption cavity, one end of the thermal compensation rod is connected to the base, and the other end extends along the length direction of the optical housing and is fixed to the reflector seat, the reflector seat is located in the optical absorption cavity, and the coaxially arranged primary reflector and secondary reflector are installed in the reflector seat; wherein, when the temperature in the optical absorption cavity changes, the length of the base and the optical housing increases or decreases, and the length of the thermal compensation rod increases or decreases, so that the distance between the vertices of the primary reflector and the secondary reflector does not change.

[0013] By adopting the above technical solution, the materials of the base and optical housing and the materials of the thermal compensation rod are carefully selected and calculated to ensure that when the temperature changes, the thermal expansion or contraction of the base and optical housing offsets the thermal expansion or contraction of the thermal compensation rod, so that the distance between the primary reflector and the secondary reflector remains constant. This design effectively reduces the change in optical path caused by temperature changes, improves the temperature stability of the optical path, and thus improves the measurement accuracy.

[0014] Optionally, the distance d between the vertices of the primary reflector and the secondary reflector satisfies: d=D+α1DT-d1-α2d1T-d2-α2d2T=D-d1-d2; α1 is the average thermal expansion coefficient of the base and the optical housing, α2 is the average thermal expansion coefficient of the thermal compensation rod, D is the length of both ends of the optical housing, d1 is the distance between one end of the optical housing and the vertex of the primary reflector, d2 is the distance between the other end of the optical housing and the vertex of the secondary reflector, and T is the temperature change value in the optical absorption cavity.

[0015] By adopting the above technical solution, it is ensured that the distance d between the vertices of the primary reflector and the secondary reflector remains constant when the temperature changes, effectively avoiding the change of the optical path caused by the temperature change, and improving the measurement accuracy. Specifically, by accurately calculating the thermal expansion coefficient of the base and the optical housing, the thermal expansion coefficient of the thermal compensation rod and the geometric dimensions of the optical housing, the change in the length of the thermal compensation rod just offsets the change in the length of the base and the optical housing, so that the distance between the primary reflector and the secondary reflector remains unchanged, ensuring the stability and reliability of the optical path.

[0016] Optionally, the reflector seat includes a flexible mirror seat arranged in a ring shape, the inner wall of the flexible mirror seat is provided with a clamping portion for clamping the primary reflector or the secondary reflector, and the side wall of the flexible mirror seat relative to the clamping portion is provided with a deformation hole, and the deformation hole penetrates the side wall of the flexible mirror seat along the axial direction of the flexible mirror seat.

[0017] By adopting the above technical solution, the inner wall of the flexible mirror seat is provided with a clamping portion, which can ensure the stable installation of the primary reflector or the secondary reflector. At the same time, the deformation hole opened in the side wall can allow the mirror seat to deform freely when the temperature changes, thereby reducing the stress transfer to the reflector, avoiding the deformation and displacement of the reflector due to temperature changes, and thus improving the temperature stability and measurement accuracy of the entire optical path system.

[0018] Optionally, the multi-reflection cavity also includes a laser alignment system, an incident adjustment reflector, an exit adjustment reflector and a detector assembly. After being collimated by the laser alignment system, the light beam is incident on the incident adjustment reflector. The incident adjustment reflector adjusts the angle of the incident light so that the incident light is incident from the incident hole at a certain angle. The exit adjustment reflector adjusts the angle of the exit light so that the exit light is reflected at a certain angle into the detector assembly, and the detector assembly collects the optical signal.

[0019] By adopting the above technical solutions, the laser alignment system ensures the collimation of the incident light beam, improves the parallelism of the light beam, and reduces the divergence of the light beam in the multi-reflector cavity, thereby improving the quality of the light spot and the stability of the optical path. The incident adjustment reflector and the exit adjustment reflector adjust the angles of the incident light and the exit light respectively, so that the light beam can accurately enter from the incident hole and exit from the exit hole after multiple reflections in the multi-reflector cavity, effectively controlling the path and direction of the light path, and improving the position accuracy of the light spot and the controllability of the optical path. The detector component efficiently collects the exit light signal, ensuring the accuracy of the measurement data and improving the detection performance of the entire system.

[0020] A second aspect of the present application provides a light spot control method using the following technical solution: A light spot control method comprises the following steps: Providing a pair of coaxially oppositely arranged primary reflectors and secondary reflectors, replacing a local area of ​​the primary reflector with a first off-axis reflector, and replacing a local area of ​​the secondary reflector with a second off-axis reflector; An incident hole or an exit hole is provided on the primary reflector or the secondary reflector, so that a light beam enters from the incident hole, and the primary reflector and the secondary reflector are used to reflect the light beam back and forth to form a plurality of light spots on the primary reflector and the secondary reflector, and concentric rings of the same level are formed between the plurality of light spots; The second off-axis reflector is used to reflect the light beam in the primary concentric ring to the secondary concentric ring, and the first off-axis reflector is used to receive the light beam reflected from the second off-axis reflector and reflect the light beam to the secondary concentric ring of the secondary reflector, so that the light beam forms multiple concentric rings after multiple reflections and is emitted from the exit hole.

[0021] By adopting the above technical solution, a plurality of concentric rings of light spot distribution can be formed on the primary reflector and the secondary reflector, and the number, radius and number of light spots of each level of concentric rings are controllable, which improves the surface utilization of the reflector, enhances the flexibility and controllability of the optical path length, and thus improves the measurement accuracy. In addition, by reasonably designing the position and surface parameters of the first off-axis reflector and the second off-axis reflector, the distribution of the light spot can be accurately controlled to ensure the stable transmission of the light beam between the multi-level concentric rings, reduce the randomness and uncontrollable factors of the optical path, and improve the reliability and stability of the system.

[0022] Optional, including: Construct the transmission matrix of the light beam from the input hole to the output hole; Adjusting the surface parameters of the first off-axis reflector and the second off-axis reflector in the transmission matrix; The required spacing between adjacent concentric rings, the number of concentric rings, and the number of light spots of a single concentric ring are obtained.

[0023] By adopting the above technical solutions, the light spot distribution is more controllable, a longer optical path can be achieved in a limited space, and the measurement accuracy and reliability can be improved. At the same time, by optimizing the surface parameters, the randomness and uncontrollability of the light spot can be reduced, and the stability and repeatability of the entire system can be improved.

[0024] Optional, including: The relative positions of the first off-axis reflector and the second off-axis reflector are adjusted to obtain the required number of single concentric ring light spots.

[0025] By adopting the above technical solution, the optical path can be finely controlled. This design not only improves the flexibility of the optical path, but also optimizes the light spot distribution according to the needs of different application scenarios, thereby improving measurement accuracy and reliability.

[0026] In summary, the present application includes at least one of the following beneficial technical effects: 1. By arranging the first off-axis reflector and the second off-axis reflector in the local area of ​​the primary reflector and the secondary reflector, a plurality of concentric rings of light spot distribution is realized, and the surface utilization rate of the reflector is improved. At the same time, the number of light spots in each concentric circle on the reflector, the radius of each concentric circle and the number of concentric circles can be controlled, which solves the problem that the light spot position and the number of reflections in the prior art are not completely controllable; 2. The design of the thermal compensation structure ensures that the distance between the reflectors does not change when the temperature changes. By calculating the length of the thermal compensation rod, when the temperature changes significantly, its thermal deformation is offset by the thermal deformation of the optical housing and the base, and its optical path remains unchanged, further improving the measurement accuracy.

[0027] 3. The use of a flexible mirror mount can greatly reduce the temperature stress on the reflector caused by temperature changes and improve the temperature stability of the optical path. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of a primary reflector according to an embodiment of the present application; Figure 2 is a schematic diagram of a secondary reflector according to an embodiment of the present application; Figure 3 This is a schematic diagram of the spot distribution when m=7, t=3mm in the implementation of this application; Figure 4is a cross-sectional schematic diagram of a thermal compensation structure of an embodiment of the present application; Figure 5 It is a schematic structural diagram of a reflector base according to an embodiment of the present application; Figure 6 It is a schematic diagram of the multi-reverse cavity optical path of an embodiment of the present application.

[0029] Figure 7 It is a schematic diagram of the overall structure explosion of the multi-reverse cavity in the embodiment of the present application.

[0030] Description of reference numerals: 10. Main reflector; 101. Incident hole; 102. Exit hole; 11. Secondary reflector; 20. First off-axis reflector; 21. Second off-axis reflector; 30. Light spot; 31. Concentric rings; 40. Base; 401. Bottom plate; 402. Base; 41. Optical housing; 411. Gas inlet connector; 412. Gas outlet connector; 42. Thermal compensation rod; 421. Threaded retaining ring; 422. Light-through hole; 43. Reflector seat; 431. Flexible seat; 432. Clamping part; 433. Deformation hole; 50. Laser alignment system; 51. Incident adjustment reflector; 52. Exit adjustment reflector; 53. Detector assembly; 60. Reflector adjustment cavity; 61. Incident light three-dimensional adjustment frame; 62. Exit light three-dimensional adjustment frame; 63. Sealing cover; 64. Cavity sealing ring. DETAILED DESCRIPTION

[0031] The following will be combined with the attached Figure 1-7 , the technical solutions in the embodiments of the present invention are clearly and completely described. The described embodiments are only possible technical implementations of the present invention, not all possible implementations. Those skilled in the art can completely combine the embodiments of the present invention to obtain other embodiments without creative work, and these embodiments are also within the scope of protection of the present invention.

[0032] The inventor of the present application has found that although the prior art can utilize the reflector surface to a large extent and achieve a higher optical path, it is easy to fall into a local optimal solution due to the optimization nature of the algorithm, and the number of reflections and the position of the light spot are not completely controllable, and there is a large randomness. In addition, due to the complexity of the use scenario of the gas pool, the temperature change may be relatively large, and the temperature stress between the structure and the reflector will affect the reflector surface shape. The distance between the reflectors will produce additional optical path changes due to the thermal expansion and contraction of the mounting structure, thereby affecting the measurement accuracy. To this end, the present application mainly adopts the following scheme to solve the above technical problems, and the present application is further described in detail below.

[0033] Example 1 The embodiment of the present application provides an athermalized intensive multi-reversal cavity based on an off-axis mirror, referring to Figure 1 and Figure 2 , comprising a primary reflector 10 and a secondary reflector 11 arranged coaxially opposite to each other, a first off-axis reflector 20 is nested in a local area of ​​the primary reflector 10, a second off-axis reflector 21 is nested in a local area of ​​the secondary reflector 11, and an entrance hole 101 or an exit hole 102 is provided on the primary reflector 10 or the secondary reflector 11. A light beam is incident from the entrance hole 101, and is reflected back and forth between the primary reflector 10 and the secondary reflector 11 to form a plurality of light spots 30 on the primary reflector 10 and the secondary reflector 11, and concentric rings 31 of the same level are formed between the plurality of light spots 30, the second off-axis reflector 21 can reflect the light beam in the primary concentric ring 31 to the secondary concentric ring 31, the first off-axis reflector 20 receives the light beam reflected from the second off-axis reflector 21 and reflects the light beam to the secondary concentric ring 31 of the secondary reflector 11, and the light beam forms a multi-level concentric ring 31 after multiple reflections, and is emitted from the exit hole 102.

[0034] In this embodiment, the reaction chamber is described based on a single-ring Herriott cavity with the same hole for incident and output. In other embodiments, the reaction chamber may also be a single-ring Herriott cavity with different holes for incident and output, a multi-ring Herriott cavity, or other similar reaction chambers. In this embodiment, the concentric rings 31 are circular rings. In other embodiments, the concentric rings 31 may also be elliptical rings.

[0035] In this embodiment, the first off-axis reflector 20 and the second off-axis reflector 21 extend radially and are in the shape of a long strip. Specifically, the first off-axis reflector 20 and the second off-axis reflector 21 are long off-axis aspheric reflectors. In other embodiments, the first off-axis reflector 20 and the second off-axis reflector 21 may also be in other shapes, as long as they extend radially. In addition, different numbers or shapes of first off-axis reflectors 20 and second off-axis reflectors 21 may also be embedded in different positions to control the number and position of the light spot 30.

[0036] The principle is as follows: the light beam is defined to reflect back and forth in the reaction chamber, and when a complete circular ring is formed on the secondary reflector 11, it is a small cycle. When the incident light is about to complete a small cycle in the reaction chamber, its last light spot 30 points are incident on the second off-axis reflector 21 of the secondary reflector 11, so that the next light spot 30 points reflected by the second off-axis reflector 21 do not fall on the incident hole 101, but fall on the second circular ring, that is, the starting position of the second cycle. The first off-axis reflector 20 is installed at the starting position of the second cycle. After the light passes through the first off-axis reflector 20, it enters the cycle of the second cycle. By analogy, multi-stage cycles can be realized, and each cycle can be controlled by design. That is, the second off-axis reflector 21 controls the starting position of other small cycles except the first circular ring, and the first off-axis reflector 20 controls the direction of the incident light of each small cycle, which can realize the nesting of multi-stage circular rings, thereby realizing controllable multi-rings.

[0037] The surface parameters of the first off-axis reflector 20 and the second off-axis reflector 21 are adjustable so as to adjust the number and radius of the concentric rings 31 and the number of light spots 30 of a single concentric ring 31. The relative position of the first off-axis reflector 20 and the second off-axis reflector 21 is adjustable so as to adjust the number of light spots 30 of a single concentric ring 31. The proof is as follows: Assuming that the radial distance of the incident light from the vertex when passing through the surface of the primary reflector 10 is r, and the angle vector relative to the optical axis is r', then its light orientation matrix is: The radius of curvature of the spherical surface of the primary reflector is R1, the radius of curvature of the spherical surface of the secondary reflector 11 is R2, and the distance between the vertices of the primary reflector 10 and the secondary reflector 11 along the optical axis is d. Then the transmission matrix of the light beam in the multi-reflector cavity is: The transmission matrix of light traveling N times in the cavity is: in The light must propagate stably in the cavity, according to the light stability conditions of the coaxial spherical reflector: You need Assume that the transmission matrix of the first off-axis reflector 20 in the local area of ​​the main reflector 10 is T A , the distance between the vertex of the first off-axis reflector and the vertex of the primary reflector 10 is x1, and the transmission matrix of the second off-axis reflector 21 in the local area of ​​the secondary reflector is T B , the distance between the vertex of the second off-axis reflector and the vertex of the secondary reflector 11 is x2, assuming that m circular rings are required, each of which has n light spots 30, and the azimuth vector of the outgoing light beam is Then the transmission matrix of the light beam in the entire reaction chamber is: Assuming that m=6, n=23, and the difference in radius between different circular rings is t=3 mm, after optimization, the surface parameters of the first off-axis reflector 20 and the second off-axis reflector 21 can be obtained: Wherein, R is the radius of curvature of the off-axis reflector; K is the cone coefficient of the off-axis reflector; a4, a6, a8, and a10 are the even-order coefficients of the off-axis reflector respectively.

[0038] The light spots 30 on the primary reflector 10 and the secondary reflector 11 are distributed as follows: Figure 1 and Figure 2As shown, according to different values ​​of m and n, and the spacing t between different circular light spots 30, the surface parameter data of the first off-axis reflector 20 and the second off-axis reflector 21 can be obtained. By modifying the surface parameter data of the first off-axis reflector 20 and the second off-axis reflector 21, the spacing t of the light spots 30 of different circular rings and the number of circular rings m and the number of light spots 30 of a single circular ring n can be obtained. When m=7, n=23, t=3mm is required, the following can be obtained: Figure 3 The distribution of the light spot 30 is shown in FIG. 1 . At this time, the surface parameters of the first off-axis reflector 20 and the second off-axis reflector 21 are: Compared with the traditional single circular spot 30 distribution light path, this design increases the optical path length. Compared with the dense spot 30 distribution, the off-axis reflector can be designed to change the spot 30 spacing of each circular ring, the number of circular rings and the number of spots 30 in a single circular ring, thereby achieving controllability of the optical path.

[0039] In this embodiment, the second off-axis reflector 21 is installed at the last light spot 30 of the small period, so as to control the number of light spots 30 of a single circular ring; in other embodiments, the second off-axis reflector 21 can also be installed at other positions, so as to control the number of light spots 30 of a single circular ring. In addition, the number of light spots 30 of a single circular ring is also related to the surface parameters of the primary reflector 10 and the secondary reflector 11, and the number of light spots 30 of a single circular ring can also be controlled by adjusting the surface parameters of the primary reflector 10 and the secondary reflector 11. This adjustment method is relatively existing and will not be described in detail here.

[0040] In addition, the primary reflector 10 , the secondary reflector 11 , the first off-axis reflector 20 and the second off-axis reflector 21 are all coated with a high-reflection film, and the surfaces are all coated with a protective layer to prevent the film system from being corroded by corrosive gases.

[0041] Reference Figure 4In the present application, the multi-reflection cavity also includes a thermal compensation structure, which includes a base 40, an optical housing 41, a thermal compensation rod 42 and a reflector seat 43. The base 40 is composed of a bottom plate 401 and a base 402 fixed on the bottom plate 401. Both ends of the optical housing 41 are installed on the base 402. The optical housing 41 and the base 402 are enclosed to form an optical absorption cavity. One end of the thermal compensation rod 42 is connected to the base 402 through a threaded clamp 421, and the other end extends along the length direction of the optical housing 41 and is fixed to the reflector seat 43. The reflector seat 43 is located in the optical absorption cavity, and the coaxially arranged primary reflector 10 and secondary reflector 11 are installed in the reflector seat 43; wherein, when the temperature in the optical absorption cavity changes, the length of the base 40 and the optical housing 41 increases or decreases, and the length of the thermal compensation rod 42 increases or decreases, so that the distance between the vertices of the primary reflector 10 and the secondary reflector 11 does not change.

[0042] Specifically, the base 40 and the optical housing 41 are made of 40Cr with an average thermal expansion coefficient of α1, and the thermal compensation rod 42 is made of SUS304 with an average thermal expansion coefficient of α2. When the overall temperature in the optical absorption cavity changes by T, the distance d between the vertices of the primary reflector 10 and the secondary reflector 11 satisfies: d=D+α1DT-d1-α2d1T-d2-α2d2T=D-d1-d2; Among them, α1 is the average thermal expansion coefficient of the base 40 and the optical housing 41, α2 is the average thermal expansion coefficient of the thermal compensation rod 42, D is the length of both ends of the optical housing 41, d1 is the distance between one end of the optical housing 41 and the vertex of the primary reflector 10, d2 is the distance between the other end of the optical housing 41 and the vertex of the secondary reflector 11, and T is the temperature change value in the optical absorption cavity. In this way, the influence of temperature change on the optical path can be effectively reduced and the measurement accuracy can be improved.

[0043] In addition, a light hole 422 is formed on the thermal compensation rod 42 which is closer to the laser light source, and the light beam can enter the optical absorption cavity through the light hole 422. The light hole 422 is sealed by a sapphire wedge protection window, which reduces interference noise while ensuring its airtightness and light transmittance.

[0044] When the temperature changes, due to the inconsistency of the thermal expansion coefficients of the structure and the reflector, temperature stress will be generated on the reflector, causing the surface shape of the reflector to change. The change in surface shape may affect the divergence angle and angle vector of the reflected light beam, causing a change in the optical path or an increase in noise.

[0045] Reference Figure 4 and Figure 5In order to solve this technical problem, the reflector base 43 includes a flexible mirror base 431 arranged in an annular shape, and the inner wall of the flexible mirror base 431 is provided with a clamping portion 432 for clamping the primary reflector 10 or the secondary reflector 11, and the side wall of the flexible mirror base 431 relative to the clamping portion 432 is provided with a deformation hole 433, and the deformation hole 433 penetrates the side wall of the flexible mirror base 431 along the axial direction of the flexible mirror base 431. The three-point clamping flexible design is adopted, and when the temperature of the structure changes, the deformation caused by its temperature stress will be concentrated and released to the deformation hole 433, reducing the impact on the reflector, thereby improving the stability of the optical path. Optionally, the material of the flexible mirror base 431 can be selected from a polymer material with high elasticity and high temperature resistance, such as polyimide or silicone rubber, to ensure that it can still maintain good flexibility and stability at high temperatures.

[0046] Reference Figure 6 The multi-reflector cavity further includes a laser collimation system 50, an incident adjustment reflector 51, an exit adjustment reflector 52, and a detector assembly 53. After being collimated by the laser collimation system 50, the light beam is incident on the incident adjustment reflector 51, the incident adjustment reflector 51 adjusts the angle of the incident light so that the incident light enters the incident hole 101 at a certain angle, and the exit adjustment reflector 52 adjusts the angle of the exit light so that the exit light is reflected at a certain angle into the detector assembly 53, and the detector assembly 53 collects the optical signal.

[0047] Optionally, the laser alignment system 50 may use a high-precision fiber coupler or lens group to ensure the collimation and stability of the light beam.

[0048] Reference Figure 6 and Figure 7 Optionally, the multi-reflection cavity also includes a reflector adjustment cavity 60 installed at one end of the base 40, and an incident light three-dimensional adjustment frame 61 and an outgoing light three-dimensional adjustment frame 62 are installed in the reflector adjustment cavity 60. The incident light adjustment reflector 51 is installed on the incident light three-dimensional adjustment frame 61, and the outgoing light adjustment reflector 52 is installed on the outgoing light three-dimensional adjustment frame 62. The incident light three-dimensional adjustment frame 61 is used to adjust the angle of light incident into the optical absorption cavity, and the outgoing light three-dimensional adjustment frame 62 is used to adjust the angle of the outgoing light in the optical absorption cavity.

[0049] Specifically, by adjusting the three-dimensional adjustment frame, the light beam can pass through the two small holes of the double-aperture diaphragm installed at a specific position, which indicates that the angle adjustment is correct; then remove the double-aperture diaphragm, and fine-tune the incident light three-dimensional adjustment frame 61, so that the light beam can pass through the middle area of ​​the exit adjustment reflector 52. At this time, adjust the exit light three-dimensional adjustment frame 62, so that the light beam can be incident on the detector assembly 53. The three-dimensional adjustment frame is adjusted by screws and springs. After the adjustment is completed, it is fixed by the top screw on the side to prevent the angle from changing due to aging of the thread or spring during operation, which affects the stability of the optical system.

[0050] In addition, a sealing cover 63 is installed at the end of the reflector adjustment cavity 60, and a cavity sealing ring 64 is provided between the sealing cover 63 and the reflector adjustment cavity 60, and the cavity sealing ring 64 is used to prevent water vapor from entering the reflector adjustment cavity 60 and affecting the use of the optical device. In addition, each component is installed by screws, and a sealing ring is designed at the contact part of each component to prevent the exchange of air or water vapor inside and outside the cavity during use, thereby affecting the measurement results.

[0051] At the same time, the optical housing 41 is provided with a gas inlet connector 411 and a gas outlet connector 412, respectively, and the gas is introduced into and out of the optical absorption cavity by using the gas inlet connector 411 and the gas outlet connector 412, so as to detect the gas content. In addition, a temperature and pressure transmitter (not shown in the figure) is provided in the optical absorption cavity, which can detect the temperature and pressure in the optical absorption cavity in real time, and feed back to the data processing end, so as to compensate the measured data in real time, thereby improving the detection accuracy.

[0052] The present application solution can realize multiple concentric rings by partially replacing the reflector with an off-axis aspheric reflector. By replacing different off-axis aspheric reflectors, the number and radius of the rings can be controlled. By replacing the off-axis aspheric reflectors at different positions, the number of light spots 30 of a single ring can be controlled. Through design and optimization, the number and position of the light spots 30 can be independently selected to achieve different optical path requirements, thereby improving the surface utilization of the reflector.

[0053] Example 2 This embodiment also provides a light spot control method, comprising the following steps: S1. Provide a pair of coaxially oppositely arranged primary reflector 10 and secondary reflector 11, replace a local area of ​​the primary reflector 10 with a first off-axis reflector 20, and replace a local area of ​​the secondary reflector 11 with a second off-axis reflector 21.

[0054] S2. An incident hole 101 or an exit hole 102 is opened on the primary reflector 10 or the secondary reflector 11, so that the light beam is incident from the incident hole 101, and the primary reflector 10 and the secondary reflector 11 are used to reflect the light beam back and forth to form a plurality of light spots 30 on the primary reflector 10 and the secondary reflector 11, and concentric rings 31 of the same level are formed between the plurality of light spots 30.

[0055] In this embodiment, both the incident hole 101 and the exit hole 102 are formed on the primary reflector 10 , and the concentric rings 31 are circular rings. The concentric rings 31 of the same level refer to circular rings with the same radius.

[0056] S3. Use the second off-axis reflector 21 to reflect the light beam in the primary concentric ring 31 to the secondary concentric ring 31. Use the first off-axis reflector 20 to receive the light beam reflected from the second off-axis reflector 21 and reflect the light beam to the secondary concentric ring 31 of the secondary reflector 11, so that the light beam forms a multi-stage concentric ring 31 after multiple reflections and is emitted from the exit hole 102.

[0057] Wherein, step S3 also comprises the following steps: S31 , constructing a transmission matrix for transforming the light beam from the incident hole 101 to the exit hole 102 .

[0058] Specifically, the constructed transmission matrix is: The specific construction method has been described above and will not be elaborated here.

[0059] S32, adjusting the surface parameters of the first off-axis reflector 20 and the second off-axis reflector 21 in the transmission matrix.

[0060] Specifically, the adjusted parameters are: R is the curvature radius of the off-axis reflector; K is the cone coefficient of the off-axis reflector; a4, a6, a8, and a10 are the even-order coefficients of the off-axis reflector respectively.

[0061] S33 , obtaining the required spacing between adjacent concentric rings 31 , the number of concentric rings 31 , and the number of light spots 30 of a single concentric ring 31 .

[0062] Specifically, by adjusting the surface parameters of the first off-axis reflector 20 and the second off-axis reflector 21 , the required spacing t of the light spots 30 of different circular rings and the number m of the circular rings as well as the number n of the light spots 30 of a single circular ring can be obtained.

[0063] For example, the surface parameters of the first off-axis reflector 20 and the second off-axis reflector 21 are: At this time, m=6, n=23, t=3mm.

[0064] For example, the surface parameters of the first off-axis reflector 20 and the second off-axis reflector 21 are: At this time, m=7, n=23, t=3 mm.

[0065] Therefore, by replacing different off-axis aspheric reflectors, the number and radius of the rings and the number of light spots 30 of a single ring can be controlled.

[0066] Meanwhile, step S3 also includes the following steps: S34, adjusting the relative positions of the first off-axis reflector 20 and the second off-axis reflector 21 to obtain the required number n of light spots 30 of the single concentric rings 31.

[0067] By replacing the off-axis aspheric mirror at different positions, the number of spots of a single ring can be controlled.

[0068] In summary, through design and optimization, the number and position of the light spot 30 can be independently selected to achieve different optical path requirements and improve the surface utilization of the reflector. The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. An athermalized dense multi-reversal cavity based on off-axis mirrors, characterized in that: The invention comprises a primary reflector (10) and a secondary reflector (11) which are coaxially arranged opposite to each other, wherein a first off-axis reflector (20) is nested in a local area of ​​the primary reflector (10), and a second off-axis reflector (21) is nested in a local area of ​​the secondary reflector (11), and an entrance hole (101) or an exit hole (102) is provided on the primary reflector (10) or the secondary reflector (11); The light beam is incident from an incident hole (101), and is reflected back and forth between a primary reflector (10) and a secondary reflector (11) to form a plurality of light spots (30) on the primary reflector (10) and the secondary reflector (11), and concentric rings (31) of the same level are formed between the plurality of light spots (30); the second off-axis reflector (21) is capable of reflecting the light beam in the primary concentric ring (31) to the secondary concentric ring (31); the first off-axis reflector (20) receives the light beam reflected from the second off-axis reflector (21) and reflects the light beam to the secondary concentric ring (31) of the secondary reflector (11); the light beam forms a plurality of concentric rings (31) after multiple reflections, and is emitted from an exit hole (102).

2. The athermalized dense multi-reversal cavity based on off-axis mirrors according to claim 1, characterized in that: The surface parameters of the first off-axis reflector (20) and the second off-axis reflector (21) are adjustable so as to be able to adjust the number and radius of the concentric rings (31) and the number of light spots (30) of a single concentric ring (31).

3. The athermalized intensive multi-reversal cavity based on off-axis mirrors according to claim 1 or 2, characterized in that: The relative positions of the first off-axis reflector (20) and the second off-axis reflector (21) are adjustable so as to be able to adjust the number of light spots (30) of a single concentric ring (31).

4. The athermalized dense multi-reversal cavity based on off-axis mirrors according to claim 1, characterized in that: The multi-reflection cavity further comprises a thermal compensation structure, which comprises a base (40), an optical housing (41), a thermal compensation rod (42) and a reflector seat (43); both ends of the optical housing (41) are mounted on the base (40); the optical housing (41) and the base (40) together form an optical absorption cavity; one end of the thermal compensation rod (42) is connected to the base (40); the other end extends along the length direction of the optical housing (41) and is fixed to the reflector seat (43); the reflector seat (43) is located in the optical absorption cavity; the primary reflector (10) and the secondary reflector (11) which are coaxially arranged opposite to each other are mounted in the reflector seat (43); wherein when the temperature in the optical absorption cavity changes, the length of the base (40) and the optical housing (41) increases or decreases, and the length of the thermal compensation rod (42) increases or decreases, so that the distance between the vertices of the primary reflector (10) and the secondary reflector (11) does not change.

5. The athermalized dense multi-reversal cavity based on off-axis mirrors according to claim 4, characterized in that: The distance d between the vertices of the primary reflector (10) and the secondary reflector (11) satisfies: d=D+α1DT-d1-α2d1T-d2-α2d2T=D-d1-d2; α1 is the average thermal expansion coefficient of the base (40) and the optical housing (41), α2 is the average thermal expansion coefficient of the thermal compensation rod (42), D is the length of the two ends of the optical housing (41), d1 is the distance between one end of the optical housing and the vertex of the primary reflector (10), d2 is the distance between the other end of the optical housing (41) and the vertex of the secondary reflector (11), and T is the temperature change value in the optical absorption cavity.

6. The athermalized dense multi-reversal cavity based on off-axis mirrors according to claim 4, characterized in that: The reflector seat (43) comprises a flexible mirror seat (431) arranged in an annular shape, the inner wall of the flexible mirror seat (431) is provided with a clamping portion (432) for clamping a primary reflector (10) or a secondary reflector (11), and a deformation hole (433) is provided on the side wall of the flexible mirror seat (431) relative to the clamping portion (432), and the deformation hole (433) penetrates the side wall of the flexible mirror seat (431) along the axial direction of the flexible mirror seat (431).

7. The athermalized dense multi-reversal cavity based on off-axis mirrors according to claim 1, characterized in that: The multi-reflection cavity further comprises a laser collimation system (50), an incident adjustment reflector (51), an exit adjustment reflector (52), and a detector assembly (53); the light beam is collimated by the laser collimation system (50) and then incident on the incident adjustment reflector (51); the incident adjustment reflector (51) adjusts the angle of the incident light so that the incident light is incident from the incident hole (101) at a certain angle; the exit adjustment reflector (52) adjusts the angle of the exit light so that the exit light is reflected at a certain angle into the detector assembly (53); and the detector assembly (53) collects the optical signal.

8. A light spot control method, characterized in that: The following steps are involved: A pair of coaxially oppositely arranged primary reflectors (10) and secondary reflectors (11) are provided; a local area of ​​the primary reflector (10) is replaced with a first off-axis reflector (20); a local area of ​​the secondary reflector (11) is replaced with a second off-axis reflector (21); an incident hole (101) or an exit hole (102) is provided on the primary reflector (10) or the secondary reflector (11); a light beam is incident from the incident hole (101); the primary reflector (10) and the secondary reflector (11) are used to reflect the light beam back and forth to generate an incident light beam between the primary reflector (10) and the secondary reflector (11); A plurality of light spots (30) are formed on the reflector (11), and concentric rings (31) of the same level are formed between the plurality of light spots (30); the second off-axis reflector (21) is used to reflect the light beam in the first-level concentric ring (31) to the second-level concentric ring (31); the first off-axis reflector (20) is used to receive the light beam reflected from the second off-axis reflector (21) and reflect the light beam to the second-level concentric ring (31) of the secondary reflector (11), so that the light beam forms multiple levels of concentric rings (31) after multiple reflections and is emitted from an exit hole (102).

9. The light spot control method according to claim 8, characterized in that: include: Constructing a transmission matrix for transforming a light beam from an incident hole (101) to an exit hole (102); Adjusting the surface parameters of a first off-axis reflector (20) and a second off-axis reflector (21) in the transmission matrix; The required spacing between adjacent concentric rings (31), the number of concentric rings (31) and the number of light spots (30) of a single concentric ring (31) are obtained.

10. The light spot control method according to claim 8 or 9, characterized in that: include: The relative positions of the first off-axis reflector (20) and the second off-axis reflector (21) are adjusted to obtain the required number of light spots (30) of single concentric rings (31).

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