A Raman spectroscopy gas detection device with long optical path and high convergence excitation

Abstract

The present invention provides a Raman spectroscopy gas detection device with long optical path and high convergence excitation, comprising: a light source module, used to emit a shaped excitation light beam to the reflective surface of a second parabolic reflector through a laser incident channel; a gas chamber, the cavity in the chamber serving as a sample pool; an excitation and collection module, built into the sample pool, used to excite the sample with the excitation light beam and to collect the Raman scattered light generated by the excitation, comprising a first parabolic reflector, a second parabolic reflector and a dichroic mirror; a lens group, provided with a pair, used to receive the Raman scattered light reflected by the dichroic mirror, and to transmit the received Raman scattered light to a Raman spectrometer; a Raman spectrometer, used to perform spectroscopic identification of the Raman scattered light input by the lens group and convert it into a Raman spectrum. The present invention can simplify the device structure and improve the system stability on the basis of simultaneously realizing the excitation and collection of high-efficiency Raman signals.

Description

Technical Field

[0001] The invention relates to a Raman spectrum detection technology, and more specifically to a Raman spectrum gas detection device with long optical path and high convergence excitation. Background Art

[0002] The importance of gas detection technology is not only reflected in the traditional field of industrial safety, but also widely involves environmental monitoring, public safety, medical health and other aspects. The development and application of gas detection technology has a far-reaching impact on protecting human life safety, maintaining environmental quality and promoting sustainable development.

[0003] Raman spectroscopy gas detection technology uses the spectral features generated by molecular vibration or rotation modes to identify and analyze the structure of substances. When photons interact with molecules, they can transfer energy to the molecules, causing the molecules to transition from the ground state vibrational energy level to a higher virtual energy level, and then the molecules transition from this virtual energy level back to a higher or lower vibrational energy level than the initial state, releasing a photon with higher or lower energy. The increase or decrease in energy in this process is exactly the frequency difference between the Raman scattered photon and the original laser photon. This frequency difference is called the Raman shift, which is the unique fingerprint of a specific molecule.

[0004] However, the scattering interface of the molecule is small, and the Raman scattering signal of the sample to be tested is very low, especially the Raman scattering signal of the gas sample is the smallest, which is 10 times that of the excitation light. -6 to 10 -9 Therefore, improving the sensitivity of Raman detection technology is a very important research field. Important research directions now include cavity enhancement and fiber enhancement, but it is difficult for current detection methods to take into account both excitation efficiency and collection efficiency. Cavity enhancement can achieve multiple reflections of lasers and convergence of lasers, but in the collection stage of Raman signals, lenses are mainly used for collection, and the collection efficiency is very low, resulting in the waste of Raman signals in the collection stage. Fiber-enhanced devices can theoretically achieve large-scale collection of Raman signals, but the improvement in excitation efficiency is limited. Some devices use certain complex collection systems to improve the collection efficiency of Raman signals to a certain extent, but this increases the complexity of the system and reduces the stability and availability of the system. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a Raman spectroscopy gas detection device with long optical path and high convergence excitation, which greatly simplifies the structural design of the device on the basis of realizing high-efficiency excitation and collection of Raman signals at the same time, and has good system stability.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A Raman spectroscopy gas detection device with long optical path and high convergence excitation has the following structural features:

[0008] A light source module, used for emitting a shaped excitation light beam to a reflective surface of the second parabolic reflector through a laser incident channel;

[0009] The air chamber, the cavity inside the chamber is used as a sample pool, which can be communicated with the outside and is used for filling and discharging samples. The communicating part can be closed, and together with the first parabolic reflector, a laser incident channel with a central axis parallel to the main axis of the first parabolic reflector and penetrating therethrough is formed. The opening of the laser incident channel at the reflecting surface of the first parabolic reflector is a light outlet;

[0010] The excitation and collection module is built into the sample pool and is used for exciting the sample with the excitation light beam and for collecting the Raman scattered light generated by the excitation, and includes the first parabolic reflector and the second parabolic reflector with opposite reflection surfaces, parallel main axes and the same structure, and also includes a dichroic mirror centrally arranged between the first parabolic reflector and the second parabolic reflector along the main axis direction, the mirror surface of the dichroic mirror is inclined and forms an angle of 45° with the main axis, and the projection surface along the main axis direction can completely cover the reflection surfaces of the first parabolic reflector and the second parabolic reflector, and the first parabolic reflector and the second parabolic reflector are parallel to each other. The object reflectors are arranged in a staggered manner along the reflection direction of the dichroic mirror, and the staggered spacing between the main axes is not less than the aperture size of the laser incident channel. The horizontal laser beam formed by multiple reflections of the excitation light beam by the reflection surfaces of the first parabolic reflector and the second parabolic reflector and the convergent light formed at two focal points excite the sample. The Raman scattered light generated by the excitation is reflected by the mirror surfaces on both sides of the dichroic mirror and is outputted through the receiving end of a pair of lens groups directly facing the air chamber wall. The Raman scattered light includes the Raman scattered light generated by the horizontal laser beam exciting the sample and the Raman scattered light generated by the convergent light exciting the sample and collimated.

[0011] A pair of lens groups are provided, which are arranged outside the air chamber along the reflection direction of the dichroic mirror, and the receiving end faces and can completely cover the projection surface of the mirror surface of the dichroic mirror on the side along the reflection direction. The pair of lens groups are used to receive the Raman scattered light reflected by the dichroic mirror, and transmit the received Raman scattered light to the Raman spectrometer after converging through the bifurcated optical fiber;

[0012] The Raman spectrometer is used for spectroscopic identification of the Raman scattered light inputted by the bifurcated optical fiber and converting it into a Raman spectrum.

[0013] The structural characteristics of the present invention also lie in:

[0014] The laser incident channel is located on the first parabolic reflector close to the outer edge of the reflective surface.

[0015] The dichroic mirror has a transmittance of not less than 99%, a transmission band range that includes the wavelength range of the excitation light, and a reflectivity of not less than 97%, a reflection band range that includes the wavelength range of the Raman scattered light.

[0016] The excitation light beam emitted by the light source module is a narrow line width excitation light.

[0017] The light source module includes an excitation light source, a first focusing lens, a second focusing lens, and a first plane mirror. The excitation light source emits an excitation light beam, which is collimated by the first focusing lens and the second focusing lens, and then reflected by the first plane mirror and emitted to the reflecting surface of the second parabolic reflector through the laser incident channel.

[0018] The reflecting surfaces of the first parabolic reflector and the second parabolic reflector are polished and coated, the substrate material is aluminum, copper or stainless steel, and the coating material is gold, silver, stainless steel or aluminum.

[0019] The air chamber is provided with a sample inlet communicated with the outside for sample input and a sample outlet for sample discharge. The sample inlet and the sample outlet are respectively provided with valves for controlling on and off. The air chamber wall is made of quartz or borosilicate glass or optical glass with a transmittance of not less than 0.98.

[0020] A pair of lens groups share a bifurcated optical fiber that divides into two paths. The bifurcated optical fiber collects Raman scattered light output by a pair of lens groups through two branches at the same time, converges and aligns the light and outputs it to the slit of the Raman spectrometer.

[0021] Each lens group includes a high-pass filter and a convex lens. The high-pass filter is used as a receiving end to receive the Raman scattered light reflected by the dichroic mirror on the side. After filtering out the scattered light, it is converged through the convex lens and outputted toward a corresponding branch of the bifurcated optical fiber.

[0022] The sample is a gas.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] First, the present invention can simultaneously realize the efficient excitation of the two modes of laser convergence and increasing the laser transmission optical path:

[0025] The traditional detection method can only realize one of the modes and cannot take both into account. The excitation light path of the present invention uses the first parabolic reflector and the second parabolic reflector to make the excitation light beam reflect multiple times between the two reflection surfaces, forming a high-density horizontal laser beam, increasing the laser transmission optical path, and increasing the laser energy accumulation. At the same time, the excitation light beam forms high-power convergent light at the focal points of the two parabolic reflectors. The high-density horizontal laser beam and the high-power convergent light at the two focal points can both excite the sample to generate Raman scattered light, so that the excitation of the two modes of laser convergence and increasing the laser transmission optical path can be realized simultaneously, which can significantly improve the excitation efficiency and detection sensitivity.

[0026] Second, the present invention can simultaneously achieve efficient collection of two modes:

[0027] The collection efficiency of the traditional cavity enhanced detection method is low, and the Raman scattering signal is wasted in the collection stage. The collection optical path of the present invention utilizes the geometric optical characteristics of the parabolic reflector, and can collimate the Raman scattered light generated by the high-power convergent light excitation at the two focal points into parallel light, and then reflect and collect it through the dichroic mirror. At the same time, the Raman scattered light parallel to the main axis direction generated by the high-density horizontal laser beam excitation can also be reflected and collected by the dichroic mirror. The collection optical path of the two parabolic reflectors combined with the dichroic mirror designed by the present invention can realize the large-scale collection of two modes of Raman scattered light at the same time, thereby improving the collection efficiency.

[0028] Third, the present invention reduces the complexity of the system and improves the integration and stability of the system:

[0029] The excitation system and the collection system of the traditional multiple reflection cavity system are in a separated state, and the system has high system complexity, low integration and poor stability. The present invention utilizes two parabolic reflectors in combination with a dichroic mirror as both the excitation system and the collection system, which can achieve both efficient excitation of the two modes and efficient collection of the two modes. Compared with the existing technical level, the detection technology has made significant progress, and the system has been greatly simplified, with high integration and good reliability, which simplifies maintenance work, reduces maintenance costs, and is more adaptable to the detection needs of various fields and has a wider range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the structure of the present invention;

[0031] Figure 2 It is a schematic diagram of the structure of the excitation and collection module;

[0032] Figure 3 is the excitation light path diagram;

[0033] Figure 4 It is a signal collection optical path diagram excited by the convergent light formed at the focus;

[0034] Figure 5 It is the optical path diagram of signal collection excited by horizontal laser beam;

[0035] Figure 6 This is a model diagram of the Raman scattering angular intensity distribution.

[0036] In the figure, 11 is an excitation light source; 12 is a first focusing lens; 13 is a second focusing lens; 14 is a first plane mirror; 15 is a laser incident channel; 2 is an air chamber; 21 is a sample inlet; 22 is a sample outlet; 31 is a first parabolic reflector; 32 is a second parabolic reflector; 33 is a dichroic mirror; 41 is a high-pass filter; 42 is a convex lens; 43 is a bifurcated optical fiber; 5 is a Raman spectrometer. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Please refer to Figures 1 to 5 The Raman spectroscopy gas detection device with long optical path and high convergence excitation of this embodiment includes:

[0039] A light source module, used for emitting a shaped excitation light beam to a reflection surface of the second parabolic reflector 32 through the laser incident channel 15;

[0040] The air chamber 2, the cavity inside the chamber is used as a sample pool, which can be communicated with the outside and is used for filling and discharging samples. The communicating part can be closed, and together with the first parabolic reflector 31, a laser incident channel 15 is formed, the central axis of which is parallel to the main axis of the first parabolic reflector 31 and is through. The opening of the laser incident channel 15 at the reflecting surface of the first parabolic reflector 31 is a light outlet;

[0041] The excitation and collection module is built into the sample pool and is used for exciting the sample with the excitation light beam and for collecting the Raman scattered light generated by the excitation. It includes a first parabolic reflector 31 and a second parabolic reflector 32 with opposite reflection surfaces, parallel main axes and the same structure, and also includes a dichroic mirror 33 centrally arranged between the first parabolic reflector 31 and the second parabolic reflector 32 along the main axis direction. The mirror surface of the dichroic mirror 33 is inclined and forms an angle of 45° with the main axis. The projection surface along the main axis direction can completely cover the reflection surfaces of the first parabolic reflector 31 and the second parabolic reflector 32. The first parabolic reflector 31 and the second parabolic reflector 32 are staggered along the reflection direction of the dichroic mirror 33. The staggered spacing between the main axes is not less than the aperture size of the laser incident channel 15. The horizontal laser beam formed by multiple reflections of the excitation light beam on the reflection surface of the first parabolic reflector 31 and the second parabolic reflector 32 and the convergent light formed at two focal points excite the sample. The excitation light path is as follows Figure 3 As shown, the Raman scattered light generated by the excitation is reflected by the two side mirrors of the dichroic mirror 33, and then outputted through the receiving end of a pair of lens groups facing the wall of the air chamber 2. The Raman scattered light includes the Raman scattered light generated by the horizontal laser beam exciting the sample. This part of the optical path is shown in FIG. Figure 5 As shown in the figure, the Raman scattered light generated by the sample excited by the focused light and then collimated, this part of the light path is as follows Figure 4 As shown;

[0042] A pair of lens groups are provided, which are arranged outside the air chamber 2 along the reflection direction of the dichroic mirror 33, and the receiving end is directly facing and can completely cover the projection surface of the mirror surface of the dichroic mirror 33 along the reflection direction. The pair of lens groups are used to receive the Raman scattered light reflected by the dichroic mirror 33, and transmit the received Raman scattered light to the Raman spectrometer 5 after converging through the bifurcated optical fiber;

[0043] The Raman spectrometer 5 is used for spectroscopic identification of the Raman scattered light inputted from the bifurcated optical fiber 43 and converting it into a Raman spectrum.

[0044] In a specific implementation, the corresponding structural setting of the device also includes:

[0045] Along the reflection direction of the dichroic mirror 33 , the position of the laser incident channel 15 on the first parabolic reflector 31 is close to the outer edge of the reflection surface.

[0046] The transmittance of the dichroic mirror 33 is not less than 99%, and the transmission band range includes the wavelength range of the excitation light. The reflectivity is not less than 97%, and the reflection band range includes the wavelength range of the Raman scattered light.

[0047] The excitation light beam emitted by the light source module is a narrow line width excitation light.

[0048] The light source module includes an excitation light source 11, a first focusing lens 12, a second focusing lens 13, and a first plane mirror 14. The excitation light source 11 emits an excitation light beam, which is collimated by the first focusing lens 12 and the second focusing lens 13, and then reflected by the first plane mirror 14 and emitted to the reflecting surface of the second parabolic reflector 32 through the laser incident channel 15.

[0049] The reflecting surfaces of the first parabolic reflector 31 and the second parabolic reflector 32 are polished and coated. The base material is aluminum, copper or stainless steel, and the coating material is gold, silver, stainless steel or aluminum.

[0050] The air chamber 2 is provided with a sample inlet 21 communicating with the outside for sample input and a sample outlet 22 for sample discharge. The sample inlet 21 and the sample outlet 22 are respectively provided with valves for controlling on and off. The wall material of the air chamber 2 is quartz or borosilicate glass or optical glass.

[0051] A pair of lens groups share a bifurcated optical fiber 43 that splits into two paths. The bifurcated optical fiber 43 collects the Raman scattered light output by the pair of lens groups through two branches at the same time, converges and aligns the light and outputs it to the slit of the Raman spectrometer 5.

[0052] Each lens group includes a high-pass filter 41 and a convex lens 42. The high-pass filter 41 is used as a receiving end to receive the Raman scattered light reflected by the dichroic mirror 33 on the side. After filtering out the scattered light, it is converged through the convex lens 42 and aligned with the corresponding branch output of the bifurcated optical fiber 43.

[0053] The sample is gas.

[0054] The laser is incident on the reflecting surface of the second parabolic reflector 32 from the laser incident channel 15, is collimated and reflected after passing through the focus of the second parabolic reflector 32, is reflected after being incident on the reflecting surface of the first parabolic reflector 31 opposite thereto, passes through the focus of the first parabolic reflector 31, and is reflected again into parallel light. According to this reflection mode, the laser is reflected multiple times between the first parabolic reflector 31 and the second parabolic reflector 32 to form a high-density horizontal laser beam, which converges at two focal points until the laser is emitted from the edges of the first parabolic reflector 31 and the second parabolic reflector 32 or the laser reflection disappears. The laser reflected between the first parabolic reflector 31 and the second parabolic reflector 32 passes through the dichroic mirror 33, and most of the Raman scattered light at the focus is collimated into parallel light by the first parabolic reflector 31 and the second parabolic reflector 32 and then reflected by the dichroic mirror 33. The Raman scattered light collimated by the first parabolic reflector 31 and the Raman scattered light collimated by the second parabolic reflector 32 are respectively reflected by the dichroic mirror 33 and output through the wall of the air chamber 2 to the receiving end of a pair of lens groups facing each other.

[0055] From the above, it can be seen that in the reflection cavity between the first parabolic reflector 31 and the second parabolic reflector 32 of the excitation and collection module, the optical path is mainly divided into two parts: one part is the excitation optical path, and the other part is the collection optical path.

[0056] The principle of the above optical path is further explained:

[0057] According to the following formula (1), the Raman scattered light intensity P s Relevant factors include: the density of the substance to be measured N , Collectible area volume (optical path) AL , Excitation light intensity I 0 , effective excitation power P 0 , effective scattered light length L , scattering cross section size And collection angle Ω 0 ;

[0058]

[0059] According to formula (1), by increasing the intensity of the excitation light I 0 , Increase the volume of the collectible area (optical path) AL , increase the collection angle Ω 0 , can effectively enhance the intensity of Raman scattered light P s The traditional detection method can only detect the intensity of Raman scattered light from one of the three aspects. P s The optical path design of this device can achieve the simultaneous enhancement of the excitation light intensity. I 0 , Collectible area volume (optical path) AL , Collection Angle Ω 0 Three aspects to achieve enhanced Raman scattered light intensity P s , the implementation is described in detail as follows:

[0060] First, by increasing the intensity of the excitation light I 0 :

[0061] The geometric optical property of the parabolic reflector is that it can reflect parallel incident light through the focus, and can also reflect the light emitted at the focus into parallel light. In this device, the excitation light beam is reflected multiple times between the reflection surfaces of the first parabolic reflector 31 and the second parabolic reflector 32. Based on the above geometric optical properties, the horizontal laser beam reflected multiple times can pass through the focus multiple times and converge at the two foci to form high-power converged light.

[0062] The second aspect is to increase the volume of the collectible area (optical path) AL :

[0063] The laser is reflected multiple times between the first parabolic reflector 31 and the second parabolic reflector 32, and each time the light passing through the focus is collimated into parallel light, so the laser reflected multiple times forms a high-density horizontal laser beam between the first parabolic reflector 31 and the second parabolic reflector 32, thereby increasing the laser power accumulation in the entire reflection cavity and further improving the excitation efficiency.

[0064] The third aspect is to increase the collection angle Ω 0 :

[0065] The angular intensity distribution of Raman scattered light is related to the incident direction of the laser and can be expressed by formula (2). Assuming that the intensity of Raman scattered light perpendicular to the incident direction of the laser is 1, Figure 6 The corresponding Raman scattering angular intensity distribution model is shown;

[0066]

[0067] In formula (2), γ is the angle between the Raman scattered light and the incident laser. According to formula (2), the Raman scattered light generated by laser excitation of the gas sample can be detected in a spatial range, especially the Raman scattered light generated by laser excitation in different directions at the focus can be assumed to be a uniformly scattered spherical light source, such as Figure 4 As shown, the Raman signal scattered at the focus can be collimated into parallel light and collected by the dichroic mirror 33;

[0068] At the same time, the horizontal laser beam will also generate Raman scattered light. Figure 6 It can be seen that the intensity of Raman scattered light is the highest in the 0° and 180° directions. Figure 5 This is a collection optical path diagram of Raman scattered light excited by a horizontal laser beam. In the figure, the black arrow represents the Raman scattered light in the 0° direction, and the red arrow represents the Raman scattered light in the 180° direction. The Raman scattered light in the 0° direction is reflected and collected by the dichroic mirror 33, and the Raman scattered light in the 180° direction is reflected by the first parabolic reflector 31 and the second parabolic reflector 32, and is reflected and collected by the dichroic mirror 33 in the 0° direction.

[0069] In summary, this embodiment can simultaneously realize efficient excitation and collection of two modes based on the excitation and collection modules, while improving the excitation efficiency and collection efficiency, reducing the complexity of the system and improving the stability of the system. In the excitation part: on the one hand, the laser can be reflected multiple times between the first parabolic reflector 31 and the second parabolic reflector 32 to form a high-density horizontal laser beam, increase the laser transmission optical path, and increase the laser accumulation in the air chamber 2. On the other hand, the laser converges multiple times at the two focal points to form a high-power laser convergence point. In the collection part: on the one hand, the laser converges at the two focal points, and the Raman scattered light generated by the excitation at the convergence point is reflected and collimated into parallel light by the first parabolic reflector 31 and the second parabolic reflector 32. On the other hand, the high-density horizontal laser beam between the first parabolic reflector 31 and the second parabolic reflector 32 will also generate Raman scattered light in the horizontal direction. Both of these Raman scattered lights are reflected by the dichroic mirror 33, thereby achieving high-efficiency collection.

[0070] The embodiment of the present invention also proposes a Raman spectroscopy gas detection method with long optical path and high convergence excitation, which is implemented using a Raman spectroscopy gas detection device with long optical path and high convergence excitation having the above structure, and is carried out in the following steps:

[0071] Step 1, turn on the excitation light source 11, and emit the shaped excitation light beam to the reflection surface of the second parabolic reflector 32 through the laser incident channel 15;

[0072] Step 2: Adjust the relative position and relative angle between the first parabolic reflector 31 and the second parabolic reflector 32 so that the received excitation light beam can form multiple reflected lights between the first parabolic reflector 31 and the second parabolic reflector 32, and form convergent lights at two focal points respectively;

[0073] Step 3, placing a dichroic mirror 33 between the first parabolic reflector 31 and the second parabolic reflector 32, and adjusting the position and angle of the dichroic mirror 33 so that the laser can pass through the dichroic mirror 33 with minimum power loss;

[0074] Step 4, filling the air chamber 2 with the sample to be tested;

[0075] Step 5, coaxially align the high-pass filter 41 and the convex lens 42 in each lens group, use the high-pass filter 41 as the receiving end of the lens group, adjust it to face and completely cover the projection surface of the mirror surface of the dichroic mirror 33 on the side along the reflection direction, so that the Raman scattered light reflected by the dichroic mirror 33 can enter the collection range of the pair of lens groups to the maximum extent, the Raman scattered light is filtered out of the stray light and the fluorescence signal by the high-pass filter 41, and then enters the corresponding branch of the bifurcated optical fiber 43 after being converged by the convex lens 42, and is sent to the Raman spectrometer 5 through the bifurcated optical fiber 43;

[0076] Step 6: After the Raman spectrometer 5 splits the received Raman scattered light through the internal grating, the optical signal is converted into an electrical signal through the CCD to generate a Raman signal spectrum.

[0077] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A Raman spectroscopy gas detection device with long optical path and high convergence excitation, characterized in that include: A light source module, used for emitting an excitation light beam through a laser incident channel (15) toward a second parabolic reflector (32); The air chamber (2) serves as a sample pool and together with the first parabolic reflector (31) forms a through laser incident channel (15) with a central axis parallel to the main axis of the first parabolic reflector (31); the opening of the laser incident channel (15) at the reflecting surface of the first parabolic reflector (31) serves as a light outlet; The excitation and collection module is built into the sample pool and includes a first parabolic reflector (31) and a second parabolic reflector (32) with opposite reflection surfaces, parallel main axes and identical structures, and also includes a dichroic mirror (33) centrally arranged between the two parabolic reflectors along the main axis direction and with an inclined mirror surface. The two parabolic reflectors are staggered along the reflection direction of the dichroic mirror (33), and the staggered spacing is not less than the aperture size of the laser incident channel (15); the laser is incident from the laser incident channel (15) onto the reflection surface of the second parabolic reflector (32), passes through the focus of the second parabolic reflector (32) and is collimated and reflected, then is incident on the reflection surface of the first parabolic reflector (31) opposite thereto and is reflected, passes through the focus of the first parabolic reflector (31), and is reflected again into parallel light. According to this reflection mode, the laser is incident on the reflection surface of the first parabolic reflector (31) and the second parabolic reflector (32). The laser beam passes through the dichroic mirror (33) for multiple reflections, and each time the light passes through the focus is collimated into parallel light. The laser beam reflected multiple times forms a high-density horizontal laser beam between the first parabolic reflector (31) and the second parabolic reflector (32). The horizontal laser beam reflected multiple times can pass through the focus multiple times and converge at the two focal points to form high-power converged light. The sample is excited by the horizontal laser beam formed by the multiple reflections of the excitation light beam by the two parabolic reflectors and the converged light formed at the two focal points. The Raman scattered light generated by the excitation is reflected by the two side mirrors of the dichroic mirror (33) and then output to a pair of lens groups. The Raman scattered light generated by the excitation includes Raman scattered light generated by the laser beam converging at the two focal points, excited at the convergence point, and reflected by the two parabolic reflectors to be collimated into parallel light, and also includes Raman scattered light generated by the high-density horizontal laser beam between the two parabolic reflectors in the horizontal direction. A pair of lens groups, used to receive the Raman scattered light and transmit it to the Raman spectrometer (5) after converging it through the bifurcated optical fiber; The Raman spectrometer (5) is used to perform spectroscopic identification on the Raman scattered light and convert it into a Raman spectrum.

2. The Raman spectroscopy gas detection device with long optical path and high convergence excitation according to claim 1 is characterized in that: The position of the laser incident channel (15) on the first parabolic reflector (31) is close to the outer edge of the reflective surface.

3. The Raman spectroscopy gas detection device with long optical path and high convergence excitation according to claim 1 is characterized in that: The dichroic mirror (33) has a transmittance of not less than 99%, a transmission wavelength range that includes the wavelength range of the excitation light, and a reflectance of not less than 97%, a reflection wavelength range that includes the wavelength range of the Raman scattered light.

4. The Raman spectroscopy gas detection device with long optical path and high convergence excitation according to claim 1 is characterized in that: The excitation light beam emitted by the light source module is a narrow line width excitation light.

5. The Raman spectroscopy gas detection device with long optical path and high convergence excitation according to claim 1 or 4, characterized in that: The light source module comprises an excitation light source (11), a first focusing lens (12), a second focusing lens (13), and a first plane mirror (14); an excitation light beam is emitted by the excitation light source (11), collimated by the first focusing lens (12) and the second focusing lens (13), and then reflected by the first plane mirror (14) and emitted to a reflection surface of the second parabolic reflector (32) through the laser incident channel (15).

6. The Raman spectroscopy gas detection device with long optical path and high convergence excitation according to claim 1 is characterized in that: The reflecting surfaces of the first parabolic reflector (31) and the second parabolic reflector (32) are polished and coated, the base material is aluminum, copper or stainless steel, and the coating material is gold, silver, stainless steel or aluminum.

7. The Raman spectroscopy gas detection device with long optical path and high convergence excitation according to claim 1 is characterized in that: The air chamber (2) is provided with a sample inlet (21) communicating with the outside for inputting a sample and a sample outlet (22) for discharging the sample. The sample inlet (21) and the sample outlet (22) are respectively provided with valves for controlling on-off. The wall material of the air chamber (2) is quartz, borosilicate glass or optical glass, and the transmittance is not less than 0.

98.

8. The Raman spectroscopy gas detection device with long optical path and high convergence excitation according to claim 1 is characterized in that: A pair of lens groups share a bifurcated optical fiber (43) that splits into two paths. The bifurcated optical fiber (43) simultaneously collects Raman scattered light output by the pair of lens groups through two branches, converges and aligns the light, and then outputs the light to the slit of the Raman spectrometer (5).

9. The Raman spectroscopy gas detection device with long optical path and high convergence excitation according to claim 8 is characterized in that: Each lens group comprises a high-pass filter (41) and a convex lens (42), wherein the high-pass filter (41) is used as a receiving end to receive Raman scattered light reflected by the mirror surface of the dichroic mirror (33) on the side where the light is located, and after filtering out the scattered light, the light is converged through the convex lens (42) and aligned with a corresponding branch of the bifurcated optical fiber (43) for output.

10. The Raman spectroscopy gas detection device with long optical path and high convergence excitation according to claim 1 is characterized in that: The sample is a gas.

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