A long optical path optical gas absorption cell and gas sensor

Abstract

The application discloses a long optical path optical gas absorption cell and a gas sensor. The long optical path optical gas absorption cell comprises a first concave mirror, a second concave mirror, an incident hole, an exit hole and an intermediate mirror. The reflecting surface of the first concave mirror and the reflecting surface of the second concave mirror are arranged in the same direction. The incident hole is arranged at a non-central position of the first concave mirror. The intermediate mirror, the first concave mirror and the second concave mirror form a reflecting cavity for guiding light between the reflecting surface of the first concave mirror and the reflecting surface of the second concave mirror. Incident light is incident from the incident hole at an angle that is not parallel to the main axis of the first concave mirror and is emitted from the exit hole after multiple reflections in the reflecting cavity. The optical gas absorption cell can realize a longer optical path under a limited gas cell volume, meet the monitoring requirement of low-concentration gas, has high lens utilization, simple structure, small size, is easy to process and effectively reduces the cost.

Description

Technical Field

[0001] This invention relates to the field of gas detection equipment technology, and in particular to a long optical path optical gas absorption cell and a gas sensor. Background Technology

[0002] Currently, tunable diode laser absorption spectroscopy (TDLAS) technology, with its advantages of no pretreatment required, high selectivity, fast response, high sensitivity, and high accuracy, has been widely applied in industrial and environmental monitoring. Especially in environmental monitoring, where the concentration of most harmful pollutants is very low, and the concentration of a particular gas is related to the optical path length of the laser in the gas and the signal intensity attenuated by gas absorption, designing a long-path gas absorption cell can effectively improve the detection accuracy of low-concentration gases.

[0003] Existing gas absorption cells typically need to be housed within a relatively small gas chamber, which severely limits the design of long-path absorption cells, especially for monitoring pollutants with concentrations in the ppm or even ppb range. This often requires achieving optical paths of tens to hundreds of meters within a limited volume. To address this, existing manufacturers typically use White cells and Herriott cells with multiple reflections. For example, Hanwei Technology proposed an optical path multiplier device and an optical path multiplier gas absorption cell in patent CN113484266B. By adding a multiplier mirror to a typical White cell optical structure, although this doubles the number of optical reflections and thus doubles the optical path, the two smaller sub-mirrors are difficult to adjust when actually adjusting the number of light reflections in the gas cell. Compared to the White cell, the Heriotte cell consists of only two spherical mirrors, making its optical system simpler and its optical path easier to adjust. However, the long-path Heriotte cell has low mirror utilization, especially under the condition of a limited volume air cell. It always encounters the problem of balancing the distance between the light spots on the mirrors and the requirement to form a long optical path of hundreds of meters. Summary of the Invention

[0004] The purpose of this invention is to provide a long optical path optical gas absorption cell and gas sensor in order to solve the problem that the high utilization rate of the optical absorption cell lens and the long optical path cannot be achieved simultaneously under the condition of limited volume in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A long-path optical gas absorption cell, comprising:

[0007] First concave reflecting mirror;

[0008] Second concave reflector;

[0009] The reflecting surfaces of the first concave mirror and the second concave mirror are arranged in the same direction, and the angle between the focal plane of the first concave mirror and the focal plane of the second concave mirror is α, where 0 < α ≤ 180°.

[0010] An entrance aperture is located off-center from the first concave reflector and is used to input light.

[0011] An output aperture is used to output light.

[0012] An intermediate reflector, together with the first concave reflector and the second concave reflector, forms a reflective cavity for guiding light between the reflective surfaces of the first and second concave reflectors.

[0013] The incident light enters through the entrance hole at an angle not parallel to the principal axis of the first concave mirror, and after multiple reflections within the reflective cavity, exits through the exit hole.

[0014] Furthermore, the radius of curvature of the first concave mirror is the same as that of the second concave mirror.

[0015] Furthermore, the emission port is located at a non-center position of the first concave reflector.

[0016] Furthermore, the exit hole coincides with the entrance hole.

[0017] Furthermore, the emission port is located at a non-center position of the second concave reflector.

[0018] Furthermore, both the first concave reflector and the second curved reflector are rectangular concave mirrors.

[0019] Furthermore, both the first concave reflector and the second curved reflector are circular concave mirrors.

[0020] Furthermore, the number of intermediate reflectors is 2N+1, where N≥0.

[0021] Furthermore, the intermediate reflecting mirror is a plane mirror.

[0022] Furthermore, the intermediate reflector includes two plane mirrors, the reflecting surfaces of the two plane mirrors are arranged facing each other and their principal axes are at 90°.

[0023] Furthermore, the intermediate reflector is a prism with an isosceles triangle cross-section and a vertices angle of 90°.

[0024] A gas sensor that uses the aforementioned long-path optical gas absorption cell.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention uses two co-directionally arranged non-coaxial concave mirrors in conjunction with an intermediate mirror to form a reflecting cavity. This not only achieves a longer optical path within a limited volume, meeting the monitoring needs of low-concentration (ppm or even ppb level) gases, but also features high lens utilization, simple structure, small size, and easy processing, effectively reducing costs. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the mirror system structure in Embodiment 1 of the present invention;

[0028] Figure 2 This is a schematic diagram of the mirror system structure in Embodiment 2 of the present invention;

[0029] Figure 3 This is a schematic diagram of the mirror system structure in Embodiment 3 of the present invention;

[0030] Figure 4 This is a schematic diagram of the mirror system structure in Embodiment 4 of the present invention;

[0031] Figure 5 This is a schematic diagram of the mirror system structure in Embodiment 5 of the present invention;

[0032] Labeling instructions: 1. First concave mirror, 11. Entrance aperture, 2. Second concave mirror, 3. Plane mirror, 4. Prism. Detailed Implementation

[0033] The invention will now be further described with reference to the accompanying drawings.

[0034] Please see Figure 1-5 As shown, a long optical path optical gas absorption cell includes a first concave mirror 1, a second concave mirror 2, an entrance aperture 11, an exit aperture, and an intermediate mirror.

[0035] The reflecting surfaces of the first concave mirror 1 and the second concave mirror 2 are arranged in the same direction, and the angle between the focal plane of the first concave mirror 1 and the focal plane of the second concave mirror 2 is α, where 0 < α ≤ 180°.

[0036] Preferably, the radius of curvature of the first concave mirror 1 is the same as the radius of curvature of the second concave mirror 2.

[0037] The entrance aperture 11 is located off-center from the first concave reflector 1 and is used to input light.

[0038] The exit aperture is located off-center of the first concave reflector 1 and coincides with the entrance aperture 11, or the exit aperture is located off-center of the second concave reflector 2, for outputting light.

[0039] The intermediate reflector, together with the first concave reflector 1 and the second concave reflector 2, forms a reflective cavity, which is used to guide light between the reflective surface of the first concave reflector 1 and the reflective surface of the second concave reflector 2.

[0040] The incident light enters through the entrance hole 11 at an angle not parallel to the principal axis of the first concave mirror 1, and after multiple reflections within the reflecting cavity, exits through the exit hole.

[0041] The following are examples illustrating different embodiments of the present invention.

[0042] Example 1:

[0043] Please see Figure 1 As shown, based on the above technical solution, the specific implementation is as follows:

[0044] Both the first concave mirror 1 and the second curved mirror 2 are rectangular concave mirrors.

[0045] The reflecting surface of the first concave mirror 1 is arranged in the same direction as the reflecting surface of the second concave mirror 2.

[0046] Furthermore, the included angle α between the focal planes of the two concave mirrors is 120°, and the number of intermediate reflectors is 2N+1, where N≥0. In this embodiment, the number of intermediate reflectors is 1.

[0047] Specifically, the middle reflecting mirror is a plane mirror 3, and the two concave mirrors are symmetrical about the principal axis of the plane mirror 3.

[0048] Example 2:

[0049] Please see Figure 2 As shown, based on the above technical solution, the specific implementation is as follows:

[0050] Both the first concave mirror 1 and the second curved mirror 2 are rectangular concave mirrors.

[0051] The reflecting surfaces of the first concave mirror 1 and the second concave mirror 2 are arranged in the same direction, and the included angle α between the focal planes of the two concave mirrors is 180°. The number of intermediate mirrors is 2N+1, where N≥0. In this embodiment, the number of intermediate mirrors is 1.

[0052] Specifically, the intermediate reflector includes two plane mirrors 3, with the reflecting surfaces of the two plane mirrors 3 facing each other and their principal axes at 90°.

[0053] Example 3:

[0054] Please see Figure 3 As shown, based on the above technical solution, the specific implementation is as follows:

[0055] Both the first concave mirror 1 and the second curved mirror 2 are rectangular concave mirrors.

[0056] The reflecting surfaces of the first concave mirror 1 and the second concave mirror 2 are arranged in the same direction, and the included angle α between the focal planes of the two concave mirrors is 180°. The number of intermediate mirrors is 2N+1, where N≥0. In this embodiment, the number of intermediate mirrors is 1.

[0057] Specifically, the middle reflector is prism 4, whose cross-section is an isosceles triangle with a vertex angle of 90°.

[0058] Example 4:

[0059] Please see Figure 4 As shown, based on the above technical solution, the specific implementation is as follows:

[0060] Both the first concave mirror 1 and the second curved mirror 2 are rectangular concave mirrors.

[0061] The reflecting surfaces of the first concave mirror 1 and the second concave mirror 2 are aligned in the same direction, and the included angle α between the focal planes of the two concave mirrors is 180°. The number of intermediate mirrors is 2N+1, where N≥0. In this embodiment, the number of intermediate mirrors is 3.

[0062] Specifically, the intermediate reflector includes two plane mirrors 3, with the reflecting surfaces of the two plane mirrors 3 facing each other and their principal axes at 90°.

[0063] Example 5:

[0064] Please see Figure 5 As shown, based on the above technical solution, the specific implementation is as follows:

[0065] Both the first concave reflector 1 and the second curved reflector 2 are circular concave mirrors. Generally, the entrance aperture 11 is located at the edge of the first concave reflector 1, and if the exit aperture is located on the second concave reflector 2, it is also located at the edge of the second concave reflector 2.

[0066] The reflecting surfaces of the first concave mirror 1 and the second concave mirror 2 are arranged in the same direction, and the included angle α between the focal planes of the two concave mirrors is 180°. The number of intermediate mirrors is 2N+1, where N≥0. In this embodiment, the number of intermediate mirrors is 1.

[0067] Specifically, the intermediate reflector includes two plane mirrors 3, with the reflecting surfaces of the two plane mirrors 3 facing each other and their principal axes at 90°.

[0068] The long optical path gas absorption cell consists of a mirror system composed of two rectangular concave mirrors and 2N+1 (N≥0) intermediate mirrors. The incident light enters the mirror system at a certain angle and exits after multiple reflections (the incident light forms elliptical light spots on different mirror surfaces).

[0069] According to the above design, this long-path optical gas absorption cell can not only achieve an optical path of tens or hundreds of meters within a relatively short length, but also effectively reduce the cost of the entire gas absorption cell due to its high lens utilization, simple structure, small size, and ease of processing. It is very suitable for gas analyzers that detect low-concentration gases.

[0070] The present invention also provides a gas sensor that uses the above-described long-path optical gas absorption cell.

[0071] In summary, this invention uses two co-directionally arranged non-coaxial concave mirrors in conjunction with an intermediate mirror to form a reflecting cavity. This not only enables a longer optical path within a limited volume, meeting the monitoring requirements for low-concentration (ppm or even ppb) gases, but also features a simple lens structure, small size, and easy processing, effectively reducing costs.

[0072] Of course, the above are only preferred embodiments of the present invention and are not intended to limit the scope of application of the present invention. Therefore, any equivalent changes made to the principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A long-path optical gas absorption cell, characterized in that, include: First concave reflecting mirror; Second concave reflector; The reflecting surfaces of the first concave mirror and the second concave mirror are arranged in the same direction, and the angle between the focal plane of the first concave mirror and the focal plane of the second concave mirror is α, where 0 < α ≤ 180°. An entrance aperture is located off-center from the first concave reflector and is used to input light. The output aperture is used to output light. An intermediate reflector, together with the first concave reflector and the second concave reflector, forms a reflective cavity for guiding light between the reflective surfaces of the first and second concave reflectors. The incident light enters from the entrance hole at an angle not parallel to the principal axis of the first concave mirror, and after multiple reflections in the reflective cavity, it exits from the exit hole. The intermediate reflector includes two plane mirrors, the reflecting surfaces of the two plane mirrors are arranged facing each other and their principal axes are at 90°, or; The intermediate reflector is a prism with an isosceles triangle cross-section and a vertex angle of 90°.

2. The long optical path optical gas absorption cell according to claim 1, characterized in that, The radius of curvature of the first concave mirror is the same as that of the second concave mirror.

3. The long optical path optical gas absorption cell according to claim 1, characterized in that, The exit hole is located at a non-center position of the first concave reflector, and the exit hole coincides with the entrance hole.

4. The long optical path optical gas absorption cell according to claim 1, characterized in that, The exit hole is located at a non-center position of the second concave reflector.

5. A long-path optical gas absorption cell according to any one of claims 1 to 4, characterized in that, Both the first concave reflector and the second curved reflector are rectangular concave mirrors or circular concave mirrors.

6. A gas sensor, characterized in that, Use a long optical path optical gas absorption cell as described in any one of claims 1 to 5.

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