A multi-path gas absorption cell

Abstract

This invention relates to the field of spectral detection technology, specifically providing a multi-path gas absorption cell, comprising: a gas chamber, and a first cavity mirror and a second cavity mirror disposed at both ends of the gas chamber. Each of the first and second cavity mirrors includes at least: a circular integrating region, and an inner annular reflection region and an outer annular reflection region surrounding the circular integrating region; wherein the optical axes of the circular integrating regions of the first and second cavity mirrors coincide; the optical axes of the inner annular reflection regions of the first and second cavity mirrors are at an angle; and the optical axes of the outer annular reflection regions of the first and second cavity mirrors coincide. This invention, by combining multi-path cell and off-axis integrating cavity technology, designs a non-standard mirror that can realize multi-path detection, replacing traditional cavity mirrors and overcoming the problem of incompatibility between different optical paths in a single gas chamber structure. It enables the detection of trace gases with multiple components and custom ranges through a single gas chamber.

Description

Technical Field

[0001] This invention belongs to the field of spectral detection technology, and in particular relates to a multi-path gas absorption cell. Background Technology

[0002] Multi-pass cells utilize a specially designed array of mirrors (typically a combination of spherical or plane mirrors) to cause multiple reflections of the incident laser within a confined space, significantly increasing the interaction path (i.e., absorption optical path) between the light and the gas. This design is based on the Lambert-Beer law, where absorbance is positively correlated with optical path length, thereby greatly improving the sensitivity of trace gas detection. Its limitation lies in the uniqueness of the optical path; the light spots cannot overlap. Influenced by factors such as the number of reflections, energy loss, light spot diffusion, and mirror diameter, the effective optical path of a multi-pass cell is typically in the range of several meters to tens of meters. While such a path can cover some gases and certain concentration conditions for gas detection, it fails to meet the requirements for gases with weaker absorption peaks and higher precision. Furthermore, existing multi-pass cell structures generally have only a single optical path, which also limits their practical application in multi-range detection fields.

[0003] In contrast, cavity enhancement output spectroscopy involves constructing a resonant cavity structure and repeatedly sending the laser beam back and forth between two cavity mirrors (in coaxial cavity enhancement, the beam spots completely overlap, while in off-axis cavity enhancement, the spots overlap as little as possible). Both cavity enhancement techniques use the transmitted light from the mirrors as the detection signal, and the beam undergoes multiple reflections between the two cavity mirrors to achieve an optical cell structure that increases the optical path length. This cell structure can achieve an extremely long effective absorption optical path within the limited cavity mirror space; the weak energy signal transmitted each time the laser beam reaches the rear mirror of the cavity mirror is the final detection signal. The optical path length of integrating cavity output spectroscopy typically ranges from several hundred to several kilometers, offering a long optical path advantage that multi-pass cell structures cannot achieve.

[0004] Currently, regardless of the type of air-cell structure, there is usually only one absorption optical path, which cannot simultaneously cover multiple optical path structures such as several meters, tens of meters, hundreds of meters, or several kilometers. Therefore, it cannot meet the detection requirements of multiple ranges, multiple bands, multiple components, and small sample sizes.

[0005] In summary, current research has reached a consensus that a method for multi-gas detection that meets the accuracy requirements of customized detection ranges is an urgent problem to be solved. Summary of the Invention

[0006] In view of this, the present invention aims to provide a multi-path gas absorption cell, which combines a multi-pass cell and an off-axis integrating cavity structure to design an irregularly shaped mirror as a cavity mirror, overcoming the problem that different optical paths cannot be compatible in a single gas cell structure. It can realize the absorption detection of trace gases with multiple components and different ranges through a single gas cell.

[0007] To achieve the above objectives, the technical solution created by this invention is implemented as follows:

[0008] This invention provides a multi-path gas absorption cell, comprising:

[0009] air chamber;

[0010] And, a first cavity mirror and a second cavity mirror located in the air chamber;

[0011] Both the first and second cavities include at least: a circular integrating region, and an inner annular reflecting region and an outer annular reflecting region surrounding the circular integrating region;

[0012] The optical axes of the circular integration regions of the first and second cavities coincide; the optical axes of the inner annular reflection regions of the first and second cavities are at an angle; and the optical axes of the outer annular reflection regions of the first and second cavities coincide.

[0013] Preferably, the outer wall of the air chamber is provided with an air inlet and an air outlet.

[0014] Preferably, both the circular integrating region of the first cavity mirror and the circular integrating region of the second cavity mirror are plano-concave lens structures, the opposite surfaces of the circular integrating regions of the first cavity mirror and the circular integrating regions of the second cavity mirror are concave, the opposite surfaces are planar, and anti-reflection coatings are provided on the concave surfaces of the circular integrating regions of the first cavity mirror and the second cavity mirror.

[0015] Preferably, the first detection light is incident from the plane of the circular integration region of the first cavity mirror, and the first detection light is reflected back and forth between the circular integration regions of the first cavity mirror and the second cavity mirror. In each reflection cycle, a portion of the first detection light is emitted from the circular integration region of the second cavity mirror, and the first gas detection is achieved based on the detection result of the integrated spectrum of the emitted light.

[0016] Preferably, the radius of curvature of the inner annular reflection zone is smaller than that of the outer annular reflection zone and the circular integration zone, and the radii of curvature of the outer annular reflection zone and the circular integration zone are the same or different.

[0017] Preferably, the outer annular reflective area of ​​the first cavity mirror is provided with a first entrance hole, and the outer annular reflective area of ​​the second cavity mirror is provided with a first exit hole. The second probe light enters through the first entrance hole and is reflected back and forth between the outer annular reflective areas of the first and second cavity mirrors. The second probe light exits through the first exit hole, and the spot of the second probe light in the outer annular reflective area presents as a single circular multi-channel cell spot.

[0018] Preferably, a semi-transparent and semi-reflective mirror is provided in the optical path after the second detection light is emitted from the first emission hole. The semi-transparent and semi-reflective mirror is used to split the second detection light emitted from the first emission hole into a third detection light and a fourth detection light. The third detection light is used for the detection of a second gas.

[0019] A second entrance hole and a second exit hole are provided on the inner annular reflective area of ​​the second cavity mirror. A reflector is provided to direct the fourth detection light from the second entrance hole into the space between the first and second cavity mirrors, and to reflect it back and forth between the inner annular reflective areas of the first and second cavity mirrors. The fourth detection light is emitted from the second exit hole. The spot of the fourth detection light in the inner annular reflective area is a non-coincident multi-circular multi-pass cell spot. The fourth detection light is used for the detection of a third gas.

[0020] Preferably, the first probe light is coherent light or incoherent light.

[0021] Preferably, the maximum cross-section of the inner annular reflection region of the first cavity mirror is not perpendicular to the optical axis of the circular integration region of the first cavity mirror, and / or the maximum cross-section of the inner annular reflection region of the second cavity mirror is not perpendicular to the optical axis of the circular integration region of the second cavity mirror.

[0022] Preferably, the optical path lengths of the probe light are different between the circular integration region, the inner annular reflection region, and the outer annular reflection region of the first and second cavity mirrors, so as to realize customized detection of multiple gases and multiple spectral bands.

[0023] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0024] This invention redesigns a traditional cavity mirror as an irregularly shaped mirror, combining a multi-pass cell and an integrating cavity structure. The central region of the cavity mirror is designed as a plano-concave lens with an anti-reflection coating on its concave surface. Probe light is incident through the planar side of the plano-concave lens. During the reflection between the two cavity mirrors, a portion of the light transmitted through the cavity mirrors is collected. Integrating detection is achieved using the output spectral technology of the integrating cavity. The optical path length of this integrating detection typically ranges from several hundred to several kilometers, offering a long optical path advantage that multi-pass cell structures cannot achieve. Furthermore, multiple annular reflection zones with different radii of curvature are designed to construct a multi-pass cell structure for detection at different optical paths, achieving compatibility between integrating detection and multi-pass cell detection with multiple different light spot points within the same absorption cell.

[0025] The present invention further designs a semi-transparent and semi-reflective mirror and a reflector structure to split the detection light emitted from the gas chamber. One beam of light is used for the detection of one gas, and the other beam of light is injected back into the gas chamber through the reflector to increase the optical path and realize the detection of another gas.

[0026] The present invention further designs the mirror of at least one annular reflection region as tilted based on the theory of non-paraxial fiber transmission. That is, the region of the front and rear cavity mirrors is not parallel and has a certain tilt angle. The optical axis of the region does not coincide, so that the reflection region is designed as a spot-dense multi-pass cell structure, that is, multiple small circular spot-shaped spots are distributed in the annular region, and the spot landing points are non-coincident multi-circular multi-pass cell spot landing points.

[0027] This invention presents a multi-path gas absorption cell. Through a unique irregular cavity mirror partition design and re-incident optical path, it can flexibly select or simultaneously acquire various effective optical paths, such as meter-level (short), ten-meter to hundred-meter-level (medium), and kilometer-level (long), according to detection requirements. This fundamentally solves the pain point of traditional gas cells having a single optical path and being unable to adapt to multi-component concentration detection. It can simultaneously achieve the detection of multiple different optical paths in a single gas absorption cell, while meeting the requirements of multi-gas, multi-spectral, and self-selected range / accuracy gas detection, greatly reducing equipment costs and improving detection efficiency. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0029] Figure 1 This is a schematic diagram of the gas detection system provided in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the structure and spatial position of the irregular-shaped endoscope provided in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of the reflection zone and light spot landing point of the cavity mirror provided in an embodiment of the present invention.

[0032] The reference numerals in the figures include:

[0033] Air chamber 1, first cavity mirror 2, first entrance port 21, second cavity mirror 3, first exit port 31, second entrance port 32, second exit port 33, light source group 4, first collimator 5, second collimator 6, semi-transparent mirror 7, reflector 8, detector group 9. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and do not constitute a limitation thereof. Similar elements in different embodiments are referred to by associated similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the invention. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, some operations related to the invention are not shown or described in the specification. This is to avoid obscuring the core parts of the invention with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0035] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined to form various implementations. Furthermore, the order of the steps or actions in the method description can be changed or adjusted in a manner readily apparent to those skilled in the art. Therefore, the various orders in the specification and drawings are merely for the clear description of a particular embodiment and do not imply a mandatory order, unless otherwise stated that a particular order must be followed.

[0036] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0037] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] Please see Figure 1 and Figure 2 In one embodiment of the present invention, a multi-path gas absorption cell is provided, comprising:

[0040] Air chamber 1;

[0041] And, a first laminar flow mirror 2 and a second laminar flow mirror 3 are provided in the air chamber 1;

[0042] Both the first cavity mirror 2 and the second cavity mirror 3 include at least: a circular integrating region (a region with radius R1), and an inner annular reflection region (an annular region between R1 and R2) and an outer annular reflection region (an annular region between R2 and R3) surrounding the circular integrating region.

[0043] The optical axes of the circular integration region of the first cavity mirror 2 and the circular integration region of the second cavity mirror 3 coincide; the optical axes of the inner annular reflection region of the first cavity mirror 2 and the inner annular reflection region of the second cavity mirror 3 are at an angle; and the optical axes of the outer annular reflection region of the first cavity mirror 2 and the outer annular reflection region of the second cavity mirror 3 coincide.

[0044] It should be understood that the present invention is not limited to dividing the first cavity mirror 2 and the second cavity mirror 3 into the above-mentioned three regions: the circular integration region (the region with a radius of R1), the inner annular reflection region (the annular region between R1 and R2), and the outer annular reflection region (the annular region between R2 and R3). The number of regions and the size of each region depend on the actual gas detection requirements, such as the detection wavelength, spot size, and shape determined according to the type of gas being detected.

[0045] The gas chamber 1 is a sealed cavity filled with the gas sample to be tested. Its function is to provide a space for the gas sample to interact with the laser for detection. An inlet and an outlet are respectively set on the outer wall of the gas chamber 1. The inlet typically needs to be equipped with a mass flow controller to configure parameters such as the gas flow rate entering the gas chamber 1. The outlet typically needs to be equipped with a pressure closed-loop control component and a tunable air pump. The pressure closed-loop control component measures the gas pressure in the gas chamber 1, and the outlet rate of the tunable air pump is controlled through a closed loop to achieve pressure balance in the gas chamber 1.

[0046] The first cavity mirror 2 and the second cavity mirror 3 are respectively located at both ends of the air chamber 1, and are generally referred to as the front cavity mirror and the rear cavity mirror. In this embodiment of the invention, the cavity mirror structure is specially designed, and a multi-section irregular-shaped mirror is designed to replace the traditional cavity mirror by combining multi-pass cell and off-axis integrating cavity enhancement technology. Specifically, since traditional absorption cells mostly adopt multi-pass cell structures, the optical path is single and cannot simultaneously meet the needs of multiple optical paths such as several meters, tens of meters, and hundreds of meters. Therefore, in this embodiment of the invention, the first cavity mirror 2 and the second cavity mirror 3 are both designed to be divided into three regions: a circular integrating region (the region with a radius of R1), an inner annular reflection region (the annular region between R1 and R2), and an outer annular reflection region (the annular region between R2 and R3), to correspond to the detection requirements of different optical paths. The description is in the order from the center part to the edge of the cavity mirror, such as... Figure 3 As shown, the circular integrating regions (regions with radius R1) of the first cavity mirror 2 and the second cavity mirror 3 are processed into coaxial plano-concave lens structures, with the concave surface facing the interior of the gas chamber 1. That is, the opposite surfaces of the circular integrating regions of the first cavity mirror 2 and the second cavity mirror 3 are concave, and the opposite surfaces are planar. An anti-reflection coating is deposited on the concave surface, and the anti-reflection coating material is a dielectric film. In this embodiment of the invention, the specific materials of the anti-reflection coating are Ta2O5 and SiO2, which are stacked together. The position of the central reflection wavelength and the highest reflectivity of the film layer are determined according to the material ratio and the number of stacked layers to meet the detection requirements of different gases. Specifically, taking the strong absorption peak of carbon monoxide as an example, its central wavelength is 2332 nm. When the reflectivity of the anti-reflection coating is designed to be 99.95%, the number of stacked layers is 27, and the film thickness is 9.3 micrometers. At this point, the radius R1 of the circular integration region is determined by the collimated beam radius designed in the coherent off-axis beam expansion detection method of this invention, that is, based on the diameter of the probe beam incident on the circular integration region, and the radius R1 of the circular integration region generally has a margin. For example, assuming that a probe beam with a beam expansion diameter of 9 micrometers is used in the embodiment of this invention, the radius R1 of the circular integration region has a margin of 12 micrometers. Furthermore, the radius of curvature of the circular integration region... Generally designed as The circular integrating region of the first cavity mirror 2 and the circular integrating region of the second cavity mirror 3 constitute an off-axis integrating cavity structure. The probe light is reflected back and forth between the circular integrating regions of the first cavity mirror 2 and the second cavity mirror 3. In each reflection cycle, when the probe light is reflected onto the second cavity mirror 3, a portion of the probe light will be emitted from the circular integrating region of the second cavity mirror 3. The higher the reflectivity of the circular integrating region, the longer the effective optical path during this part of the reflection process, which can reach hundreds of meters to kilometers. Therefore, based on the integrated spectrum detection results of this part of the emitted light, the carbon monoxide gas concentration at the ppm level and even higher precision can be detected.

[0047] In traditional multi-pass cell structures, coherent light is relied upon to form stable interference, while incoherent light cannot be detected due to its random phase. Therefore, traditional detection requires coherent light. However, this invention uses a circular integrating region to form an integrating cavity structure, relying on a high-reflectivity film to achieve long-path oscillatory reflection, which does not depend on coherence. Therefore, the first detection light can also be incoherent. The intensity of the light transmitted from the exit surface has been significantly reduced due to gas absorption accumulated from multiple reflections. The spectrum can be measured using a spectral detection device and compared with the incident spectrum. Based on the Lambert-Beer law, the gas concentration can be inverted from the absorbance.

[0048] The outer side of the circular integrating region is the inner annular reflection region (the annular area between R1 and R2). Through processing, this region is fabricated such that the optical axes of the inner annular reflection regions of the first cavity mirror 2 and the second cavity mirror 3 are at an angle, meaning the inner annular reflection regions of the first cavity mirror 2 and the second cavity mirror 3 are relatively tilted and not parallel to each other, exhibiting a certain angle of inclination. Figure 2 The diagram shows the inner annular reflective area of ​​the first cavity mirror 2 being machined into an inclined state. In practice, either the inner annular reflective area of ​​the first cavity mirror 2 or the second cavity mirror 3 can be machined into an inclined state, or even simultaneously. That is, the maximum tangent plane of the inner annular reflective area of ​​the first cavity mirror 2 is not perpendicular to the optical axis of the circular integrating region of the first cavity mirror 2, and / or the maximum tangent plane of the inner annular reflective area of ​​the second cavity mirror 3 is not perpendicular to the optical axis of the circular integrating region of the second cavity mirror 3. The centers of the inner annular reflective areas of the first cavity mirror 2 and the second cavity mirror 3 are spaced a certain distance k in the vertical direction. Furthermore, the radius of curvature of the inner annular reflective area... The radius of curvature is significantly smaller than that of the circular integral region. Specific radius of curvature The radius of curvature can be selected from tens to hundreds of millimeters in this embodiment of the invention. The purpose of this design is to achieve a densely packed multi-pass cell structure in the inner annular reflective region, where multiple small circular light spots are distributed within the inner annular reflective region. The coating on the inner annular reflective region can be made of metallic materials, such as gold or silver, to achieve a wide spectral range of reflection, with a reflectivity generally designed to be above 95%. The probe light oscillates between the inner annular reflective regions of the first cavity mirror 2 and the second cavity mirror 3. The light spot landing points in the inner annular reflective region exhibit non-overlapping multi-circular multi-pass cell spot landing points, forming a long optical path multi-pass cell structure.

[0049] The outer ring of the inner annular reflection area is the outer annular reflection area (the annular region between R2 and R3). Through manufacturing processes, this region is processed so that the optical axes of the outer annular reflection areas of the first cavity mirror 2 and the second cavity mirror 3 coincide, meaning that the outer annular reflection areas of the first cavity mirror 2 and the second cavity mirror 3 are parallel to each other. Furthermore, the radius of curvature of the outer annular reflection area... For a large radius of curvature, it can also be designed as The design aims to make the light spot landing point in the outer annular reflection region resemble the circular light spot landing point of a traditional single-circular multi-pass cell, forming a short-path multi-pass cell structure. This region is coated with a metallic material, such as gold or silver, to achieve broad-spectrum reflection, with a reflectivity typically designed to be above 95%. It is important to note that the radii of curvature of the circular integration region (R1 region) and the outer annular reflection region (the annular region between R2 and R3) can be designed to be the same. They can also be designed differently, but all are significantly larger than the radius of curvature of the inner annular reflection zone (the annular area between R1 and R2).

[0050] The three regions mentioned above are used to provide three different optical path designs with different optical paths. The circular integrating region forms an off-axis integrating cavity structure, and the effective optical path of this region can reach hundreds of meters to kilometers. The inner annular reflecting region forms a long optical path small dense multi-pass cell structure, and the effective optical path of this region is less than that of the circular integrating region. The outer annular reflecting region forms a short optical path traditional multi-pass cell structure, and its effective optical path is significantly less than that of the inner annular reflecting region.

[0051] To further explain the optical path length and detection principle of the three reflection regions mentioned above, this embodiment of the invention uses two probe beams as an example to describe the gas detection process. In actual detection, more probe beams can be designed to enter the absorption cell. Specifically, as follows... Figure 1As shown, a light source group 4 and a collimator group are designed at the front end of the gas absorption cell. The light source group 4 is used to provide detection light of different wavelengths. The collimator group includes a first collimator 5 and a second collimator 6. These two collimators collimate the two detection beams respectively, and can further perform beam reduction or expansion. One of the detection beams is designated as the first detection beam. After being collimated by the first collimator 5, the first detection beam is directed towards the circular integrating region of the first cavity mirror 2, and then enters the gas chamber 1. The first detection beam is reflected back and forth between the circular integrating regions of the first cavity mirror 2 and the second cavity mirror 3, forming a stable integrating cavity structure. A small amount of light beam is transmitted out in each reflection cycle. The energy amplitude of each transmission is determined by the scattering, absorption, and reflection functions of the mirrors. The emitted light after integration is the light signal required for detection. This light signal continues to be directed towards the detector group 9 at the rear end of the absorption cell to achieve the first type of gas detection. The optical path length of the circular integrating region depends not only on the distance between the first cavity mirror 2 and the second cavity mirror 3, but also on the reflectivity of the circular integrating region. The higher the reflectivity of the circular integrating region, the longer the optical path length, generally reaching the level of hundreds of meters to kilometers. This invention creatively proposes to design an integrating cavity structure in the gas absorption cell, achieving an ultra-long optical path length of hundreds of meters to kilometers to meet the requirements for carbon monoxide gas concentration detection at the ppm level and above. Furthermore, it combines a multi-pass cell structure to achieve gas detection of multiple gases, multiple spectral bands, and selectable range / accuracy.

[0052] This invention designs an integrating cavity structure at the center of a multi-path gas absorption cell. The circular integrating regions of the first cavity mirror 2 and the second cavity mirror 3 are relatively parallel and possess high reflectivity. Regarding off-axis integration detection methods for circular integrating regions, this invention, combined with the specific structure of the multi-path gas absorption cell, proposes a novel integration detection method. This method differs from traditional off-axis integrating cavity enhanced spectroscopy techniques by not employing an optical path design that de-axisizes the coaxial beam; that is, the spot point in the circular integrating region is not a dense ring. Instead, it expands the first probe beam as much as possible. The expanded first probe beam still has a narrow linewidth, but the light energy is evenly distributed over a larger circular spot. This design inevitably introduces a certain degree of optical interference, i.e., incomplete off-axis integration. However, its advantage lies in achieving off-axis integration without complex optical adjustments. The degree of off-axis integration depends on the size of the collimated spot. This off-axis method also differs from broadband off-axis integrating cavity enhancement techniques. The off-axis integration detection method of this invention does not use broadband light and does not necessarily require a spectrometer or other similar devices as detection tools. This narrow-linewidth, large-spot off-axis integration detection method is well-suited to the limited area of ​​the circular integration region of the irregular-shaped mirror optical absorption cell designed in this invention, achieving the goal of ultra-long optical path integration detection within a limited space.

[0053] The other probe beam provided by the light source group 4 is designated as the second probe beam. After being collimated by the second collimator 6, the second probe beam is directed towards the outer annular reflection area of ​​the first cavity mirror 2. A first entrance aperture 21 is provided on the outer annular reflection area of ​​the first cavity mirror 2. The second probe beam enters the gas chamber 1 through the first entrance aperture 21 and is repeatedly reflected between the outer annular reflection area of ​​the first cavity mirror 2 and the outer annular reflection area of ​​the second cavity mirror 3. Multiple reflections form a single circular multi-channel cell spot, i.e., as shown in the image. Figure 3 The diagram illustrates the landing points of the outer and middle annular reflection zones. A first exit aperture 31 is provided on the outer annular reflection zone of the second cavity mirror 3. After multiple reflections, the second probe light exits through the first exit aperture 31 on the second cavity mirror 3 and leaves the gas chamber 1. The optical path of the outer annular reflection zone depends on the distance between the first cavity mirror 2 and the second cavity mirror 3, as well as the number of light spots; that is, the optical path is determined by the number of reflections.

[0054] Because the light spots in a multi-channel cell structure cannot overlap, the number of reflections is limited, and the typical optical path is on the order of meters to tens of meters. In this invention, it is assumed that the effective absorption optical path is L1. A semi-transparent mirror 7 is placed on the optical path after the second probe light exits from the first exit hole 31. The reflectivity and transmittance of the semi-transparent mirror are not limited to 1:1 and can be replaced with other ratios to adjust the signal-to-noise ratio of the final received signal. After the second probe light is incident on the semi-transparent mirror 7, the semi-transparent mirror 7 splits the second probe light into a third probe light and a fourth probe light. The third probe light is transmitted through the semi-transparent mirror 7 and continues to be incident on the detector group 9 and converted into an electrical signal. The effective absorption optical path of this part of the signal has been determined to be L1, which is used to realize the second type of gas detection. The fourth probe light is reflected by the semi-transparent mirror 7 to the reflector 8. The reflector 8 adjusts the angle of the fourth probe light. Under the action of the semi-transparent mirror 7 and the reflector 8, the incident angle of the fourth probe light can be flexibly changed to realize the adjustment of the optical path. To allow the fourth detection light to re-enter the gas chamber 1, a second entrance aperture 32 and a second exit aperture 33 are further formed on the inner annular reflective area of ​​the second cavity mirror 3. Under the adjustment of the reflector 8, the fourth detection light enters the gas chamber 1 through the second entrance aperture 32 and is repeatedly reflected between the inner annular reflective areas of the first cavity mirror 2 and the second cavity mirror 3, forming a small, dense, multi-circular light spot on the inner annular reflective area—that is, a non-overlapping multi-circular multi-pass cell light spot landing point. This reflected light path has a longer optical path and occupies a larger mirror area than the ordinary circular light path of the outer annular reflective area, and leaves the gas chamber 1 through the second exit aperture 33. Assuming the effective optical path of the repeated reflections in the inner annular reflective area is L2, the effective optical path of the fourth detection light is L1+L2, typically between tens and hundreds of meters. After the fourth detection light is emitted, it is received by the detector group 9 and converted into an electrical signal to achieve the third type of gas detection.

[0055] The reason for the formation of small, dense, multi-circular light spots in the inner annular reflection area is explained as follows: In this embodiment of the invention, the optical axes of the inner annular reflection areas of the first cavity mirror 2 and the second cavity mirror 3 are at an angle and are not relatively parallel. Therefore, each reflection of the fourth probe light will be offset by a certain angle due to the tilt of the first cavity mirror 2 and / or the second cavity mirror 3. Thus, it will not continue the traditional single-circular multi-pass cell light spot landing point as in the outer annular reflection area, but will instead exhibit a pattern similar to... Figure 3 The non-overlapping multi-circular multi-pass cell beam landing points shown in the diagram will result in the fourth probe beam landing point forming multiple different circular trajectories. It is important to note that... Figure 3 The effect of a small-to-medium-sized dense multi-pass cell is not that the fourth probe beam forms a complete small-diameter circular landing point all at once, but rather that it undergoes multiple reflections, with each landing point being one of the circular landing points, gradually forming a shape like... Figure 3 The effect of landing points in a small, dense multi-channel pool is shown.

[0056] Through the above design, this invention combines a multi-pass cell and an off-axis integrating cavity structure with a uniquely shaped mirror as the cavity mirror. This allows a single optical integrating cavity to provide an extremely wide effective optical path range from meters to kilometers, flexibly selecting the detection range for different gas concentrations, such as 20%-1ppm. It enables gas detection of multiple gases, multiple spectral bands, and selectable range / accuracy. This solves the problems of traditional gas absorption cells using multi-pass cell structures, such as the single optical path, the fact that multi-pass cells only have a single spot structure, and the inability to flexibly increase the optical path even with re-incidence, as well as the limitations of not being able to simultaneously realize the multi-pass cell optical structure and the integrating cavity optical structure in the same gas absorption cell.

[0057] In summary, the above are merely preferred embodiments of this specification and are not intended to limit the scope of protection of this specification. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this specification should be included within the scope of protection of this specification.

[0058] The systems, apparatuses, modules, or units described in one or more of the above embodiments may be implemented by a computer chip or entity, or by a product having a certain function. A typical implementation device is a computer. Specifically, a computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smartphone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or any combination of these devices.

[0059] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0060] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

Claims

1. A multi-path gas absorption cell, characterized in that, include: air chamber; And, a first cavity mirror and a second cavity mirror disposed in the air chamber; Both the first cavity mirror and the second cavity mirror include at least: a circular integrating region, and an inner annular reflecting region and an outer annular reflecting region surrounding the circular integrating region; Wherein, the optical axes of the circular integrating regions of the first cavity mirror and the second cavity mirror coincide; the optical axes of the inner annular reflecting regions of the first cavity mirror and the second cavity mirror are at an angle; and the optical axes of the outer annular reflecting regions of the first cavity mirror and the second cavity mirror coincide. The first cavity mirror has a first entrance hole on its outer annular reflective area, and the second cavity mirror has a first exit hole on its outer annular reflective area. The second probe light enters through the first entrance hole and is reflected back and forth between the outer annular reflective areas of the first cavity mirror and the second cavity mirror. The second probe light exits through the first exit hole, and the spot of the second probe light in the outer annular reflective area is a single circular multi-channel cell spot. A semi-transparent and semi-reflective mirror is provided in the optical path after the second detection light is emitted from the first emission hole. The semi-transparent and semi-reflective mirror is used to split the second detection light emitted from the first emission hole into a third detection light and a fourth detection light. The third detection light is used for the detection of a second gas. A second entrance hole and a second exit hole are provided on the inner annular reflection area of ​​the second cavity mirror. A reflector is provided to direct the fourth detection light into the space between the first cavity mirror and the second cavity mirror through the second entrance hole, and to reflect it back and forth between the inner annular reflection areas of the first cavity mirror and the second cavity mirror. The fourth detection light is emitted from the second exit hole. The spot of the fourth detection light in the inner annular reflection area presents a non-overlapping multi-circular multi-pass cell spot. The fourth detection light is used for the detection of a third gas.

2. The multi-path gas absorption cell according to claim 1, characterized in that, The outer wall of the air chamber is provided with an air inlet and an air outlet.

3. The multi-path gas absorption cell according to claim 1, characterized in that, Both the circular integrating region of the first cavity mirror and the circular integrating region of the second cavity mirror are plano-concave lens structures. The opposing surfaces of the circular integrating regions of the first cavity mirror and the second cavity mirror are concave, and the opposing surfaces are planar. Furthermore, an anti-reflection coating is provided on the concave surface of the circular integrating region of both the first cavity mirror and the second cavity mirror. The specific materials of the anti-reflection coating are Ta2O5 and SiO2.

4. The multi-path gas absorption cell according to claim 3, characterized in that, The first detection light is incident on the plane of the circular integration region of the first cavity mirror. The first detection light is reflected back and forth between the circular integration regions of the first cavity mirror and the second cavity mirror. In each reflection cycle, a portion of the first detection light is emitted from the circular integration region of the second cavity mirror. The first gas is detected based on the integrated spectrum detection result of the emitted light.

5. The multi-path gas absorption cell according to claim 1, characterized in that, The radius of curvature of the inner annular reflective region is smaller than that of the outer annular reflective region and the circular integration region. The radii of curvature of the outer annular reflective region and the circular integration region may be the same or different.

6. The multi-path gas absorption cell according to claim 4, characterized in that, The first probe light is either coherent or incoherent.

7. The multi-path gas absorption cell according to claim 1, characterized in that, The maximum cross-section of the inner annular reflection region of the first cavity mirror is not perpendicular to the optical axis of the circular integration region of the first cavity mirror, and / or the maximum cross-section of the inner annular reflection region of the second cavity mirror is not perpendicular to the optical axis of the circular integration region of the second cavity mirror.

8. The multi-path gas absorption cell according to claim 1, characterized in that, The probe light has different optical path lengths between the circular integration region, inner annular reflection region, and outer annular reflection region of the first and second cavity mirrors, which is used to realize customized detection of multiple gases and multiple spectral bands.

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