Multi-reflection cavity-enhanced raman system and method for using same

Abstract

A multi-reflection cavity-enhanced Raman system and a method for using same. The multi-reflection cavity-enhanced Raman system comprises a concave mirror (1), a converging lens (2), and an optical fiber bundle (3); the optical fiber bundle (3) comprises a plurality of optical fibers (31) that are horizontally arranged; the converging lens (2), a parallel lens (21), a reaction position (4), and the concave mirror (1) are distributed at the input ends of the optical fibers (31); two ends of the reaction position (4) are provided with a first lens (5), a first retroreflector (51), a second lens (8), and a second retroreflector (81); during use, a laser signal is converged at the reaction position (4) multiple times, then the laser signal reacts with a gas to be detected, so as to generate a Raman signal, a part of the Raman signal is reflected by the concave mirror (1), and then the Raman signal is converged in the optical fibers (31) by the converging lens (2) and the parallel lens (21) and are received by the optical fibers; the Raman signal excited on a horizontal plane cooperates with the horizontally arranged optical fibers (31), and thus, a receiving effect is good; the intensity of the laser signal at the reaction position (4) is high, and thus, the intensity of the generated Raman signal is high.

Description

A multi-reflection cavity enhanced Raman system and its usage method Technical Field

[0001] This invention relates to an enhanced Raman system, belonging to the field of Raman gas detection, and particularly to a multi-reflection cavity enhanced Raman system and its usage method. Background Technology

[0002] Raman spectroscopy is a powerful gas sensing method that overcomes the weaknesses of traditional non-spectral methods, such as long detection times and poor repeatability, while also compensating for the limitation of absorption spectroscopy in directly measuring homonuclear diatomic molecules. Furthermore, it allows for convenient qualitative and quantitative analysis of multi-component gas mixtures using a single-frequency laser. However, the inherently weak Raman effect of substances, coupled with the fact that the Raman effect of gases is typically much weaker than that of solids and liquids, significantly limits the application of Raman spectroscopy in gas sensing.

[0003] In recent years, many studies have proposed corresponding enhancement techniques to improve the detection performance of gas Raman spectroscopy. However, in the current enhancement techniques, the shape of the optical fiber in the fiber bundle cannot be well matched with the shape of the Raman signal, so the optical fiber has poor reception effect for the Raman signal.

[0004] The information disclosed in this background section is intended only to enhance understanding of the overall background of this application and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects and problems of poor Raman signal reception in the prior art, and to provide a cavity-enhanced Raman system and its usage method with better Raman signal reception.

[0006] To achieve the above objectives, the technical solution of the present invention is:

[0007] A multi-reflection cavity enhanced Raman system, the system comprising a concave mirror, a converging lens, and an optical fiber bundle;

[0008] The fiber bundle includes multiple horizontally arranged optical fibers, the input ends of all optical fibers are located at the focal point of one side of a converging lens, the side of the converging lens away from the optical fibers faces the side of the parallel lens, the other side of the parallel lens faces the concave end of the concave mirror, and a reaction point is provided between the concave end and the parallel lens.

[0009] A first lens is provided on one side of the reaction site, and a first retroreflector is provided on the extension line of the first lens away from the reaction site. A laser emitter is provided on the first retroreflector away from the first lens, and the output end of the laser emitter is aligned with one end of the first lens. A second lens is provided on the side of the reaction site away from the first lens, and a second retroreflector is provided on the second lens away from the reaction site.

[0010] The output of all optical fibers is connected to one end of the spectrometer.

[0011] The number of optical fibers in the optical fiber bundle is six to ninety-six, and the numerical aperture range of the spectrometer is 0.05 to 0.2.

[0012] The core diameter of the optical fiber is 10 to 200 micrometers, and the numerical aperture of the optical fiber is 0.1 to 0.4.

[0013] The distance from the concave end to the reaction point is twice the focal length of the concave mirror.

[0014] The focal length ratio of the parallel lens to the converging lens ranges from one-half to twice.

[0015] The width of the first and second retroreflectors is between one-half an inch and two inches.

[0016] The optical axis of the converging lens and the optical axis of the parallel lens are located on the same horizontal line.

[0017] The first retroreflector includes a first horizontal plane and a first vertical plane, one end of the first vertical plane is perpendicularly connected to one end of the first horizontal plane, and the angle between the first horizontal plane and the vertical plane is forty-five degrees.

[0018] The second retroreflector includes a second horizontal plane and a second vertical plane, one end of the second vertical plane is perpendicularly connected to one end of the second horizontal plane, and the angle between the second horizontal plane and the vertical plane is forty-five degrees.

[0019] A method of using a multi-reflection cavity enhanced Raman system, the method comprising the following steps:

[0020] Step 1: Make the laser emitter emit a laser signal;

[0021] The second step is to first focus the laser signal toward the reaction point using the first lens, then turn the laser signal into a parallel laser signal through the second lens, and then reflect the laser signal multiple times in the second and first retroreflectors, so the laser signal will pass through the reaction point multiple times.

[0022] Step 3: The laser signal at the reaction point reacts with the gas to be tested at the reaction point to generate a Raman signal. Part of the Raman signal is directed toward the parallel lens, and part of the Raman signal is directed toward the concave end. The Raman signal directed toward the concave end is then reflected by the concave end, and then the Raman signal directed toward the concave end is transformed into a Raman signal directed toward the parallel lens.

[0023] Step 4: Because the focal point of the parallel lens coincides with the focal point of the laser reflected multiple times at the reaction site, the parallel lens converts the Raman signal into a parallel Raman signal. Then, the converging lens re-images the parallel Raman signal and focuses it into multiple optical fibers on the focal plane of the converging lens. The optical fibers then receive the Raman signal and import it into the spectrometer for analysis.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. In the present invention, a multi-reflection cavity enhanced Raman system and its usage method, the system includes a concave mirror, a converging lens, and an optical fiber bundle. The optical fiber bundle includes multiple horizontally arranged optical fibers. A converging lens, a parallel lens, and a concave mirror are arranged sequentially on the front side of the input end of the optical fibers. A reaction point is provided between the parallel lens and the concave mirror. A first lens, a first retroreflector, and a laser emitter are provided on one side of the reaction point, and a second lens and a second retroreflector are provided on the other side of the reaction point. The output end of the optical fiber is connected to a spectrometer. In application, the laser signal is repeatedly converged at the reaction point under the action of the first and second lenses. Then, the laser signal at the reaction point reacts with the gas to be measured to generate a Raman signal. The Raman signal is then gradually reduced by the parallel lens and the converging lens, and finally converged into the input end of a relatively wide horizontally arranged optical fiber. The spectrometer then processes the Raman signal to determine the type of gas to be measured. The advantages of the present invention also include:

[0026] First, Raman signals are excited in the horizontal plane of the reaction site, and the horizontally arranged optical fibers are aligned with the Raman signals in the horizontal plane, so the shape of the optical fibers and the Raman signals are well matched. Compared with the existing technology, setting the optical fibers in a horizontal arrangement increases the width of the optical fiber range, and the Raman signals located at and near the laser optical path focal point can also be effectively received, increasing the range of Raman signal reception. Therefore, the optical fiber has a better Raman signal reception effect.

[0027] Secondly, the first and second lenses cause the laser signal to converge multiple times at the reaction point, so the laser signal intensity at the reaction point is the greatest, and the Raman signal generated at the reaction point is the strongest, thus increasing the intensity of the Raman signal. Part of the Raman signal is scattered towards the parallel lens, and another part is scattered towards the mirror. The mirror reflects the Raman signal scattered towards the mirror back into the parallel lens, which also increases the intensity of the Raman signal.

[0028] Thirdly, the present invention has a high efficiency in receiving Raman signals, so it can detect the gas even when the content of the gas to be tested is low. Therefore, the present invention can improve the limit of gas detection.

[0029] Fourthly, during the detection process, due to optical components such as the first lens, spherical noise will be generated. However, the spherical noise is outside the optical fiber receiving range and will not be received by the optical fiber. Therefore, the signal-to-noise ratio of this invention is high.

[0030] Therefore, the present invention has a better Raman signal reception effect and the intensity of the received Raman signal is relatively large.

[0031] 2. In the multi-reflection cavity enhanced Raman system and its usage method of the present invention, the distance from the concave mirror to the reaction point is twice the focal length of the concave mirror, the focal length ratio of the parallel lens and the converging lens is 1:1, and the width of the first and second retroreflector mirrors is one inch. In application, because the focal length ratio of the parallel lens and the converging lens is 1:1, the parallel lens, the converging lens, and the optical fiber cooperate well, resulting in good Raman signal reception by the optical fiber. When the distance from the concave mirror to the reaction point is twice the focal length of the concave mirror, the Raman signal can be returned along its original path, at which point the optical fiber has the highest Raman signal reception efficiency. The relatively large width of the first and second retroreflector mirrors enables the laser to achieve multiple reflections. Therefore, the present invention has high Raman signal reception efficiency.

[0032] 3. In the multi-reflection cavity enhanced Raman system and its usage method of the present invention, the first retroreflector includes a first horizontal surface and a first vertical surface, and the second retroreflector includes a second horizontal surface and a second vertical surface. In application, the laser signal is reflected by the first horizontal surface and the first vertical surface to reach the first lens, and the laser signal is reflected by the second horizontal surface and the second vertical surface to reach the second lens. Combined with the first lens and the second lens, the laser signal is converged, thus improving the utilization rate of the laser signal. Therefore, the present invention has a better laser signal convergence effect. Attached Figure Description

[0033] Figure 1 is a schematic diagram of the structure of the present invention.

[0034] Figure 2 is a path diagram of the laser signal in Figure 1.

[0035] Figure 3 is a schematic diagram of the Raman signal being reflected in Figure 1.

[0036] Figure 4 is an enlarged view of the reaction area in Figure 1.

[0037] Figure 5 is a schematic diagram of the fiber bundle in Figure 1.

[0038] Figure 6 is a schematic diagram of the optical fiber structure in Figure 5.

[0039] Figure 7 is a schematic diagram of the laser signal at the reaction site in Figure 4.

[0040] Figure 8 is a schematic diagram of the fiber optic reception of Raman signals in Figure 4.

[0041] Figure 9 is a schematic diagram illustrating the application effect of the present invention.

[0042] In the figure: concave mirror 1, concave end 11, converging lens 2, parallel lens 21, fiber bundle 3, fiber 31, reaction point 4, first lens 5, first retroreflector 51, first horizontal surface 511, first vertical surface 512, laser emitter 6, spectrometer 7, second lens 8, second retroreflector 81, second horizontal surface 811, second vertical surface 812, receiving range 9, Raman signal shape 91, laser signal shape 92. Detailed Implementation

[0043] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0044] Please refer to Figures 1-9 for a multiple reflection cavity enhanced Raman system, the system comprising a concave mirror 1, a converging lens 2, and an optical fiber bundle 3;

[0045] The fiber bundle 3 includes multiple horizontally arranged optical fibers 31. The input ends of all optical fibers 31 are located at the focal point of one side of the converging lens 2. The side of the converging lens 2 away from the optical fibers 31 faces the side of the parallel lens 21. The other side of the parallel lens 21 faces the concave end 11 of the concave mirror 1. A reaction point 4 is provided between the concave end 11 and the parallel lens 21.

[0046] A first lens 5 is provided on one side of the reaction site 4. A first retroreflector 51 is provided on the extension line of the first lens 5 away from the reaction site 4. A laser emitter 6 is provided on the first retroreflector 51 away from the first lens 5. The output end of the laser emitter 6 is aligned with one end of the first lens 5. A second lens 8 is provided on the side of the reaction site 4 away from the first lens 5. A second retroreflector 81 is provided on the second lens 8 away from the reaction site 4.

[0047] The output of all optical fibers 31 is connected to one end of the spectrometer 7.

[0048] The number of optical fibers 31 in the optical fiber bundle 3 is six to ninety-six, and the numerical aperture range of the spectrometer 7 is 0.05 to 0.2.

[0049] The core diameter of the optical fiber 31 is between 10 and 200 micrometers, and the numerical aperture of the optical fiber 31 is between 0.1 and 0.4.

[0050] The distance from the concave end 11 to the reaction point 4 is twice the focal length of the concave mirror 1.

[0051] The focal length ratio of the parallel lens 21 to the converging lens 2 ranges from one-half to twice.

[0052] The width of the first retroreflector 51 and the second retroreflector 81 is between one-half an inch and two inches.

[0053] The optical axis of the converging lens 2 and the optical axis of the parallel lens 21 are located on the same horizontal line.

[0054] The first retroreflector 51 includes a first horizontal surface 511 and a first vertical surface 512. One end of the first vertical surface 512 is perpendicularly connected to one end of the first horizontal surface 511. The angle between the first horizontal surface 511 and the vertical surface is forty-five degrees.

[0055] The second retroreflector 81 includes a second horizontal surface 811 and a second vertical surface 812. One end of the second vertical surface 812 is perpendicularly connected to one end of the second horizontal surface 811. The angle between the second horizontal surface 811 and the vertical surface is forty-five degrees.

[0056] A method of using a multi-reflection cavity enhanced Raman system, the method comprising the following steps:

[0057] Step 1: Make laser emitter 6 emit a laser signal;

[0058] The second step is to first focus the laser signal toward the reaction point 4 using the first lens 5, and then the laser signal becomes a parallel laser signal through the second lens 8. The laser signal is then reflected multiple times in the second retroreflector 81 and the first retroreflector 51, so the laser signal will pass through the reaction point 4 multiple times.

[0059] Step 3: The laser signal located at reaction point 4 reacts with the gas to be tested at reaction point 4 to generate a Raman signal. Part of the Raman signal is directed toward the parallel lens 21, and part of the Raman signal is directed toward the concave end 11. The Raman signal directed toward the concave end 11 is then reflected by the concave end 11, and then the Raman signal directed toward the concave end 11 is transformed into a Raman signal directed toward the parallel lens 21.

[0060] Step 4: Since the focal point of the parallel lens 21 coincides with the focal point of the laser reflected multiple times at the reaction point 4, the parallel lens 21 converts the Raman signal into a parallel Raman signal. Then, the converging lens 2 re-images the parallel Raman signal and focuses it into multiple optical fibers 31 on the focal plane of the converging lens 2. The optical fibers 31 then receive the Raman signal and import it into the spectrometer 7 for analysis.

[0061] The following are supplementary descriptions of the present invention:

[0062] The application of this invention is to increase the receiving efficiency of Raman signals to improve the gas detection limit; by placing the optical fiber 31 on the focal plane of the converging lens 2, it can receive Raman signals from the laser beam focus and nearby; when the number of optical fibers 31 increases, the distribution of the optical fibers 31 on the focal plane is also wider, the range of receiving Raman signals increases, and therefore the intensity of the received Raman signal also increases. Please refer to Figure 7, the intensity of the Raman signal received by 8 optical fibers 31 is about 6 times the intensity of the Raman signal received by 1 optical fiber 31; the receiving efficiency of the Raman signal is high, that is, the gas to be measured can be detected even when the content of the gas to be measured is very weak, which can improve the gas detection limit.

[0063] The laser signal shape 92 described in this invention is as follows: Please refer to Figures 7 and 8. Due to the focusing effect of the first lens 5 and the second lens 8 on the laser signal, the diameter of the laser signal at the reaction point 4 gradually decreases along the direction close to the reaction point 4. Therefore, the laser signal shape 92 consists of two opposing triangles centered on the center of the reaction point 4. The Raman signal shape 91 has the same shape as the laser signal shape 92. Example 1:

[0064] Please refer to Figures 1-9. A multiple reflection cavity enhanced Raman system is described. The system includes a concave mirror 1, a converging lens 2, and an optical fiber bundle 3. The optical fiber bundle 3 includes multiple horizontally arranged optical fibers 31. The input ends of all optical fibers 31 are located at the focal point of one side of the converging lens 2. The side of the converging lens 2 away from the optical fibers 31 faces the side of the parallel lens 21. The other side of the parallel lens 21 faces the concave end 11 of the concave mirror 1. A reaction point 4 is provided between the concave end 11 and the parallel lens 21. A first lens 5 is provided on one side of the reaction point 4. A first retroreflector 51 is provided on the extension line of the first lens 5 away from the reaction point 4. A laser emitter 6 is provided on the first retroreflector 51 away from the first lens 5. The output end of the laser emitter 6 is aligned with one end of the first lens 5. A second lens 8 is provided on the side of the reaction point 4 away from the first lens 5. A second retroreflector 81 is provided on the second lens 8 away from the reaction point 4. The output ends of all optical fibers 31 are connected to one end of a spectrometer 7. The number of optical fibers 31 within the optical fiber bundle 3 is six to ninety-six, and the numerical aperture of the spectrometer 7 ranges from 0.05 to 0.2. The core diameter of the optical fiber 31 is ten to two hundred micrometers, and the numerical aperture of the optical fiber 31 ranges from 0.1 to 0.4. Preferably, the numerical aperture of the spectrometer 7 is 0.2. Preferably, the diameter of the optical fiber is one hundred and five micrometers, and the numerical aperture of the optical fiber 31 is 0.2.

[0065] A method of using a multi-reflection cavity enhanced Raman system, the method comprising the following steps:

[0066] Step 1: Make laser emitter 6 emit a laser signal;

[0067] The second step is to first focus the laser signal toward the reaction point 4 using the first lens 5, and then the laser signal becomes a parallel laser signal through the second lens 8. The laser signal is then reflected multiple times in the second retroreflector 81 and the first retroreflector 51, so the laser signal will pass through the reaction point 4 multiple times.

[0068] Step 3: The laser signal located at reaction point 4 reacts with the gas to be tested at reaction point 4 to generate a Raman signal. Part of the Raman signal is directed toward the parallel lens 21, and part of the Raman signal is directed toward the concave end 11. The Raman signal directed toward the concave end 11 is then reflected by the concave end 11, and then the Raman signal directed toward the concave end 11 is transformed into a Raman signal directed toward the parallel lens 21.

[0069] Step 4: Since the focal point of the parallel lens 21 coincides with the focal point of the laser reflected multiple times at the reaction point 4, the parallel lens 21 converts the Raman signal into a parallel Raman signal. Then, the converging lens 2 re-images the parallel Raman signal and focuses it into multiple optical fibers 31 on the focal plane of the converging lens 2. The optical fibers 31 then receive the Raman signal and import it into the spectrometer 7 for analysis. Example 2:

[0070] The basic content is the same as in Example 1, except that:

[0071] Please refer to Figures 1-4. The distance from the concave end 11 to the reaction point 4 is twice the focal length of the concave mirror 1. The focal length ratio of the parallel lens 21 to the converging lens 2 ranges from half to twice. The width of the first retroreflector 51 and the second retroreflector 81 is from half an inch to two inches. The optical axis of the converging lens 2 and the optical axis of the parallel lens 21 are located on the same horizontal line. Preferably, the focal length ratio of the parallel lens 21 to the converging lens 2 is 1:1. Preferably, the width of the first retroreflector 51 and the second retroreflector 81 is one inch.

[0072] In application, the parallel lens 21 converts the Raman signal into a parallel Raman signal, and then the converging lens 2 re-images the Raman signal, converging it into multiple optical fibers on the focal plane of the converging lens. Therefore, the reception effect of the Raman signal is better. When the focal length ratio of the parallel lens and the converging lens 2 is 1:1, it matches well with parameters such as the numerical aperture of the optical fiber 31, which can improve the reception effect of the Raman signal. The concave end 11 can reflect the Raman signal towards the concave end 11 back to the parallel lens 21. The distance from the concave end 11 to the reaction point 4 is twice the focal length of the concave mirror 1. At this time, the reflection effect of the concave end 11 on the Raman signal is the best, thus increasing the reception efficiency of the Raman signal. When the optical axis of the converging lens 2 and the optical axis of the parallel lens 21 are on the same horizontal line, the effect of converging the Raman signal into the optical fiber 31 is better. The width of the first retroreflector 51 and the second retroreflector 81 is relatively large, so it can increase the number of reflections of the laser signal, thereby increasing the laser intensity at the reaction point 4. Example 3:

[0073] The basic content is the same as in Example 1, except that:

[0074] Please refer to Figures 1-3. The first retroreflector 51 includes a first horizontal surface 511 and a first vertical surface 512. One end of the first vertical surface 512 is perpendicularly connected to one end of the first horizontal surface 511. The angle between the first horizontal surface 511 and the vertical surface is 45 degrees. The second retroreflector 81 includes a second horizontal surface 811 and a second vertical surface 812. One end of the second vertical surface 812 is perpendicularly connected to one end of the second horizontal surface 811. The angle between the second horizontal surface 811 and the vertical surface is 45 degrees.

[0075] In application, the laser emitter 6 first generates a laser signal, which is then focused at the reaction point 4 by the first lens 5. The laser signal then passes through the reaction point 4 and is then converted into parallel light by the second lens 8. The laser signal is then reflected by the second horizontal surface 811 to the second vertical surface 812, and then reflected by the second vertical surface 812 to the second lens 8. The laser signal is then focused at the reaction point 4 by the second lens 8, passes through the reaction point 4, is converted into parallel light by the first lens 5, and is then reflected by the first horizontal surface 511 to the first vertical surface 512. The laser signal is then focused at the reaction point 4 by the first lens 5. Thus, multiple reflections of the laser signal are achieved. In the aforementioned process, the laser signal passes through the reaction point 4 multiple times, so the laser signal intensity at the reaction point 4 is the greatest, that is, the intensity of the generated Raman signal is the greatest. Example 4:

[0076] The basic content is the same as in Example 1, except that:

[0077] Please refer to Figures 1-9 for a method of using a multiple reflection cavity enhanced Raman system, the method comprising the following steps:

[0078] Step 1: Make laser emitter 6 emit a laser signal;

[0079] Step 2: First, the first lens 5 focuses the laser signal toward the reaction site 4. The laser signal then reacts with the gas to be measured at the reaction site 4 to generate a Raman signal. Then, part of the Raman signal is directed toward the parallel lens 21 and part of the Raman signal is directed toward the concave end 11. The Raman signal moving toward the concave end 11 is reflected by the concave end 11. Then, the Raman signal directed toward the concave end 11 is converted into a Raman signal directed toward the parallel lens 21. The Raman signal directed toward the parallel lens 21 is then converted into a parallel Raman signal by the parallel lens 21. Then, the parallel Raman signal is converted into a converged Raman signal by the converging lens 2. The converged Raman signal is then collected by the optical fiber 31. Then, the optical fiber 31 guides the Raman signal into the spectrometer 7.

[0080] Step 3: The laser signal located at reaction point 4 moves to the second lens 8, then the second lens 8 moves the laser signal to the second retroreflector 81, then the second retroreflector 81 moves the laser signal to the second lens 8, and then the second lens 8 moves the laser signal to reaction point 4. The laser signal then reacts with the gas to be measured at reaction point 4 to generate a Raman signal. Then, part of the Raman signal moves toward the parallel lens 21, and part of the Raman signal moves toward the concave end 11. The Raman signal moving toward the concave end 11 is then reflected by the concave end 11. Then, the Raman signal moving toward the concave end 11 becomes a Raman signal moving toward the parallel lens 21. The Raman signal moving toward the parallel lens 21 is then converted into a parallel Raman signal by the parallel lens 21. Then, the parallel Raman signal is converted into a converged Raman signal by the converging lens 2. The converged Raman signal is then collected by the optical fiber 31, and then the optical fiber 31 guides the Raman signal into the spectrometer 7.

[0081] Step 4: The laser signal located at the reaction point 4 moves to the first lens 5, and then the first lens 5 moves the laser signal to the first retroreflector 51, and then the first retroreflector 51 moves the laser signal to the first lens 5.

[0082] Step 5: Repeat steps 2, 3, and 4 in sequence until the laser signal reaches the reflection limit.

[0083] The above description is only a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Any equivalent modifications or changes made by those skilled in the art based on the content disclosed in the present invention should be included within the scope of protection set forth in the claims.

Claims

1. A multi-reflection cavity enhanced Raman system, characterized in that: The system includes a concave mirror (1), a converging lens (2), and an optical fiber bundle (3). The fiber bundle (3) includes multiple horizontally arranged optical fibers (31), the input ends of all optical fibers (31) are located at the focal point of one side of the converging lens (2), the side of the converging lens (2) away from the optical fibers (31) faces the side of the parallel lens (21), the other side of the parallel lens (21) faces the concave end (11) of the concave mirror (1), and a reaction point (4) is provided between the concave end (11) and the parallel lens (21). A first lens (5) is provided on one side of the reaction site (4). A first retroreflector (51) is provided on the extension line of the first lens (5) away from the reaction site (4). A laser emitter (6) is provided on the first retroreflector (51) away from the first lens (5). The output end of the laser emitter (6) is aligned with one end of the first lens (5). A second lens (8) is provided on the side of the reaction site (4) away from the first lens (5). A second retroreflector (81) is provided on the second lens (8) away from the reaction site (4). The output of all optical fibers (31) is connected to one end of the spectrometer (7).

2. The multi-reflection cavity enhanced Raman system according to claim 1, characterized in that: The number of optical fibers (31) in the optical fiber bundle (3) is six to ninety-six, and the numerical aperture range of the spectrometer (7) is 0.05 to 0.

2.

3. The multi-reflection cavity enhanced Raman system according to claim 2, characterized in that: The core diameter of the optical fiber (31) is 10 to 200 micrometers, and the numerical aperture of the optical fiber (31) is 0.1 to 0.

4.

4. A multi-reflection cavity enhanced Raman system according to claim 1, 2 or 3, characterized in that: The distance from the concave end (11) to the reaction point (4) is twice the focal length of the concave mirror (1).

5. The multi-reflection cavity enhanced Raman system according to claim 4, characterized in that: The focal length ratio of the parallel lens (21) to the converging lens (2) ranges from one-half to twice.

6. The multi-reflection cavity enhanced Raman system according to claim 5, characterized in that: The width of the first retroreflector (51) and the second retroreflector (81) is between one-half an inch and two inches.

7. The multi-reflection cavity enhanced Raman system according to claim 6, characterized in that: The optical axis of the converging lens (2) and the optical axis of the parallel lens (21) are on the same horizontal line.

8. A multi-reflection cavity enhanced Raman system according to claim 1, 2 or 3, characterized in that: The first retroreflector (51) includes a first horizontal surface (511) and a first vertical surface (512). One end of the first vertical surface (512) is perpendicularly connected to one end of the first horizontal surface (511). The angle between the first horizontal surface (511) and the vertical surface is forty-five degrees.

9. A multi-reflection cavity enhanced Raman system according to claim 8, characterized in that: The second retroreflector (81) includes a second horizontal surface (811) and a second vertical surface (812). One end of the second vertical surface (812) is perpendicularly connected to one end of the second horizontal surface (811). The angle between the second horizontal surface (811) and the vertical surface is forty-five degrees.

10. A method of using the multiple reflection cavity enhanced Raman system according to claim 1, characterized in that: The method of use includes the following steps: Step 1: Make the laser emitter (6) emit a laser signal; Step 2: First, the laser signal is focused by the first lens (5), and then the laser signal is converted into a parallel laser signal by the second lens (8). Then the laser signal is reflected multiple times in the second retroreflector (81) and the first retroreflector (51), so the laser signal will pass through the reaction point (4) multiple times. Step 3: The laser signal located at the reaction point (4) reacts with the gas to be tested at the reaction point (4) to generate a Raman signal. Part of the Raman signal is directed toward the parallel lens (21), and part of the Raman signal is directed toward the concave end (11). The Raman signal directed toward the concave end (11) is reflected by the concave end (11), and then the Raman signal directed toward the concave end (11) is transformed into a Raman signal directed toward the parallel lens (21). Step 4: Since the focal point of the parallel lens (21) coincides with the focal point of the laser reflected multiple times at the reaction point (4), the parallel lens (21) converts the Raman signal into a parallel Raman signal. Then, the converging lens (2) re-images the parallel Raman signal and converges it into multiple optical fibers (31) on the focal plane of the converging lens (2). The Raman signal is then received by the optical fiber (31) and then introduced into the spectrometer (7) for analysis.

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