CN118882823A - Confocal Raman enhancement cavity and Raman spectrum measurement system including the enhancement cavity - Google Patents

Abstract

The present invention provides a confocal Raman enhancement cavity and a Raman spectrum measurement system including the enhancement cavity. The enhancement cavity comprises: a front end convex lens; a rear end convex lens, which is arranged downstream of the front end convex lens, the distance between the front end convex lens and the rear end convex lens is the sum of their focal lengths, and their focal positions overlap to form a confocal point, and the optical axes are on a straight line; a front end reflector array, which is arranged upstream of the front end convex lens and comprises a plurality of first reflective units, the first reflective units reflect the first incident light incident through the front end convex lens back to the front end convex lens in parallel, and the light reflected by the first reflective unit is offset from the optical axis of the first incident light; and a terminal reflector array, which is arranged downstream of the rear end convex lens and comprises a plurality of second reflective units, the second reflective units reflect the second incident light incident through the rear end convex lens back to the rear end convex lens in parallel, and the light reflected by the second reflective unit is offset from the optical axis of the second incident light.

Description

Confocal Raman enhancement cavity and Raman spectrum measurement system including the enhancement cavity

Technical Field

The present invention relates to the technical field of Raman spectroscopy, and more particularly to a confocal Raman enhancement cavity and a Raman spectroscopy measurement system comprising the enhancement cavity, which are used for detecting multi-component gases.

Background Art

Multi-component gas detection is widely needed in social production, such as petroleum refining, industrial process control, online monitoring of natural gas components, and monitoring of dissolved gases in seawater. Raman spectroscopy is based on the Raman scattering effect of matter. When incident light of a certain frequency passes through the gas to be tested, the incident laser will excite the gas (except monatomic gases) molecules to produce Raman scattered light. Different gases have their own specific Raman frequency shifts, and the intensity of Raman scattered light is linearly related to the concentration of the gas. Therefore, by detecting the Raman frequency shift and intensity of Raman scattered light, a variety of different substances can be qualitatively and quantitatively analyzed simultaneously. Compared with traditional detection methods, the use of Raman spectroscopy to detect multi-component mixed gases has the following advantages: (1) All gas components except monatomic gases (He, Ne, Ar, etc.) can be detected; (2) Single-wavelength laser can realize the simultaneous measurement of multi-component mixed gases; (3) Different gas components have little mutual interference and do not destroy the gas to be tested, which can achieve non-destructive detection. However, since the Raman effect is a weak effect, the intensity of Raman scattered light is only 10 ^-10 of the incident light intensity, and it is easy to be annihilated in the background signal in practical applications, making it difficult to obtain an ideal Raman spectrum. In addition, the gas scattering cross section is extremely low, and conventional spontaneous Raman spectroscopy technology is difficult to measure trace gases.

Domestic and foreign researchers often use various enhancement methods to improve the sensitivity of Raman scattering detection, mainly including surface enhancement, cavity enhancement and fiber enhanced Raman spectroscopy. Surface enhanced Raman technology (SERS) usually uses precious metal nanostructures or nano-ceramic probes as substrates and places them at the focal position of the Raman spectrometer. Through the localized surface plasmon resonance effect on the sample surface or near the surface, the Raman scattering signal of the adsorbed molecules can be enhanced to 10 ⁶ -10 ⁹ , thereby achieving Raman signal amplification. However, due to the limitations of the substrate morphology, this type of substrate is only suitable for solid and liquid detection and cannot be used for gas analysis. Cavity enhanced Raman technology (CERS) improves the Raman signal intensity by increasing the intensity of the excitation light and the action path of the laser and gas. It mainly includes multiple reflection cavity enhancement, FP cavity enhancement, etc. Among them, the multi-reflection cavity is generally composed of two front and rear cavity mirrors. The incident laser is reflected multiple times between the two cavity mirrors through the same focus, so that the laser intensity increases at the focus, thereby improving the detection sensitivity. The multiple reflection cavity enhancement technology generally enhances the Raman signal by dozens of times, mainly because the multiple reflection cavity has a limited number of reflections and the gain of the excitation light is limited. How to improve the efficiency of the reflector is the key to enhancing the Raman signal. Fiber-enhanced Raman technology (FERS) improves the Raman signal intensity by improving the collection efficiency of spherical Raman scattered light, mainly including silver-coated capillary enhancement and hollow-core fiber enhancement. Raman scattered light is spherical scattering, and only Raman scattered light within a small range can enter the detector. FERS can greatly improve the collection efficiency of Raman scattered light while also enhancing the interaction between gas and excitation light, thereby enhancing the Raman signal intensity.

Summary of the invention

In order to solve the above problems, the present invention provides a confocal Raman enhancement cavity, which realizes multiple reflections of laser in the optical cavity formed by the confocal Raman enhancement cavity and each reflection passes through a unique focusing point, thereby obtaining a Raman signal with increased intensity.

In order to achieve the above-mentioned object, according to one aspect of the present invention, a confocal Raman enhancement cavity is provided, which comprises: a front end convex lens; a rear end convex lens, which is arranged downstream of the front end convex lens, the distance between the front end convex lens and the rear end convex lens is the sum of the focal lengths of the front end convex lens and the rear end convex lens, and the focal positions of the front end convex lens and the rear end convex lens overlap to form a confocal point, and the optical axes of the front end convex lens and the rear end convex lens are on a straight line; a front end reflector array, which is arranged upstream of the front end convex lens, and the front end reflector array comprises a plurality of first reflective units with a reflective function, the first reflective unit reflects the first incident light incident through the front end convex lens back to the front end convex lens in parallel, and the light reflected by the first reflective unit is offset from the optical axis of the first incident light; and a terminal reflector array, which is arranged downstream of the rear end convex lens, and the terminal reflector array comprises a plurality of second reflective units with a reflective function, the second reflective unit reflects the second incident light incident through the rear end convex lens back to the rear end convex lens in parallel, and the light reflected by the second reflective unit is offset from the optical axis of the second incident light.

Furthermore, the confocal Raman enhancement cavity also includes a plane reflector for reflecting the outgoing light finally emitted from the terminal convex lens after multiple reflections by the front-end reflector array and the terminal reflector array back to the terminal convex lens along the original path, and the plane reflector is arranged downstream of the terminal convex lens.

Furthermore, the first reflecting unit and/or the second reflecting unit comprises two mutually perpendicular plane reflecting mirrors.

Further, the first reflecting unit and/or the second reflecting unit is configured as a retroreflective mirror, the retroreflective mirror includes a plurality of plane reflecting mirrors, and two adjacent plane reflecting mirrors among the plurality of plane reflecting mirrors are perpendicular to each other.

According to another aspect of the present invention, a Raman spectrum measurement system for detecting multi-component gas is provided, the system comprising the above-mentioned confocal Raman enhancement cavity.

Furthermore, the Raman spectrum measurement system further comprises a Raman signal collecting device for collecting Raman signals from the confocal Raman enhancement cavity.

Furthermore, the Raman signal collecting device includes a Raman signal collecting unit, which includes a collimating lens, a focusing lens coaxial with the collimating lens, and a filter located between the collimating lens and the focusing lens, wherein the common focal point of the front convex lens and the rear convex lens coincides with the focus of the collimating lens.

Furthermore, the Raman signal collection unit also includes a concave reflecting mirror, the concave reflecting mirror is coaxial with the collimating lens and the focusing lens, and the cofocal point is located at a position twice the focal length of the concave reflecting mirror.

Further, the Raman signal collecting device is configured to include a single Raman signal collecting unit, and further includes a single optical fiber coupled to the Raman signal collected by the single Raman signal collecting unit.

Furthermore, the Raman signal collection device is configured to include multiple Raman signal collection units, and also includes a multi-core bifurcated optical fiber having multiple optical fiber cores and multiple branches, wherein each branch of the multi-core bifurcated optical fiber is coupled to a Raman signal collected by the Raman signal collection unit.

Furthermore, the multiple optical fiber cores are arranged in a line.

Furthermore, the end face of the optical fiber is close to the focus of the focusing lens, so that the focus of the focusing lens and the collection angle formed by the end face of the optical fiber and the numerical aperture of the optical fiber match.

Furthermore, the Raman spectrum measurement system further comprises an optical isolator arranged upstream of the confocal Raman enhancement cavity, so that the light beam returning from the confocal Raman enhancement cavity is deflected after passing through the optical isolator.

Furthermore, the Raman spectrum measurement system also includes a filter coupling device for filtering the Raman signal collected by the multi-core bifurcated optical fiber, the filter coupling device includes a first lens, a second lens located downstream of the first lens, and a filter located between the first lens and the second lens, wherein the end face of the multi-core bifurcated optical fiber is located at the focus of the imaging lens group upstream of the filter.

Furthermore, the Raman spectroscopy measurement system also includes a filter coupling device for filtering the Raman signal collected by the single optical fiber, the filter coupling device includes a first lens, a second lens located downstream of the first lens, and a filter located between the first lens and the second lens, wherein the end face of the multi-core bifurcated optical fiber is located at the focus of the imaging lens group upstream of the filter.

Furthermore, the Raman signal collection device comprises a multi-core bifurcated optical fiber having multiple optical fiber cores and multiple branches, and the branches of the multi-core bifurcated optical fiber are distributed around the confocal point of the confocal Raman enhancement cavity.

Furthermore, the Raman spectrum measurement system also includes a sample pool provided with a sealed environment for measuring Raman signals, and the confocal Raman enhancement cavity is arranged in the sample pool.

Furthermore, the Raman spectrum measurement system also includes a sample pool provided with a sealed environment for measuring Raman signals, the sample pool is located inside the confocal Raman enhancement cavity, and the confocal point of the confocal Raman enhancement cavity is located in the sample pool.

According to the present invention, the confocal Raman enhancement cavity is used to realize multiple reflections of laser light in an optical cavity formed by the confocal Raman enhancement cavity, and each reflection passes through a unique focusing point, thereby obtaining a Raman signal with increased intensity.

Moreover, according to the present invention, by providing a Raman signal collection device, the Raman signal collection efficiency is greatly improved, and the Raman signal enhancement can be achieved by more than 200 times, and the Raman spectrum detection limit of hydrocarbon gases such as _CH4 can reach the ppm level.

Moreover, in the present invention, the Raman spectrum measurement system including the confocal Raman enhancement cavity and the Raman signal collection device can realize high-sensitivity detection of Raman signals. At the same time, the Raman spectrum measurement system of the present invention has the advantages of small size and easy integration.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

FIG. 1 shows a confocal Raman enhanced

Schematic diagram of the Raman spectroscopy measurement system structure of the cavity;

FIG2 shows a schematic diagram of the principle of a confocal Raman enhancement cavity;

FIG. 3 shows a first reflection unit and a second reflection unit according to an embodiment of the present application.

A schematic diagram of the structure of the reflection unit;

FIG. 4 shows a first reflection unit and a second reflection unit according to another embodiment of the present application.

A schematic diagram of the structure of the reflection unit;

FIG. 5A and FIG. 5B respectively show a confocal

Schematic diagram of the incident and exit positions of the multi-reflected light in the Raman enhanced cavity at the front reflector array and the terminal reflector array;

FIG. 6 shows a pull-out circuit provided with an optical isolator according to an embodiment of the present application.

Schematic diagram of the Mann signal enhancement device;

FIG. 7 shows a single channel having a single optical fiber according to an embodiment of the present application.

Schematic diagram of the optical fiber Raman signal collection device;

FIG. 8 shows the structure of a multi-core bifurcated optical fiber according to an embodiment of the present application.

Schematic diagram;

FIG9 shows a Raman signal collection device based on the multi-core bifurcated optical fiber shown in FIG8.

Schematic diagram of the device;

FIG. 10 shows a diagram of a multi-core bifurcated optical fiber device according to an embodiment of the present application.

Schematic diagram of a Raman signal filtering coupling device;

FIG. 11 shows a single-channel Raman signal collection according to another embodiment of the present application.

Schematic diagram of the device;

FIG. 12 shows a single-lens device provided with a reflector according to yet another embodiment of the present application.

Schematic diagram of the channel Raman signal collection device;

FIG. 13 shows a multi-channel Raman signal collection device according to an embodiment of the present application.

Schematic diagram of the device;

FIG. 14 shows a schematic diagram of a multi-channel Raman signal collection device provided with a reflector according to another embodiment of the present application.

DETAILED DESCRIPTION

The specific embodiments of the present invention are described in detail below.

The embodiments are only used to illustrate and explain the present invention, but not to limit the present invention.

The embodiments of the present invention are described below in conjunction with the accompanying drawings in the examples. Although exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

It should be understood that the terms used herein are only for the purpose of describing specific example embodiments and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms "one", "an" and "said" as used herein may also be meant to include plural forms. The terms "include", "comprise", "contain", and "have" are inclusive, and therefore specify the existence of stated features, steps, operations, elements and/or parts, but do not exclude the existence or addition of one or more other features, steps, operations, elements, parts, and/or combinations thereof. The method steps, processes, and operations described herein are not interpreted as necessarily requiring them to be performed in the specific order described or illustrated, unless the execution order is clearly indicated. It should also be understood that additional or alternative steps may be used.

For ease of description, spatially relative terms may be used herein to describe the relationship of one element or feature relative to another element or feature as shown in the figures, such as "upstream", "downstream", "inside", "outside", "below", "above", etc. Such spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation depicted in the figures.

FIG. 1 is a schematic diagram showing the structure of a Raman spectroscopy measurement system with a confocal Raman enhancement cavity according to an embodiment of the present application.

The system includes a laser 1, a sample cell 2, a confocal Raman enhancement cavity 3, a Raman signal collection device 4 and a spectrometer 5. The laser 1 is a continuous laser and the output laser is a single wavelength, and its function is to provide a laser source for the excitation of the Raman signal. The sample cell 2 provides a closed environment for the measurement of gas Raman signals, and the gas to be measured can flow into and out of the sample cell. The sample cell 2 has at least one optical window (as shown in Figure 1), and the laser beam 6 enters the confocal Raman enhancement cavity 3 from the optical window of the sample cell. The Raman signal collection device 4 collects the Raman signal at the confocal point in the confocal Raman enhancement cavity 3, and the collected Raman signal is transmitted to the spectrometer 5 through an optical fiber. The spectrometer has the functions of spectroscopic and photoelectric detection, and its function is to record the Raman spectrum.

As shown in FIG1 , the laser outputs laser light, and the laser beam 6 is coupled to the confocal Raman enhancement cavity 3 through the optical window of the sample cell 2. The laser light is reflected multiple times in the confocal Raman enhancement cavity 3, and the laser light after each reflection is focused to the confocal point. The Raman signal generated at the laser confocal point is collected by the Raman signal collection device 4. The Raman signal collected by the Raman signal collection device 4 is coupled to the spectrometer 5 via an optical fiber, and finally the Raman signal is recorded.

FIG1 shows an example in which the confocal Raman enhancement cavity is located inside the sample cell and is used to measure flowing gas and static gas samples, however, the present invention is not limited thereto. According to another embodiment of the present application, the sample cell 2 may be located inside the confocal Raman enhancement cavity 3, and the confocal point of the confocal Raman enhancement cavity 3 is located inside the sample cell 2. With this structure, since the sample cell is designed to be smaller, it saves more space and the optical path adjustment is also easier.

Fig. 2 shows a schematic diagram of the principle of the confocal Raman enhancement cavity. As shown in Fig. 2, the confocal Raman enhancement cavity 3 comprises a front convex lens 7, a rear convex lens 8, a front reflector array 10, and a terminal reflector array 11.

The rear convex lens 8 is arranged downstream of the front convex lens 7, and the distance between the front convex lens 7 and the rear convex lens 8 is the sum of the focal lengths of the front convex lens 7 and the rear convex lens 8, and the focal positions of the front convex lens 7 and the rear convex lens 8 coincide, and the coincident position is called the common focal point 9. The optical axes of the front convex lens and the rear convex lens are on a straight line, that is, the front convex lens 7 and the rear convex lens 8 are coaxial.

The front end reflector array 10 is arranged upstream of the front end convex lens 7, and the front end reflector array 10 includes a plurality of first reflective units with a reflective function, such as first reflective units 13-02, 13-04 (as shown in FIG5A), etc. The first reflective unit reflects the first incident light incident through the front end convex lens 7 back to the front end convex lens 7 in parallel, and the light reflected by the first reflective unit 13-02 is offset from the optical axis of the first incident light.

The terminal reflector array 11 is arranged downstream of the rear end convex lens 8, and the terminal reflector array 11 includes a plurality of second reflective units with a reflective function, such as second reflective units 13-01, 13-03 (as shown in FIG5B ), etc. The second reflective unit reflects the second incident light incident through the rear end convex lens back to the rear end convex lens 8 in parallel, and the light reflected by the second reflective unit 13-01 is offset from the optical axis of the second incident light.

As described above, the front reflector array 10 and the terminal reflector array 11 each include a plurality of reflective units. The reflective unit is used to reflect the incident light incident to the reflective unit, and the reflected light beam is parallel to the incident light, and there is a certain position offset between the reflected light beam and the incident light.

FIG3 shows a schematic structural diagram of a first reflecting unit and a second reflecting unit according to an embodiment of the present application.

As shown in FIG3 , the first reflection unit 13-02 or the second reflection unit 13-01 includes two plane reflectors 20-1 and 20-2, that is, the first plane reflector 20-1 and the second plane reflector 20-2. The first plane reflector 20-1 and the second plane reflector 20-2 are perpendicular to each other. When the incident light 21 is incident on the second plane reflector 20-2, the incident light 21 is reflected to the first plane reflector 20-1, and under the reflection effect of the first plane reflector 20-1, the outgoing light 22 is parallel to the incident light 21. As shown in the figure, after the incident light 21 is reflected twice, the propagation direction changes by 180°, and there is a certain position offset between the outgoing light 22 and the incident light 21.

According to some preferred embodiments of the present application, a retroreflector 23 composed of more plane reflectors can be directly used as a reflective unit, as shown in Figure 4. Figure 4 shows a schematic structural diagram of a first reflective unit and a second reflective unit according to another embodiment of the present application. As shown in the figure, two adjacent plane reflectors among the multiple plane reflectors constituting the retroreflector 23 are perpendicular to each other.

Similar to the reflection unit shown in FIG. 3 , the outgoing light 22 and the incident light 21 in FIG. 4 are parallel and have a certain position offset.

The working principle of the confocal Raman enhancement cavity will be explained below.

After the laser beam 6 output by the laser 1 is incident on the confocal Raman enhancement cavity from a direction parallel to the optical axis 12, it is focused at the confocal point 9 under the convergence of the front convex lens 7. The focused laser beam becomes parallel light after passing through the rear convex lens 8, and the parallel light is reflected by a second reflection unit 13-01 located in the terminal reflector array 11, and the propagation direction changes by 180° and the beam position is displaced.

The incident point position and the exit point position of the laser at the second reflection unit 13-01 are indicated as 14-01 and 15-01 respectively. The reflected laser beam is refocused at the common focal point 9 under the action of the rear convex lens 8, and then becomes a parallel beam under the action of the front convex lens 7, and the parallel beam is reflected under the action of a first reflection unit 13-02 in the front reflector array 10.

By analogy, the laser beam 6 can be reflected multiple times in the confocal Raman enhancement cavity 3, and after each reflection, it is focused at the position of the confocal point 9. Finally, after multiple reflections, the laser beam is emitted from the confocal Raman enhancement cavity 3 and becomes an output beam 18.

5A and 5B are schematic diagrams showing the incident and exit positions of multiply reflected light at the front-end reflector array and the terminal reflector array in a confocal Raman enhancement cavity according to an embodiment of the present application.

In Fig. 5, X in the reflection unit 13-X indicates the order of the reflection units that successively act on the incident light beam during the multiple reflections of the incident light beam in the confocal Raman enhancement cavity. 14-X and 15-X respectively indicate the incident and exit positions of the incident light beam at the reflection unit 13-X located at the terminal reflection mirror array 11; 16-X and 17-X respectively indicate the incident and exit positions of the incident light beam at the reflection unit 13-X located at the front reflection mirror array 10.

As shown in the figure, the laser beam 6 enters the confocal Raman enhancement cavity 3 at the laser incident position 30 in the front end reflector array 10. After passing through the front end convex lens 7 and the rear end convex lens 8, the beam is incident on the second reflection unit 13-01 located at the terminal reflector array 11 at position 14-01. After the beam is reflected by the second reflection unit 13-01, it is emitted at position 15-01. The beam emitted from position 15-01 passes through the rear end convex lens 8 and the front end convex lens 7 successively, and then enters the first reflection unit 13-02 in the front end reflector array 10 at position 16-02, and then is reflected at position 17-02. After that, it passes through the front end convex lens 7 and the rear end convex lens 8, and then enters the second reflection unit 13-03 located at the terminal reflector array 11 at position 14-03, and is reflected at position 15-03. After multiple reflections in the confocal Raman enhancement cavity 3, the beam finally exits at position 31.

According to one embodiment of the present application, as shown in FIG5 , the front-end reflector array 10 and the terminal reflector array 11 both contain 59 reflective units, which can realize 108 reflections of the laser beam in the confocal enhancement cavity, and the laser beam is focused to the confocal point 9 position a total of 110 times.

According to other embodiments of the present application, the number of reflection units in the front-end reflector array 10 and the terminal reflector array 11 may be appropriately increased or decreased.

According to another embodiment of the present application, the exit position 31 of the laser beam in the confocal Raman enhancement cavity 3 may be located in the front end reflective mirror array.

According to another embodiment of the present application, as shown in FIG2 , a plane reflector 41 can be added to reflect the outgoing light beam 18 of the laser beam 6 after multiple reflections in the confocal Raman enhancement cavity 3 back to the confocal Raman enhancement cavity 3, thereby further enhancing the Raman signal. As shown in the figure, the plane reflector 41 is arranged downstream of the terminal convex lens 8.

As described above, after the laser beam 6 is incident from the front convex lens 7, it passes through the terminal convex lens 8, and after multiple reflections by the front reflector array 10 and the rear reflector array 11, the outgoing light beam 18 finally emitted from the terminal convex lens 8 is reflected back to the terminal convex lens 8 by the plane lens 41 along the original path.

According to an embodiment of the present application, an optical isolator 40 is disposed between the laser 1 and the confocal Raman enhancement cavity 3 , as shown in FIG6 .

As shown in FIG2 , the outgoing light beam 18 enters the confocal Raman enhancement cavity 3 again after being reflected by the reflector 41, and the laser beam is emitted from the front convex lens 7 after multiple reflections in the confocal Raman enhancement cavity 3. By arranging an optical isolator between the laser 1 and the confocal Raman enhancement cavity 3 as shown in FIG6 , the propagation direction of the laser beam returned from the confocal Raman enhancement cavity 3 is deflected after passing through the optical isolator 40, and the return light beam 42 deflected by the optical isolator 40 will not enter the laser 1, thereby achieving protection of the laser.

According to an embodiment of the present application, a Raman signal collection device having a single optical fiber may be used to collect the Raman signal at the confocal point 9 in the confocal Raman enhancement cavity 3 , as shown in FIG. 7 , for example.

As shown in FIG7 , when the Raman signal is directly collected using the optical fiber 50, the end face of the optical fiber 50 is close to the position of the confocal point 9, so that the Raman signal collection angle 51 formed by the confocal point 9 and the two end faces of the optical fiber 50 matches the numerical aperture of the optical fiber 50, thereby improving the Raman signal collection efficiency.

According to another embodiment of the present application, the Raman signal may be collected by using a Raman signal collection device having a multi-core bifurcated optical fiber 52 (as shown in FIG. 8 ), as shown in FIG. 9 , for example.

As shown in Fig. 8, one end of the multi-core bifurcated optical fiber 52, that is, all the sub-fiber cores in the end face 54 are arranged in a straight line. And, the other end of the multi-core bifurcated optical fiber 52 shows eight branches 53-1, 53-2, 53-3, 53-4, 53-5, 53-6, 53-7, 53-8. However, the multi-core bifurcated optical fiber 52 can be provided with more or fewer branches as needed.

As shown in Fig. 9, the branches 53-1, 53-2, 53-3, 53-4, 53-5, 53-6, 53-7, 53-8 of the multi-core bifurcated optical fiber 52 of the Raman signal collection device are distributed around the confocal point 9 in the confocal Raman enhancement cavity 3, so as to collect Raman signals from multiple angles and effectively increase the Raman signal collection efficiency. In this embodiment, the end face 54 of the multi-core bifurcated optical fiber 52 of the multi-core bifurcated optical fiber 52 is directly connected to the spectrometer.

According to an embodiment of the present application, in order to reduce the interference of the excitation light, a filter coupling device is added before coupling the Raman signal collected by the multi-core bifurcated optical fiber 52 or a single optical fiber into the spectrometer.

FIG. 10 shows a schematic diagram of a Raman signal filtering and coupling device provided for a multi-core bifurcated optical fiber according to an embodiment of the present application.

As shown in Figure 10, the filter coupling device is used to filter the Raman signal collected by the multi-core bifurcated optical fiber, and the filter coupling device includes an imaging lens group 57 and a filter 55 located between the imaging lens groups. According to an embodiment of the present application, the imaging lens group 57 includes a first lens and a second lens located downstream of the first lens. The end face 54 of the multi-core bifurcated optical fiber is located at the focal position of the first lens, and the slit 56 of the spectrometer is located at the focal position of the second lens.

One end of the multi-core bifurcated optical fiber 52 is close to the confocal point 9 in the confocal Raman enhancement cavity 3. After the Raman signal enters the optical fiber, it is emitted in parallel from the end face 54 at the other end.

The filter coupling device images the end face 54 of the multi-core bifurcated optical fiber 52 onto the slit 56 of the spectrometer through the imaging lens group. In addition, by placing a filter 55 in the middle of the imaging lens group 57, the excitation light component in the Raman signal light can be reduced.

According to yet another embodiment of the present application, Raman signals may be collected by using the Raman signal collection device shown in FIG. 11 .

As shown in the figure, the Raman signal collecting device includes a Raman signal collecting unit, which includes a collimating lens 66, a focusing lens 68 coaxial with the collimating lens 66, and a filter 55 located between the collimating lens 66 and the focusing lens 68, wherein the common focal point 9 of the front convex lens 7 and the rear convex lens 8 coincides with the focus of the collimating lens 66.

The Raman signal 65 generated at the confocal point 9 in the confocal Raman enhancement cavity 3 is collimated by the collimating lens 66 to become parallel light, and then filtered by the filter 55 and coupled into the optical fiber 50 by the focusing lens 68. The optical fiber 50 is directly connected to the spectrometer 5.

According to another embodiment of the present application, on the basis of the Raman signal collection unit shown in FIG. 11 , a concave reflector 70 is added to form a Raman signal collection unit provided with a reflector. The concave reflector 70 is coaxial with the collimating lens 66 and the focusing lens 68, and the common focal point 9 is located at a position twice the focal length of the concave reflector 70. The Raman signal generated at the common focal point 9 is refocused to the common focal point 9 after being reflected by the concave reflector 70, and is coupled into the Raman signal collection unit including the collimating lens 66, the filter 55 and the focusing lens 68, thereby increasing the Raman signal collection efficiency.

According to yet another embodiment of the present application, a plurality of single-channel Raman signal collection units as shown in FIG. 11 may be used to achieve efficient collection of Raman signals.

As shown in Fig. 13, a schematic diagram of a multi-channel Raman signal collection device including six single-channel Raman signal collection units is schematically shown. The Raman signals collected by each channel are respectively coupled to the branches 53-1, 53-2, 53-3, 53-4, 53-5, 53-6, 53-7, and 53-8 of the multi-core bifurcated optical fiber 52, and the end face 54 of the multi-core bifurcated optical fiber is directly connected to the incident slit 56 of the spectrometer 5.

According to yet another embodiment of the present application, in order to reduce the number of branches of the multi-core bifurcated optical fiber 52 , the Raman signal may be collected by using a plurality of Raman signal collection units provided with concave reflectors 70 as shown in FIG. 12 .

As shown in Fig. 14, a multi-channel Raman signal collection device is schematically shown, which includes three Raman signal collection units provided with concave reflectors 70. This arrangement can reduce the number of branches of the multi-core bifurcated optical fiber 52.

For a traditional near-confocal cavity, the number of reflections is limited and the focusing point is not unique, so the Raman signal enhancement effect is limited. However, the present invention uses a confocal Raman enhancement cavity equipped with a reflector array to make the laser reflect more than a hundred times in the cavity and the focusing point is at the same point, so that the power density at the laser focus is higher.

The present invention uses the confocal Raman enhancement cavity as described above to achieve multiple reflections of laser light in the optical cavity formed by the confocal Raman enhancement cavity, and each reflection passes through a unique focusing point, thereby obtaining a Raman signal with increased intensity.

Furthermore, the Raman signal collection device according to the present invention greatly improves the Raman signal collection efficiency, can achieve Raman signal enhancement > 200 times, and can achieve a Raman spectrum detection limit of _CH4 and other hydrocarbon gases to the ppm level.

In addition, in the present invention, a Raman spectrum measurement system including a confocal Raman enhancement cavity and a Raman signal collection device can realize high-sensitivity detection of Raman signals. At the same time, the device of the present invention has the advantages of small size and easy integration.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (18)

1. A confocal Raman enhancement cavity, characterized in that the confocal Raman enhancement cavity comprises: Front convex lens; A rear convex lens is arranged downstream of the front convex lens, the distance between the front convex lens and the rear convex lens is the sum of the focal lengths of the front convex lens and the rear convex lens, and the focal positions of the front convex lens and the rear convex lens overlap to form a common focal point, and the optical axes of the front convex lens and the rear convex lens are on a straight line; a front end reflector array, arranged upstream of the front end convex lens, and comprising a plurality of first reflective units having a reflective function, wherein the first reflective units reflect the first incident light incident through the front end convex lens back to the front end convex lens in parallel, and the light reflected by the first reflective units is offset from the optical axis of the first incident light; and A terminal reflector array is arranged downstream of the rear end convex lens, and the terminal reflector array includes a plurality of second reflective units with a reflective function, the second reflective units reflect the second incident light incident through the rear end convex lens back to the rear end convex lens in parallel, and the light reflected by the second reflective unit is offset from the optical axis of the second incident light. 2. The confocal Raman enhancement cavity according to claim 1 is characterized in that the confocal Raman enhancement cavity also includes a plane reflector for reflecting the outgoing light finally emitted from the terminal convex lens after multiple reflections by the front-end reflector array and the terminal reflector array back to the terminal convex lens along the original path, and the plane reflector is arranged downstream of the terminal convex lens. 3 . The confocal Raman enhancement cavity according to claim 1 , wherein the first reflection unit and/or the second reflection unit comprises two mutually perpendicular plane mirrors. 4. The confocal Raman enhancement cavity according to claim 1 or 2, characterized in that the first reflection unit and/or the second reflection unit is configured as a retroreflective mirror, the retroreflective mirror comprises a plurality of plane reflectors, and two adjacent plane reflectors among the plurality of plane reflectors are perpendicular to each other. 5. A Raman spectroscopy measurement system for detecting multi-component gases, characterized in that the Raman spectroscopy measurement system comprises the confocal Raman enhancement cavity according to any one of claims 1 to 4. 6 . The Raman spectroscopy measurement system according to claim 5 , further comprising a Raman signal collecting device for collecting the Raman signal from the confocal Raman enhancement cavity. 7. The Raman spectrum measurement system according to claim 6 is characterized in that the Raman signal collection device includes a Raman signal collection unit, and the Raman signal collection unit includes a collimating lens, a focusing lens coaxial with the collimating lens, and a filter located between the collimating lens and the focusing lens, wherein the common focal point of the front convex lens and the rear convex lens coincides with the focus of the collimating lens. 8. The Raman spectrum measurement system according to claim 7, characterized in that the Raman signal collection unit further comprises a concave reflector, the concave reflector is coaxial with the collimating lens and the focusing lens, and the cofocal point is located at a position twice the focal length of the concave reflector. 9. The Raman spectrum measurement system according to claim 7 or 8, characterized in that the Raman signal collection device is configured to include a single Raman signal collection unit, and further includes a single optical fiber coupled to the Raman signal collected by the single Raman signal collection unit. 10. The Raman spectrum measurement system according to claim 7 or 8, characterized in that the Raman signal collection device is configured to include a plurality of Raman signal collection units, and also includes a multi-core bifurcated optical fiber having a plurality of optical fiber cores and a plurality of branches, wherein each branch of the multi-core bifurcated optical fiber is coupled to a Raman signal collected by the Raman signal collection unit. 11 . The Raman spectrum measurement system according to claim 10 , wherein the plurality of optical fiber cores are arranged in a line. 12. The Raman spectrum measurement system according to claim 9, characterized in that the end face of the optical fiber is close to the focus of the focusing lens, so that the focus of the focusing lens and the collection angle formed by the end face of the optical fiber and the numerical aperture of the optical fiber match. 13. The Raman spectroscopy measurement system according to any one of claims 5 to 8, characterized in that the Raman spectroscopy measurement system further comprises an optical isolator arranged upstream of the confocal Raman enhancement cavity, so that the light beam returning from the confocal Raman enhancement cavity is deflected after passing through the optical isolator. 14. The Raman spectroscopy measurement system according to claim 10, characterized in that the Raman spectroscopy measurement system also includes a filter coupling device for filtering the Raman signal collected by the multi-core bifurcated optical fiber, the filter coupling device includes a first lens, a second lens located downstream of the first lens, and a filter plate located between the first lens and the second lens, wherein the end face of the multi-core bifurcated optical fiber is located at the focus of the imaging lens group upstream of the filter plate. 15. The Raman spectroscopy measurement system according to claim 9, characterized in that the Raman spectroscopy measurement system also includes a filter coupling device for filtering the Raman signal collected by the single optical fiber, the filter coupling device includes a first lens, a second lens located downstream of the first lens, and a filter located between the first lens and the second lens, wherein the end face of the multi-core bifurcated optical fiber is located at the focus of the imaging lens group upstream of the filter. 16. The Raman spectrum measurement system according to claim 6, characterized in that the Raman signal collection device comprises a multi-core bifurcated optical fiber having multiple optical fiber cores and multiple branches, and the branches of the multi-core bifurcated optical fiber are distributed around the confocal point of the confocal Raman enhancement cavity. 17 . The Raman spectroscopy measurement system according to claim 5 , further comprising a sample cell provided with a sealed environment for measuring Raman signals, wherein the confocal Raman enhancement cavity is provided in the sample cell. 18. The Raman spectroscopy measurement system according to claim 5, characterized in that the Raman spectroscopy measurement system further comprises a sample cell provided with a sealed environment for measuring Raman signals, the sample cell is located inside the confocal Raman enhancement cavity, and the confocal point of the confocal Raman enhancement cavity is located inside the sample cell.