Multi-path gas detection system compatible with multi-pass cell and integral detection

Abstract

The invention relates to the technical field of spectrum detection, and particularly provides a multi-path gas detection system compatible with a multi-pass cell and integral detection, the system comprises a light source, a gas absorption cell and a detection unit, the light source is used for providing corresponding wave band light for detection of various gases, the gas absorption cell is an area for measuring sample gas, and the detection unit is used for detecting the sample gas. Endoscopes of the gas absorption cell are optimally designed to at least comprise an integration region and a multi-pass cell annular reflection region, at least two endoscopes have an included angle between optical axes of one annular reflection region, and transmission of multiple optical paths is realized; and the detection unit is used for detecting the detection light with different optical paths so as to realize detection of different gases. According to the invention, a heterotype mirror capable of realizing multi-optical-path detection is designed by combining a multi-pass cell and an off-axis integral cavity technology to replace a traditional cavity mirror, so that the problem that different optical paths cannot be compatible in a single gas chamber structure is solved, and multi-component trace gas absorption detection with a self-defined range can be realized through a single gas chamber.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of spectral detection, and particularly relates to a multi-optical-path gas detection system compatible with a multi-pass cell and integral detection. BACKGROUND

[0002] At present, the technical route for improving the sensitivity of a gas detection system in detecting trace gases is mainly to increase the action path of light and gas (i.e. the absorption optical path). The relatively mature technologies are the integral cavity output spectrum technology and the multi-pass cell technology. The multi-pass cell uses a specially designed mirror array (usually a combination of spherical mirrors or plane mirrors) to make the incident laser light reflect multiple times in a limited space, thereby significantly increasing the action path of light and gas (i.e. the absorption optical path), and greatly improving the sensitivity of trace gas detection. The limitation is the uniqueness of the optical path, i.e. the light spots cannot overlap. Due to factors such as the number of reflections, energy loss, light spot diffusion, mirror diameter, etc., the effective optical path of the multi-pass cell is usually in the range of several meters to tens of meters, and it is impossible to achieve an ultra-long optical path of hundreds of meters or kilometers. Such an optical path can cover the detection of some gases under certain concentration conditions, but when it comes to gases with higher precision and weaker absorption peaks, it cannot meet the detection conditions. At the same time, the existing multi-pass cell structure generally only has a unique optical path, which also limits its practical application in the multi-range field.

[0003] Compared with the multi-pass cell, the integral cavity enhanced output spectrum technology is to construct a resonant cavity structure and let the light beam repeatedly go back and forth between the two cavity mirrors (in which the coaxial cavity enhances the complete overlap of the light beam, and the off-axis cavity enhances the non-overlapping light spots as much as possible). Regardless of which cavity enhancement technology is used, the mirror transmissive light is used as the detection signal, and the light beam repeatedly reflects between the two cavity mirrors to achieve the effect of increasing the optical path of the optical cell structure. This cell structure can achieve an extremely long effective absorption optical path in a limited mirror space, and the weak energy signal transmitted by the laser beam when it reaches the mirror is the final detection signal.

[0004] At the present stage, regardless of which cell structure is used, there is usually only a unique absorption optical path, and it is impossible to cover several meters, tens of meters, hundreds of meters or kilometers of optical path at the same time.

[0005] In summary, at the present stage, it has been recognized that the method of multi-gas detection and meeting the self-defined detection range accuracy is a difficult problem that needs to be solved, and the demand for multi-range, multi-band, multi-component and small sample size detection is becoming increasingly urgent. SUMMARY

[0006] Therefore, the application aims to provide a multi-path gas detection system compatible with multi-cell and integral detection, which overcomes the problem that different optical paths cannot be compatible in a single gas chamber structure by combining a multi-cell and an integral cavity structure to design a special-shaped mirror as a cavity mirror, and can realize multi-component and different range trace gas absorption detection in a single gas chamber.

[0007] To achieve the above-mentioned purpose, the technical scheme of the application is as follows: The application provides a multi-path gas detection system compatible with multi-cell and integral detection, comprising a light source, a gas absorption cell and a detection unit, wherein the gas absorption cell comprises a gas chamber, a first cavity mirror and a second cavity mirror arranged in the gas chamber, and a half-transmission half-reflection mirror. The first cavity mirror and the second cavity mirror each comprise an integral zone, a first annular reflection zone and a second annular reflection zone arranged outside the integral zone. The optical axes of the first annular reflection zone of the first cavity mirror and the first annular reflection zone of the second cavity mirror form an included angle, and the optical axes of the second annular reflection zone of the first cavity mirror and the second annular reflection zone of the second cavity mirror coincide. The second annular reflection zone of the first cavity mirror is provided with a first entrance hole, and the second annular reflection zone of the second cavity mirror is provided with a first exit hole; the first annular reflection zone of the second cavity mirror is provided with a second entrance hole and a second exit hole. The light source is configured to provide first detection light transmitted into the integral zone of the first cavity mirror and reciprocally reflected between the integral zones of the first cavity mirror and the second cavity mirror, and to provide second detection light emitted from the first entrance hole and reciprocally reflected between the second annular reflection zones of the first cavity mirror and the second cavity mirror. During the integral reflection between the integral zones, part of the first detection light is emitted from the integral zone of the second cavity mirror to the detection unit each time. The second detection light is emitted from the first exit hole to the half-transmission half-reflection mirror, the half-transmission half-reflection mirror is configured to split the second detection light into third detection light and fourth detection light, the third detection light is transmitted from the half-transmission half-reflection mirror to the detection unit, and the fourth detection light is reflected from the half-transmission half-reflection mirror to the second entrance hole and reciprocally reflected between the first annular reflection zones of the first cavity mirror and the second cavity mirror and emitted from the second exit hole to the detection unit.

[0008] Preferably, the outer wall of the gas chamber is provided with an air inlet and an air outlet, a mass flow controller is arranged at the position of the air inlet, the mass flow controller is configured to configure the gas flow parameter of the gas entering the gas chamber through the air inlet, a pressure closed-loop measurement and control component and a tunable air pump are arranged at the position of the air outlet, the pressure closed-loop measurement and control component is configured to measure the gas pressure in the gas chamber, and the tunable air pump is configured to control the air outlet rate according to the measured gas pressure in the gas chamber.

[0009] Preferably, the integrating zone of the first cavity mirror and the integrating zone of the second cavity mirror are both plano-concave lens structures, the opposite faces of the integrating zone of the first cavity mirror and the integrating zone of the second cavity mirror are concave, and the opposite faces are flat, and the concave faces of the integrating zone of the first cavity mirror and the integrating zone of the second cavity mirror are both provided with a reflection-increasing film.

[0010] Preferably, the first probe light is coherent light or incoherent light.

[0011] Preferably, the curvature radius of the first type of annular reflection zone is smaller than the curvature radius of the second type of annular reflection zone and the integrating zone, and the curvature radius of the second type of annular reflection zone and the integrating zone is the same or different.

[0012] Preferably, the spot landing point of the second probe light on the second type of annular reflection zone presents a single circular multi-cell spot landing point, and the spot landing point of the fourth probe light on the first type of annular reflection zone presents a non-coincident multi-circular multi-cell spot landing point.

[0013] Preferably, the processor is further used to collect the probe light signals of multiple light paths obtained by the probe unit, and realize self-defined detection of different gases according to the probe light signals of different light paths, wherein the probe light signals of multiple light paths include: a first probe light collection signal of a first light path, a third probe light collection signal of a second light path, and a fourth probe light collection signal of a third light path.

[0014] Preferably, a special-shaped light beam adjusting assembly is arranged between the second cavity mirror and the probe unit, and the special-shaped light beam adjusting assembly is used to adjust the inclination angles of different probe lights incident into different detection target surfaces of the probe unit.

[0015] Preferably, the inclination angles of different probe lights incident into different detection target surfaces are adjusted by the special-shaped light beam adjusting assembly, so that the different detection target surfaces in the probe unit can be arranged in different planes, or the spot spacing of different probe lights incident onto the same plane is increased.

[0016] Preferably, the special-shaped light beam adjusting assembly is a special-shaped lens, and the special-shaped lens includes multiple lens zones corresponding to different probe lights, and the different lens zones of the special-shaped lens have different thicknesses and inclination angles of probe light exit surfaces. The special-shaped lens is arranged between the second cavity mirror and the probe unit as an independent optical element, or the special-shaped lens is obtained by integrating and processing the surface of the second cavity mirror facing away from the first cavity mirror.

[0017] Compared with the prior art, the application can achieve the following beneficial effects: The gas chamber cavity mirror of the gas detection system is innovatively designed, the cavity mirror is designed as a special-shaped mirror by combining a multi-pass cell and an integrating cavity structure, a center area of the cavity mirror is designed as a plano-concave lens with a concave surface coated with a reflection-increasing film, the detection light is injected through the plane side of the plano-concave lens, part of the detection light transmitted by the cavity mirror is collected during the reflection between the two cavity mirrors, and the integral detection is realized by using the integrating cavity output spectrum technology. The optical path of the integral detection is generally hundreds of meters to several kilometers, and the multi-pass cell structure cannot realize the long optical path advantage. In addition, a plurality of annular reflection areas with different radii of curvature are designed to construct a multi-pass cell structure for different optical path detection, and the integral detection and the multi-pass cell detection of different light spot landing points in the same absorption cell are realized.

[0018] Since the special-shaped optical gas chamber can realize multiple gas detection through a single absorption cell, a plurality of detectors for detecting different gases need to be arranged on the detection plane. However, the traditional detection plane has limited space, and it is difficult to arrange multiple detectors in the same plane, especially for large volume detection. Therefore, the special-shaped beam adjusting assembly is additionally arranged outside the gas absorption cell exit cavity mirror, different wavelength beams (different gas detection) are separated in space and converged on different detectors, the disadvantage that the traditional detection method cannot simultaneously detect multiple separated wavelength beams is solved, and the simultaneous detection of multiple detectors avoids the time consumption of time division multiplexing and the introduction of additional spectral noise of frequency division multiplexing.

[0019] Since the optical path of the multi-pass cell is limited, the semi-transmissive and semi-reflective mirror and the reflecting mirror structure are further designed to split the detection light emitted by the gas chamber, one of the beams is used for short optical path gas detection, and the other beam is reflected by the reflecting mirror and then enters the gas chamber again to increase the optical path. Since the light spots of the traditional multi-pass cell structure cannot overlap and the number of reflections is limited, in order to as far as possible increase the optical path of the light beam entering the gas chamber for the second time, at least one mirror surface of the annular reflection area is designed to be inclined based on the non-axial fiber transmission theory, that is, the front and rear cavity mirrors in the area are not parallel and have a certain inclination angle, and the optical axes of the area do not coincide, so that the light beam has a small deflection angle during each reflection in the annular reflection area. In this way, the light beam can realize non-coincident multi-turn transmission, the light spot overlap is avoided, and the optical path is as far as possible increased. Therefore, the light spot landing points of the annular reflection area with the optical axis angle present a dense light spot multi-pass cell structure, that is, a plurality of small circular ring light spots are distributed in the annular area, and the light spot landing points present a non-coincident multi-circular multi-pass cell light spot landing point, rather than a traditional single-circular multi-pass cell light spot landing point.

[0020] The application designs a multi-optical-path gas detection system compatible with multiple cells and integral detection, which can flexibly select or synchronously acquire in multiple effective optical paths such as meter (short), ten to one hundred meters (medium), kilometer (long) according to detection requirements through the unique special-shaped cavity mirror partition design and secondary incident light path, fundamentally solves the pain points of single optical path of the traditional gas detection system and the inability to adapt to multi-component concentration detection, can realize multiple different optical path detection in a single gas absorption cell, simultaneously meet multi-gas, multi-spectrum, self-selected range / precision gas detection, greatly reduce the equipment cost and improve the detection efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0021] The drawings constituting a part of this application provide further understanding of the application, the schematic embodiments of the application and the description thereof are used to explain the application, and do not constitute improper limitation on the application. In the drawings: Figure 1 is a schematic diagram of a multi-optical-path gas detection system compatible with multiple cells and integral detection provided according to an embodiment of the application; Figure 2 is a structure and spatial position schematic diagram of a special-shaped cavity mirror provided according to an embodiment of the application; Figure 3 is a reflection partition and spot landing point schematic diagram of a cavity mirror provided according to an embodiment of the application; Figure 4 is a structure schematic diagram of a special-shaped light beam adjusting assembly provided according to an embodiment of the application.

[0022] The reference signs in the drawings include: Light source 1, first collimator 201, second collimator 202, gas chamber 301, gas inlet 3011, gas outlet 3012, mass flow controller 3013, pressure closed-loop measurement and control component 3014, tunable gas pump 3015; First cavity mirror 302, first incident hole 3021; Second cavity mirror 303, first exit hole 3031, second incident hole 3032, second exit hole 3033; Semi-transparent mirror 4, mirror 5, detection unit 6, first detector 601, second detector 602, third detector 603, data acquisition unit 701, FPGA 702, communication interface 703, light source driving circuit 704, special-shaped light beam adjusting assembly 8. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below with reference to the drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and do not constitute a limitation on the present application. In different embodiments, similar elements are associated with similar element labels. In the following embodiments, many details are described in order to make the present application better understood. However, those skilled in the art can easily recognize that some features can be omitted in different cases, or can be replaced by other elements, materials or methods. In some cases, some operations related to the present application are not shown or described in the specification in order to avoid the core part of the present application being overwhelmed by too much description, and it is not necessary for those skilled in the art to describe these related operations in detail according to the description in the specification and general technical knowledge in the art.

[0024] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other to form various embodiments without conflict. Meanwhile, each step or action in the method description can be sequentially adjusted or adjusted in a manner that can be easily seen by those skilled in the art. Therefore, the various sequences in the specification and drawings are only for the purpose of clearly describing a certain embodiment, and do not mean that the sequence is necessary, unless otherwise stated that a certain sequence must be followed.

[0025] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the device or element indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features limited by "first", "second" and the like can explicitly or implicitly include one or more features. In the description of the present application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0026] 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.

[0027] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0028] Please see Figure 1 , Figure 2 and Figure 3 In one embodiment of the present invention, a multi-path gas detection system compatible with multi-pass cell and integral detection is provided, comprising: The light source 1, the gas absorption cell, the semi-transparent and semi-reflective mirror 4, and the detection unit 6, wherein the gas absorption cell includes a gas chamber 301, and a first cavity mirror 302 and a second cavity mirror 303 disposed in the gas chamber 301; Both the first cavity mirror 302 and the second cavity mirror 303 include at least: an integrating region (a region with radius R1), and a first-class annular reflection region (annular region between R1 and R2) and a second-class annular reflection region (annular region between R2 and R3) surrounding the integrating region. There is an angle between the optical axes of the first type annular reflection region of the first cavity mirror 302 and the first type annular reflection region of the second cavity mirror 303; the optical axes of the second type annular reflection region of the first cavity mirror 302 and the second type annular reflection region of the second cavity mirror 303 coincide. The first cavity mirror 302 has a first entrance hole 3021 on the second type annular reflection area, and the second cavity mirror 303 has a first exit hole 3031 on the second type annular reflection area; the second cavity mirror 303 has a second entrance hole 3032 and a second exit hole 3033 on the first type annular reflection area. The light source 1 is used to provide a first detection light that is transmitted into the integrating region of the first cavity mirror 302 and reciprocated between the integrating regions of the first cavity mirror 302 and the second cavity mirror 303; and to provide a second detection light that is incident into the first entrance aperture 3021 and reciprocated between the second type of annular reflection regions of the first cavity mirror 302 and the first cavity mirror 303. During the integration and reflection process between the integration regions, a portion of the first probe light is emitted from the integration region of the second cavity mirror 303 to the detection unit 6 each time. The second detection light is emitted from the first exit hole 3031 to the semi-transparent mirror 4. The semi-transparent mirror 4 is used to split the second detection light into a third detection light and a fourth detection light. The third detection light is transmitted through the semi-transparent mirror 4 to the detection unit 6. The fourth detection light is reflected by the semi-transparent mirror 4 to the second entrance hole 3032, and is reflected back and forth between the first cavity mirror 302 and the second cavity mirror 303 in a ring-shaped reflection area, and is emitted from the second exit hole 3033 to the detection unit 6.

[0029] As an optional embodiment, the light source 1 includes lasers of various wavelengths, specifically a set of DFB lasers, each corresponding to the center wavelength of the absorption peak of a different sample gas. When measuring a certain sample gas, the light source 1 simply provides probe light of the corresponding wavelength. Furthermore, a light source driving circuit 704 is provided for driving and controlling the light source 1.

[0030] As an optional embodiment, a collimator group is further provided at the front end of the gas absorption cell. The collimator group includes multiple collimators corresponding to different beams, and probe light of different wavelengths emitted by the light source enters different collimators. The probe light is collimated and shaped by the collimators. In addition, the transmission angle of the probe light beam can be changed by adjusting the angle of each collimator.

[0031] It should be understood that this invention is not limited to dividing the first cavity mirror 302 and the second cavity mirror 303 into only the aforementioned three regions: the integration region (the region with radius R1), the first type of annular reflection region (the annular region between R1 and R2), and the second type of annular reflection region (the annular region between R2 and R3). The number of regions and the size of each region depend specifically on the actual gas detection requirements, such as the detection wavelength, spot size, and shape determined according to the type of gas being detected. In this embodiment of the invention, the first cavity mirror 302 and the second cavity mirror 303 of the gas absorption cell are specifically divided into a circular integration region based on the integrating cavity output spectroscopy technology, and multiple annular reflection regions outside the integration region based on multi-pass cell technology. Among the annular reflection regions of the first cavity mirror 302 and the second cavity mirror 303, there is at least one pair of annular reflection regions with an angle between their optical axes. This type of annular reflection region is denoted as the first type of annular reflection region, and the other annular reflection regions with coincident optical axes are denoted as the second type of annular reflection region.

[0032] As an optional embodiment, the gas chamber 301 is a sealed cavity filled with the gas sample to be tested, serving as a space for the gas to interact with the probe light. An inlet 3011 and an outlet 3012 are respectively provided on the outer wall of the gas chamber 301. A mass flow controller 3013 is located at the inlet 3011, used to configure the gas flow rate parameters entering the gas chamber 301 through the inlet 3011. A pressure closed-loop control component 3014 and a tunable air pump 3015 are located at the outlet 3012. The pressure closed-loop control component 3014 measures the internal gas pressure of the gas chamber 301 and controls the outlet rate of the tunable air pump 3015 through a closed loop to achieve pressure balance in the gas chamber 301. Ensuring the gas pressure within the gas chamber 301 allows the probe light and the gas sample to react under optimal conditions.

[0033] The first cavity mirror 302 and the second cavity mirror 303 are respectively disposed at both ends of the gas chamber 301, and are commonly 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 with a single optical path, they cannot simultaneously meet the needs of multiple optical path lengths such as several meters, tens of meters, and hundreds of meters. Therefore, in this embodiment of the invention, both the first cavity mirror 302 and the second cavity mirror 303 are divided into an integrating region based on off-axis integrating cavity enhancement technology and multiple annular reflection regions based on multi-pass cell technology. At least one pair of annular reflection regions with an angle between their optical axes exists in the annular reflection regions of the first cavity mirror 302 and the second cavity mirror 303. Specifically, in this embodiment, the first cavity mirror 302 and the second cavity mirror 303 are designed and divided into three regions: an integrating region (region with radius R1), a type I annular reflection region (annular region between R1 and R2), and a type II annular reflection region (annular region between R2 and R3), to meet the detection requirements of different optical paths. Described sequentially from the center to the edge of the cavity mirror, the integrating region (region with radius R1) of the first cavity mirror 302 and the second cavity mirror 303 is processed into a coaxial plano-concave lens structure, with the concave surface facing the interior of the gas chamber 301. That is, the opposite surfaces of the integrating regions of the first cavity mirror 302 and the second cavity mirror 303 are concave, and the opposite surfaces are planar. Furthermore, an anti-reflection film is deposited on the concave surface, and the anti-reflection film material is a dielectric film. In this embodiment, the specific materials of the anti-reflection film are Ta2O5 and SiO2, 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. Taking the strong absorption peak of carbon monoxide as an example, its center wavelength is 2332 nm. When the reflectivity of the anti-reflective coating is designed to be 99.95%, the number of stacked layers is 27, and the film thickness is 9.3 micrometers. In this case, the radius R1 of the integration region is determined by the collimated light 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 integration region, and the radius R1 of the integration region generally has a margin. For example, assuming that in this embodiment of the invention, the first probe light provided by the light source 1 is transmitted into the integration region of the first cavity mirror 302 and reflects back and forth between the integration regions of the first cavity mirror 302 and the second cavity mirror 303, and the first probe light has a diameter of 9 micrometers after beam expansion by the collimator, then the radius R1 of the integration region needs to be 12 micrometers. Furthermore, the radius of curvature of the integration region... Generally designed as The first cavity mirror 302 and the second cavity mirror 303 form an off-axis integrating cavity structure. The first probe light is reflected back and forth between the integrating regions of the first cavity mirror 302 and the second cavity mirror 303. In each reflection cycle, when the first probe light is reflected onto the second cavity mirror 303, a portion of the first probe light will be emitted from the integrating region of the second cavity mirror 303. The higher the reflectivity of the integrating region, the longer the effective optical path during this part of the reflection process, which can reach hundreds of meters to kilometers. Therefore, the carbon monoxide gas concentration at the ppm level and higher precision can be detected based on the integrated spectrum detection results of this part of the emitted light.

[0034] 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, in this invention, the integrating regions of the first cavity mirror 302 and the second cavity mirror 303 form an integrating cavity structure. Relying on a high-reflection film, long-path oscillating reflection is achieved, independent of coherence. Therefore, the first detection light can also be incoherent. The intensity of the first detection light transmitted from the exit surface has been significantly weakened 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. The integrating regions of the first cavity mirror 302 and the second cavity mirror 303 can achieve long-path beam transmission, with optical paths reaching hundreds of meters to kilometers. Therefore, the integrating region can serve as a detection area for gases such as carbon monoxide at the ppm level and even higher precision.

[0035] The outer side of the integrating region is a type of annular reflection region (annular area between R1 and R2). Through processing, this region is fabricated so that the optical axes of the type of annular reflection region of the first cavity mirror 302 and the type of annular reflection region of the second cavity mirror 303 have an angle, meaning that the type of annular reflection region of the first cavity mirror 302 and the type of annular reflection region of the second cavity mirror 303 are relatively tilted and not parallel to each other, exhibiting a certain tilt angle. Figure 2 The diagram shows the process of machining a type-one annular reflective region of the first cavity mirror 302 into an inclined state. In reality, the type-one annular reflective region of the first cavity mirror 302, the type-one annular reflective region of the second cavity mirror 303, or even both of them can be machined into an inclined state. That is, the maximum tangent plane of the type-one annular reflective region of the first cavity mirror 302 is not perpendicular to the optical axis of the integrating region of the first cavity mirror 302, and / or the maximum tangent plane of the type-one annular reflective region of the second cavity mirror 303 is not perpendicular to the optical axis of the integrating region of the second cavity mirror 303. The centers of the type-one annular reflective regions of the first cavity mirror 302 and the first cavity mirror 303 are spaced a certain distance k in the vertical direction. Furthermore, the radius of curvature of the type-one annular reflective region... The radius of curvature is significantly smaller than that in the integration 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 for the reflection of a type of annular reflective region, i.e., multiple small circular light spots distributed within the annular reflective region. The coating on the 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%.

[0036] The outer side of the first-type annular reflection region is the second-type annular reflection region (the annular area between R2 and R3). Through processing techniques, this region is fabricated so that the optical axes of the second-type annular reflection regions of the first cavity mirror 302 and the second cavity mirror 303 coincide, meaning that the second-type annular reflection regions of the first cavity mirror 302 and the second cavity mirror 303 are parallel to each other. Furthermore, the radius of curvature of the second-type annular reflection region... For a large radius of curvature, it can also be designed as The design aims to make the light spot landing point in the type-II annular reflector region resemble the circular light spot landing point in 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 integration region (R1 region) and the type-II annular reflector 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 a type of annular reflective region (the annular region between R1 and R2).

[0037] The three regions mentioned above are used to provide three different optical path designs with different optical paths. The integration region forms an off-axis integrating cavity structure, and the effective optical path of this region can reach hundreds of meters to kilometers. The first type of annular reflection 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 integration region. The second type of annular reflection region forms a short optical path traditional multi-pass cell structure, and its effective optical path is significantly less than that of the first type of annular reflection region.

[0038] In this embodiment of the invention, the first cavity mirror 302 and the second cavity mirror 303 are divided into three reflection zones, each corresponding to one of three different optical paths. The light source 1 in this embodiment provides two probe beams, namely a first probe beam and a second probe beam. Correspondingly, the collimator assembly is designed to include a first collimator 201 and a second collimator 202, which are used to process the first probe beam and the second probe beam, respectively.

[0039] For the integration region, its mirror body is a lens structure, so the first detection light can be directly transmitted into the integration region through the outer surface of the integration region and reflected back and forth between the integration regions of the first cavity mirror 302 and the second cavity mirror 303 to achieve long optical path transmission, corresponding to the first type of gas detection.

[0040] Since the mirrors in the first and second type annular reflection regions are non-lens structures, this embodiment of the invention first provides a first entrance aperture 3021 on the first cavity mirror 302 to facilitate the entry of the second probe light through the first entrance aperture 3021, and to allow it to reciprocate between the second type annular reflection regions of the first and second cavity mirrors 302 and 303. Furthermore, a first exit aperture 3031, a second entrance aperture 3032, and a second exit aperture 3033 are provided on the second cavity mirror 303. The first exit aperture 3031 facilitates the exit of the second probe light, and the spot of the second probe light in the second type annular reflection region presents a single circular multi-pass cell spot.

[0041] After the second detection light is emitted from the first exit hole 3031, a semi-transparent and semi-reflective mirror 4 is also provided in the optical path between the second cavity mirror 303 and the detection unit 6. The second detection light shines on the semi-transparent and semi-reflective mirror 4 and is split into two beams by the semi-transparent and semi-reflective mirror 4, namely the third detection light and the fourth detection light. Among them, the third detection light is transmitted to the detection unit 6 through the semi-transparent and semi-reflective mirror 4. The effective absorption optical path of the third detection light between the two types of annular reflection areas of the first cavity mirror 302 and the second cavity mirror 303 is set to L1 to achieve short optical path transmission, corresponding to the second type of gas detection.

[0042] Because the light spots in a multi-pass cell structure cannot overlap, the number of reflections is limited, and the optical path is generally in the range of meters to tens of meters. To increase the optical path and achieve a path of tens to hundreds of meters, this invention designs a semi-transparent and semi-reflective mirror 4 to achieve secondary incidence of the probe light. After the fourth probe light exits the gas chamber 301 through the first exit hole 3031, it is again reflected back into the gas chamber through the second entrance hole 3032 by the semi-transparent and semi-reflective mirror 4, and is reflected back and forth between the first type of annular reflection area of ​​the first cavity mirror 302 and the second type of annular reflection area of ​​the second cavity mirror 303. Since the first type of annular reflection areas of the first cavity mirror 302 and the second cavity mirror 303 are not parallel and have a certain tilt angle, the fourth probe light will have a small deflection angle during each reflection in the first type of annular reflection area. In this way, the fourth probe light can achieve non-overlapping multi-turn transmission, forming a small, dense multi-circular light spot on the first type of annular reflection area, that is, the non-overlapping multi-circular multi-pass cell light spot landing point. This reflected light path has a longer optical path than the ordinary circular light path in the type II annular reflection zone, and finally leaves the gas chamber 301 through the second exit hole 3033. Assuming that the effective optical path of reciprocating reflection in the type I annular reflection zone is L2, then the effective optical path of the fourth detection light is L1+L2, which is generally between tens of meters and hundreds of meters. After the fourth detection light is emitted, it is received by the detector group 6 and converted into an electrical signal to achieve medium-to-long optical path transmission, corresponding to the third type of gas detection.

[0043] As an optional embodiment, a reflector 5 is also provided. The fourth detection light is reflected by the semi-transparent and semi-reflective mirror 4 to the reflector 5. The angle of the fourth detection light can be adjusted by the reflector 5. Under the action of the semi-transparent and semi-reflective mirror 4 and the reflector 5, the incident angle of the fourth detection light can be flexibly changed, so that the fourth detection light is transmitted between the first cavity mirror 302 and the second cavity mirror 303 through the second entrance hole 3032.

[0044] As an alternative embodiment, the reflectivity to transmittance of the semi-transparent mirror is not limited to 1:1 and can be replaced with other ratios to adjust the signal-to-noise ratio of the final received signal.

[0045] The reason for the formation of small, dense, multi-circular light spots in the type-one annular reflection region is explained as follows: In this embodiment of the invention, the optical axes of the type-one annular reflection region of the first cavity mirror 302 and the type-one annular reflection region of the second cavity mirror 303 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 302 and / or the second cavity mirror 303. Thus, it will not continue the traditional single-circular multi-pass cell light spot landing point as in the type-one annular reflection region, 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 3The 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.

[0046] 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.

[0047] As an optional embodiment, the detection unit 6 includes a first detector 601, a second detector 602, and a third detector 603, which are respectively used to detect detection light signals with multiple optical paths obtained on the detection unit. Custom detection of different gases is achieved based on the detection light signals with different optical paths. The detection light signals with multiple optical paths include: a first detection light acquisition signal with a first optical path, a third detection light acquisition signal with a second optical path, and a fourth detection light acquisition signal with a third optical path. The light signal acquisition process of the detection unit 6 is as follows: the detection unit 6 acquires the detection light signal after absorption by the gas.

[0048] As an optional embodiment, the multi-path gas detection system compatible with multi-channel and integral detection further includes a processor. The processor specifically includes a data acquisition unit 701, an FPGA 702, and a communication interface 703. The data acquisition unit 701 acquires the optical signals recorded by the detection unit 6 and converts them into electrical signals to obtain gas detection data. The gas detection data is then transmitted to the FPGA 702, which processes the data and transmits it outward as a scanning signal via the communication interface 703. Furthermore, in this embodiment, the FPGA 702 enables multi-line parallel control. The FPGA 702 can also control the mass flow controller 3013, the pressure closed-loop measurement and control component 3014, and the tunable gas pump 3015 to perform real-time measurement and control of the gas pressure in the gas chamber 301. On the other hand, the FPGA 702 can also control the light source drive circuit 704 by sending modulation signals to control different lasers in the light source 1 to provide detection light of different wavelengths.

[0049] As an optional embodiment, the first detector 601, the second detector 602, and the third detector 603 are arranged in the same plane.

[0050] As an optional embodiment, since the second cavity mirror 303 has a second exit hole 3033 on the annular reflection region of the second cavity mirror 303 and a first exit hole 3031 on the second annular reflection region of the second cavity mirror 303, the integration region is the transmitted signal. The three sets of signals to be measured are at different distances from the center of the second cavity mirror 303 in space. That is, if the first detector 601, the second detector 602 and the third detector 603 are arranged in the same plane, the detectors need to be arranged in a longitudinal space on one plane. However, when the detector volume is large or the number of detectors to be designed is large, such as when there is a cooled mercury cadmium telluride detector in the detection unit 6, it is difficult to arrange multiple wavelength detectors simultaneously on the same plane. Therefore, the present invention adds a feature such as between the second cavity mirror 303 and the detection unit 6. Figure 4 The irregular beam adjustment component 8 shown adjusts the tilt angles of the first, third, and fourth probe beams incident on the different detection target surfaces of the first detector 601, second detector 602, and third detector 603 in the detection unit 6. Specifically, the irregular beam adjustment component 8 is an irregularly shaped lens, which includes multiple annular lens areas corresponding to different probe beams. Different lens areas of the irregularly shaped lens have different thicknesses and probe beam exit surface tilt angles. The lens thickness of each annular lens area increases or decreases from its inner diameter to its outer diameter. The design is tailored to different optical paths and exit points in different regions, achieving focusing or changing the direction of the optical path. The adjusted probe beams are focused or transmitted to the first detector 601, second detector 602, and third detector 603 for reception. In this design, the first detector 601, second detector 602, and third detector 603 can be distributed horizontally, solving the pressure of a compact planar layout of the detectors. It should be noted that the distribution of the first detector 601, the second detector 602, and the third detector 603 is related to the focusing degree or the direction of probe light transmission. The first detector 601, the second detector 602, and the third detector 603 can not only be arranged strictly horizontally, but they may also have distances in both the horizontal and vertical directions. That is, the target surfaces of the first detector 601, the second detector 602, and the third detector 603 can be arranged on different planes.

[0051] Furthermore, the target surfaces of the first detector 601, the second detector 602, and the third detector 603 are arranged on the same plane. The irregular beam adjustment component 8 can also be used to increase the spacing between the light spots of different detection beams incident on the same plane, which facilitates the arrangement of detectors.

[0052] As an optional embodiment, for the irregular beam adjustment component 8, the angle at which the probe light is incident on the detector surface can be changed by adjusting the optical parameters such as the tilt angle, thickness, and detector spatial position of multiple lens areas. When the geometric parameters such as the tilt angle and width of each lens area are perfectly symmetrical about the center of the circle, the incident angle on the detector surface is fixed and exhibits perfect axisymmetry with the circle as the center. In this case, the probe signal received by the detector does not have a phase difference caused by the incident angle. Alternatively, the lens area can be designed to be non-axially symmetrical. By appropriately adjusting the tilt angle and width at different positions of the lens area, the angle of the probe light will exhibit an asymmetrical angular difference. In this case, the deviation of the 360-degree incident angle cannot be completely canceled out, resulting in an angular deviation of the incident light, which manifests as a phase difference in the received electrical signal. This method can achieve phase modulation of the electrical signal after photoelectric conversion.

[0053] As an optional embodiment, the irregular beam adjustment component 8 can be fabricated as a separate optical element and disposed between the first cavity mirror 303 and the detection unit 6.

[0054] As an optional embodiment, the irregular beam adjustment component 8 can be directly integrated into the back surface of the first cavity mirror 303, i.e., the surface facing away from the first cavity mirror 302. The irregular beam adjustment component 8 is formed by integrating and processing the back surface of the first cavity mirror 303.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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 detection system compatible with multi-pass cell and integral detection, comprising: A light source, a gas absorption cell, and a detection unit, wherein the gas absorption cell includes a gas chamber, and a first cavity mirror and a second cavity mirror disposed within the gas chamber, characterized in that it further includes a semi-transparent and semi-reflective mirror; Both the first cavity mirror and the second cavity mirror include at least: an integrating region, and a first-class annular reflection region and a second-class annular reflection region disposed outside the integrating region; The optical axes of the first type of annular reflection region of the first cavity mirror and the second type of annular reflection region of the second cavity mirror are at an angle; the optical axes of the second type of annular reflection region of the first cavity mirror and the second type of annular reflection region of the second cavity mirror coincide. The first cavity mirror has a first entrance aperture on its type II annular reflection area, and the second cavity mirror has a first exit aperture on its type II annular reflection area; the second cavity mirror has a second entrance aperture and a second exit aperture on its type I annular reflection area. The light source is used to provide a first probe light that is transmitted through the integrating region of the first cavity mirror and reciprocated between the integrating regions of the first cavity mirror and the second cavity mirror; and to provide a second probe light that is incident through the first entrance aperture and reciprocated between the two types of annular reflection regions of the first cavity mirror and the second cavity mirror. During the integration and reflection process between the integration regions, a portion of the first probe light is emitted from the integration region of the second cavity mirror to the detection unit each time. The second detection light is emitted from the first exit hole to the semi-transparent mirror, which splits the second detection light into a third detection light and a fourth detection light. The third detection light is transmitted through the semi-transparent mirror to the detection unit. The fourth detection light is reflected by the semi-transparent mirror to the second entrance hole and is reflected back and forth between a type of annular reflection area of ​​the first cavity mirror and the second cavity mirror, and is emitted from the second exit hole to the detection unit.

2. The multi-path gas detection system compatible with multi-pass cells and integral detection according to claim 1, characterized in that, The outer wall of the air chamber is provided with an air inlet and an air outlet. A mass flow controller is installed at the air inlet, which is used to configure the gas flow rate parameters entering the air chamber through the air inlet. A pressure closed-loop measurement and control component and an adjustable air pump are installed at the air outlet. The pressure closed-loop measurement and control component is used to measure the air pressure inside the air chamber, and the adjustable air pump is used to control the air outlet rate according to the measured air pressure inside the air chamber.

3. The multi-path gas detection system compatible with multi-pass cells and integral detection according to claim 1, characterized in that, Both the integrating regions of the first and second cavitation mirrors are plano-concave lens structures. The opposite surfaces of the integrating regions of the first and second cavitation mirrors are concave, while the opposite surfaces are planar. Furthermore, anti-reflection coatings are provided on the concave surfaces of the integrating regions of both the first and second cavitation mirrors.

4. The multi-path gas detection system compatible with multi-pass cell and integral detection according to claim 1, characterized in that, The first probe light is either coherent or incoherent.

5. The multi-path gas detection system compatible with multi-pass cell and integral detection according to claim 1, characterized in that, The radius of curvature of the first type of annular reflection region is smaller than that of the second type of annular reflection region and the integral region. The radii of curvature of the second type of annular reflection region and the integral region may be the same or different.

6. The multi-path gas detection system compatible with multi-pass cell and integral detection according to claim 4, characterized in that, The second probe light spot in the type II annular reflection region appears as a single circular multi-pass cell spot; the fourth probe light spot in the type I annular reflection region appears as a non-overlapping multi-circular multi-pass cell spot.

7. The multi-path gas detection system compatible with multi-pass cell and integral detection according to claim 1, characterized in that, Also includes: The processor is used to collect detection light signals of multiple optical paths obtained by the detection unit, and to realize customized detection of different gases according to the detection light signals of different optical paths. The detection light signals of multiple optical paths include: a first detection light acquisition signal of a first optical path, a third detection light acquisition signal of a second optical path, and a fourth detection light acquisition signal of a third optical path.

8. The multi-path gas detection system compatible with multi-pass cell and integral detection according to claim 1, characterized in that, An irregular beam adjustment component is provided between the second cavity mirror and the detection unit. The irregular beam adjustment component is used to adjust the tilt angle of different detection beams incident on different detection target surfaces in the detection unit.

9. The multi-path gas detection system compatible with multi-pass cell and integral detection according to claim 8, characterized in that, The tilt angle of different probe beams incident on different probe target surfaces is adjusted by the irregular beam adjustment component, so that different probe target surfaces in the detection unit can be arranged on different planes, or the spacing between the light spots of different probe beams incident on the same plane can be increased.

10. The multi-path gas detection system compatible with multi-pass cells and integral detection according to claim 8, characterized in that, The irregular beam adjustment component is an irregular lens, which includes multiple lens areas corresponding to different probe beams. The different lens areas of the irregular lens have different thicknesses and probe beam exit surface tilt angles. The irregularly shaped lens is disposed as an independent optical element between the second cavity mirror and the detection unit; or the irregularly shaped lens is integrated and processed on the surface of the second cavity mirror facing away from the first cavity mirror.

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