A thermally insensitive multi-pass cell for enhancing gas raman spectroscopy

Abstract

This application belongs to the field of gas Raman scattering, and specifically discloses a thermally insensitive multi-reflection cavity for enhancing gas Raman spectra. It includes an inner cavity and an outer cavity, with the inner cavity disposed within the outer cavity, and a vacuum evacuated between the inner and outer cavities. The inner cavity includes a neck, a body, and a tail. The neck includes an opening with a constant outer diameter and a shoulder that is continuous with the tail side of the opening but gradually increases in outer diameter. An opening is provided on the first side of the opening, and an incident window is provided on the opening to seal it. The incident window provides an incident channel for the laser required to acquire the Raman spectrum of the gas to be measured. The body is cylindrical with openings at both ends and a constant outer diameter; the opening on the first side of the body is continuous with the tail side of the shoulder. The opening side of the curved surface of the tail is the first side of the tail, and the first side of the tail is continuous with the opening on the tail side of the body. The radius of curvature of the shoulder is smaller than that of the tail. This application provides a thermally insensitive environment for the gas to be measured, making the Raman spectral signal of the gas more stable.

Description

Technical Field

[0001] This application belongs to the field of gas Raman scattering, and more specifically, relates to a thermally insensitive multi-reflection cavity for enhancing gas Raman spectroscopy. Background Technology

[0002] Raman spectroscopy is a spectroscopic analysis technique based on the Raman scattering effect of matter. It detects the Raman scattered light produced when an excitation light illuminates a substance, forming a spectrum of different scattered wavelengths. The type of substance is determined by the position of the scattered wavelengths, and the content of the substance is determined by the intensity of the scattered light. As a highly sensitive molecular detection method, Raman spectroscopy has been widely used in gas analysis. Cavity-enhanced Raman spectroscopy is a technique that has attracted much attention in recent years. It utilizes a laser to generate constructive interference of multiple beams back and forth within a cavity, increasing the laser intensity and effective optical path to enhance the Raman scattering signal. To further improve the detection sensitivity and applicability of this technique, researchers have designed cavity configurations with different shapes to meet the application requirements of various scenarios.

[0003] However, according to the research in the literature [Journal of Raman Spectroscopy 51.3 (2020): 555-568], it was found that in cavity-enhanced gas Raman spectroscopy, temperature not only affects the Raman scattering cross section of gas molecules, but may also cause instability in the Raman signal intensity within the cavity by altering the optical properties and gas distribution. Temperature changes lead to a redistribution of vibrational and rotational energy levels of gas molecules, causing significant fluctuations in the Raman signal intensity and further increasing the uncertainty of the signal. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this application is to provide a thermally insensitive multi-reflection cavity for enhancing gas Raman spectroscopy, aiming to solve the problem that temperature affects the Raman signal intensity within the cavity in existing cavity-enhanced gas Raman applications, causing uncertainty in the Raman signal intensity.

[0005] To achieve the above objectives, this application provides a thermally insensitive multi-reflection cavity for enhancing gas Raman spectroscopy, used to carry the gas to be measured in order to acquire the Raman spectrum of the gas to be measured. The thermally insensitive multi-reflection cavity includes an inner cavity and an outer cavity, the inner cavity being disposed within the outer cavity, and a vacuum is drawn between the inner cavity and the outer cavity.

[0006] The inner cavity includes: a neck, a body, and a tail;

[0007] The neck includes: a cavity with a constant outer diameter and a shoulder that is continuous with the tail side of the cavity and gradually increases in outer diameter; the front side of the cavity is provided with an opening, and an incident window is provided on the opening to seal it; the incident window is used to provide an incident channel for the laser required to obtain the Raman spectrum of the gas to be measured.

[0008] The main body is a cylindrical shape with openings at both ends and a constant outer diameter. The opening on the front side of the main body is continuous with the tail side of the shoulder.

[0009] The tail is a centrally symmetrical curved surface, and the opening side of the curved surface is the head side of the tail. The head side of the tail is continuous with the opening of the tail side of the main body, which is used to seal the tail side of the main body.

[0010] The radius of curvature of the shoulder is smaller than that of the tail.

[0011] It should be noted that the reflective cavity provided in this application has a small radius of curvature at both the neck and tail ends, which can significantly enhance the high reflectivity performance at multiple angles, allowing the excitation light to be reflected multiple times in the cavity. At the same time, the main body is a non-spherical cylinder, which can increase the effective interaction distance of the excitation light and the gas in a single reflection within a certain space. The high reflectivity silver-plated liner can reduce the optical loss of the laser in each reflection, improve the laser utilization rate, and thus further enhance the multi-reflection signal of the gas Raman spectrum.

[0012] Furthermore, due to the multi-curvature configuration of the reflecting cavity, the tail is an imperfect sphere with a relatively small radius of curvature, which can reflect the thermal radiation inside the cavity to the curved side. The main body forms a thermal radiation propagation channel, causing the thermal radiation to converge towards the side closer to the neck. The neck has a cavity opening and a shoulder with a small radius of curvature. The shoulder with a small radius of curvature and the tail with a large radius of curvature have strong focusing and weak focusing characteristics, respectively. By utilizing the balance between strong and weak focusing, the beam cross-section size can be controlled to enhance the beam concentration. At the same time, increasing the Rayleigh length slows down the beam divergence, making the beam more stable. In this process, multiple reflections occur, and the gas molecules to be measured are excited multiple times, increasing the effective interaction distance between the laser beam and the gas molecules to be measured. Furthermore, the resulting thermal radiation field can cause the thermal radiation from the neck to converge towards the cavity opening, and then conduct heat outward from the entrance window of the cavity opening. This achieves the processing of the temperature radiation generated by the multiple reflections of the laser beam inside the cavity, providing a thermally insensitive environment inside the cavity and obtaining a relatively stable Raman scattering signal.

[0013] In one possible implementation, both the outer side of the inner cavity and the inner side of the outer cavity are coated with a highly reflective material.

[0014] In one possible implementation, a gas conduit is provided on the incident window.

[0015] In one possible implementation, the cavity, shoulder, body, and tail transition smoothly and continuously, forming a smooth curved surface.

[0016] In one possible implementation, the height of the cavity is less than the height of the main body, and the height of the shoulder is greater than the height of the tail.

[0017] In one possible implementation, the radius of curvature of the cavity is in the range of 15mm to 30mm, the radius of curvature of the shoulder is in the range of 5mm to 25mm, the radius of curvature of the transition portion between the shoulder and the cavity is in the range of 2mm to 15mm, the height of the cavity is in the range of 10mm to 30mm, and the height of the shoulder is in the range of 15mm to 45mm.

[0018] In one possible implementation, the radius of curvature of the body ranges from 30 mm to 60 mm, and the height of the body ranges from 50 mm to 200 mm.

[0019] In one possible implementation, the radius of curvature of the tail ranges from 20 mm to 40 mm, and the height of the tail ranges from 20 mm to 60 mm.

[0020] In one possible implementation, the inner cavity and the outer cavity are integrally formed; and / or the gap between the inner cavity and the outer cavity ranges from 1 mm to 5 mm.

[0021] In one possible implementation, the incident window is a quartz window.

[0022] Both the inner and outer cavities are made of glass.

[0023] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art:

[0024] This application provides a thermally insensitive multi-reflection cavity for enhancing gas Raman spectroscopy. In this application, the thermally insensitive multi-reflection cavity has three main parts: a neck, a body, and a tail. Its configuration is optimized and has different curvatures. The neck includes an opening and a shoulder. The curvature radii at both ends of the shoulder and tail are small, which can significantly enhance the multi-angle high reflectivity performance, allowing the excitation light to be reflected multiple times in the cavity. At the same time, the body is a non-spherical cylinder, which can increase the effective interaction distance of the excitation light and the gas in a single reflection within a certain space. The high-reflectivity liner can reduce the optical loss of the laser in each reflection and improve the laser utilization rate, thereby further enhancing the multi-reflection signal of the gas Raman spectrum.

[0025] This application provides a thermally insensitive multi-reflection cavity for enhancing gas Raman spectroscopy. The complete cavity of the thermally insensitive multi-reflection cavity has a multi-curvature configuration, with the tail being a non-spherical shape with a relatively small radius of curvature. This allows for the reflection of thermal radiation within the cavity towards the curved side, forming a thermal radiation propagation channel in the main body, causing the thermal radiation to converge towards the side near the neck. The neck has a cavity opening and a shoulder with a small radius of curvature, and the resulting thermal radiation field allows the thermal radiation from the neck to converge towards the cavity opening, thereby conducting heat outward from the entrance window of the cavity opening. This effectively processes the temperature radiation generated by multiple reflections of the laser beam within the cavity. Therefore, the reflection cavity provided in this application can form a special temperature field inside the cavity, providing an internal thermally insensitive environment for the gas molecules to be excited. This is crucial in multi-reflection Raman enhancement systems because temperature changes affect the energy level distribution of gas molecules, the Raman scattering cross section, and the stability of the optical path within the cavity, leading to significant fluctuations in the Raman signal intensity. Furthermore, during the multiple reflections and interactions of the excitation light with the gas molecules, temperature release is inevitable, causing signal instability.

[0026] This application provides a thermally insensitive multi-reflection cavity for enhancing gas Raman spectroscopy. Due to its double-layer vacuum structure design, the thermally insensitive multi-reflection cavity can isolate the gas inside the cavity from the external environment, blocking heat transfer and heat convection pathways. The high-reflectivity liner coated on the cavity can also suppress infrared thermal radiation interference from the external environment. Through the above-mentioned thermal shielding mechanism, a thermally insensitive environment can be provided for the gas molecules inside the cavity, which is not affected by the external temperature and allows the internal temperature to be discharged, making the multi-reflection enhanced gas Raman spectral signal more stable. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the heat-insensitive multi-reflection cavity provided in the embodiments of this application;

[0028] Figure 2 Here is a structural diagram of the high-transparency quartz window sheet provided in the embodiments of this application:

[0029] Figure 3 This is a structural block diagram of the gas detection device provided in the embodiments of this application;

[0030] Figure 4 This is a comparison diagram of the gas Raman intensity of the thermally insensitive multi-reflection cavity and the traditional quartz glass gas chamber provided in the embodiments of this application;

[0031] Figure 5 This is a schematic diagram showing the gas Raman intensity variation of the thermally insensitive multi-reflection cavity provided in this application embodiment under different external temperatures;

[0032] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein 1 is a heat-insensitive multi-reflection cavity; 11 is the neck; 111 is the shoulder; 112 is the cavity opening; 12 is the main body; 13 is the tail; 14 is a quartz high-transparency window; 141 is the air inlet; 142 is the air outlet; 143 is the gas conduit; 15 is the inner cavity layer; 16 is the outer cavity layer; 17 is the laser beam; 2 is the laser driver; 3 is the fiber optic collimating lens; 4 is the filter; 5 is the fiber optic collecting lens; 6 is the grating spectrometer; 7 is the CCD detector; and 8 is the computer equipment. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0034] The embodiments of this application are described below with reference to the accompanying drawings.

[0035] This application relates to the field of gas Raman scattering and discloses a thermally insensitive multi-reflection cavity for enhancing gas Raman spectra. In this application, the complete cavity of the thermally insensitive multi-reflection cavity has a multi-curvature configuration, which can form a special temperature field inside the cavity. This field can handle the temperature release generated during the interaction between the excitation beam and gas molecules through multiple reflections within the cavity, providing an internal thermally insensitive environment for the gas molecules to be excited. Furthermore, the thermally insensitive multi-reflection cavity has a vacuum isolation layer and a high-reflectivity silver-plated liner, which can block heat transfer and convection paths with the external environment and suppress thermal radiation interference, providing a thermally insensitive environment for the gas molecules to be excited and obtaining a relatively stable thermally insensitive gas Raman signal. The multi-reflection cavity, with its high-reflectivity silver-plated liner and curvature configuration resulting in a small laser reflection angle, allows the laser to form a multi-pass round-trip beam within the cavity, enhancing the Raman scattering signal. In addition, the radiation field formed by the cavity further focuses the Raman scattered light to the port, further enhancing the gas Raman signal.

[0036] To enhance the Raman scattering intensity of a gas while reducing the interference of temperature changes on the gas Raman signal, this application provides a thermally insensitive multi-reflection cavity for enhancing gas Raman spectra. This thermally insensitive multi-reflection cavity has a high-reflectivity silver-plated liner, and its curvature configuration results in a small laser reflection angle, allowing the laser to form a multi-pass round-trip beam within the cavity, thereby enhancing the Raman scattering signal. The thermally insensitive multi-reflection cavity comprises a double-layer vacuum optical cavity, consisting of an inner cavity and an outer cavity. The inner layer is the multi-reflection cavity, used to contain the gas and perform Raman signal detection, while the outer layer is the structural cavity, used to maintain the stability of the cavity. A vacuum isolation layer is formed between the inner and outer layers, which significantly reduces the effects of heat conduction and convection. The outer surface of the inner cavity and the inner surface of the outer cavity are coated with a high-reflectivity silver-plated liner, which can suppress thermal radiation interference from the external environment, ensuring that the temperature inside the inner multi-reflection cavity is unaffected by the external environment.

[0037] The thermally insensitive multi-reflection cavity is a multi-curvature cavity, and it is defined that the thermally insensitive multi-reflection cavity can form a thermally insensitive temperature field inside; the high-reflectivity silver-plated liner is chemically silver-plated, and the high-reflectivity silver-plated liner is formed by using a chemical reducing agent to reduce silver ions into metallic silver, which is then uniformly deposited on the surface of the thermally insensitive multi-reflection cavity.

[0038] Preferably, the silver-plated liner has a laser reflectivity greater than 95%.

[0039] Preferably, the heat-insensitive multi-reflection cavity includes three different configurations: a neck, a body, and a tail.

[0040] Preferably, the neck of the heat-insensitive multi-reflection cavity is a narrow-mouthed cylinder or cone, consisting of a shoulder and a cavity opening. The radius of curvature of the cavity opening ranges from 15mm to 30mm, the radius of curvature of the shoulder ranges from 5mm to 25mm, the radius of curvature of the transition portion between the shoulder and the cavity opening ranges from 2mm to 15mm, the height of the cavity opening ranges from 10mm to 30mm, and the height of the shoulder ranges from 15mm to 45mm.

[0041] Preferably, the thermally insensitive multi-reflection cavity body is a regular cylinder or frustum with a radius of curvature ranging from 30mm to 60mm, and the body height ranging from 50mm to 200mm.

[0042] Preferably, the tail of the heat-insensitive multi-reflection cavity is arc-shaped or hemispherical with a radius of curvature ranging from 20mm to 40mm, and the height of the tail ranges from 20mm to 60mm.

[0043] Preferably, the neck port of the heat-insensitive multi-reflection cavity is joined to an optical quartz high-transmittance window, the quartz high-transmittance window having a thickness of 0.5 mm and two through holes with a diameter of 6.5 mm, the center of the through holes being 7.5 mm from the edge of the window.

[0044] Preferably, the heat-insensitive multi-reflection cavity includes an inner cavity and an outer cavity, wherein the inner cavity and the outer cavity are coaxial glass bodies.

[0045] Preferably, the inner cavity and the outer cavity are fused together by heating and melting, and fixed at the sealing point at the front end, forming a vacuum isolation layer between the two layers.

[0046] Preferably, the thickness of the inner cavity glass ranges from 1 mm to 1.5 mm.

[0047] Preferably, the thickness of the outer cavity glass ranges from 2 mm to 3 mm.

[0048] Preferably, the vacuum gap between the inner and outer glass layers ranges from 1 mm to 5 mm.

[0049] Preferably, the heat-insensitive multi-reflection cavity is made of borosilicate material.

[0050] This application also provides a gas detection device, including a Raman scattering light detector, which is located near the neck window of the cavity and includes a laser and a detector. The laser is used to generate a laser beam that is incident into the heat-insensitive multi-reflection cavity to excite the gas molecules to be tested to generate Raman scattered light. The detector is located near the neck window of the cavity to collect the Raman scattered light generated by the gas molecules.

[0051] Preferably, the laser includes a laser driver, a multimode fiber, and a fiber collimating lens. The laser and the fiber collimating lens are connected by a multimode fiber. The multimode fiber transmits the laser beam generated by the laser to the fiber collimating lens, and the fiber collimating lens focuses the beam transmitted from the multimode fiber into the thermally insensitive multi-reflection cavity to excite the gas molecules to be tested to generate Raman scattering signals.

[0052] Preferably, the detector includes an optical fiber collecting lens, a multimode fiber, a grating spectrometer, and a CCD detector. The optical fiber collecting lens is located at the neck window and collects the gas Raman scattered light generated in the heat-insensitive multi-reflection cavity into the multimode fiber. The multimode fiber transmits the Raman scattered light collected by the optical fiber collecting lens to the grating spectrometer.

[0053] Preferably, the grating spectrometer transmits the filtered Raman scattered light through a slit to the grating, the grating separates the Raman scattered light of different wavelengths, and the grating spectrometer focuses the separated Raman scattered light into the CCD detector; the CCD detector converts the optical signal into an electrical signal, and pixels at different positions record the light intensity of different wavelengths.

[0054] Preferably, it also includes a computer device connected to the output of the CCD detector, which controls the CCD detector and performs Raman spectroscopy analysis.

[0055] Preferably, the Raman frequency shift range detected by the grating spectrometer and CCD detector includes the Raman frequency shift range of the gas to be measured.

[0056] Preferably, the laser excitation wavelength is kept at a certain power while minimizing the fluorescence effect.

[0057] like Figure 1 As shown, a preferred embodiment of this application provides a thermally insensitive multi-reflection cavity 1 for enhancing gas Raman spectroscopy, comprising: an inner cavity 15 and an outer cavity 16, wherein the inner cavity 15 is disposed within the outer cavity 16, and a vacuum is drawn between the inner and outer cavities; the inner cavity 15 comprises: a neck 11, a body 12, and a tail 13; the neck 11 comprises: a cavity opening 112 with a constant outer diameter and a shoulder 111 that is continuous with the tail side of the cavity opening and gradually increases in outer diameter; the cavity opening 112 has an opening on its front side, and an incident window 14 (also called a quartz window) is provided on the opening to seal it; the incident window 14 is used to provide an incident channel for the laser required to obtain the Raman spectrum of the gas to be measured;

[0058] The main body 12 is a cylindrical shape with openings at both ends and the outer diameter remains unchanged. The opening on the front side of the main body 12 is continuous with the tail side of the shoulder 111.

[0059] The tail portion 13 is a centrally symmetrical curved surface, and the opening side of the curved surface is the head side of the tail portion 13. The head side of the tail portion 13 is continuous with the opening of the tail side of the main body 12, which is used to seal the tail side of the main body 12.

[0060] The radius of curvature of the shoulder 111 is smaller than that of the tail 13.

[0061] It should be noted that the radius of curvature refers to the direction perpendicular to the tangent at any point on the curved surface, pointing towards the center of curvature. The center of curvature of the shoulder 111 and tail 13 refers to the center of curvature of their sectional curves; the center of curvature of the cavity 112 and body 12 refers to the center of curvature of their cross-sectional curves, and their radius of curvature is the radius of the cylinder they present. It can be understood that the aforementioned sectional surface refers to the plane presented after cutting along the axis of symmetry of the heat-insensitive multi-reflection cavity 1; the aforementioned cross-section refers to the plane presented after cutting perpendicular to the axis of symmetry of the heat-insensitive reflection cavity 1.

[0062] More preferably, the heat-insensitive multi-reflection cavity 1 is a double-layered vacuum coaxial glass body, including an inner cavity 15 and an outer cavity 16. The inner cavity 15 and the outer cavity 16 are fused and fixed at the sealing point at the front end by a heating and melting method. The side closer to the inner cavity 15 is defined as the inner side, and the side closer to the outer cavity 16 is defined as the outer side. The intermediate layer between the inner side and the outer side is a vacuum isolation layer. The inner cavity 15 and the outer cavity 16 can be parallel to each other or non-parallel, as long as the inner cavity 15 can be contained by the outer cavity 16. Figure 1 The following example illustrates the situation with the inner cavity 15 and the outer cavity 16 being parallel to each other.

[0063] Specifically, the principle of using the thermally insensitive multi-reflection cavity 1 to enhance gas Raman spectroscopy is as follows: The thermally insensitive multi-reflection cavity 1 is placed on the same platform as the laser beam 17, allowing the laser beam 17 to enter the cavity without obstruction from the quartz window 14. During testing, the laser beam 17 enters from one end of the quartz window 14 at a certain angle, passes through the neck 11, passes through the main body 12, and irradiates the tail 13. After being reflected by the tail 13, the laser beam 17 irradiates the neck 11, and after being reflected again by the neck 11, it irradiates the tail 13 again. Finally, the thermally insensitive multi-reflection cavity 1 forms an excitation beam 17 that travels back and forth multiple times. In this process, the laser beam 17 excites the molecules of the gas to be tested to produce a Raman scattering effect, and then forms the corresponding gas Raman spectrum. The Raman frequency shift of the Raman spectrum produced by the gas to be tested is related to the type of gas molecules, and the Raman spectrum intensity is related to the concentration of the gas to be tested. Therefore, by analyzing the gas Raman spectrum, the type and concentration information of the gas to be tested can be obtained.

[0064] In existing technologies, the temperature of the internal environment of the cavity is not addressed. After the laser beam 17 undergoes multiple reflections within the cavity, heat release occurs, causing changes in the energy level distribution of gas molecules and the Raman scattering cross section. This leads to fluctuations in the Raman scattering intensity, resulting in reduced gas detection accuracy. Furthermore, the external environment of the cavity must be thermally shielded to ensure the multi-reflection cavity is in a thermally insensitive environment and to obtain a relatively stable Raman scattering signal. Current technologies, however, use a sealed environment to enhance gas Raman scattering, thus neglecting to address the thermal radiation generated by the internal multi-reflection laser. Existing methods for handling the internal laser temperature rely on sensor control or algorithms to construct thermal compensation mechanisms, without directly addressing the source of thermal radiation. This prevents the immediate and direct extraction of internal thermal radiation, leading to unstable gas Raman scattering intensity. Additionally, the additional components increase the complexity and instability of the gas detection system, reducing its practical application potential.

[0065] In this embodiment, the complete cavity of the thermally insensitive multi-reflection cavity 1 has a multi-curvature configuration. The tail 13 is an imperfect sphere with a relatively small radius of curvature, which can reflect the thermal radiation inside the cavity to the curved side. The main body 12 forms a thermal radiation propagation channel. The radiation field formed by the tail 13 and the main body 12 can cause the thermal radiation to converge towards the cavity opening near the neck 11. The neck 11 has a neck-shaped transition configuration and a small radius of curvature. The thermal radiation field formed by the neck 11 can cause the thermal radiation of the neck 11 to converge towards the cavity opening. The neck-shaped configuration of the neck 11 can keep the thermal radiation converged by the thermal radiation conduction field formed by the tail 13 and the main body 12 at the cavity opening, and then conduct heat outward from the quartz high-transmittance window 14 at the cavity opening. This realizes the processing of the temperature radiation generated by the multiple reflections of the laser beam 17 inside the cavity, provides a thermally insensitive environment inside the cavity, and obtains a relatively stable Raman scattering signal.

[0066] Secondly, the heat-insensitive multi-reflection cavity 1 can also achieve thermal shielding against the external environment. The inner cavity 15 and the outer cavity 16 are fused together at the neck 11 port by heating and melting. The only connection between the inner cavity 15 and the outer cavity 16 is the port formed by melting at the neck 11, thereby avoiding unnecessary contact area between the inner cavity 15 and the outer cavity 16 and reducing the heat transfer path. While the inner cavity 15 and the outer cavity 16 are fused together, a vacuum isolation layer is formed between the inner and outer sides. The external environment contacts the outer cavity 16 on the outside, and the gas molecules to be excited contact the inner cavity 15 on the inside. The vacuum isolation layer formed in the middle physically separates the outer cavity 16 and the inner cavity 15. The outer cavity 16 and the inner cavity 15 are isolated from each other. When the external ambient temperature changes, the vacuum isolation layer prevents heat transfer between gas and solid molecules, thus blocking the heat conduction path between the outside and inside, and preventing heat convection. Furthermore, the outer cavity 16 and the inner cavity 15 near the vacuum isolation layer are coated with a highly reflective material, which reflects external thermal radiation back to the external environment, suppressing infrared thermal radiation interference. This achieves temperature shielding between the gas molecules to be excited inside and the external environment, providing a thermally insensitive environment within the cavity and obtaining a relatively stable Raman scattering signal. The specific principle is as follows:

[0067] The temperature transfer direction of the chamber is closely related to the thermal radiation field formed by the chamber configuration. Taking the tail end of the chamber axis as the origin and the direction along the chamber opening as the positive direction, the heat conduction equation is used to describe the diffusion of heat in the chamber along a one-dimensional direction (the axis of the chamber):

[0068]

[0069] in, Indicates the position within the cavity Temperature at ( x (distance relative to the origin) Indicates thermal diffusivity, This refers to a heat source per unit volume. In the case of achieving thermal shielding from the external environment and having no external heat source, this is relevant. We can obtain:

[0070]

[0071] For a cavity with a multi-curvature configuration, its cross-sectional area Will vary depending on location Changes in cross-sectional area affect heat flow, and the rate of heat flow is inversely proportional to the cross-sectional area. According to the continuity equation, the heat flux density... It can be represented as:

[0072]

[0073] in, Indicates thermal conductivity, Indicates position The cross-sectional area at that point, It is the temperature gradient along the cavity direction. And... , For in position The radius of curvature at the cavity neck is smaller, and the cross-sectional area at the cavity opening is smaller. The smaller the heat flux density, the greater the temperature gradient in the region. This enhances the temperature, causing it to converge at the neck of the cavity.

[0074] The main body of the cavity is a regular cylinder, connected to the rear and neck of the cavity respectively. Heat diffusion is relatively uniform, according to the steady-state heat diffusion equation. Integrating, we can obtain: Integrating again yields... ,in, and These are constants, representing the offsets of the temperature gradient and temperature distribution, respectively. (Based on the tail of the cavity) and cervical cavity Boundary conditions We can obtain: , Substituting into Therefore, the temperature distribution in the middle part of the cavity body is as follows:

[0075]

[0076] It can be seen that the temperature is linearly distributed along the central axis of the cavity body from the tail to the neck opening. In the thermally insensitive multi-reflection cavity of this embodiment, due to the small radius of curvature at the tail of the cavity, which has a hemispherical cavity shape, thermal radiation will be strongly reflected over a large area in this region. The main body of the cavity is in a steady state with a small range of change, while it gradually changes at the neck. The radius of curvature of the transition part of the cavity at the shoulder and the opening decreases, which shortens the path of the reflected thermal radiation beam. This causes different thermal radiation waves to superimpose in space, resulting in a convergence effect on the thermal radiation waves. Furthermore, its cross-sectional area gradually decreases, and the heat flux density increases accordingly. The heat generated by the beam of light traveling back and forth between the shoulder and the tail and the gas molecules is more smoothly converged to the opening through the transition part of the shoulder with a smaller radius of curvature. The columnar configuration and small radius of curvature of the opening can lock the heat gathered from the cavity at the opening, maintaining a high-density heat flux, thereby guiding the temperature to the opening and releasing it to the outside. This enables the processing of the temperature release generated by the gas molecules to be excited during multiple reflection excitations, providing a multi-reflection enhanced cavity environment with internal thermally insensitive properties.

[0077] Thermal radiation shielding from the external environment is primarily achieved by reducing heat conduction, convection, and radiation effects. The space between the inner and outer cavity layers is a vacuum, minimizing heat conduction. It can be represented as:

[0078]

[0079] in, Indicates thermal conductivity, Indicates the contact area of ​​the cavity layer. Indicates the temperature difference between the inner and outer layers. This represents the distance between cavity layers, due to the vacuum. Heat conduction is blocked.

[0080] Convection heat transfer It can be represented as:

[0081]

[0082] in, The convective heat transfer coefficient is due to the fact that in a vacuum... Convective heat transfer is negligible.

[0083] According to the Stefan-Boltzmann law, thermal radiation... It can be represented as:

[0084]

[0085] Among them, Stefan-Boltzmann constant , Indicates the surface area of ​​the radiation. Indicates the emissivity of the material. , This indicates the temperature of the inner and outer cavities.

[0086] As can be seen from the above formulas, the main heat loss is determined by thermal radiation. The equivalent emissivity can be expressed as: If the emissivity of the two surfaces is the same ( ),but By applying a high-reflectivity material, the problem of thermal radiation can be greatly solved. In the thermally insensitive multi-reflection cavity 1 of this embodiment, the vacuum isolation layer prevents heat transfer between gas molecules and solid molecules, blocks the heat conduction path between the outer and inner sides, and prevents thermal convection. The only connection between the inner cavity 15 and the outer cavity 16 is the port formed by melting at the neck 11, thereby avoiding unnecessary contact area between the inner cavity 15 and the outer cavity 16, reducing the heat transfer path, and achieving thermal shielding against the external environment. Together with the aforementioned treatment of temperature release from multiple reflections of the excitation beam 17 inside the cavity, a complete thermally insensitive multi-reflection cavity is formed, making the obtained enhanced gas Raman signal relatively stable.

[0087] In some embodiments, the thickness of the inner cavity 15 glass ranges from 1 mm to 1.5 mm, the thickness of the outer cavity 16 glass ranges from 2 mm to 3 mm, and the gap between the vacuum isolation layer between the inner cavity 15 and the outer cavity 16 glass is 1 mm to 5 mm.

[0088] In a specific embodiment, the glass thickness of the inner cavity 15 is 1.2 mm, the glass thickness of the outer cavity 16 is 2.5 mm, and the gap between the vacuum isolation layer formed by the inner cavity 15 and the outer cavity 16 is 2 mm.

[0089] In this embodiment, the port formed by melting the neck 11 is also covered by a high-transmittance quartz window 14. The laser beam will pass through the quartz window 14 and generate Raman scattered light with the gas to be measured in the chamber 1, and then pass through the quartz window 14 again to the detector.

[0090] Specifically, the high transmittance range of the quartz window 14 includes the wavelength of the laser beam 17 and the wavelength of the Raman scattered light excited by the gas to be measured. The quartz window 14 has a transmittance range of 220 nm. Up to 2500 It has good transmittance between wavelengths of light, and for 280 Up to 1500 The light transmittance of the wavelength exceeds 90%. After the laser beam passes through the quartz window 14, it reaches the interior of the cavity 1 and generates Raman scattering with the gas molecules to be excited. The Raman scattered light will pass through the quartz window 14 and be received by the fiber optic collecting lens 5.

[0091] In a specific embodiment, the laser beam 17 is an excitation light centered at a wavelength of 785nm; such as Figure 2As shown, the quartz window 14 has two through holes and a gas conduit 143. The two through holes are defined as an air inlet 141 and an air outlet 142. The diameter of the through hole is 6.5 mm, and the center of the through hole is 7.5 mm away from the edge of the quartz window 14. The outer diameter of the gas conduit 143 is 6 mm. One end of the gas conduit 143 is wrapped with PTFE tape and rotates through the through hole in the same direction to achieve a tight contact with the through hole. Then, the through holes on both sides of the quartz window 14 are sealed with airtight glass glue.

[0092] This application can also provide multi-reflection gas Raman signal enhancement. The heat-insensitive multi-reflection cavity 1 includes a neck 11, a body 12, a tail 13, and a highly reflective silver-plated liner uniformly deposited on the cavity surface near the vacuum isolation layer of the inner cavity 15 and the outer cavity 16. The surfaces of different parts of the cavity have different curvatures, which can reflect the laser beam 17 multiple times, increase the effective interaction length between the laser beam 17 and the gas molecules to be excited, and thus enhance the Raman intensity.

[0093] Specifically, the principle of using the thermally insensitive multi-reflection cavity 1 to enhance gas Raman spectroscopy is as follows: The thermally insensitive multi-reflection cavity 1 is placed on the same platform as the laser beam 17, so that the laser beam 17 can enter the cavity without obstruction from the quartz window 14. During testing, the laser beam 17 enters from one end of the quartz window 14 at a certain angle, passes through the neck 11, passes through the main body 12, and irradiates the tail 13, exciting the gas molecules to be tested for the first time. Then, after being reflected by the tail 13, the laser beam 17 irradiates the neck 11, exciting the gas molecules to be tested for the second time. After being reflected by the neck 11 again, it irradiates the tail 13 again, exciting the gas molecules to be tested for the third time. This cycle continues, and finally, the thermally insensitive multi-reflection cavity 1 forms an excitation beam 17 that travels back and forth multiple times. Because the gas molecules are evenly distributed in the inner space of the cavity, the more times the laser beam 17 travels back and forth, the greater the effective length of interaction with the gas molecules to be tested will be, thereby achieving gas Raman spectroscopy enhancement.

[0094] In this embodiment, firstly, the surfaces of the cavity neck 11, cavity body 12, and cavity tail 13 have a multi-curvature configuration. In particular, the smaller curvature radii of the cavity neck 11 and cavity tail 13 can reduce the laser reflection angle, making it easier to achieve round-trip within the cavity. In addition, the cavity body 12 is a regular cylinder, which can provide a longer excitation path for the laser beam 17 reflected back and forth at the cavity neck 11 and cavity tail 13.

[0095] Furthermore, based on the aforementioned processing of the internal temperature release of the heat-insensitive multi-reflection cavity 1, it can be known that the radiation field inside the heat-insensitive multi-reflection cavity 1 can be concentrated towards the port region of the cavity neck 11, thereby enabling the concentrated collection of Raman scattered light and the generation of Raman scattered light.

[0096] In some embodiments, the radius of curvature of the cavity 112 ranges from 15mm to 25mm, and the height ranges from 15mm to 20mm; the radius of curvature of the shoulder 111 ranges from 10mm to 25mm, and the height ranges from 20mm to 40mm; furthermore, the radius of curvature of the transition portion ranges from 5mm to 10mm; the tail portion 13 of the cavity is arc-shaped or hemispherical, with a radius of curvature ranging from 20mm to 35mm and a height ranging from 30mm to 50mm; the main body 12 of the cavity is a regular cylinder or frustum, with a radius of curvature ranging from 40mm to 50mm and a height ranging from 70mm to 120mm.

[0097] In a more specific embodiment, the radius of curvature of the cavity opening 112 is 23 mm and the height is 18 mm, the radius of curvature of the transition portion ranges from 5 mm to 9 mm, the radius of curvature of the shoulder 111 is 20 mm and the height is 30 mm, the radius of curvature of the cavity tail 13 is 30 mm and the height is 50 mm, and the radius of curvature of the cavity body 12 is 50 mm and the height is 100 mm; in addition, the laser beam 17 and the fiber optic collecting lens 5 are on the same horizontal plane.

[0098] In some embodiments, different incident angles of the laser beam 17 will cause the laser beam to irradiate different positions in the cavity. Due to the different curvatures of the different parts of the heat-insensitive multi-reflection cavity 1, different reflection directions will be generated, forming different multi-pass reflection optical paths.

[0099] like Figure 3 The diagram illustrates the structure of the detection device used in this application embodiment, including a Raman scattering signal excitation device 9, a Raman scattering signal receiving device 10, and the aforementioned heat-insensitive multi-reflection cavity 1. The Raman scattering signal excitation device outputs an excitation beam 17, which enters the heat-insensitive multi-reflection cavity 1 and excites the gas molecules to be tested to generate Raman scattered light. The Raman scattered light is received and analyzed by the Raman scattering signal receiving device 10.

[0100] Furthermore, the thermally insensitive multi-reflection cavity 1 serves as a gas cell to contain the gas to be measured, thereby maintaining the temperature stability of the gas environment and enhancing the gas Raman spectral signal; the Raman scattering signal excitation device 9 includes a laser driver 2, an optical fiber collimating lens 3, and a filter 4; the Raman scattering signal receiving device 10 includes an optical fiber collecting lens 5, a grating spectrometer 6, a CCD detector 7, and a computer device 8.

[0101] Specifically, the laser driver 2 provides a high-energy, highly coherent laser beam 17 to excite the gas molecules to be measured; the fiber collimating lens 3 focuses the laser beam 17 into the heat-insensitive multi-reflection cavity 1; the filter 4 makes the output laser beam purer; the fiber collecting lens 5 collects the generated Raman scattered light into the fiber; the grating spectrometer 6 can be used to split the Raman scattered light; the CCD detector 7 can form a spectrum from the split beam; and the computer device 8 is used to analyze the spectrum and control the CCD detector 7.

[0102] In a specific embodiment, the laser driver 2 provides a laser beam 17 centered at a wavelength of 785 nm with a maximum power of 210 mW; the fiber collimating lens 3 has a focal length of 15 mm, the focusing lens has a focal length of 100 mm, and the collimated spot diameter is 4 mm; the filter 4 can transmit light beams in the wavelength range of 820 nm to 2000 nm and cuts off in the wavelength range of 200 nm to 780 nm; the fiber collecting lens 5 has a focal length of 100 mm; the grating spectrometer 6 and the CCD detector 7 can detect light in the wavelength range of 775.42 nm to 928.13 nm, and the detectable Raman frequency shift range is -153 nm. By 1969 .

[0103] In a more specific embodiment, the laser driver 2 provides a 785nm wavelength laser, which is focused into the thermally insensitive multi-reflection cavity 1 by the fiber collimating lens 3. The position of the fiber collimating lens 3 is adjusted to be 40mm away from the neck port 11, so that the focal point of the incident laser is in the thermally insensitive multi-reflection cavity 1, and the beam waist is on the same plane as the focal plane of the fiber collecting lens 5, so that the high-power laser can excite gas molecules. After the beam is reflected multiple times in the thermally insensitive multi-reflection cavity 1, the effective interaction distance between the laser and the target molecule is increased, and an enhanced gas Raman signal is obtained. The signal is then transmitted to the neck port 11 through the light reflection field. The filter 4 can filter out excess pump light to reduce interference from other beams. The Raman scattered light is then collected by the fiber collecting lens 5 into the grating spectrometer 6, and the spectrum is generated by the CCD detector 7. The position of the fiber collecting lens 5 is adjusted to be 30mm away from the neck port 11, so that the signal receiving distance and signal receiving angle are highly efficient. Finally, the CCD detector 7 is controlled and the gas concentration is calculated by the program on the computer device 8.

[0104] In one specific embodiment, the laser beam 17 is an excitation light centered at a wavelength of 785 nm. The laser beam 17 is on the same horizontal line as the fiber optic collecting lens 5 and is incident into the cavity at a horizontal angle of 25 degrees. Most of the gas molecules to be excited in the first stage are located on the focal line of the fiber optic collecting lens 5, thereby obtaining a higher intensity Raman scattered light. The laser beam 17 illuminates the tail 13 with a radius of curvature of 30 mm and is then reflected again to the cavity shoulder 111 with a radius of curvature of 20 mm. The shoulder 111 has a small radius of curvature and the tail 13 has a large radius of curvature. It possesses both strong and weak focusing characteristics. By balancing strong and weak focusing, the beam cross-sectional size can be controlled to enhance beam concentration. Simultaneously, increasing the Rayleigh length reduces beam divergence, making the beam more stable. During this process, multiple reflections occur, repeatedly exciting the gas molecules to be measured, increasing the effective interaction distance between the laser beam 17 and the gas molecules. Raman scattered light from various directions is also collected in the reflected light field at the cavity neck 11 port, passes through the quartz window 14, and is then received by the fiber optic collecting lens 5. This allows for the acquisition of a gas Raman spectrum enhanced several times over, such as... Figure 4 As shown.

[0105] Furthermore, such as Figure 5 As shown, the thermal shielding effect of the thermally insensitive multi-reflection cavity 1 is detected by controlling the change of external temperature through a heating device. By setting a gradient ambient temperature of 25℃, 40℃, 60℃ and 80℃, the gas Raman molecules in the cavity are excited, and a gas Raman spectrum with strong thermal stability can be obtained, demonstrating that the cavity has a superior thermal shielding effect.

[0106] In some embodiments, the cavity is made of borosilicate glass.

[0107] Specifically, the effects provided by this device are as follows: Figure 3 and Figure 4 As shown, the gas used in the experiment was carbon dioxide, and the Raman shift of the Fermi branch was at 1286 cm⁻¹. -1 and 1388cm -1 Location, Figure 3 The Raman spectral intensity comparison between the heat-insensitive multi-reflection cavity 1 and the conventional quartz glass gas cell is shown. Figure 4 The stability of the Raman intensity of the thermally insensitive multi-reflection cavity 1 under different temperature conditions is demonstrated; Appendix Figure 3 The gas Raman spectral intensity (solid line) of the medium-heat insensitive multi-reflection cavity is significantly higher than that of the gas Raman spectral intensity (dashed line) of the traditional quartz glass gas cell. It can achieve several times the gas Raman enhancement in the Raman shift of the Fermi branch of carbon dioxide. Figure 4In the figure, the Raman intensity at room temperature of 25°C is represented by a solid line, the Raman intensity at 40°C is represented by a dotted line, the Raman intensity at 60°C is represented by a diamond-shaped dotted line, and the Raman intensity at 80°C is represented by a triangular dotted line. When the external temperature changes significantly, the gas Raman intensity in the thermally insensitive multi-reflection cavity 1 remains at a relatively consistent level and is hardly affected by the external temperature change, demonstrating excellent thermal insensitivity.

[0108] In summary, this application provides a thermally insensitive multi-reflection cavity 1 for enhancing gas Raman spectroscopy. The complete cavity of the thermally insensitive multi-reflection cavity 1 has a multi-curvature configuration, forming a special temperature conduction field inside the cavity. As the radius of curvature changes, the heat flux density in different parts of the cavity changes accordingly. The tail 13 with a larger radius of curvature can reflect thermal radiation over a large area, while the shoulder with a smaller radius of curvature can converge the thermal radiation wave. Then, the transition part of the cavity guides the converged thermal radiation generated inside the cavity to the cavity opening, where it is locked and released to the outside. This allows for the processing of the temperature release generated during the interaction between the excitation beam 17 and gas molecules after multiple reflections, providing an internal thermally insensitive environment for the gas molecules to be excited. In the thermally insensitive multi-reflection cavity 1, its inner cavity layer 15 and outer cavity layer 16 form... The vacuum isolation layer can isolate the gas inside the cavity from the external environment, blocking heat transfer and heat convection. The high-reflectivity silver coating on the outer surface of the inner cavity layer 15 and the inner surface of the outer cavity layer 16 can suppress the thermal radiation interference from the external environment. Through the above-mentioned thermal shielding mechanism, an external thermally insensitive environment can be provided for the gas molecules to be excited. The shoulder 111 has a small radius of curvature and the tail 13 of the cavity has a relatively large radius of curvature, which balances the strong and weak focusing, controls the beam cross-section size to enhance the beam concentration, and increases the Rayleigh length to slow down the beam divergence, making the beam more stable. The main body of the cavity 12 is a regular cylinder, which can provide a longer effective working length after the laser beam 17 is reflected, thereby enhancing the gas Raman signal and making it easier to achieve high-quality round trip within the cavity. In addition, the radiation field formed by the cavity allows the Raman scattered light to be focused to the port, further enhancing the gas Raman signal.

[0109] It should be understood that expressions such as “comprising” and “may include” used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as “comprising” and / or “having” are to be interpreted as indicating a particular characteristic, number, operation, constituent element, component, or combination thereof, but not to exclude the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0110] Furthermore, in this application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0111] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. "Fixed connection" refers to a connection where the relative positional relationship remains unchanged after connection. "Rotary connection" refers to a connection where the components can rotate relative to each other after connection. "Sliding connection" refers to a connection where the components can slide relative to each other after connection. The directional terms mentioned in the embodiments of this application, such as "top," "bottom," "inner," "outer," "left," and "right," are only for reference to the directions in the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of this application, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0112] Furthermore, the mathematical concepts mentioned in the embodiments of this application, such as symmetry, equality, parallelism, and perpendicularity, are limitations specific to the current technological level, rather than absolute and strict mathematical definitions. Slight deviations are permissible; approximations of symmetry, equality, parallelism, and perpendicularity are all acceptable. For example, "A and B are parallel" means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. "A and B are perpendicular" means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0113] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A thermally insensitive multi-reflection cavity for enhancing gas Raman spectroscopy, used to hold the gas to be measured in order to acquire the Raman spectrum of the gas to be measured, characterized in that, The heat-insensitive multi-reflection cavity includes an inner cavity and an outer cavity, wherein the inner cavity is disposed within the outer cavity, and a vacuum is drawn between the inner cavity and the outer cavity; The inner cavity includes: a neck, a body, and a tail; The neck includes: a cavity with a constant outer diameter and a shoulder that is continuous with the tail side of the cavity and gradually increases in outer diameter; the front side of the cavity is provided with an opening, and an incident window is provided on the opening to seal it; the incident window is used to provide an incident channel for the laser required to obtain the Raman spectrum of the gas to be measured. The main body is a cylindrical shape with openings at both ends and a constant outer diameter. The opening on the front side of the main body is continuous with the tail side of the shoulder. The tail is a centrally symmetrical curved surface, and the opening side of the curved surface is the head side of the tail. The head side of the tail is continuous with the opening of the tail side of the main body, which is used to seal the tail side of the main body. The radius of curvature of the shoulder is smaller than that of the tail.

2. The heat-insensitive multi-reflection cavity according to claim 1, characterized in that, The outer side of the inner cavity and the inner side of the outer cavity are both coated with a highly reflective material.

3. The heat-insensitive multi-reflection cavity according to claim 1, characterized in that, A gas conduit is provided on the incident window.

4. The heat-insensitive multi-reflection cavity according to claim 1, characterized in that, The cavity, shoulder, body, and tail transition smoothly and continuously, forming a smooth curved surface.

5. The thermally insensitive multi-reflection cavity according to claim 1, characterized in that, The height of the cavity is less than the height of the main body, and the height of the shoulder is greater than the height of the tail.

6. The heat-insensitive multi-reflection cavity according to any one of claims 1 to 5, characterized in that, The radius of curvature of the cavity is in the range of 15mm to 30mm, the radius of curvature of the shoulder is in the range of 5mm to 25mm, and the radius of curvature of the transition portion between the shoulder and the cavity is in the range of 2mm to 15mm; the height of the cavity is in the range of 10mm to 30mm, and the height of the shoulder is in the range of 15mm to 45mm.

7. The heat-insensitive multi-reflection cavity according to any one of claims 1 to 5, characterized in that, The curvature radius of the main body ranges from 30mm to 60mm, and the height of the main body ranges from 50mm to 200mm.

8. The heat-insensitive multi-reflection cavity according to any one of claims 1 to 5, characterized in that, The radius of curvature of the tail ranges from 20mm to 40mm, and the height of the tail ranges from 20mm to 60mm.

9. The heat-insensitive multi-reflection cavity according to claim 1, characterized in that, The inner cavity and the outer cavity are integrally formed; and / or the gap between the inner cavity and the outer cavity ranges from 1 mm to 5 mm.

10. The heat-insensitive multi-reflection cavity according to claim 1, characterized in that, The incident window is a quartz window; Both the inner and outer cavities are made of glass.

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