A symmetrical optical cavity for long optical path infrared gas detection

Abstract

The embodiment of the present invention discloses a symmetrical long optical path infrared gas detection optical cavity, comprising: a first reflecting surface, a second reflecting surface, an infrared light source, an infrared detector and a top plane mirror, wherein: the first reflecting surface comprises a first parabolic reflector, a first corner plane mirror and a first optical path extension plane mirror, the first parabolic reflector is used to collimate the diffuse infrared light beam emitted by the infrared light source, and reflect the collimated infrared light beam to the first corner plane mirror; the second parabolic reflector, the second corner plane mirror and the second optical path extension plane mirror in the second reflecting surface are symmetrical with the first parabolic reflector, the first corner plane mirror and the first optical path extension plane mirror based on the optical cavity symmetry axis, and the center of the infrared detector is placed at the focus of the second parabolic reflector. The symmetrical long optical path infrared gas detection optical cavity is a small volume, long optical path and extendable optical path optical cavity, which can improve the gas detection accuracy.

Description

Technical Field

[0001] The invention relates to the field of optical technology, and in particular to a long optical path infrared gas detection optical cavity with a symmetrical structure. Background Art

[0002] In order to accurately detect the concentration of gases such as acetaldehyde, hydrogen sulfide, and carbon dioxide in a specific space, non-dispersive infrared gas detectors are widely used in industries and agriculture. For polar gas molecules composed of two or more atoms, due to the absorption of infrared radiation by rotation and vibration transitions, infrared gas detectors can calculate the concentration of the corresponding gas by measuring the change in light intensity at a specific absorption wavelength. In order to make the detection results accurate and reliable, the infrared light needs to be reflected multiple times in the optical cavity filled with gas to increase the absorption path so that the infrared light is fully absorbed by the gas molecules. Therefore, a long absorption path makes it easy to achieve high detection accuracy, such as sub-ppm or ppb level accuracy.

[0003] The existing long optical path optical cavities mainly include reflective Herriot cavity and White cavity. Both optical cavities can obtain an optical path of several meters to tens of meters, but they are suitable for laser light sources with low divergence angles. In addition, the surface processing accuracy of this long optical path optical cavity is high and the cost is expensive. For low-cost gas concentration detection applications, it is more appropriate to use an inexpensive thermal light source instead of an expensive laser source. Due to the incoherent characteristics of the thermal light source, its emission angle is large. In order to achieve a long optical path, it is necessary to add a collimating optical element to the optical cavity to constrain the divergence angle of the light beam. If a refractive lens is used for collimation, a large loss will be introduced and the collimation effect is limited. Chinese patent CN109406404A discloses a solution for increasing the optical path by staggering an array of corner cube prisms, but the processing of the corner cube prism array is relatively complicated. Chinese patent CN108169170A discloses a solution of using two plane mirrors to reflect light multiple times, in order to maximize the optical path within a limited volume. However, this optical path design makes the volume of the optical cavity only used once, the optical efficiency is low, and the volume is large. Summary of the invention

[0004] An embodiment of the present invention provides a symmetrical long optical path infrared gas detection optical cavity, which is a reusable optical cavity with a small volume and a long optical path, and can improve the gas detection accuracy.

[0005] The present invention provides a symmetrical long optical path infrared gas detection optical cavity, comprising:

[0006] A first reflecting surface, a second reflecting surface, an infrared light source, an infrared detector and a top plane mirror, wherein the first reflecting surface and the second reflecting surface are symmetrical based on the symmetry axis of the optical cavity, wherein:

[0007] The first reflecting surface includes a first parabolic reflector, a first corner plane mirror and a first optical path extension plane mirror, the equivalent point source of the infrared light source is placed at the focus of the first parabolic reflector, the first parabolic reflector is used to collimate the diffuse infrared light beam emitted by the infrared light source, and reflect the collimated infrared light beam to the first corner plane mirror, the first corner plane mirror is connected to the first optical path extension plane mirror, and the angle between the first corner plane mirror and the symmetry axis of the optical cavity is an acute angle, and the first optical path extension plane mirror is parallel to the symmetry axis of the optical cavity;

[0008] The second reflecting surface includes a second parabolic reflector, a second corner plane mirror and a second optical path extension plane mirror, the top plane mirror is perpendicular to the symmetry axis of the optical cavity, one end of the top plane mirror is connected to the first optical path extension plane mirror, and the other end of the top plane mirror is connected to the second optical path extension plane mirror;

[0009] The second parabolic reflector, the second corner plane mirror and the second optical path extension plane mirror are respectively symmetrical with the first parabolic reflector, the first corner plane mirror and the first optical path extension plane mirror based on the optical cavity symmetry axis, and the center of the infrared detector is placed at the focus of the second parabolic reflector.

[0010] In some embodiments, the infrared light source has a beam divergence full angle less than or equal to 30 degrees.

[0011] In some embodiments, the focal lengths of the first parabolic reflector and the second parabolic reflector are both 1.4 cm.

[0012] In some embodiments, the curvature radius of the first parabolic reflector and the second parabolic reflector are both 2.8 cm.

[0013] In some embodiments, the angle between the first parabolic reflector and the symmetry axis of the optical cavity is 60 degrees, and the angle between the second parabolic reflector and the symmetry axis of the optical cavity is negative 60 degrees.

[0014] In some embodiments, the angle between the first corner plane mirror and the symmetry axis of the optical cavity is 25 degrees, and the angle between the second corner plane mirror and the symmetry axis of the optical cavity is negative 25 degrees.

[0015] In some embodiments, the symmetrically structured long optical path infrared gas detection optical cavity further comprises a chamber protection cover, and the chamber protection cover is disposed outside the symmetrically structured long optical path infrared gas detection optical cavity.

[0016] In some embodiments, the chamber protection cover is a sliding cover.

[0017] In some embodiments, the chamber protection cover is provided with a through hole.

[0018] In some embodiments, the first parabolic reflector, the first corner plane mirror, the first optical path extension plane mirror, the second parabolic reflector, the second corner plane mirror and the second optical path extension plane mirror are all coated with metal.

[0019] An embodiment of the present invention provides a symmetrically structured long-path infrared gas detection optical cavity, comprising: a first reflecting surface, a second reflecting surface, an infrared light source, an infrared detector, and a top plane mirror, wherein the first reflecting surface and the second reflecting surface are symmetrical based on the optical cavity symmetry axis, wherein: the first reflecting surface comprises a first parabolic reflector, a first corner plane mirror, and a first optical path extension plane mirror, the equivalent point source of the infrared light source is placed at the focus of the first parabolic reflector, the first parabolic reflector is used to collimate the diffuse infrared light beam emitted by the infrared light source, and reflect the collimated infrared light beam to the first corner plane mirror, the first corner plane mirror is connected to the first optical path extension plane mirror, and the first corner plane mirror is connected to the light path extension plane mirror. The angle of the optical cavity symmetry axis is an acute angle, the first optical path extension plane mirror is parallel to the optical cavity symmetry axis; the second reflective surface includes a second parabolic reflector, a second corner plane mirror and a second optical path extension plane mirror, the top plane mirror is perpendicular to the optical cavity symmetry axis, one end of the top plane mirror is connected to the first optical path extension plane mirror, and the other end of the top plane mirror is connected to the second optical path extension plane mirror; the second parabolic reflector, the second corner plane mirror and the second optical path extension plane mirror are symmetrical with the first parabolic reflector, the first corner plane mirror and the first optical path extension plane mirror based on the optical cavity symmetry axis, and the center of the infrared detector is placed at the focus of the second parabolic reflector. The long optical path infrared gas detection optical cavity of this symmetrical structure is a small-volume, long optical path and extendable optical path optical cavity, which can improve the gas detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0021] Figure 1 It is a schematic structural diagram of an embodiment of a symmetrical long optical path infrared gas detection optical cavity provided in an embodiment of the present invention;

[0022] Figure 2ais a top view of a chamber protection cover provided by an embodiment of the present invention;

[0023] Figure 2b is a three-dimensional diagram of a chamber protection cover provided by an embodiment of the present invention;

[0024] Figure 3a 1 is a front view of a symmetrical long optical path infrared gas detection optical cavity provided by an embodiment of the present invention;

[0025] Figure 3b It is a left view of the symmetrical long optical path infrared gas detection optical cavity provided by an embodiment of the present invention;

[0026] Figure 3c It is a right view of the symmetrical long optical path infrared gas detection optical cavity provided by an embodiment of the present invention;

[0027] Figure 4a is an energy distribution diagram provided by an embodiment of the present invention;

[0028] Figure 4b is another energy distribution diagram provided by an embodiment of the present invention;

[0029] Figure 4c is another energy distribution diagram provided by an embodiment of the present invention;

[0030] Figure 4d is another energy distribution diagram provided by an embodiment of the present invention;

[0031] Figure 5 is a simulation modeling diagram provided by an embodiment of the present invention;

[0032] Figure 6 It is a schematic diagram of an application scenario provided by an embodiment of the present invention. Specific embodiments

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0034] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0035] In the present invention, the word "exemplary" is used to mean "used as an example, illustration or description". Any embodiment described as "exemplary" in the present invention is not necessarily to be construed as being preferred or advantageous over other embodiments. The following description is given to enable any technician in the field to implement and use the present invention. In the following description, details are listed for the purpose of explanation. It should be understood that a person of ordinary skill in the art can recognize that the present invention can be implemented without using these specific details. In other instances, well-known structures and processes will not be elaborated in detail to avoid obscuring the description of the present invention with unnecessary details. Therefore, the present invention is not intended to be limited to the embodiments shown, but is consistent with the widest scope consistent with the principles and features disclosed in the present invention.

[0036] See also Figure 1 , Figure 1 It is a schematic structural diagram of an embodiment of a symmetrical long optical path infrared gas detection optical cavity provided in an embodiment of the present invention.

[0037] The embodiment of the present invention provides a symmetrical long-path infrared gas detection optical cavity, which includes a first reflecting surface, a second reflecting surface, an infrared light source 30, an infrared detector 40, and a top plane mirror 50, wherein the first reflecting surface and the second reflecting surface are symmetrical based on the optical cavity symmetry axis. They are described in detail below.

[0038] The first reflecting surface includes a first parabolic reflector 11, a first corner plane mirror 12 and a first optical path extension plane mirror 13. The equivalent point source of the infrared light source 30 is placed at the focus of the first parabolic reflector 11. The first parabolic reflector 11 is used to collimate the diffuse infrared light beam emitted by the infrared light source 30 and reflect the collimated infrared light beam to the first corner plane mirror 12. The first corner plane mirror 12 is connected to the first optical path extension plane mirror 13, and the angle between the first corner plane mirror 12 and the symmetry axis of the optical cavity is an acute angle. The first optical path extension plane mirror 13 is parallel to the symmetry axis of the optical cavity.

[0039] The second reflecting surface includes a second parabolic reflector 21, a second corner plane mirror 22 and a second optical path extension plane mirror 23, a top plane mirror 50 is perpendicular to the symmetry axis of the optical cavity, one end of the top plane mirror 50 is connected to the first optical path extension plane mirror 13, and the other end of the top plane mirror 50 is connected to the second optical path extension plane mirror 23;

[0040] The second parabolic reflector 21 , the second corner plane mirror 22 and the second optical path extension plane mirror 23 are symmetrical with the first parabolic reflector 11 , the first corner plane mirror 12 and the first optical path extension plane mirror 13 based on the optical cavity symmetry axis, and the center of the infrared detector 40 is placed at the focus of the second parabolic reflector 21 .

[0041] In some embodiments, the symmetrical long optical path infrared gas detection optical cavity provided in this embodiment is a semi-closed cavity.

[0042] In some embodiments, the full angle of beam divergence of the infrared light source 30 is less than or equal to 30 degrees.

[0043] In some embodiments, the focal lengths of the first parabolic reflector 11 and the second parabolic reflector 21 are both 1.4 cm.

[0044] In some embodiments, the curvature radius of the first parabolic reflector 11 and the second parabolic reflector 21 are both 2.8 cm.

[0045] In some embodiments, the angle between the first parabolic reflector 11 and the optical cavity symmetry axis is 60 degrees (60 degrees clockwise of the optical cavity symmetry axis), and the angle between the second parabolic reflector 21 and the optical cavity symmetry axis is negative 60 degrees (60 degrees counterclockwise of the optical cavity symmetry axis).

[0046] In some embodiments, the angle between the first corner plane mirror 12 and the optical cavity symmetry axis is 25 degrees (25 degrees clockwise of the optical cavity symmetry axis), and the angle between the second corner plane mirror 22 and the optical cavity symmetry axis is negative 25 degrees (25 degrees counterclockwise of the optical cavity symmetry axis).

[0047] In some embodiments, the symmetrical long optical path infrared gas detection optical cavity further includes a chamber protection cover 60, and the chamber protection cover 60 is arranged outside the symmetrical long optical path infrared gas detection optical cavity. Figure 2a FIG. 6 is a top view of the chamber protection cover 60 in this embodiment, which includes a protrusion 61, a protrusion 62 and a through hole 63. Figure 2b FIG. 6 is a three-dimensional diagram of the chamber protection cover 60 in this embodiment. The chamber protection cover 60 is installed on both sides of the optical cavity.

[0048] like Figure 3a , Figure 3b as well as Figure 3c As shown, Figure 3a A front view of a symmetrical long optical path infrared gas detection optical cavity provided in this embodiment, Figure 3b A left view of the symmetrical long optical path infrared gas detection optical cavity provided in this embodiment, Figure 3c A right side view of the symmetrical long optical path infrared gas detection optical cavity provided in this embodiment,

[0049] In the actual design of the optical cavity model, in order to meet the requirements of actual production and application, the mirror surface of the optical cavity in this embodiment is thickened as a whole, and the various parts are connected to form a semi-enclosed structure as shown in FIG. 3( a ).

[0050] In actual applications, in order to prevent foreign particles in the air from entering the chamber and affecting the reflection effect of the mirror, a chamber protection cover 60 is designed. The chamber protection cover 60 includes a convex body 61, a convex body 62 and a through hole 63. In actual applications, a filter paper that can filter out foreign particles in the air is pasted on the upper part of the chamber protection cover 60. The chamber protection cover 60 is connected to the semi-closed cavity according to the corresponding rules of the groove 14 and the convex body 61, and the groove 15 and the convex body 62, and the gas enters the chamber from the through hole 63.

[0051] In practical applications, four fixing through holes are designed to fix the optical cavity on the PCB circuit board used in conjunction with it. Figure 3a Through hole 71, through hole 72, through hole 73 and through hole 74 in it.

[0052] In some embodiments, the chamber protection cover 60 is a sliding cover.

[0053] In some embodiments, the first parabolic reflector 11 , the first corner plane mirror 12 , the first optical path extension plane mirror 13 , the second parabolic reflector 21 , the second corner plane mirror 22 , and the second optical path extension plane mirror 23 are all coated with metal.

[0054] In order to further understand the long optical path infrared gas detection optical cavity of a symmetrical structure mentioned in the embodiment of the present invention, the optical path of the optical cavity is further described as follows:

[0055] The infrared light source 30 emits an infrared light beam, which irradiates the first parabolic reflector 11. The first parabolic reflector 11 collimates the infrared light beam and reflects the infrared light beam to the first corner plane mirror 12. The first corner plane mirror 12 deflects the parallel infrared light beam, reduces the angle between the parallel infrared light beam and the horizontal direction, and reflects the infrared light beam to the second optical path extension plane mirror 23. The infrared light beam is reciprocated between the first optical path extension plane mirror 13 and the second optical path extension plane mirror 23 placed in parallel. After multiple reflections (for example, 5 times), the infrared light beam is reflected to the top plane After being reflected by the top plane mirror 50 to the first optical path extension plane mirror 13, the infrared beam continues to reflect back and forth between the first optical path extension plane mirror 13 and the second optical path extension plane mirror 23, and the propagation path is symmetrical with the previous path along the optical cavity symmetry axis. After multiple reflections (for example, 5 times), the infrared beam is reflected to the second corner plane mirror 22, increasing the angle between the parallel infrared beam and the horizontal direction and reflecting the infrared beam to the second parabolic reflector 21, which focuses the infrared beam, and the focus is on the rectangular infrared detector 40. The specific parameters of the above optical path are designed using Zemax software.

[0056] The divergence half angle of the infrared light source is designed to be 15°, and the output power of the light source in the model is 1W. The focal length of the first parabolic reflector 11 is designed to be 14.14mm, and the focus is placed at the point source of the infrared light source 30. The curvature radius of the first parabolic reflector 11 is 28.28mm. Figure 1 The structure sequence in the figure is to design the first corner plane mirror 12, the first optical path extension plane mirror 13, the second parabolic reflector 21, the second corner plane mirror 22, the second optical path extension plane mirror 23, the top plane mirror 50, and the infrared detector 40. The center of the infrared detector 40 is placed at the focus of the second parabolic reflector 21. The specific structure of the optical path in the Zemax software is as follows: Figure 1 As shown, Figure 1 Where d is the distance between two adjacent reflection points of the light on the first optical path extension plane mirror 13 or the second optical path extension plane mirror 23. The energy at the first corner plane mirror 12, the second corner plane mirror 22 and the infrared detector 40, 5 mm to the right of the infrared light source 30, is as follows: Figure 4a , Figure 4b , Figure 4c as well as Figure 4d shown.

[0057] According to the energy distribution of the simulation output Figure 4a It can be seen that a circular spot with a radius of 1 mm is output 5 mm to the right of the infrared light source 30, and the energy is evenly distributed on the circle, and the total light energy power is 1 W. After being collimated by the parabolic reflector 1, we get Figure 4bThe circular spot has a radius of 5 mm, and the energy is evenly distributed on the circle. The total power of the light energy is 1W. After multiple reflections, the light beam is obtained at the second corner plane mirror 22. Figure 4c The nearly circular light spot shown in the figure has uniform energy distribution and a total light energy power of 0.99 W. Finally, the light beam is focused on the infrared detector 40 by the second parabolic reflector 21 to form a very small light spot. Figure 4d As shown in the figure, the total power of the light spot is 0.99W. The simulation shows that the energy transmission efficiency of the optical path reaches 99%.

[0058] See also Figure 5 , Figure 5 The Zemax simulation light path is modeled and then imported into Zemax again for light path simulation results. The volume parameters of the model are 95mm×92mm×30mm, the light path length is 870mm, and the light energy transmission efficiency reaches 99%.

[0059] In this embodiment, if the lengths of the first optical path extension plane mirror 13 and the second optical path extension plane mirror 23 are increased simultaneously by an integer multiple of d, the optical path can further be increased to the meter level.

[0060] See also Figure 6 , Figure 6 A schematic diagram of an application scenario of the symmetrical long optical path infrared gas detection optical cavity provided in this embodiment. Gas absorbs light of a specific wavelength from an infrared light source, and the light energy received by the infrared detector 40 can be used to measure the concentration of the gas.

[0061] In summary, an embodiment of the present invention provides a symmetrically structured long-path infrared gas detection optical cavity, comprising: a first reflecting surface, a second reflecting surface, an infrared light source, an infrared detector, and a top plane mirror, wherein the first reflecting surface and the second reflecting surface are symmetrical based on the optical cavity symmetry axis, wherein: the first reflecting surface comprises a first parabolic reflector, a first corner plane mirror, and a first optical path extension plane mirror, the equivalent point source of the infrared light source is placed at the focus of the first parabolic reflector, the first parabolic reflector is used to collimate the diffuse infrared light beam emitted by the infrared light source, and reflect the collimated infrared light beam to the first corner plane mirror, the first corner plane mirror is connected to the first optical path extension plane mirror, and the first corner plane mirror is connected to the first optical path extension plane mirror. The angle of the optical cavity symmetry axis is an acute angle, the first optical path extension plane mirror is parallel to the optical cavity symmetry axis; the second reflective surface includes a second parabolic reflector, a second corner plane mirror and a second optical path extension plane mirror, the top plane mirror is perpendicular to the optical cavity symmetry axis, one end of the top plane mirror is connected to the first optical path extension plane mirror, and the other end of the top plane mirror is connected to the second optical path extension plane mirror; the second parabolic reflector, the second corner plane mirror and the second optical path extension plane mirror are symmetrical with the first parabolic reflector, the first corner plane mirror and the first optical path extension plane mirror based on the optical cavity symmetry axis, and the center of the infrared detector is placed at the focus of the second parabolic reflector. The long optical path infrared gas detection optical cavity of this symmetrical structure is a small-sized, long optical path and extendable optical path optical cavity, which can improve the gas detection accuracy.

[0062] In practical applications, the infrared light beam is reflected multiple times by the first reflective surface and the second reflective surface in the entire optical path, and finally focused on the infrared detector. The collimation of the first parabolic reflector effectively prevents the diffusion of the light beam, and the second parabolic reflector focuses the parallel light rays at the focal point. The multiple reflections of the plane mirrors (the first corner plane mirror, the first optical path extension plane mirror, the second corner plane mirror, and the second optical path extension plane mirror) greatly increase the optical path of the light beam in a limited space. In addition, by increasing the length of the first optical path extension plane mirror and the second optical path extension plane mirror, the optical path can be further increased, so the present invention has the ability to expand the optical path. Due to the symmetrical structural characteristics of the optical cavity, the light beam doubles the optical path in the same propagation space, and the manufacturing difficulty of this symmetrical structure is relatively low.

[0063] The above is a detailed introduction to a symmetrically structured long-path infrared gas detection optical cavity provided in an embodiment of the present invention. Specific examples are used in this article to illustrate the principles and embodiments of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific embodiments and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A symmetrical long optical path infrared gas detection optical cavity, characterized in that: The symmetrical long optical path infrared gas detection optical cavity comprises: a first reflecting surface, a second reflecting surface, an infrared light source, an infrared detector and a top plane mirror, wherein the first reflecting surface and the second reflecting surface are symmetrical based on the optical cavity symmetry axis, wherein: The first reflecting surface includes a first parabolic reflector, a first corner plane mirror and a first optical path extension plane mirror, the equivalent point source of the infrared light source is placed at the focus of the first parabolic reflector, the first parabolic reflector is used to collimate the diffuse infrared light beam emitted by the infrared light source, and reflect the collimated infrared light beam to the first corner plane mirror, the first corner plane mirror is connected to the first optical path extension plane mirror, and the angle between the first corner plane mirror and the symmetry axis of the optical cavity is an acute angle, and the first optical path extension plane mirror is parallel to the symmetry axis of the optical cavity; The second reflecting surface includes a second parabolic reflector, a second corner plane mirror and a second optical path extension plane mirror, the top plane mirror is perpendicular to the symmetry axis of the optical cavity, one end of the top plane mirror is connected to the first optical path extension plane mirror, and the other end of the top plane mirror is connected to the second optical path extension plane mirror; The second parabolic reflector, the second corner plane mirror and the second optical path extension plane mirror are respectively symmetrical with the first parabolic reflector, the first corner plane mirror and the first optical path extension plane mirror based on the symmetry axis of the optical cavity, and the center of the infrared detector is placed at the focus of the second parabolic reflector; The full angle of beam divergence of the infrared light source is less than or equal to 30 degrees; The focal lengths of the first parabolic reflector and the second parabolic reflector are both 1.4 cm; The curvature radius of the first parabolic reflector and the second parabolic reflector are both 2.8 cm; The included angle between the first parabolic reflector and the symmetry axis of the optical cavity is 60 degrees, and the included angle between the second parabolic reflector and the symmetry axis of the optical cavity is negative 60 degrees; The included angle between the first corner plane mirror and the symmetry axis of the optical cavity is 25 degrees, and the included angle between the second corner plane mirror and the symmetry axis of the optical cavity is negative 25 degrees.

2. The symmetrical long optical path infrared gas detection optical cavity according to claim 1 is characterized in that: The symmetrically structured long optical path infrared gas detection optical cavity further comprises a chamber protection cover, and the chamber protection cover is arranged outside the symmetrically structured long optical path infrared gas detection optical cavity.

3. The symmetrical long optical path infrared gas detection optical cavity according to claim 2 is characterized in that: The chamber protection cover is a sliding cover.

4. The symmetrical long optical path infrared gas detection optical cavity according to claim 2 is characterized in that: The chamber protection cover is provided with a through hole.

5. The symmetrical long optical path infrared gas detection optical cavity according to any one of claims 1 to 4, characterized in that: The first parabolic reflector, the first corner plane mirror, the first optical path extension plane mirror, the second parabolic reflector, the second corner plane mirror and the second optical path extension plane mirror are all coated with metal.

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