Raman probe optical system and design method thereof

Abstract

The application discloses a Raman probe optical system and a design method thereof, and relates to the technical field of low-temperature Raman probe optical system design. The design method comprises the following steps: based on Gaussian optical formula, according to the numerical aperture and working distance of a plano-convex lens, the size of the probe and the basic parameters of each optical element, the initial structure parameters of each optical element in the Raman probe optical system are determined; a simulation model of the Raman probe optical system is built in optical design software according to the initial structure parameters; taking the minimum spot radius RMS value output by the simulation model as the target, the conic constant is continuously adjusted in the optical design software, and the surface shape parameters are optimized by means of the conic constant and the curvature radius of the minimum spot radius RMS value; the initial structure parameters are updated according to the optimized surface shape parameters, and the final structure parameters of the Raman probe optical system are obtained. The Raman probe optical system designed by the application can stably and reliably work under low-temperature working conditions.

Description

Technical Field

[0001] This invention relates to the technical field of low-temperature Raman probe optical system design, and more particularly to a Raman probe optical system and its design method. Background Technology

[0002] The Raman effect refers to the change in the frequency of scattered light when light interacts with matter. At its core, when a beam of monochromatic light shines on a sample, most of it is elastically scattered, meaning the frequency of the scattered light is the same as the incident light—a phenomenon known as Rayleigh scattering. However, a small portion of the light undergoes inelastic scattering, causing a slight change in the frequency of the scattered light; this is Raman scattering. These frequency changes reflect energy transfer within molecules. Therefore, by analyzing Raman scattering spectra, we can obtain detailed information about molecular structure, material composition, and crystal phase. Due to its non-destructive, rapid, and highly sensitive characteristics, the Raman effect has become an indispensable tool in modern scientific research.

[0003] Raman probes are one of the key devices for effectively utilizing the Raman effect. The main task of a Raman probe is to focus a laser beam onto a sample and collect the scattered Raman signal, then transmit the collected signal to a Raman spectrometer for detailed analysis. Based on their operating temperature, Raman probes can be classified into standard, high-temperature, and low-temperature types. Standard probes operate in environments between -50°C and 40°C, suitable for measurements in conventional laboratory environments. High-temperature probes can operate in environments up to 300°C, allowing them to function under extreme high-temperature conditions, such as monitoring the property changes of high-temperature materials during industrial production. Cryogenic probes operate in environments below -160°C. Compared to standard and high-temperature probes, their application scenarios are relatively limited, but they are crucial in research in certain specialized fields. For example, in cryogenic physics experiments, researchers need to study the properties of superconducting materials at extremely low temperatures; in aerospace engineering, cryogenic probes can be used to monitor the state of rocket fuel to ensure launch safety; in the study of superconducting materials, cryogenic Raman spectroscopy can reveal changes in the microstructure of materials at different temperatures; and in the extraction and transportation of liquefied natural gas (LNG), cryogenic probes can be used for online dynamic monitoring of its composition and proportion, enabling accurate measurement of the calorific value of LNG.

[0004] Existing cryogenic Raman probes undergo a phase change at extremely low temperatures, such as -160°C, where the air inside the probe transforms from a gaseous to a liquid state. This change not only interferes with the normal operation of the Raman probe's optical system, reducing its efficiency, but may even cause irreversible damage to the probe; for example, liquefied air may seep into the probe, leading to optical path misalignment or component corrosion. Therefore, we need to design a Raman probe suitable for cryogenic environments to ensure its stability and reliability under cryogenic conditions. Summary of the Invention

[0005] This invention provides a Raman probe optical system and its design method, which can ensure the stability and reliability of the Raman probe under low temperature conditions.

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

[0007] In a first aspect, the present invention provides a design method for a Raman probe optical system, the Raman probe optical system comprising a sealed housing, one end of which is fitted with a sealing window, and the other end through which an emitting optical fiber and a collecting optical fiber pass; further comprising an emitting optical path disposed inside the sealed housing, which is formed by a collimating lens, a narrow-band filter, and a reflector arranged in sequence and cooperating with the emitting optical fiber; and a dichroic mirror coaxial with the emitting and receiving optical fibers, wherein a high-pass filter and a converging lens are arranged in sequence between the dichroic mirror and the collecting optical fiber, and a focusing lens is arranged between the sealing window and the dichroic mirror;

[0008] Based on Gaussian optics formulas, and according to the obtained numerical aperture and working distance of the plano-convex lens, probe size, and basic parameters of each optical element, the initial structural parameters of each optical element in the Raman probe optical system are determined. These initial structural parameters include the surface profile parameters of the plano-convex lens's convex surface, the effective aperture of each optical element, and the spacing between adjacent optical elements. The plano-convex lens includes the collimating lens, the converging lens, and the focusing lens. The surface profile parameters include the radius of curvature and conic constant when the convex surface of the plano-convex lens is spherical.

[0009] Based on the initial structural parameters, a simulation model of the Raman probe optical system is built in optical design software.

[0010] With the goal of minimizing the RMS value of the spot radius output by the simulation model, the conic constant is continuously adjusted in the optical design software. The surface parameters are optimized by using the conic constant and radius of curvature that minimize the RMS value of the spot radius.

[0011] The initial structural parameters are updated based on the optimized surface parameters to obtain the final structural parameters of the Raman probe optical system.

[0012] In one possible implementation, the basic parameters include the lens center thickness and refractive index of the plano-convex lens; the gap distance between the sealing window and the focusing lens, the refractive index of the sealing window, and the thickness of the sealing window; the incident angle and / or exit angle of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector; based on the obtained numerical aperture and working distance of the plano-convex lens, the probe size, and the basic parameters of each optical element, the initial structural parameters of each optical element in the Raman probe optical system are determined, specifically including:

[0013] Based on the obtained numerical aperture, working distance, lens center thickness, and refractive index of the plano-convex lens, the effective light-passing aperture and surface parameters of the convex surface of the plano-convex lens are determined.

[0014] Based on the working distance of the focusing lens, the gap distance between the sealing window and the focusing lens, the refractive index of the sealing window, the thickness of the sealing window, and the effective light-transmitting aperture of the plano-convex lens, the effective light-transmitting half-aperture of the sealing window and the working distance of the sealing window are determined.

[0015] The lateral displacement of the dichroic mirror / reflector is determined based on the angle of incidence and / or the angle of exit of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector.

[0016] The effective light-passing diameters of the narrow-band filter and the high-pass filter are determined based on the effective light-passing diameter of the convex surface of the plano-convex lens.

[0017] The spacing between two adjacent optical elements is determined based on the probe size, the working distance of the plano-convex lens, the gap distance between the sealing window and the focusing lens, and the thickness of each optical element.

[0018] In one possible implementation, the effective aperture and surface parameters of the plano-convex lens are determined based on the obtained numerical aperture, working distance, lens center thickness, and refractive index, specifically including:

[0019] The distance between the image principal point and the back surface of the plano-convex lens is determined based on the ratio of the lens center thickness to the refractive index of the plano-convex lens.

[0020] The image-side focal length of the plano-convex lens is determined by the sum of the distance between the principal point and the rear surface and the working distance of the plano-convex lens.

[0021] The effective aperture of the convex surface of the plano-convex lens is determined by multiplying twice the image-side focal length by the tangent function of the image-side aperture angle of the plano-convex lens; the image-side aperture angle is the arcsine function of the numerical aperture of the plano-convex lens.

[0022] Combining the elevation equation of a quadratic surface, the surface shape of the plano-convex lens is represented by the radius of curvature and the conic constant. The radius of curvature and the conic constant when the plano-convex lens surface is spherical are used as the surface shape parameters of the plano-convex lens surface.

[0023] In one possible implementation, the effective half-aperture of the sealing window and the working distance of the sealing window are determined based on the working distance of the focusing lens, the gap distance between the sealing window and the focusing lens, the refractive index of the sealing window, the thickness of the sealing window, and the effective light-transmitting aperture of the plano-convex lens surface. Specifically, this includes:

[0024] The working distance of the sealing window is determined according to a first formula, which is specifically:

[0025] WD' W =WD' + L3 - L1 - L2;

[0026] Among them, WD′ W The working distance of the sealing window is represented by WD′, the working distance of the focusing lens is represented by L3, the back focal distance before and after the sealing window is set is represented by L1, the gap distance between the sealing window and the focusing lens is represented by L2, and the thickness of the sealing window is represented by L2.

[0027] The distance between the front and rear focal points of the sealing window is determined according to the second formula, which is as follows:

[0028]

[0029] Where, n W The refractive index of the sealed window is indicated;

[0030] The effective light-transmitting half-aperture of the sealed window is determined according to the third formula, which is specifically:

[0031]

[0032] Among them, a W denoted by , where 'a' represents the effective half-aperture of the sealed window, and 'a' represents the effective half-aperture of the focusing lens plane.

[0033] The effective half-aperture of the focusing lens plane is determined according to the fourth formula, which is specifically:

[0034]

[0035] Wherein, D represents the effective aperture of the convex surface of the plano-convex lens, and f′ represents the image-side focal length of the plano-convex lens.

[0036] In one possible implementation, the incident angle and the exit angle are equal; the lateral displacement of the dichroic mirror / reflector is determined based on the incident angle and / or exit angle, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector, specifically including:

[0037] The lateral displacement of the dichroic mirror / reflector is determined according to the fifth formula, which is specifically:

[0038]

[0039] Where Δ represents the lateral displacement of the dichroic mirror / reflector, and τ represents the thickness of the dichroic mirror / reflector. The angle n represents the incident angle of the dichroic mirror / reflector. p This represents the refractive index of the dichroic mirror / reflector.

[0040] In one possible implementation, the effective light-passing apertures of the narrow-band filter and the high-pass filter are determined based on the effective light-passing aperture of the convex surface of the plano-convex lens, specifically as follows:

[0041] The effective aperture of the narrowband filter and the high-pass filter is set to be the same as the effective aperture of the convex surface of the plano-convex lens.

[0042] In one possible implementation, the initial structural parameters of each optical element in the Raman probe optical system further include the number of high-pass filters; determining the initial structural parameters of each optical element in the Raman probe optical system further includes:

[0043] The number of high-pass filters is determined based on the obtained optical density value of the Raman scattered light and the transmittance of a single high-pass filter within the Raman scattered light band.

[0044] In one possible implementation, with the goal of minimizing the RMS value of the spot radius output by the simulation model, the conic constant is continuously adjusted in the optical design software. The surface parameters are optimized by using the conic constant and radius of curvature that minimize the RMS value of the spot radius. Specifically, this includes:

[0045] In optical design software, the conic constant when the convex surface of the plano-convex lens is spherical is taken as the center, and the constant is increased or decreased sequentially with a preset interval as the step size.

[0046] The conic constant that minimizes the RMS value of the light spot radius output by the simulation model is determined, and the conic constant is taken as the optimized conic constant, and the radius of curvature corresponding to the conic constant is taken as the optimized radius of curvature.

[0047] Secondly, embodiments of the present invention provide a Raman probe optical system, the system comprising: a sealing window embedded at one end of the sealed tube housing, and a transmitting optical fiber and a collecting optical fiber passing through the other end; further comprising an transmitting optical path disposed inside the sealed tube housing, formed by a collimating lens, a narrow-band filter and a reflector arranged in sequence and cooperating with the transmitting optical fiber; and a dichroic mirror coaxial with the transmitting and receiving, wherein a high-pass filter and a converging lens are arranged in sequence between the dichroic mirror and the collecting optical fiber, and a focusing lens is arranged between the sealing window and the dichroic mirror;

[0048] The sealed window is made of sapphire crystal.

[0049] The collimating lens, the narrow-band filter, the reflecting mirror, the dichroic mirror, the high-pass filter, and the converging lens are all made of fused silica.

[0050] The sealed tube shell is filled with inert gas.

[0051] In one possible implementation, the collimating lens, the converging lens, and the focusing lens are all plano-convex lenses of the same type.

[0052] In practical applications, the design method for the Raman probe optical system provided by this invention can efficiently construct the initial structure of the Raman probe optical system based on the initial structural parameters. It can also quickly and easily optimize the surface parameters of the convex surface of the plano-convex lens in the Raman probe optical system. The final structure of the Raman probe optical system determined by the design method of this invention can work stably and reliably under low-temperature conditions.

[0053] The design method for Raman probe optical systems provided in this invention enables the construction of Raman probe optical systems with arbitrary probe size and working distance, thereby matching different types of application scenarios.

[0054] The Raman probe optical system provided in this embodiment of the invention can not only work stably and reliably under low temperature conditions, but also seal the optical path of the Raman probe optical system through a sealed shell and a sealed window, preventing the analyte from penetrating into the sealed shell and damaging the internal optical components; filling the sealed shell with inert gas can also prevent the condensation of air inside the sealed shell at low temperatures from damaging the stability of the Raman probe optical system. Attached Figure Description

[0055] Figure 1This is a schematic diagram of a detection scenario provided by an embodiment of the Raman probe optical system of the present invention;

[0056] Figure 2 This is a schematic diagram of the overall structure of a Raman probe optical system provided in an embodiment of the present invention;

[0057] Figure 3 This is a schematic diagram of the optical path structure of a Raman probe optical system provided in an embodiment of the present invention;

[0058] Figure 4 A flowchart illustrating the steps of a design method for a Raman probe optical system provided in this embodiment of the invention;

[0059] Figure 5 A schematic diagram of the calculation model of the plano-convex lens in the design method of a Raman probe optical system provided in an embodiment of the present invention;

[0060] Figure 6 A schematic diagram of the calculation model of the sealing window and focusing lens in a design method of a Raman probe optical system provided in an embodiment of the present invention;

[0061] Figure 7 A schematic diagram of the calculation model of a dichroic mirror / reflector in a design method for a Raman probe optical system provided in an embodiment of the present invention;

[0062] Figure 8 This is a schematic diagram of the structure of a high-pass filter stacked in a design method for a Raman probe optical system provided in an embodiment of the present invention;

[0063] Figure 9 The graph shows the trend of the radius of curvature and the optimal spot radius RMS value output by the simulation model as a function of the conic constant in the design method of a Raman probe optical system provided in this embodiment of the invention.

[0064] Figure 10 The optical path structure diagram of the Raman probe optical system determined by the design method of the Raman probe optical system provided in the embodiment of the present invention;

[0065] Figure 11 The Raman probe optical system, as determined by the design method of a Raman probe optical system provided in this embodiment of the invention, is shown in the dot pattern of the laser focused spot at room temperature of 20°C.

[0066] Figure 12 The Raman probe optical system, as determined by the design method of a Raman probe optical system provided in this embodiment of the invention, is shown in the dot plot of the Raman scattering signal collection spot at room temperature of 20°C.

[0067] Figure 13The Raman probe optical system provided in this embodiment of the invention uses 4J32 alloy as the optical element support structure of the Raman probe, and the dot pattern of the laser focused spot is shown in the figure below at a low temperature of -180℃.

[0068] Figure 14 The Raman probe optical system provided in this embodiment of the invention uses 4J32 alloy as the sealing shell and optical element support structure of the Raman probe. The dot pattern of the Raman scattering signal collection spot is shown in the figure below -180℃.

[0069] Figure labels and descriptions:

[0070] 1. Raman probe optical system; 11. Sealed housing; 12. Sealed window; 13. Emitting fiber; 14. Collecting fiber; 15. Collimating lens; 16. Narrowband filter; 17. Mirror; 18. Dichroic mirror; 19. High-pass filter; 110. Converging lens; 111. Focusing lens; 2. Object under test; 3. Laser; 4. Raman spectrometer. Detailed Implementation

[0071] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0072] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, the use of "based on" or "according to" implies openness and inclusiveness, because processes, steps, calculations, or other actions "based on" or "according to" one or more of the stated conditions or values ​​may in practice be based on additional conditions or beyond the stated values.

[0073] Currently, the most common Raman probes on the market are standard and high-temperature types, while low-temperature Raman probes are relatively rare. This is because low-temperature environments present numerous challenges to Raman probe technology. For example:

[0074] At extremely low temperatures of -160°C, the air inside a cryogenic probe undergoes a phase change, transforming from a gaseous state to a liquid state. This change not only interferes with the normal operation of the Raman probe's optical system and reduces its efficiency, but may even cause irreversible damage to the probe; for example, liquefied air may seep into the probe, leading to optical path misalignment or component corrosion.

[0075] Many materials that perform well at room temperature may become unsuitable at extremely low temperatures. Specifically, taking commonly used optical glass as an example, BK7 and SF2 materials will experience thermal shrinkage at low temperatures, leading to a decrease in the optical performance of optical components, and may even cause cracks or breakage.

[0076] To address the issues of low stability and poor reliability of existing Raman probes under low-temperature conditions, this invention provides a Raman probe optical system and its design method.

[0077] In a first aspect, embodiments of the present invention provide a Raman probe optical system. This Raman probe optical system 1 is a common-aperture Raman probe optical system, consisting of a laser excitation optical path and a signal collection optical path. For example... Figure 1 As shown, the laser emitted by laser 3 is coupled into the Raman probe optical system 1 through an optical fiber. The laser is transmitted forward in the Raman probe optical system 1 to the object under test 2 for excitation. The Raman scattered signal light is transmitted backward through the Raman probe optical system 1 and then continues to be transmitted backward through an optical fiber for collection. It then enters the Raman spectrometer 4 for material composition analysis.

[0078] The Raman probe optical system 1 is one of the core components of Raman detection, such as... Figure 2 , Figure 3 As shown, the Raman probe optical system of the present invention includes: a sealed tube shell 11, one end of which is fitted with a sealing window 12, and the other end is provided with a transmitting optical fiber 13 and a collecting optical fiber 14, and the transmitting optical fiber 13 and the collecting optical fiber 14 are parallel to each other.

[0079] The Raman probe optical system also includes an emission optical path formed by a collimating lens 15, a narrow-band filter 16, and a reflector 17 arranged sequentially inside the sealed housing 11, in conjunction with the emitting optical fiber 13; and a dichroic mirror 18 that is coaxial with the transmitting and receiving optical fibers. A high-pass filter 19 and a converging lens 110 are arranged sequentially between the dichroic mirror 18 and the collecting optical fiber 14, and a focusing lens 111 is arranged between the sealed window 12 and the dichroic mirror 18.

[0080] The transmitting fiber 13 is the incident laser fiber connected to the laser 3. The collecting fiber 14 is the Raman scattered light collecting fiber connected to the Raman spectrometer 4.

[0081] Collimating lens 15 minimizes the emission angle of the incident laser emitted from laser 3, making it a parallel beam. Focusing lens 111 not only focuses the incident laser onto the object under test 2 but also collects the Raman scattered light. Converging lens 110 focuses the Raman scattered signal light onto collecting fiber 14. Narrowband filter 16 filters out stray light from the laser itself and Raman signals from the fiber optic cable caused by the laser passing through it. Dichroic mirror 18 has high reflectivity for the excitation light and high transmittance for the Raman scattered signal light. High-pass filter 19 filters out collected Rayleigh scattering, and the optical density of the high-pass filter has a significant impact on the performance of the Raman probe optical system 1. Reflector 17 is a plane mirror used to deflect the excitation light path. Sealing window 12, in conjunction with sealing housing 11, seals the Raman probe optical path, preventing the object under test from penetrating the probe and damaging the optical components within the Raman probe optical system 1.

[0082] Furthermore, to prevent air condensation inside the sealed housing 11 from damaging the stability of the Raman probe optical system 1 under low-temperature conditions, the sealed housing 11 is filled with inert gas.

[0083] Specifically, the inert gas used for filling can be helium with a freezing point of -269℃, neon with a freezing point of -248℃, nitrogen with a freezing point of -210℃, argon with a freezing point of -189℃, etc.

[0084] Furthermore, the sealed housing 11 is a pressure-resistant sealed housing, and the sealing window 12 is embedded in the pressure-resistant sealed housing. The Raman probe optical path is located inside the pressure-resistant sealed housing. Under the protection of the pressure-resistant sealed housing, the other optical elements in the probe optical system 1, except for the sealing window 12, will not come into direct contact with the substance to be measured, and the performance of these optical elements will not be affected by the external pressure of the pressure-resistant sealed housing.

[0085] Furthermore, the sealing window 12 is made of sapphire crystal.

[0086] The collimating lens 15, narrowband filter 16, reflector 17, dichroic mirror 18, high-pass filter 19, and converging lens 110 are all made of fused silica.

[0087] Specifically, conventional lens materials are generally difficult to withstand ultra-low temperature working environments. Therefore, the materials that can be selected for the optical components of the probe optical system 1 are limited during the fabrication process. Sapphire and fused silica, due to their excellent thermal stability, can be used in ultra-low temperature working environments.

[0088] Sapphire has a relatively high hardness, making it suitable for processing into flat, sealed windows 12.

[0089] Because the support structure of the optical elements in the Raman probe optical system 1 uses a structural material with a low coefficient of thermal expansion, for example, a coefficient of thermal expansion of 1×10⁻⁶. -6 The 4J32 alloy of / K has a coefficient of thermal expansion of 1.2 × 10⁻⁶. -6 / K Ni36 alloy; the coefficient of thermal expansion of fused silica is 0.51×10 -6 Fused silica has good thermal stability and a low coefficient of thermal expansion. Therefore, the collimating lens 15, narrowband filter 16, reflector 17, dichroic mirror 18, high-pass filter 19, and converging lens 110 in the probe optical system 1 are all made of fused silica. This not only maintains the optical performance of the optical components but also matches the structural material with a low coefficient of thermal expansion, so as to better realize the athermal characteristics of the optical path. This allows the Raman probe optical system 1 to be directly applied in a low-temperature environment after being assembled and adjusted at room temperature, without having to consider the phase plane drift caused by temperature changes, thus eliminating the need for a focusing mechanism.

[0090] Furthermore, the collimating lens 15, the converging lens 110, and the focusing lens 111 are all plano-convex lenses of the same type.

[0091] Specifically, the collimating lens 15, converging lens 110, and focusing lens 111 are all plano-convex lenses with identical optical parameters. When adjusting the parameters in the future, only the optical parameters of one plano-convex lens need to be calculated to obtain the optical parameters of the above three plano-convex lenses. This not only facilitates the optimization of the optical element parameters in the Raman probe optical system 1, but also facilitates the mass production of the Raman probe optical system 1.

[0092] The Raman probe optical system of the present invention can not only work stably and reliably under low temperature conditions, but also seal the optical path of the Raman probe optical system through the sealed shell 11 and the sealed window 12, so as to prevent the substance to be measured from penetrating into the sealed shell 11 and damaging the internal optical components. Filling the sealed shell 11 with inert gas can also prevent the air inside the sealed shell 11 from condensing and damaging the stability of the Raman probe optical system under low temperature conditions.

[0093] Secondly, embodiments of the present invention provide a design method for a Raman probe optical system, which is used to quickly and accurately determine the structural parameters of the Raman probe optical system.

[0094] like Figure 2 , Figure 3As shown, the Raman probe optical system 1 of the present invention includes a sealed housing 11, one end of which is fitted with a sealing window 12, and the other end is fitted with an emitting optical fiber 13 and a collecting optical fiber 14; it also includes an emitting optical path disposed inside the sealed housing 11, which is formed by a collimating lens 15, a narrow-band filter 16 and a reflector 17 arranged in sequence and cooperating with the emitting optical fiber 13; and a dichroic mirror 18 that is coaxial with the emitting and receiving optical fibers, a high-pass filter 19 and a converging lens 110 arranged in sequence between the dichroic mirror 18 and the collecting optical fiber 14, and a focusing lens 111 arranged between the sealing window 12 and the dichroic mirror 18.

[0095] like Figure 3 , Figure 4 As shown, the design method of the Raman probe optical system of the present invention specifically includes:

[0096] Step 101: Based on the Gaussian optical formula, determine the initial structural parameters of each optical element in the Raman probe optical system according to the obtained numerical aperture and working distance of the plano-convex lens, the probe size, and the basic parameters of each optical element.

[0097] Gaussian optics formula is a crucial formula in optics used to describe the relationship between object distance, image distance, and focal length. Its derivation is based on fundamental principles of geometrical optics, obtained through graphical and geometrical analysis. This formula has wide applications in optical design, particularly in the design and analysis of optical systems such as lenses and mirrors. For example, in the design of photographic lenses, Gaussian optics formula is used to calculate the imaging position and magnification at different object distances.

[0098] Specifically, the initial structural parameters include the surface profile parameters of the plano-convex lens, the effective aperture of each optical element, and the spacing between two adjacent optical elements.

[0099] The surface parameters include the radius of curvature and the conic constant when the convex surface of the plano-convex lens is spherical.

[0100] Plano-convex lenses include collimating lenses, converging lenses, and focusing lenses.

[0101] The effective aperture refers to the effective diameter of the light-transmitting surface of an optical element, also known as the cross-section, effective aperture, or effective exit aperture. It reflects the size of the main beam after the optical path passes through the element and directly affects the sharpness and resolution of the image. The effective aperture of each optical element can be obtained through graphing and geometric analysis using Gaussian optics formulas.

[0102] The convex surface of a plano-convex lens is a quadratic surface, and its shape is determined by the radius of curvature and the conic constant. When k = 0, the convex surface of the plano-convex lens is spherical, and the corresponding radius of curvature can be calculated based on the image-side focal length and the refractive index of the plano-convex lens.

[0103] When determining the spacing between optical elements, it is necessary to consider the working distance, thickness, and probe size of each optical element and to reasonably allocate the distance between them.

[0104] Step 102: Based on the initial structural parameters, build a simulation model of the Raman probe optical system in the optical design software.

[0105] Optical design software refers to computer programs used to design and analyze optical systems. These programs help designers optimize the performance of optical systems and meet various application requirements by simulating light propagation and calculating optical performance parameters.

[0106] Specifically, optical design software such as ZEMAX, CODE V, and SOD88 can be selected.

[0107] The initial structural parameters determined in step 101 are input into the optical design software, and a simulation model of the Raman probe optical system is constructed in the optical design software. This simulation model can simulate the testing process of the Raman probe and output the RMS radius of the corresponding focused spot, which is the RMS value of the spot radius in this application.

[0108] The RMS radius of a focused beam is an indicator used to describe the size of a light beam, also known as the "root mean square radius." The RMS radius of a focused beam is typically related to factors such as the wavelength of the beam and the imaging quality of the optical system, and is an important parameter commonly used in optical design and analysis.

[0109] Step 103: With the goal of minimizing the RMS value of the light spot radius output by the simulation model, continuously adjust the conic constant in the optical design software, and optimize the surface parameters by minimizing the RMS value of the light spot radius and the radius of curvature.

[0110] Specifically, in optical design software, by continuously changing the value of the conic constant, the corresponding radius of curvature and spot radius RMS values ​​can be obtained. By observing the changing trend of the spot radius RMS value corresponding to different surface parameters, when the spot radius RMS value reaches a minimum value, the corresponding conic constant and radius of curvature are the optimal surface parameters of the plano-convex lens.

[0111] Step 104: Update the initial structural parameters based on the optimized surface parameters to obtain the final structural parameters of the Raman probe optical system.

[0112] Specifically, after determining the optimal surface parameters of the plano-convex lens, the surface parameters of the plano-convex lens in the initial structural parameters are replaced with the optimal surface parameters to obtain the final structural parameters of the Raman probe optical system, and the specific Raman probe optical system is constructed based on the final structural parameters.

[0113] In practical applications, the design method for the Raman probe optical system provided by this invention can efficiently construct the initial structure of the Raman probe optical system based on the initial structural parameters. It can also quickly and easily optimize the surface parameters of the convex surface of the plano-convex lens in the Raman probe optical system. The final structure of the Raman probe optical system determined by the design method of this invention can work stably and reliably under low-temperature conditions.

[0114] The design method for Raman probe optical systems provided in this invention enables the construction of Raman probe optical systems with arbitrary probe size and working distance, thereby matching different types of application scenarios.

[0115] The basic parameters obtained in step 101 include the lens center thickness and refractive index of the plano-convex lens; the gap distance between the sealing window and the focusing lens, the refractive index of the sealing window, and the thickness of the sealing window; the angle of incidence and / or the angle of exit of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector.

[0116] Furthermore, based on the obtained numerical aperture and working distance of the plano-convex lens, the probe size, and the basic parameters of each optical element, the initial structural parameters of each optical element in the Raman probe optical system are determined, specifically including:

[0117] Based on the obtained numerical aperture, working distance, lens center thickness, and refractive index of the plano-convex lens, the effective light-passing aperture and surface parameters of the convex surface of the plano-convex lens are determined.

[0118] Based on the working distance of the focusing lens, the gap distance between the sealing window and the focusing lens, the refractive index of the sealing window, the thickness of the sealing window, and the effective light-transmitting aperture of the convex surface of the plano-convex lens, determine the effective light-transmitting half-aperture of the sealing window and the working distance of the sealing window.

[0119] The lateral displacement of the dichroic mirror / reflector is determined based on the angle of incidence and / or the angle of exit, the thickness, and the refractive index of the dichroic mirror / reflector.

[0120] The effective aperture of the narrowband filter and the high-pass filter are determined based on the effective aperture of the convex surface of the plano-convex lens.

[0121] The spacing between two adjacent optical elements is determined based on the probe size, the working distance of the plano-convex lens, the gap distance between the sealing window and the focusing lens, and the thickness of each optical element.

[0122] like Figure 3As shown, in the laser excitation optical path, the optical path from the collimating lens to the focusing lens is a parallel optical path; in the signal collection optical path, the optical path from the focusing lens to the converging lens is also a parallel optical path. Therefore, the effective aperture of the convex surfaces of the collimating lens, focusing lens, and converging lens can all be circular. Specifically, the numerical aperture of the collimating lens is the numerical aperture of the collimating fiber, the numerical aperture of the converging lens is the numerical aperture of the collecting fiber, and the numerical aperture of the focusing lens is the numerical aperture for laser focusing and Raman scattering light collection. The working distance of a plano-convex lens refers to the distance between the lens and the object or imaging plane. The center thickness of the plano-convex lens can be set to 1 / 8 to 1 / 2 of the effective aperture of the convex surface of the converging lens.

[0123] In this embodiment of the invention, in order to facilitate mass production, the collimating lens, focusing lens and converging lens are plano-convex lenses with exactly the same optical parameters.

[0124] Furthermore, based on the obtained numerical aperture, working distance, lens center thickness, and refractive index of the plano-convex lens, the effective light-passing aperture and surface parameters of the convex surface of the plano-convex lens are determined, specifically including:

[0125] The distance between the image principal point and the back surface of a plano-convex lens is determined by the ratio of the lens center thickness to the refractive index of the plano-convex lens.

[0126] The image-side focal length of the plano-convex lens is determined by the sum of the distance between the image-side principal point and the back surface and the working distance of the plano-convex lens.

[0127] The effective aperture of the convex surface of the plano-convex lens is determined by multiplying twice the image-side focal length by the tangent function of the image-side aperture angle of the plano-convex lens.

[0128] Here, the image aperture angle is the arcsine function of the numerical aperture of the plano-convex lens.

[0129] Combining the elevation equation of a quadratic surface, the surface shape of the convex surface of a plano-convex lens is represented by the radius of curvature and the conic constant. The radius of curvature and the conic constant when the convex surface of the plano-convex lens is spherical are used as the surface shape parameters of the convex surface of the plano-convex lens.

[0130] In this embodiment of the invention, the plano-convex lens has the following light-convexity convergence effect: Figure 5As shown, the thickness at the center of the plano-convex lens is denoted by t, the effective aperture of the convex surface is denoted by D, the effective aperture of the plane of the plano-convex lens is denoted by 2a, t is set in the range of D / 8 to D / 2, and the refractive index of the plano-convex lens is denoted by n. The object-side principal point H of the plano-convex lens coincides with the vertex V of the convex surface of the plano-convex lens. The image-side principal point H′ of the plano-convex lens is located inside the plano-convex lens, and the distance between it and the plane of the plano-convex lens is d′. The front-side focal length of the plano-convex lens is f′. The working distance of the plane of the plano-convex lens, i.e., the back working distance, is WD′, the back focal point is F′, the front-side aperture angle is θ, and the numerical aperture of the plano-convex lens is denoted by NA.

[0131] Specifically, the phase aperture angle θ of a plano-convex lens and the numerical aperture NA of the plano-convex lens have the following relationship:

[0132] θ=sin -1 NA (1);

[0133] The distance d′ between the image-side principal point and the back surface of the plano-convex lens is calculated using the following formula:

[0134]

[0135] Calculate the image-side focal length f′ of the plano-convex lens using the following formula:

[0136] f′=d′+WD′ (3);

[0137] The effective aperture D of the convex surface of a plano-convex lens is calculated using the following formula:

[0138] D=2·f′·tan((sin -1 NA)) (4);

[0139] To improve the focusing and beam collection quality of the plano-convex lens, the convex surface of the plano-convex lens is set as a quadratic surface, and its elevation equation is as follows:

[0140]

[0141] Where z(x, y) represents the surface profile elevation of the quadratic surface corresponding to the convex surface of the plano-convex lens, (x, y) represents the position coordinates of the aperture of the quadratic surface, c represents the curvature of the quadratic surface, and k represents the conic constant of the quadratic surface. The radial coordinates of the aperture of the quadratic surface, and the radius of curvature of the convex surface of the plano-convex lens.

[0142] Specifically, the shape of the convex surface of a plano-convex lens is determined by both the radius of curvature R and the conic constant k. Furthermore, when the convex surface of the plano-convex lens is spherical, k = 0, and the corresponding radius of curvature R can be calculated using the following formula:

[0143]

[0144] The focusing lens and sealed window have a converging effect on light, such as... Figure 6 As shown, the gap distance between the sealing window and the focusing lens is denoted by L1. When the sealing window is absent, the working distance of the focusing lens plane remains WD′, and the back focal point remains F′. The thickness of the sealing window is denoted by L2, and the refractive index of the sealing window is denoted by n. W This indicates that the working distance of the sealed window is WD′ W This indicates that the back focus of the sealed window is F′. W Indicates F′ and F′ W The distance between them is L3, and the effective light transmission diameter of the sealed window is Where a W This indicates the effective half-diameter of the sealed window.

[0145] Furthermore, based on the working distance of the focusing lens, the gap distance between the sealing window and the focusing lens, the refractive index of the sealing window, the thickness of the sealing window, and the effective light-transmitting aperture of the plano-convex lens, the effective light-transmitting half-aperture of the sealing window and the working distance of the sealing window are determined, specifically including:

[0146] The working distance of the sealing window is determined according to the first formula, which is as follows:

[0147] WD′ W =WD′+L3-L1-L2 (7);

[0148] Among them, WD′ W L1 represents the working distance of the sealing window, WD′ represents the working distance of the focusing lens, L3 represents the back focal distance before and after setting the sealing window, L1 represents the gap distance between the sealing window and the focusing lens, and L2 represents the thickness of the sealing window.

[0149] The distance between the front and rear focal points of the sealing window is determined according to the second formula, which is as follows:

[0150]

[0151] Where, n W Indicates the refractive index of the sealed window;

[0152] The effective light-transmitting half-diameter of the sealed window is determined according to the third formula, which is as follows:

[0153]

[0154] Among them, a W 'a' represents the effective half-aperture of the sealed window, and 'a' represents the effective half-aperture of the focusing lens plane.

[0155] The effective half-aperture of the focusing lens plane is determined according to the fourth formula, which is as follows:

[0156]

[0157] Where D represents the effective aperture of the convex surface of the plano-convex lens, and f′ represents the image-side focal length of the plano-convex lens.

[0158] Furthermore, the angle of incidence and the angle of emergence are equal; based on the angle of incidence and / or the angle of emergence of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector, the lateral displacement of the dichroic mirror / reflector is determined, specifically including:

[0159] The lateral displacement of the dichroic mirror / reflector is determined according to the fifth formula, which is as follows:

[0160]

[0161] Where Δ represents the lateral displacement of the dichroic mirror / reflector, and τ represents the thickness of the dichroic mirror / reflector. The angle n represents the angle of incidence of a dichroic mirror / reflector. p This represents the refractive index of a dichroic mirror / reflector.

[0162] In embodiments of the present invention, such as Figure 7 As shown, both the dichroic mirror and the reflecting mirror are placed at a 45° angle in the light path, i.e. Both the dichroic mirror and the reflecting mirror are set to rectangular apertures of size D×1.414D. Considering the machining strength and component machinability, the thickness of the dichroic mirror and the reflecting mirror is set to D / 8~D / 2.

[0163] Taking a dichroic mirror as an example, in the Raman light collecting path, the dichroic mirror is considered as a parallel plate, which causes a lateral displacement on both sides of the transmitted light, so the outgoing light does not coincide with the incident light. When this happens, formula (11) can be simplified to:

[0164]

[0165] Furthermore, based on the effective aperture of the convex surface of the plano-convex lens, the effective apertures of the narrowband filter and the high-pass filter are determined, specifically as follows:

[0166] Set the effective aperture of the narrowband filter and the high-pass filter to be the same as the effective aperture of the convex surface of the plano-convex lens.

[0167] Specifically, considering the light transmission direction within the Raman probe optical system, the aperture of the laser excitation path is positioned on the side of the narrow-band filter near the collimating lens, while the aperture of the signal collection path is positioned on the side of the high-pass filter near the converging lens. Therefore, the effective apertures of the narrow-band filter and the high-pass filter are respectively the optical apertures of the laser excitation path and the signal collection path, i.e., both are set to have the same effective aperture D as the convex surface of the plano-convex lens. Considering the mechanical strength and manufacturability of the components, the thickness of both the narrow-band filter and the high-pass filter is set to D / 8 to D / 2.

[0168] like Figure 8 As shown, the initial structural parameters of each optical element in the Raman probe optical system also include the number of high-pass filters.

[0169] Determining the initial structural parameters of each optical element in the Raman probe optical system also includes:

[0170] Based on the obtained optical density value of the Raman scattered light and the transmittance of a single high-pass filter in the Raman scattered light band, the number of high-pass filters to be set is determined.

[0171] The transmittance of a single high-pass filter in the Raman scattering band is the OD value of the high-pass filter.

[0172] Specifically, depending on the application requirements, the intensity of Raman scattered light may be relatively weak in certain application scenarios, resulting in a lower signal-to-noise ratio (SNR) of the detected Raman spectrum and affecting the measurement accuracy of the Raman probe. In existing technologies, the OD value of a single high-pass filter is 3–4. Increasing the OD value of the high-pass filter can improve the SNR of the Raman scattered light, but this significantly increases the difficulty of coating the high-pass filter.

[0173] Since the high-pass filter is located in the parallel optical path, increasing the number of high-pass filters will not affect the focusing and collection effect of the optical system. Multiple high-pass filters can be stacked together, and the final OD value is obtained by adding the OD values ​​of each high-pass filter.

[0174] Furthermore, with the goal of minimizing the RMS value of the spot radius output by the simulation model, the conic constant is continuously adjusted in the optical design software. The surface parameters are optimized by using the conic constant and spot radius that minimize the RMS value of the spot radius. Specifically, this includes:

[0175] In optical design software, the conic constant of a plano-convex lens with a spherical convex surface is used as the center, and the constant is increased or decreased sequentially with a preset interval as the step size.

[0176] The conic constant that minimizes the RMS value of the light spot radius output by the simulation model is determined, and the conic constant is used as the optimized conic constant. The radius of curvature corresponding to the conic constant is used as the optimized radius of curvature.

[0177] In this embodiment of the invention, the numerical aperture and working distance of the plano-convex lens, the probe size, and the basic parameters of each optical element are obtained as follows:

[0178] The collimating fiber has a numerical aperture of 0.22, the collecting fiber has a numerical aperture of 0.22, and both the laser focusing and Raman scattering light collecting fibers have numerical apertures of 0.22. The collimating lens has a working distance of 9.5 mm, and the converging lens has a working distance of 9.5 mm. The excitation light emitted by the laser has a wavelength of 785 nm, and the Raman scattering signal light has a wavelength range of 795 nm-1145 nm, corresponding to a wavenumber range of 160 cm⁻¹. -1 -4005cm -1 The total length of the optical part in the Raman probe optical system is 100mm, that is, the straight line length between the end of the emitting fiber near the collimating lens and the end of the analyte near the sealing window is 100mm; the diameter of the optical part in the Raman probe optical system does not exceed 25.4mm; the OD value of the Raman scattered light is not less than 6.

[0179] When setting the initial structural parameters of the plano-convex lens, given that the refractive index of fused silica is n = 1.45 and the lens center thickness is t = 3 mm, the specific value of the distance d′ between the image principal point and the back surface of the plano-convex lens can be calculated according to formula (2).

[0180] Specifically,

[0181] Given that the working distance WD′ of the convex surface of the plano-convex lens is 9.5, the specific value of the image-side focal length f′ of the plano-convex lens can be calculated according to formula (3).

[0182] Specifically, f′=d′+WD′=11.57mm.

[0183] Given that the numerical aperture NA of the plano-convex lens is 0.22, the specific value of the effective light-passing aperture D of the convex surface of the plano-convex lens can be calculated according to formula (4).

[0184] Specifically, D = 2·f′·tan((sin -1 NA))≈5.22mm.

[0185] After obtaining an effective light-transmitting aperture of 5.22mm for the convex surface of the plano-convex lens, and reserving assembly allowance for the structural components, the diameter of the plano-convex lens is set to 6mm.

[0186] When k = 0, the value of the radius of curvature R of the convex surface of the plano-convex lens is calculated according to formula (6).

[0187] Specifically,

[0188] When setting the initial structural parameters of the narrowband filter and the high-pass filter, the mechanical aperture and effective light transmission aperture of the narrowband filter and the high-pass filter are set to be the same as those of the plano-convex lens; the thickness of the narrowband filter and the high-pass filter is set to 2mm.

[0189] When setting the initial structural parameters of the dichroic mirror and the reflector, the rectangular aperture of both the dichroic mirror and the reflector is calculated to be 6mm × 8.5mm according to D × 1.414D. The thickness of both the dichroic mirror and the reflector is set to 2mm, and the lateral displacement of the dichroic mirror / reflector is calculated according to formula (12).

[0190] Specifically,

[0191] When setting the initial structural parameters of the sealing window, firstly, calculate the specific value of the effective light-passing half-aperture a of the focusing lens plane according to formula (10).

[0192] Specifically,

[0193] Secondly, given a gap distance L1 of 2mm between the sealed window and the focusing lens, the effective light-transmitting half-aperture a of the sealed window is determined according to formula (9). W The specific value.

[0194] Specifically,

[0195] After determining the effective light-transmitting half-diameter of the sealed window to be 1.69 mm, according to The effective light-transmitting aperture of the sealing window is calculated, the assembly allowance of the structural components is reserved, and the outer diameter of the sealing window is set to 4.5mm and the thickness of the sealing window is set to 2mm.

[0196] Finally, the working distance of the sealing window is determined according to formulas (7) and (8).

[0197] Specifically,

[0198] When setting the number of high-pass filters, it is known that the OD value of Raman scattered light is not less than 6. In this embodiment, the OD value of the Raman scattered signal light corresponding to the relatively mature commercial high-pass filters can be greater than 3. Therefore, in this embodiment, two high-pass filters with the same optical parameters are used in combination, and the distance between the high-pass filters is set to 1mm.

[0199] In this embodiment, the total length of the optical part is known to be 100mm, the distance between the given focusing lens and the dichroic mirror is 55mm, the distance between the given dichroic mirror and the first high-pass filter is 10mm, and the distance between the given reflecting mirror and the narrowband filter is 15mm.

[0200] Given that the diameter of the optical part does not exceed 25.4 mm, and considering that the diameter of the optical element in the parallel light path is 6 mm, the distance between the dichroic mirror and the reflecting mirror is given as 12 mm.

[0201] Based on the initial structural parameters described above, a simulation model of the Raman probe optical system was built in the ZEMAX optical design software. Furthermore, within the ZEMAX software, the total length of the optical components of the Raman probe optical system, the working distance of the plano-convex lens, and the numerical aperture of the optical fiber can be adjusted according to the specific design requirements.

[0202] like Figure 9 As shown, when optimizing the surface parameters of the convex surface of a plano-convex lens, a value of k is given each time, and the values ​​are increased or decreased sequentially with a step size of 0.1 centered on 0.

[0203] With the goal of minimizing the RMS value of the light spot radius output by the simulation model, and using the radius of curvature R of the plano-convex lens as a variable, the R value and RMS value corresponding to each k are obtained.

[0204] The k and R values ​​corresponding to the minimum RMS value of the spot radius are used as the optimized cone constant and radius of curvature, respectively.

[0205] In this embodiment, according to Figure 9 It can be seen that the point with the smallest RMS value of the spot radius is the point corresponding to k = -0.5. At this time, the radius of curvature R is 5.29 mm, and the RMS value of the spot radius is 9.979 μm.

[0206] After the surface parameters are optimized, the final structure of the Raman probe optical system is as follows: Figure 10 As shown, the overall spatial dimensions of its optical components are less than 7.5mm (X) × 21.5mm (Y) × 100mm (Z).

[0207] Furthermore, in embodiments of the present invention, such as Figure 11 As shown, at room temperature of 20℃, the RMS value of the laser spot radius can be obtained from the dot plot of the laser focused spot as 9.979μm.

[0208] like Figure 12 As shown, at room temperature of 20℃, the RMS value of the light spot radius can be obtained from the spot diagram of the Raman scattering signal collection spot.

[0209] like Figure 13As shown, 4J32 alloy is used as the optical element support structure of the Raman probe. At a low temperature of -180℃, the RMS value of the laser spot radius can be obtained from the dot plot of the laser focused spot.

[0210] like Figure 14 As shown, 4J32 alloy is used as the optical element support structure of the Raman probe. At a low temperature of -180℃, the RMS value of the spot radius can be obtained from the spot pattern of the Raman scattering signal collection spot.

[0211] Therefore, by using the same lens material and matching structural materials with similar coefficients of thermal expansion, the Raman probe can achieve calorific operation over a wide temperature range, and the optical performance of the Raman probe remains almost unchanged.

[0212] Therefore, in addition to being usable over a wide temperature range, the Raman probe optical system of the present invention can also be used directly in a low-temperature environment after the Raman probe has been assembled and adjusted at room temperature, eliminating the hassle of focusing or presetting the focal plane.

[0213] In summary, the design method of the Raman probe optical system of the present invention efficiently determines the initial structural parameters of the Raman probe optical system using the Gaussian optical formula.

[0214] In the design method of the Raman probe optical system of the present invention, the numerical aperture can be adjusted within a certain range, which helps to adapt to different transmitting or collecting optical fibers and improve the transmission efficiency of optical signals.

[0215] In the design method of the Raman probe optical system of the present invention, the total length of the Raman probe and the working distance of the optical elements can be freely set within a certain range, which helps to match different application scenarios.

[0216] The number of high-pass filters inside the Raman probe optical system of the present invention can be adjusted within a certain range, which helps to improve the signal-to-noise ratio of the Raman probe when the Raman scattered light signal is relatively weak, thereby ensuring measurement accuracy.

[0217] The Raman probe optical system of the present invention can operate stably over a wide temperature range. After assembly and adjustment at room temperature, it can be directly placed for use at low temperatures without any further adjustments.

[0218] In the Raman probe optical system of the present invention, the collimating lens, converging lens and focusing lens are plano-convex lenses with identical optical parameters, which has advantages in terms of cycle time and cost in mass production.

[0219] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of the present invention is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., a solid-state disk (SSD)).

[0220] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A design method for a Raman probe optical system, characterized in that, The Raman probe optical system includes a sealed housing with a sealing window embedded at one end and a transmitting fiber and a collecting fiber passing through the other end; it also includes an emission optical path formed by a collimating lens, a narrow-band filter, and a reflector arranged sequentially inside the sealed housing, in conjunction with the transmitting fiber; and a dichroic mirror coaxial with the transmitting and receiving fibers, with a high-pass filter and a converging lens arranged sequentially between the dichroic mirror and the collecting fiber, and a focusing lens arranged between the sealing window and the dichroic mirror; the sealed housing is filled with an inert gas, is a pressure-resistant sealed housing, the sealing window is made of sapphire, and the supporting structure of the optical elements in the Raman probe optical system is made of a structural material with a low coefficient of thermal expansion; the method includes: Based on Gaussian optics formulas, and according to the obtained numerical aperture and working distance of the plano-convex lens, probe size, and basic parameters of each optical element, the initial structural parameters of each optical element in the Raman probe optical system are determined. These initial structural parameters include the surface profile parameters of the plano-convex lens's convex surface, the effective aperture of each optical element, and the spacing between adjacent optical elements. The plano-convex lens includes the collimating lens, the converging lens, and the focusing lens. The surface profile parameters include the radius of curvature and conic constant when the convex surface of the plano-convex lens is spherical. Based on the initial structural parameters, a simulation model of the Raman probe optical system is built in optical design software. With the goal of minimizing the RMS value of the spot radius output by the simulation model, the conic constant is continuously adjusted in the optical design software. The surface parameters are optimized by using the conic constant and radius of curvature that minimize the RMS value of the spot radius. The initial structural parameters are updated based on the optimized surface parameters to obtain the final structural parameters of the Raman probe optical system.

2. The design method of the Raman probe optical system according to claim 1, characterized in that, The basic parameters include the lens center thickness and refractive index of the plano-convex lens; the gap distance between the sealing window and the focusing lens, the refractive index of the sealing window, and the thickness of the sealing window; the incident angle and / or exit angle of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector; based on the obtained numerical aperture and working distance of the plano-convex lens, the probe size, and the basic parameters of each optical element, the initial structural parameters of each optical element in the Raman probe optical system are determined, specifically including: Based on the obtained numerical aperture, working distance, lens center thickness, and refractive index of the plano-convex lens, the effective light-passing aperture and surface parameters of the convex surface of the plano-convex lens are determined. Based on the working distance of the focusing lens, the gap distance between the sealing window and the focusing lens, the refractive index of the sealing window, the thickness of the sealing window, and the effective light-transmitting aperture of the plano-convex lens, the effective light-transmitting half-aperture of the sealing window and the working distance of the sealing window are determined. The lateral displacement of the dichroic mirror / reflector is determined based on the angle of incidence and / or the angle of exit of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector. The effective light-passing diameters of the narrow-band filter and the high-pass filter are determined based on the effective light-passing diameter of the convex surface of the plano-convex lens. The spacing between two adjacent optical elements is determined based on the probe size, the working distance of the plano-convex lens, the gap distance between the sealing window and the focusing lens, and the thickness of each optical element.

3. The design method of the Raman probe optical system according to claim 2, characterized in that, Based on the obtained numerical aperture, working distance, lens center thickness, and refractive index of the plano-convex lens, the effective light-passing aperture and surface parameters of the convex surface of the plano-convex lens are determined, specifically including: The distance between the image principal point and the back surface of the plano-convex lens is determined based on the ratio of the lens center thickness to the refractive index of the plano-convex lens. The image-side focal length of the plano-convex lens is determined by the sum of the distance between the image principal point and the rear surface and the working distance of the plano-convex lens. The effective aperture of the convex surface of the plano-convex lens is determined by multiplying twice the image-side focal length by the tangent function of the image-side aperture angle of the plano-convex lens; the image-side aperture angle is the arcsine function of the numerical aperture of the plano-convex lens. Combining the elevation equation of a quadratic surface, the surface shape of the plano-convex lens is represented by the radius of curvature and the conic constant. The radius of curvature and the conic constant when the plano-convex lens surface is spherical are used as the surface shape parameters of the plano-convex lens surface.

4. The design method of the Raman probe optical system according to claim 3, characterized in that, Based on the working distance of the focusing lens, the gap distance between the sealing window and the focusing lens, the refractive index of the sealing window, the thickness of the sealing window, and the effective light-transmitting aperture of the plano-convex lens, the effective light-transmitting half-aperture of the sealing window and the working distance of the sealing window are determined, specifically including: The working distance of the sealing window is determined according to a first formula, which is specifically: ； in, Indicates the working distance of the sealed window. This indicates the working distance of the focusing lens. This indicates the distance between the back focal points before and after setting the sealing window. This indicates the gap distance between the sealing window and the focusing lens. This indicates the thickness of the sealing window; The distance between the front and rear focal points of the sealing window is determined according to the second formula, which is as follows: ； in, The refractive index of the sealed window is indicated; The effective light-transmitting half-aperture of the sealed window is determined according to the third formula, which is specifically: ； in, This indicates the effective light-transmitting half-diameter of the sealed window. This represents the effective half-aperture of the focusing lens plane; The effective half-aperture of the focusing lens plane is determined according to the fourth formula, which is specifically: ； in, This indicates the effective aperture of the convex surface of the plano-convex lens. This indicates the image-side focal length of the plano-convex lens.

5. The design method of the Raman probe optical system according to claim 2, characterized in that, The incident angle and the exit angle are equal; the lateral displacement of the dichroic mirror / reflector is determined based on the incident angle and / or exit angle, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector, specifically including: The lateral displacement of the dichroic mirror / reflector is determined according to the fifth formula, which is specifically: ； in, This indicates the lateral displacement of the dichroic mirror / reflector. This indicates the thickness of the dichroic mirror / reflector. The angle representing the incident angle of the dichroic mirror / reflector. This represents the refractive index of the dichroic mirror / reflector.

6. The design method of the Raman probe optical system according to claim 2, characterized in that, Based on the effective aperture of the convex surface of the plano-convex lens, the effective apertures of the narrowband filter and the high-pass filter are determined, specifically as follows: The effective aperture of the narrowband filter and the high-pass filter is set to be the same as the effective aperture of the convex surface of the plano-convex lens.

7. The design method of the Raman probe optical system according to claim 1, characterized in that, The initial structural parameters of each optical element in the Raman probe optical system also include the number of high-pass filters. Determining the initial structural parameters of each optical element in the Raman probe optical system also includes: The number of high-pass filters is determined based on the obtained optical density value of the Raman scattered light and the transmittance of a single high-pass filter within the Raman scattered light band.

8. The design method of the Raman probe optical system according to claim 1, characterized in that, With the goal of minimizing the RMS value of the light spot radius output by the simulation model, the conic constant is continuously adjusted in the optical design software. The surface parameters are optimized by using the conic constant and radius of curvature that minimize the RMS value of the light spot radius. Specifically, this includes: In optical design software, the conic constant when the convex surface of the plano-convex lens is spherical is taken as the center, and the constant is increased or decreased sequentially with a preset interval as the step size. The conic constant that minimizes the RMS value of the light spot radius output by the simulation model is determined, and the conic constant is taken as the optimized conic constant, and the radius of curvature corresponding to the conic constant is taken as the optimized radius of curvature.

9. An optical system for a Raman probe, characterized in that, The device includes a sealed housing with a sealing window embedded at one end and a transmitting optical fiber and a collecting optical fiber passing through the other end; it also includes a transmitting optical path formed by a collimating lens, a narrow-band filter, and a reflector arranged sequentially inside the sealed housing, in conjunction with the transmitting optical fiber; and a dichroic mirror that is coaxial with the transmitting and receiving optical fibers, with a high-pass filter and a converging lens arranged sequentially between the dichroic mirror and the collecting optical fiber, and a focusing lens arranged between the sealing window and the dichroic mirror; The sealed window is made of sapphire crystal. The collimating lens, the narrow-band filter, the reflecting mirror, the dichroic mirror, the high-pass filter, and the converging lens are all made of fused silica. The sealed tube shell is filled with inert gas.

10. The Raman probe optical system according to claim 9, characterized in that, The collimating lens, the converging lens, and the focusing lens are all plano-convex lenses of the same type.

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