Wide dynamic range laser spectroscopy gas concentration detection device and method

Abstract

This invention relates to a wide dynamic range laser spectroscopy gas concentration detection device and method. The device includes: a long-path absorption cell comprising two opposing first and second concave mirrors, wherein during operation, a first laser beam undergoes multiple reflections between the two concave mirrors to form a first absorption optical path; an optical resonant cavity sharing a gas cavity with the long-path absorption cell, comprising a second entrance window and a second exit window disposed at the geometric center region of the first and second concave mirrors, wherein the geometric center region is the non-spot region of the first laser beam; and a pair of high-reflectivity mirrors respectively disposed on the second entrance window and the second exit window, wherein during operation, the second laser beam undergoes multiple reflections between the two high-reflectivity mirrors to form a second absorption optical path; the second absorption optical path is not less than 100 times the first absorption optical path. This invention combines the advantages of both the long-path absorption cell and the optical resonant cavity, achieving full-range gas concentration measurement from ultra-low concentrations (ppb) to percentage concentrations through a single gas chamber.

Description

Technical Field

[0001] This invention relates to the field of laser spectroscopy gas detection technology, and in particular to a wide dynamic range laser spectroscopy gas concentration detection device and method. Background Technology

[0002] Existing laser spectroscopy gas detection technologies typically employ a single optical structure, including a long-path absorption cell and an optical resonant cavity. The long-path absorption cell, using designs such as White cells or Herriott cells, extends the interaction path between light and gas through multiple reflections (the laser spot distribution can be controlled by the mirror spacing and curvature to achieve tens to hundreds of reflections). Based on laser absorption spectroscopy (LAS) technology, it achieves high-sensitivity gas detection within a limited volume, suitable for medium to high concentration detection (ppm-% level). The optical resonant cavity is based on cavity enhancement technology (off-axis integrating cavity OA-ICOS, cavity ring-down spectroscopy, etc.), utilizing two cavity mirrors with ultra-high reflectivity (typically ≥99.99%) to repeatedly reflect the laser between the mirrors, forming a stable standing wave. Stimulated emission amplifies the light intensity, achieving an effective absorption optical path of several kilometers or even tens of kilometers, particularly suitable for trace detection (ppb-ppm level). However, neither of these single optical structures can simultaneously meet the detection requirements of an extremely wide dynamic range from ppb to percentage concentration. ppm represents parts per million, or 10. -6 ppb represents one part per hundred million, or 10 -9 .

[0003] If the two devices are used in series, it will not only make the system complex and costly, but also cause time and space differences in detection, resulting in changes in the gas state and poor consistency of the detection results. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a wide dynamic range laser spectroscopy gas concentration detection device and method, solving the technical problem that existing technologies cannot achieve full-range measurement from ultra-low concentration (ppb) to percentage concentration using a single gas concentration detection device.

[0005] The technical solution adopted in this invention is as follows:

[0006] This invention provides a wide dynamic range laser spectroscopy gas concentration detection device, the detection device comprising a composite optical gas cell formed by coupling a long optical path absorption cell and an optical resonant cavity;

[0007] The structure of the long optical path absorption cell is as follows: it includes a gas cavity with two low-reflection mirrors arranged opposite each other on both sides, namely a first concave mirror and a second concave mirror; and a first entrance window and a first exit window, which are respectively disposed on the first and second concave mirrors, or both disposed on the first concave mirror; the first entrance window is used to transmit a first laser beam, which is used to reflect multiple times between the two oppositely arranged low-reflection mirrors to form a first absorption optical path, and finally emitted from the first exit window and received by the first detector;

[0008] The optical resonant cavity and the long-path absorption cell share a gas cavity, including two opposing transmission windows: a second entrance window located in the geometric center region of the first concave mirror and a second exit window located in the geometric center region of the second concave mirror, the geometric center region being the non-spot region of the first laser; and two opposing high-reflectivity mirrors: a first high-reflectivity mirror located on the inner wall of the second entrance window and a second high-reflectivity mirror located on the inner wall of the second exit window; the second entrance window is used to transmit the second laser, which is reflected multiple times between the first and second high-reflectivity mirrors to form a second absorption optical path, and finally emitted from the second exit window and received by the second detector;

[0009] The gas chamber is provided with a gas inlet and a gas outlet for introducing and exporting the gas to be tested, respectively.

[0010] The low-reflectivity mirror has a reflectivity of 99%-99.9%, and the high-reflectivity mirror has a reflectivity of ≥99.99%.

[0011] The second absorption optical path is not less than 100 times the first absorption optical path.

[0012] As a preferred technical solution:

[0013] The distance between the non-spot area and the spot area of ​​the nearest first laser is greater than 5 mm.

[0014] The spot area of ​​the first laser is distributed in a ring shape with the geometric center area as the center, the cross-section of the air cavity is circular, and the non-spot area is located in the central area of ​​the low-reflection mirror.

[0015] The first absorption optical path is 1-100m, and the second absorption optical path is 1-50km.

[0016] The incident angle of the first laser ranges from 0.5° to 5°; the incident angle of the second laser is 0°, i.e., horizontal incident.

[0017] The first laser and the second laser are generated by two independent lasers, or by the same laser that is split by a beam splitter.

[0018] The present invention also provides a detection method for the wide dynamic range laser spectroscopy gas concentration detection device, comprising:

[0019] Inject the gas to be tested into the gas chamber;

[0020] The first method of detection includes:

[0021] First, the long optical path absorption cell is activated to excite the first laser. The laser is reflected multiple times between the two low-reflection mirrors to form the first absorption optical path, which is absorbed by the gas to be measured and finally received by the first detector. Thus, the first detection value of the concentration of the gas to be measured is obtained based on wavelength modulation spectroscopy or direct absorption spectroscopy.

[0022] If the first detection value is within the first concentration range detectable by the long optical path absorption cell, it shall be taken as the final detection result;

[0023] If the first detected value is close to the minimum limit of the first concentration range, then the optical resonant cavity is activated:

[0024] The second laser is excited, and it is reflected multiple times between the two highly reflective mirrors to form a second absorption optical path. It is absorbed by the gas to be tested and finally received by the second detector. Thus, a second detection value of the concentration of the gas to be tested is obtained based on cavity enhancement spectroscopy or cavity ring-down spectroscopy. The second detection value is used as the final detection result.

[0025] The first concentration range is (10 ppm, 100%).

[0026] As a preferred technical solution:

[0027] The detection method further includes:

[0028] Alternatively, a second method can be used for detection, including:

[0029] Simultaneously, a long-path absorption cell and an optical resonant cavity are activated, and the first laser and the second laser are used for synchronous detection to obtain the first detection value and the second detection value.

[0030] If the first detection value is close to the limit of the first concentration range, the second detection value will be used as the final detection result;

[0031] If the first detection value is within the first concentration range and the second detection value is within the second concentration range, the second detection value shall be taken as the final detection result;

[0032] The second concentration range is (1 ppb, 10 ppm).

[0033] The wavelengths of the first and second lasers are located in the near-infrared or mid-infrared bands.

[0034] The first laser and the second laser have the same response time.

[0035] The technical solution of the present invention can achieve at least some of the following beneficial effects:

[0036] This invention directly integrates a high-reflectivity mirror on the reflecting surface of a long-path absorption cell, coupling the advantages of both the long-path absorption cell and the optical resonant cavity. By performing dual-path detection based on laser absorption spectrum and optical cavity ring decay in the same gas chamber, it achieves full-range concentration measurement from ultra-low concentration (ppb) to percentage concentration in the same gas chamber. The device has a compact structure and is easy to operate.

[0037] Compared with the direct physical connection of long-path absorption cells and optical resonant cavities, this invention only has one air cavity, shares the same mechanical reference (the same set of reflector brackets), and shares the same sealing system and temperature control system, which improves the stability of the measurement system, ensures consistent thermal drift, and thus ensures the consistency of measurement results.

[0038] This invention can measure gas concentration in two ways, each suitable for different operating conditions. The first method enables automatic switching of the measurement range. The second method enables simultaneous detection of gas at the same time and location using two optical paths, resulting in good synchronization and improved consistency of gas concentration during detection.

[0039] Other features and advantages of the invention will be set forth in the following description or may be learned by practicing the invention. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the detection device according to an embodiment of the present invention.

[0041] Figure 2 This is a schematic diagram of the optical path distribution on the low-reflection mirror inside the air cavity of the detection device according to an embodiment of the present invention.

[0042] Explanation of reference numerals in the attached drawings: 1. First concave mirror; 2. Second concave mirror; 3. Gas inlet; 4. Gas outlet; 5. First high-reflectivity mirror; 6. Second high-reflectivity mirror; 7. Gas cavity; 8. Laser I; 9. Laser II; 10. First detector; 11. Second detector; 12. First entrance window; 13. Second entrance window; 14. Second exit window; 15. First exit window. Detailed Implementation

[0043] The specific embodiments of the present invention are described below with reference to the accompanying drawings.

[0044] Example 1

[0045] See Figure 1The wide dynamic range laser spectrum gas concentration detection device of this embodiment includes a composite optical gas cell, which is formed by coupling a long optical path absorption cell and an optical resonant cavity.

[0046] The structure of the long-path absorption cell includes: a gas cavity 7 with two low-reflection mirrors arranged opposite each other on both sides, namely a first concave mirror 1 and a second concave mirror 2; a first entrance window 12 and a first exit window 15, respectively disposed on the first and second concave mirrors, or both disposed on the first concave mirror 1; the first entrance window 12 is used to transmit the first laser (see reference). Figure 1 The red line in the middle is used to reflect multiple times between two oppositely arranged low-reflection mirrors to form the first absorption optical path, which is finally emitted from the first exit window 15 and received by the first detector 10.

[0047] The optical resonant cavity and the long-path absorption cell share a gas cavity 7, and include two opposing transmission windows: a second entrance window 13 located in the geometric center region of the first concave mirror 1 and a second exit window 14 located in the geometric center region of the second concave mirror 2, the geometric center region being the non-spot region of the first laser; and two opposing high-reflectivity mirrors: a first high-reflectivity mirror 5 located on the inner wall of the second entrance window 13 and a second high-reflectivity mirror 6 located on the inner wall of the second exit window 14; the second entrance window 13 is used to transmit the second laser (see...). Figure 1 The green line in the middle is used for multiple reflections between the first high-reflection mirror 5 and the second high-reflection mirror 6 to form the second absorption optical path, and finally it is emitted from the second exit window 14 and received by the second detector 11.

[0048] The gas chamber 7 is equipped with a gas inlet 3 and a gas outlet 4, which are used to introduce and export the gas to be tested, respectively.

[0049] The second absorption path length is not less than 100 times that of the first absorption path length.

[0050] The detection device in this embodiment essentially combines the advantages of two individual optical structures—a long-path absorption cell and an optical resonant cavity—to achieve dual-path composite detection within the same optical chamber, thereby enabling full-range coverage from ppb to percentage concentration. Based on the working principles and characteristics of these two individual optical structures, it is known that the two low-reflectivity mirrors of the long-path absorption cell have a reflectivity of 99%-99.9%, while the two high-reflectivity mirrors of the optical resonant cavity have a reflectivity ≥99.99%.

[0051] In one specific embodiment, the long optical path absorption cell can be designed as a Herriott-type multi-pass cell or a similar multi-pass cell. In this form, both the first incident window 12 and the first exit window 15 are located on the first concave mirror 1, such as... Figure 1 As shown.

[0052] By adaptively adjusting the specific positions of the first entrance window 12 and the first exit window 15, as well as the structural parameters and spacing of the first concave mirror 1 and the second concave mirror 2, interference between the first laser and the second laser optical paths can be avoided. This ensures that the geometric center area where the two highly reflective mirrors are located is a non-spot area not used by the first laser, thus avoiding the competition and conflict between the two optical paths at the center of the mirror surface. This achieves rational use of space and solves the contradiction that the resonant cavity requires a mirror with extremely high reflectivity while the long optical path cell does not.

[0053] As a preferred approach, the first laser incident angle is controlled within the range of 0.5° to 5°, consistent with the incident angle requirements of a typical Herriott cell. The specific angle depends on adaptive adjustments such as the required number of reflections, total optical path, and mirror size. The second laser incident angle is strictly 0°, consistent with the incident angle requirements of an optical resonator employing cavity ring-down spectroscopy technology.

[0054] As a preferred method, the distance between the non-spot area and the spot area of ​​the nearest first laser is greater than 5 mm by adjusting the spacing between the first and second laser incident points. In actual implementation, it is sufficient to ensure that the incident point spot and the spectrum in the absorption cell do not overlap.

[0055] See Figure 2 The cross-section of the air cavity 7 is circular, and the non-spot area is located at the center of the low-reflection mirror. In one specific embodiment, the spot area of ​​the first laser is distributed in a ring shape with the geometric center area as the center, such as... Figure 2 As shown by the red dot. The second laser beam is concentrated in the center of the highly reflective mirror, as shown... Figure 2 As shown by the green dot in the middle.

[0056] As a preferred embodiment, the first absorption optical path is 1-100m, and the second absorption optical path is 1-50km. The specific values ​​of the two absorption paths can be adjusted using conventional techniques based on the working principles of the two optical structures, which will not be elaborated in this embodiment.

[0057] In one specific embodiment, the dimensions (diameter) of the two low-reflectivity mirrors are in the centimeter range, preferably 10 cm; the dimensions (diameter) of the two high-reflectivity mirrors are in the millimeter range, preferably 5 mm.

[0058] In one specific embodiment, the high-reflectivity lens is fixed to the second entrance / exit window by means of optical adhesive or the like.

[0059] In one specific embodiment, the first entrance window, the first exit window, the second entrance window, and the second exit window employ transmissive optical elements, such as optical windows coated with antireflective films.

[0060] In one specific embodiment, the first laser and the second laser are respectively output by two independent lasers, namely Figure 1 As shown in Laser 8 and Laser 9, the beams can be formed by splitting the output of the same laser through a beam splitter. When the output is from the same laser, the lasers can be controlled by time-division multiplexing to achieve alternating output of the two lasers.

[0061] Specifically, the laser used in this embodiment has a tuning function component, and both the first and second lasers are tunable lasers.

[0062] Specifically, other accessories that meet the working requirements of the long-path absorption cell and optical resonant cavity configuration, such as temperature control system, airtight system, air source and other devices, are set according to actual needs and will not be elaborated further.

[0063] Example 2

[0064] This embodiment provides a gas concentration detection method for the wide dynamic range laser spectral gas concentration detection device according to Embodiment 1, including:

[0065] S1. Inject the gas to be tested into the gas chamber 7;

[0066] S2. The first method is used for detection, including

[0067] S21. First, the long optical path absorption cell is activated to excite the first laser. The laser is reflected multiple times between two low-reflection mirrors to form the first absorption optical path, which is absorbed by the gas to be measured and finally received by the first detector 10. Thus, the first detection value of the concentration of the gas to be measured is obtained based on wavelength modulation spectroscopy or direct absorption spectroscopy.

[0068] S22. If the first detection value is within the first concentration range detectable by the long optical path absorption cell, then it shall be taken as the final concentration detection result;

[0069] S23. If the first detection value is close to the minimum limit of the first concentration range, it indicates that the concentration of the gas to be measured may be less than the concentration detection range of the long optical path absorption cell, that is, the gas concentration is low and the long optical path absorption cell may not be able to detect its concentration. Then, the optical resonant cavity is activated: the second laser is excited, which is reflected multiple times between the two high reflectivity mirrors to form the second absorption optical path, and is absorbed by the gas to be measured, and finally received by the second detector 11. Thus, the second detection value of the concentration of the gas to be measured is obtained based on cavity enhancement spectroscopy or cavity ring-down spectroscopy technology, and the second detection value is used as the final concentration detection result.

[0070] Specifically, the first concentration range is (10ppm, 100%), that is, greater than 10ppm and less than 100%, and the maximum limit of the first concentration range is the limit of ppm.

[0071] As a preferred embodiment, the response times of the first laser and the second laser are the same, preferably 100 milliseconds to 10 seconds.

[0072] In one specific embodiment, the wavelengths of the first laser and the second laser are located in the near-infrared band or the mid-infrared band. The wavelengths of the first laser and the second laser are preferably 1-3 μm or 3-20 μm. When the near-infrared band is selected, the overtone transition lines of the gas molecules are utilized; when the mid-infrared band is selected, the fundamental frequency transition lines of the gas molecules are utilized.

[0073] As a preferred embodiment, the method further includes:

[0074] S3. Use the second method instead of the first method for detection, including:

[0075] Simultaneously, a long-path absorption cell and an optical resonant cavity are activated, and the first laser and the second laser are used for synchronous detection to obtain the first detection value and the second detection value.

[0076] If the first detection value is close to the limit of the first concentration range, the second detection value will be used as the final detection result;

[0077] If the first detection value is within the first concentration range and the second detection value is within the second concentration range, the second detection value shall be taken as the final detection result; the second concentration range is (1ppb, 10ppm], that is, greater than 1ppb and not greater than 10ppm.

[0078] The first method demonstrates the convenience of range switching in this embodiment, exhibiting excellent adaptability for concentration detection where the gas concentration is far from the overlapping region of the first and second concentration ranges. The second method demonstrates the good real-time performance of this embodiment's detection method, employing dual-optical-path synchronous detection to achieve dynamic response. It offers better identification for concentration detection where the gas concentration is close to the overlapping region of the first and second concentration ranges. For example, if the first detection value is 11 ppm and the second detection value is 9 ppm, considering the higher detection accuracy of the optical intensity resonant cavity, the second detection value is taken as the final result.

[0079] In summary, this invention creatively couples two chambers into a single detection device, achieving automatic switching of gas concentration measurement range and full coverage of the concentration range through a single gas chamber. It has the advantages of compact structure, convenient operation, and accurate measurement results.

[0080] It will be understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A wide dynamic range laser spectroscopy gas concentration detection device, characterized in that, The detection device includes a composite optical gas cell formed by coupling a long optical path absorption cell and an optical resonant cavity; The structure of the long optical path absorption cell is as follows: it includes a gas cavity (7), on both sides of which are two low-reflection mirrors arranged opposite each other, namely a first concave mirror (1) and a second concave mirror (2); and a first entrance window (12) and a first exit window (15), which are respectively arranged on the first and second concave mirrors, or both are arranged on the first concave mirror (1); the first entrance window (12) is used to transmit the first laser, which is used to reflect multiple times between the two low-reflection mirrors arranged opposite each other to form a first absorption optical path, and finally emitted from the first exit window (15) and received by the first detector (10); The optical resonant cavity and the long optical path absorption cell share a gas cavity (7), which includes two opposing transmission windows, namely a second entrance window (13) located in the geometric center area of ​​the first concave mirror (1) and a second exit window (14) located in the geometric center area of ​​the second concave mirror (2), the geometric center area being the non-spot area of ​​the first laser; and two opposing high reflective mirrors, namely a first high reflective mirror (5) located on the inner wall of the second entrance window (13) and a second high reflective mirror (6) located on the inner wall of the second exit window (14); the second entrance window (13) is used to transmit the second laser, which is used to reflect multiple times between the first high reflective mirror (5) and the second high reflective mirror (6) to form a second absorption optical path, and finally emitted from the second exit window (14) and received by the second detector (11); The gas chamber (7) is provided with a gas inlet (3) and a gas outlet (4) for introducing and exporting the gas to be tested, respectively. The low-reflectivity mirror has a reflectivity of 99%-99.9%, and the high-reflectivity mirror has a reflectivity of ≥99.99%. The second absorption optical path is not less than 100 times the first absorption optical path.

2. The wide dynamic range laser spectroscopy gas concentration detection device according to claim 1, characterized in that, The distance between the non-spot area and the spot area of ​​the nearest first laser is greater than 5 mm.

3. The wide dynamic range laser spectroscopy gas concentration detection device according to claim 1, characterized in that, The spot area of ​​the first laser is distributed in a ring shape with the geometric center area as the center, the cross-section of the air cavity (7) is circular, and the non-spot area is located in the center area of ​​the low reflection mirror.

4. The wide dynamic range laser spectroscopy gas concentration detection device according to claim 1, characterized in that, The first absorption optical path is 1-100m, and the second absorption optical path is 1-50km.

5. The wide dynamic range laser spectroscopy gas concentration detection device according to claim 1, characterized in that, The incident angle of the first laser ranges from 0.5° to 5°; the incident angle of the second laser is 0°, i.e., horizontal incident.

6. The wide dynamic range laser spectroscopy gas concentration detection device according to claim 1, characterized in that... The first laser and the second laser are generated by two independent lasers, or by the same laser that is split by a beam splitter.

7. A detection method for a wide dynamic range laser spectroscopy gas concentration detection device according to any one of claims 1 to 6, characterized in that, include: Inject the gas to be tested into the gas chamber (7); The first method of detection includes: First, the long optical path absorption cell is activated to excite the first laser, which is reflected multiple times between the two low-reflection mirrors to form the first absorption optical path and is absorbed by the gas to be measured. Finally, it is received by the first detector (10), thereby obtaining the first detection value of the concentration of the gas to be measured based on wavelength modulation spectroscopy or direct absorption spectroscopy. If the first detection value is within the first concentration range detectable by the long optical path absorption cell, it shall be taken as the final detection result; If the first detected value is close to the minimum limit of the first concentration range, then the optical resonant cavity is activated: The second laser is excited, and it is reflected multiple times between the two highly reflective mirrors to form a second absorption optical path. It is absorbed by the gas to be tested and finally received by the second detector (11). Thus, the second detection value of the concentration of the gas to be tested is obtained based on cavity enhancement spectroscopy or cavity ring-down spectroscopy technology, and the second detection value is used as the final detection result. The first concentration range is (10 ppm, 100%).

8. The detection method according to claim 7, characterized in that, Also includes: Alternatively, a second method can be used for detection, including: Simultaneously, a long-path absorption cell and an optical resonant cavity are activated, and the first laser and the second laser are used for synchronous detection to obtain the first detection value and the second detection value. If the first detection value is close to the limit of the first concentration range, the second detection value will be used as the final detection result; If the first detection value is within the first concentration range and the second detection value is within the second concentration range, the second detection value shall be taken as the final detection result; The second concentration range is (1 ppb, 10 ppm).

9. The detection method according to claim 7, characterized in that, The wavelengths of the first and second lasers are located in the near-infrared or mid-infrared bands.

10. The detection method according to claim 7, characterized in that, The first laser and the second laser have the same response time.

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