Raman probe optical system and design method thereof

Abstract

The invention discloses a Raman probe optical system and a design method thereof, and relates to the technical field of low-temperature Raman probe optical system.The design method comprises the steps that on the basis of a Gaussian optical formula, according to the obtained numerical aperture and working distance of a plano-convex lens, the probe size and the basic parameters of all optical elements, the working distance of the plano-convex lens is calculated; determining initial structure parameters of each optical element in the Raman probe optical system; building a simulation model of the Raman probe optical system in optical design software according to the initial structure parameters; taking the minimum RMS value of the light spot radius output by the simulation model as a target, continuously adjusting a cone constant in optical design software, and optimizing the surface profile parameters through the cone constant with the minimum RMS value of the light spot radius and the curvature radius; and updating the initial structure parameters according to the optimized surface type parameters to obtain final structure parameters of the Raman probe optical system. The Raman probe optical system designed by the invention can stably and reliably work under a low-temperature working condition.

Description

Technical Field

[0001] The invention relates to the technical field of low-temperature Raman probe optical system design, and in particular to a Raman probe optical system and a design method thereof. Background Art

[0002] The Raman effect refers to the change in the frequency of scattered light when light interacts with matter. The core is that when a beam of monochromatic light is irradiated onto a sample, most of it will be elastically scattered, that is, the frequency of the scattered light is the same as the incident light. This phenomenon is called Rayleigh scattering. However, a small part of the light will be inelastically scattered, resulting in a slight change in the frequency of the scattered light. This is Raman scattering. These frequency changes reflect the energy transfer within the molecule. Therefore, by analyzing the Raman scattering spectrum, we can obtain detailed information about the molecular structure, material composition, and crystal phase. The Raman effect has become an indispensable tool in modern scientific research because it is non-destructive, fast, and very sensitive.

[0003] Raman probe is one of the key devices to achieve effective use of Raman effect. The main task of Raman probe is to focus the laser on the sample and collect the scattered Raman signal, and then transmit the collected Raman signal to the Raman spectrometer for detailed analysis. According to the working temperature, Raman probe can be divided into standard type, high temperature type and low temperature type. Among them, the working environment of the standard type is between -50℃ and 40℃, which is suitable for measurement in conventional laboratory environment. The working environment of the high temperature probe can reach up to 300℃, and it can work under extreme high temperature conditions, for example: monitoring the property changes of high temperature materials in industrial production processes. The working environment of the cryogenic probe is below -160℃. Compared with standard probes and high-temperature probes, the application scenarios of the cryogenic probe are relatively few, but it is crucial in the research of some special fields; for example, in low-temperature 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, low-temperature Raman spectroscopy can reveal the microstructural changes of materials at different temperatures; in the process of liquefied natural gas extraction and transportation, cryogenic probes can be used for online dynamic monitoring of its components and proportions to achieve accurate measurement of the calorific value of liquefied natural gas.

[0004] At extremely low temperatures, such as -160°C, the air inside the existing cryogenic Raman probe will undergo a phase change, from gas to liquid. This change will not only interfere with the normal operation of the Raman probe optical system and reduce its efficiency, but may even cause irreversible damage to the probe; for example, liquefied air may penetrate into the probe, causing optical path misalignment or component corrosion. Therefore, we need to design a Raman probe suitable for cryogenic environments to ensure the stability and reliability of the Raman probe under cryogenic conditions. Summary of the invention

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

[0006] In order to achieve the above object, the present invention adopts the following technical scheme:

[0007] In a first aspect, the present invention provides a method for designing a Raman probe optical system, wherein the Raman probe optical system comprises a sealed tube shell, one end of which is embedded with a sealed window, and the other end of which is penetrated with a transmitting optical fiber and a collecting optical fiber; further comprising a transmitting optical path formed by a collimating lens, a narrow-band filter and a reflector arranged in sequence inside the sealed tube shell and cooperating with the transmitting optical fiber; and a dichroic mirror coaxial for transmitting and receiving, 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 sealed window and the dichroic mirror;

[0008] Based on the Gaussian optical formula, the initial structural parameters of each optical element in the Raman probe optical system are determined according to the 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 include the surface parameters of the convex surface of the plano-convex lens, the effective aperture of each optical element, and the distance between two adjacent optical elements; the plano-convex lens includes the collimating lens, the converging lens and the focusing lens; the surface parameters include the radius of curvature and the cone constant when the convex surface of the plano-convex lens is spherical;

[0009] Building a simulation model of the Raman probe optical system in optical design software according to the initial structural parameters;

[0010] Taking the minimum RMS value of the spot radius output by the simulation model as the goal, the cone constant is continuously adjusted in the optical design software, and the surface parameters are optimized by the cone constant and the curvature radius that minimize the RMS value of the spot radius;

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

[0012] In a 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 angle of the incident angle and / or the exit angle of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector; 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, the initial structural parameters of each optical element in the Raman probe optical system are determined, specifically including:

[0013] Determine the effective aperture and surface parameters of the convex surface of the plano-convex lens according to the obtained numerical aperture, working distance, lens center thickness and refractive index of the plano-convex lens;

[0014] Determine the effective light-clearance semi-aperture of the sealing window and the working distance of the sealing window according to 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-clearance aperture of the convex surface of the plano-convex lens;

[0015] Determining the lateral displacement of the dichroic mirror / reflector according to the angle of the incident angle and / or the exit angle of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector;

[0016] Determine the effective light apertures of the narrowband filter and the high-pass filter according to the effective light aperture of the convex surface of the plano-convex lens;

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

[0018] In a possible implementation, according to the acquired numerical aperture, working distance, lens center thickness and refractive index of the plano-convex lens, the effective aperture and surface parameters of the convex surface of the plano-convex lens are determined, specifically including:

[0019] Determining the distance between the image-side principal point and the rear surface of the plano-convex lens according to the ratio of the center thickness of the plano-convex lens to the refractive index of the plano-convex lens;

[0020] Determine the image-side focal length of the plano-convex lens according to the sum of the distance between the image-side principal point and the rear surface and the working distance of the plano-convex lens;

[0021] Determine the effective aperture of the convex surface of the plano-convex lens according to the product of twice the image-side focal length and 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] Combined with the vector height equation of the quadratic surface, the curvature radius and the cone constant are used to represent the surface shape of the convex surface of the plano-convex lens. When the convex surface of the plano-convex lens is spherical, the curvature radius and the cone constant are used as the surface shape parameters of the convex surface of the plano-convex lens.

[0023] In a possible implementation, determining the effective light-clearance semi-aperture of the sealing window and the working distance of the sealing window according to 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-clearance aperture of the convex surface of the plano-convex lens specifically includes:

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

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

[0026] Among them, WD′ W represents the working distance of the sealing window, WD′ represents the working distance of the focusing lens, L3 represents the back focus distance before and after the sealing window is set, L1 represents the gap distance between the sealing window and the focusing lens, and L2 represents the thickness of the sealing window;

[0027] The back focus distance before and after the sealing window is determined according to a second formula, wherein the second formula is specifically:

[0028]

[0029] Among them, n W represents the refractive index of the sealing window;

[0030] The effective semi-aperture of the sealing window is determined according to the third formula, and the third formula is specifically:

[0031]

[0032] Among them, a W represents the effective semi-aperture of the sealing window, and a represents the effective semi-aperture of the focusing lens plane;

[0033] The effective semi-aperture of the focusing lens plane is determined according to the fourth formula, and the fourth formula 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 a possible implementation, the incident angle is equal to the exit angle; and determining the lateral displacement of the dichroic mirror / reflector according to the incident angle and / or the exit angle of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector specifically includes:

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

[0038]

[0039] Wherein, Δ represents the lateral displacement of the dichroic mirror / reflector, τ represents the thickness of the dichroic mirror / reflector, represents the angle of incidence of the dichroic mirror / mirror, n p represents the refractive index of the dichroic mirror / mirror.

[0040] In a possible implementation, the effective light apertures of the narrowband filter and the high-pass filter are determined according to the effective light aperture of the convex surface of the plano-convex lens, specifically:

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

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

[0043] The number of high-pass filters to be set is determined according to the optical density value of the acquired Raman scattered light and the transmittance of a single high-pass filter within the Raman scattered light band.

[0044] In a possible implementation, the cone constant is continuously adjusted in the optical design software with the goal of minimizing the RMS value of the spot radius output by the simulation model, and the surface parameters are optimized by the cone constant and the curvature radius that minimize the RMS value of the spot radius, specifically including:

[0045] In the optical design software, the cone constant when the convex surface of the plano-convex lens is spherical is taken as the center, and the preset interval is used as the step length to increase or decrease in sequence;

[0046] A cone constant that minimizes the RMS value of the spot radius output by the simulation model is determined, the cone constant is used as the optimized cone constant, and the curvature radius corresponding to the cone constant is used as the optimized curvature radius.

[0047] In a second aspect, an embodiment of the present invention provides a Raman probe optical system, which includes: a sealing window is embedded at one end of the sealed tube shell, and a transmitting optical fiber and a collecting optical fiber are passed through the other end; it also includes a transmitting optical path formed by a collimating lens, a narrow-band filter and a reflector arranged in sequence inside the sealed tube shell and cooperating with the transmitting optical fiber; and a dichroic mirror coaxial for transmitting and receiving, 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 sealed window and the dichroic mirror;

[0048] The sealing window is made of sapphire;

[0049] The collimating lens, the narrow-band filter, the reflector, the dichroic mirror, the high-pass filter and the converging lens are all made of fused quartz;

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

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

[0052] When the design method of the Raman probe optical system provided by the embodiment of the present invention is actually applied, the initial structure of the Raman probe optical system can be efficiently constructed according to the initial structural parameters, and the surface parameters of the convex surface of the plano-convex lens in the Raman probe optical system can be quickly and conveniently optimized. The final structure of the Raman probe optical system determined by the design method of the present invention can work stably and reliably under low temperature conditions.

[0053] The design method of the Raman probe optical system provided by the embodiment of the present invention can realize the construction of a Raman probe optical system with any probe size and working distance, thereby matching different types of application scenarios.

[0054] The Raman probe optical system provided by the embodiment of the present invention can not only work stably and reliably under low temperature conditions, but also can seal the optical path of the Raman probe optical system through a sealed tube shell and a sealed window to prevent the substance to be tested from penetrating into the sealed tube shell and damaging the internal optical components; the sealed tube shell is filled with inert gas to prevent air condensation inside the sealed tube shell at low temperature from damaging the stability of the Raman probe optical system. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0058] Figure 4 A flowchart of a method for designing a Raman probe optical system provided by an embodiment of the present invention;

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

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

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

[0062] Figure 8 A schematic diagram of the structure of superimposed use of high-pass filters in a design method for a Raman probe optical system provided by an embodiment of the present invention;

[0063] Fig. 9 A trend diagram of the curvature radius and the optimal spot radius RMS value output by the simulation model in a design method of a Raman probe optical system provided by an embodiment of the present invention, as the cone constant changes;

[0064] Fig.10 An optical path structure diagram of a Raman probe optical system determined by a design method of a Raman probe optical system provided by an embodiment of the present invention;

[0065] Fig.11 A Raman probe optical system determined by a design method of a Raman probe optical system provided by an embodiment of the present invention, a spot diagram of a laser focus spot at a room temperature of 20° C.;

[0066] Fig.12 A Raman probe optical system determined by a design method of a Raman probe optical system provided by an embodiment of the present invention, a point arrangement diagram of a Raman scattering signal collection spot at a room temperature of 20° C.;

[0067] Fig.13A Raman probe optical system determined by a design method of a Raman probe optical system provided by an embodiment of the present invention uses 4J32 alloy as an optical element support structure of the Raman probe, and a point diagram of a laser focus spot at a low temperature of -180°C;

[0068] Fig.14 A Raman probe optical system determined by a design method of a Raman probe optical system provided in an embodiment of the present invention uses 4J32 alloy as a sealed tube shell and an optical element support structure of the Raman probe. At a low temperature of -180°C, a point arrangement diagram of a Raman scattering signal collection spot is shown.

[0069] Reference numerals and descriptions:

[0070] 1. Raman probe optical system; 11. Sealed tube shell; 12. Sealed window; 13. Transmitting optical fiber; 14. Collecting optical fiber; 15. Collimating lens; 16. Narrowband filter; 17. Reflector; 18. Dichroic mirror; 19. High-pass filter; 110. Converging lens; 111. Focusing lens; 2. Object to be measured; 3. Laser; 4. Raman spectrometer. DETAILED DESCRIPTION

[0071] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0072] In the following, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, unless otherwise specified, "multiple" means two or more. In addition, the use of "based on" or "according to" means openness and inclusiveness, because the process, steps, calculations or other actions "based on" or "according to" one or more of the conditions or values ​​may be based on additional conditions or values ​​beyond the described values ​​in practice.

[0073] At present, the common Raman probes on the market are mainly standard and high temperature types, while low temperature Raman probes are relatively rare. The reason behind this phenomenon is that the low temperature environment brings many challenges to Raman probe technology. For example:

[0074] At extremely low temperatures of -160°C, the air inside the cryogenic probe will undergo a phase change from gas to liquid. This change will not only interfere with the normal operation of the Raman probe optical system and reduce its efficiency, but may even cause irreversible damage to the probe; for example, liquefied air may penetrate into the probe, causing optical path misalignment or component corrosion.

[0075] Many materials that perform well at room temperature may no longer be suitable at extremely low temperatures. Specifically, taking commonly used optical glass as an example, BK7 and SF2 materials will shrink at low temperatures, causing the optical performance of optical components to deteriorate, and may even cause cracks or breakage.

[0076] In order to solve the problem of low stability and poor reliability of the existing Raman probe under low temperature conditions, an embodiment of the present invention provides a Raman probe optical system and a design method thereof.

[0077] In a first aspect, an embodiment of the present invention provides a Raman probe optical system, wherein the Raman probe optical system 1 is a common aperture Raman probe optical system, which is composed of a laser excitation optical path and a signal collection optical path. Figure 1 As shown, the laser light emitted by the laser 3 enters the Raman probe optical system 1 through optical fiber coupling, and the laser light is transmitted forward in the Raman probe optical system 1 to the object to be measured 2 for excitation. After the obtained Raman scattered signal light passes through the Raman probe optical system 1 in the reverse direction, the Raman scattered signal light continues to be transmitted backward and is collected through the optical fiber, and 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 comprises: a sealed tube shell 11, one end of which is embedded with a sealed window 12, and the other end is penetrated by 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 arranged inside the sealed tube shell 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 emission optical fiber 13; and a dichroic mirror 18 coaxial with the emission and reception, a high-pass filter 19 and a converging lens 110 are arranged in sequence between the dichroic mirror 18 and the collection optical fiber 14, and a focusing lens 111 is arranged between the sealed window 12 and the dichroic mirror 18.

[0080] The emitting optical fiber 13 is an incident laser optical fiber connected to the laser 3 , and the collecting optical fiber 14 is a Raman scattered light collecting optical fiber connected to the Raman spectrometer 4 .

[0081] The collimating lens 15 adjusts the emission angle of the incident laser emitted by the laser 3 to the minimum, so that it becomes a parallel beam of light. The focusing lens 111 in the optical path not only focuses the incident laser on the object to be measured 2, but also collects the Raman scattered light. The converging lens 110 is used to converge the Raman scattered signal light to the collection optical fiber 14. The narrowband filter 16 is used to filter out the stray light of the laser itself and the Raman signal of the optical fiber caused by the laser passing through the optical fiber. The dichroic mirror 18 has a high reflectivity for the excitation light and a high transmittance for the Raman scattered signal light. The high-pass filter 19 can filter out the collected Rayleigh scattering, and the size of the optical density value of the high-pass filter has an important influence on the performance of the Raman probe optical system 1. The reflector 17 is a plane reflector, which is used to turn the excitation light path. The sealing window 12 cooperates with the sealing tube shell 11 to seal the Raman probe optical path, so as to prevent the substance to be measured from penetrating into the probe and damaging the optical components in the Raman probe optical system 1.

[0082] Furthermore, in order to prevent the air condensation inside the sealed tube shell 11 in a low temperature environment from damaging the stability of the Raman probe optical system 1 , the sealed tube shell 11 is filled with an inert gas.

[0083] Specifically, the inert gas filled may be helium with a condensation point of -269°C, neon with a condensation point of -248°C, nitrogen with a condensation point of -210°C, argon with a condensation point of -189°C, or the like.

[0084] Furthermore, the sealed tube shell 11 is a pressure-resistant sealed tube shell, the sealed window 12 is embedded in the pressure-resistant sealed tube shell, and the Raman probe optical path is located inside the pressure-resistant sealed tube shell. Under the protection of the pressure-resistant sealed tube shell, the remaining optical elements in the probe optical system 1 except the sealed window 12 will not directly contact the substance to be tested, and the performance of these optical elements will not be affected by the external pressure of the pressure-resistant sealed tube shell.

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

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

[0087] Specifically, conventional lens materials are generally difficult to withstand ultra-low temperature working environments. Therefore, the optical elements of the probe optical system 1 have limited optional materials when being prepared. Sapphire and fused quartz can be used in ultra-low temperature working environments due to their excellent thermal stability.

[0088] Among them, sapphire has a relatively high hardness and is suitable for being processed into a planar sealing window 12 .

[0089] Since the supporting structure of the optical element in the Raman probe optical system 1 is made of a structural material with a low thermal expansion coefficient, for example, a thermal expansion coefficient of 1×10 -6 / K 4J32 alloy, thermal expansion coefficient is 1.2×10 -6 / K Ni36 alloy; the thermal expansion coefficient of fused quartz is 0.51×10 -6 / K, fused quartz has good thermal stability and low thermal expansion coefficient, so 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 quartz, which can not only maintain the optical performance of the optical elements, but also match the structural materials with low thermal expansion coefficients to better achieve the athermal characteristics of the optical path, thereby achieving the direct application of the Raman probe optical system 1 in a low-temperature environment after being assembled and adjusted at room temperature, without considering the phase plane drift caused by temperature changes, thereby eliminating the focusing mechanism.

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

[0091] Specifically, the collimating lens 15, the converging lens 110 and the focusing lens 111 use plano-convex lenses with exactly the same optical parameters. When adjusting the subsequent parameters, it is only necessary to calculate the optical parameters of one of the plano-convex lenses to obtain the optical parameters of the above three plano-convex lenses, which 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 can seal the optical path of the Raman probe optical system through the sealing tube shell 11 and the sealing window 12 to prevent the substance to be measured from penetrating into the sealed tube shell 11 and damaging the internal optical components; the sealed tube shell 11 is filled with inert gas, which can also prevent the air condensation inside the sealed tube shell 11 under low temperature environment from damaging the stability of the Raman probe optical system.

[0093] In a second aspect, an embodiment of the present invention provides a design method for a Raman probe optical system, where the design method is used to quickly and accurately determine structural parameters of the Raman probe optical system.

[0094] like Figure 2 , Figure 3As shown, the Raman probe optical system 1 targeted by the present invention includes a sealed tube shell 11, one end of which is embedded with a sealed window 12, and the other end is penetrated by a transmitting optical fiber 13 and a collecting optical fiber 14; it also includes a transmitting optical path arranged inside the sealed tube shell 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 transmitting optical fiber 13; and a dichroic mirror 18 coaxial for transmission and reception, a high-pass filter 19 and a converging lens 110 are arranged in sequence 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.

[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, the initial structural parameters of each optical element in the Raman probe optical system are determined 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] Among them, the Gaussian optics formula is an important formula in optics used to describe the relationship between object distance, image distance and focal length. The derivation of the Gaussian optics formula is based on the basic principles of geometric optics and is obtained through drawing and geometric analysis. The formula is widely used in optical design, especially in the design and analysis of optical systems such as lenses and reflectors. For example, in the design of photographic lenses, the 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 parameters of the convex surface of the plano-convex lens, the effective aperture of each optical element, and the distance between two adjacent optical elements.

[0099] The surface parameters include the radius of curvature and the cone 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] Among them, the effective aperture refers to the effective diameter of the light-transmitting surface of the optical element, also known as the wide cross section, effective aperture, effective exit aperture, etc. It reflects the size of the main light beam after the optical system passes through the element, and directly affects the clarity and resolution of the imaging. The effective aperture of each optical element can be obtained by combining the Gaussian optical formula, through drawing and geometric analysis.

[0102] The convex surface of the plano-convex lens is a quadratic surface, and its surface shape is determined by the radius of curvature and the cone 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 focal length of the plano-convex lens 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 and thickness of each optical element and the reasonable distribution of the distance between the optical elements based on the probe size.

[0104] Step 102: Building a simulation model of the Raman probe optical system in optical design software according to the initial structural parameters.

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

[0106] Specifically, the optical design software can include ZEMAX, CODE V, SOD88 and other software.

[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. The simulation model can simulate the test process of the Raman probe and output the corresponding RMS radius of the focused light spot, that is, the RMS value of the light spot radius in this application.

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

[0109] Step 103, with the goal of minimizing the RMS value of the spot radius output by the simulation model, the cone constant is continuously adjusted in the optical design software, and the surface parameters are optimized by the cone constant and the curvature radius that minimize the RMS value of the spot radius.

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

[0111] Step 104: Update the initial structural parameters according to 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 a specific Raman probe optical system is constructed according to the final structural parameters.

[0113] When the design method of the Raman probe optical system provided by the embodiment of the present invention is actually applied, the initial structure of the Raman probe optical system can be efficiently constructed according to the initial structural parameters, and the surface parameters of the convex surface of the plano-convex lens in the Raman probe optical system can be quickly and conveniently optimized. The final structure of the Raman probe optical system determined by the design method of the present invention can work stably and reliably under low temperature conditions.

[0114] The design method of the Raman probe optical system provided by the embodiment of the present invention can realize the construction of a Raman probe optical system with any 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 incident angle and / or the exit angle of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector.

[0116] Furthermore, 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, the initial structural parameters of each optical element in the Raman probe optical system are determined, including:

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

[0118] The effective light clearance semi-aperture of the sealing window and the working distance of the sealing window are determined according to 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 clearance aperture of the convex surface of the plano-convex lens.

[0119] The lateral displacement of the dichroic mirror / reflector is determined according to the angle of the incident angle and / or the exit angle of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector.

[0120] According to the effective aperture of the convex surface of the plano-convex lens, the effective aperture of the narrow-band filter and the high-pass filter is determined.

[0121] The spacing between two adjacent optical elements is determined according to the size of the probe, 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 apertures of the collimating lens, the focusing lens, and the convex surface of the converging lens can all be circular apertures. 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 of the laser focusing and the Raman scattered light collection. The working distance of the plano-convex lens refers to the distance between the lens and the object or the imaging plane. The lens 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 the embodiment of the present invention, in order to facilitate batch processing, the collimating lens, the focusing lens and the converging lens are plano-convex lenses with completely the same optical parameters.

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

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

[0126] The image side focal length of the plano-convex lens is determined based on the sum of the distance between the image side principal point and the rear 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 the product of twice the image-side focal length and the tangent function of the image-side aperture angle of the plano-convex lens.

[0128] The image-side aperture angle is the inverse sine function of the numerical aperture of the plano-convex lens.

[0129] Combined with the vector height equation of the quadratic surface, the curvature radius and the cone constant are used to represent the surface shape of the convex surface of the plano-convex lens. When the convex surface of the plano-convex lens is spherical, the curvature radius and the cone constant are used as the surface shape parameters of the convex surface of the plano-convex lens.

[0130] In the embodiment of the present invention, the convergence effect of the plano-convex lens on light is as follows: Figure 5As shown, the lens center thickness of the plano-convex lens is represented by t, the effective clear aperture of the convex surface of the plano-convex lens is represented by D, the effective clear aperture of the plane of the plano-convex lens is represented by 2a, t is set in the range of D / 8 to D / 2, and the refractive index of the plano-convex lens is represented 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 the image-side principal point H′ and the plane of the plano-convex lens is d′, and the phase 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 focus is F′, the phase aperture angle is θ, and the numerical aperture of the plano-convex lens is represented by NA.

[0131] Specifically, there is the following relationship between the relative aperture angle θ of the plano-convex lens and the numerical aperture NA of the plano-convex lens:

[0132] θ=sin -1 NA (1);

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

[0134]

[0135] The image side focal length f' of a plano-convex lens is calculated using the following formula:

[0136] f′=d′+WD′ (3);

[0137] Calculate the effective aperture D of the convex surface of the plano-convex lens according to the following formula:

[0138] D = 2·f′·tan((sin -1 NA)) (4);

[0139] In order to improve the quality of the beam focused and collected by the plano-convex lens, the convex surface of the plano-convex lens is set as a quadratic surface, and its vector height equation is as follows:

[0140]

[0141] Wherein, z(x, y) represents the surface sag 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, k represents the conic constant of the quadratic surface, Represents the radial coordinate of the aperture of the quadratic surface, the radius of curvature of the convex surface of the plano-convex lens

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

[0143]

[0144] The focusing lens and the sealed window have the following effects on the convergence of light: Figure 6 As shown in the figure, the gap distance between the sealing window and the focusing lens is represented by L1. When there is no sealing window, the working distance of the focusing lens plane is still WD', and the back focus is still F'. The thickness of the sealing window is represented by L2, and the refractive index of the sealing window is represented by n W Indicates that the working distance of the sealed window is WD′ W Indicated by the rear focus of the sealed window, F' W Indicates. F′ and F′ W The distance between them is L3, and the effective aperture of the sealed window is where a W Indicates the effective semi-aperture of the sealed window.

[0145] Furthermore, according to 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 clearance diameter of the convex surface of the plano-convex lens, the effective light clearance semi-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 specifically:

[0147] WD′ W = WD′ + L3-L1-L2 (7);

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

[0149] The back focus distance before and after the sealed window is determined according to the second formula, and the second formula is specifically:

[0150]

[0151] Among them, n W represents the refractive index of the sealing window;

[0152] The effective semi-aperture of the sealed window is determined according to the third formula, which is specifically:

[0153]

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

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

[0156]

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

[0158] Further, the angle of incidence is equal to the angle of emission; according to the angle of incidence and / or the angle of emission 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 specifically:

[0160]

[0161] Where Δ represents the lateral displacement of the dichroic mirror / reflector, τ represents the thickness of the dichroic mirror / reflector, Angle representing the incident angle to the dichroic mirror / reflector, n p Represents the refractive index of the dichroic / mirror.

[0162] In the embodiment of the present invention, Figure 7 As shown, the dichroic mirror and the reflector are placed at an angle of 45° in the optical path, that is, The dichroic mirror and the reflector are both set to have a rectangular aperture of D×1.414D. Considering the mechanical processing strength and component processability, the thickness of the dichroic mirror and the reflector is set to D / 8 to D / 2.

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

[0164]

[0165] Furthermore, according to the effective aperture of the convex surface of the plano-convex lens, the effective aperture of the narrow-band filter and the high-pass filter is determined, specifically:

[0166] 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.

[0167] Specifically, according to the light transmission direction in the Raman probe optical system, the aperture of the laser excitation optical path is set on the side of the narrowband filter close to the collimating lens, and the aperture of the signal collection optical path is set on the side of the high-pass filter close to the converging lens. Therefore, the effective apertures of the narrowband filter and the high-pass filter are the optical apertures of the laser excitation optical path and the signal collection optical path, respectively, that is, they are both set to be the same as the effective aperture D of the convex surface of the plano-convex lens. Considering the mechanical strength and processability of the components, the thickness of the narrowband filter and the high-pass filter are 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] Determine the initial structural parameters of each optical element in the Raman probe optical system, including:

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

[0171] Among them, the transmittance of a single high-pass filter within the Raman scattered light band is the OD value of the high-pass filter.

[0172] Specifically, according to application requirements, the intensity of Raman scattered light may be relatively weak in some application scenarios, so the signal-to-noise ratio of the detected Raman spectrum is relatively low, affecting the measurement accuracy of the Raman probe. In the prior art, the OD value of a single high-pass filter is 3 to 4. Increasing the OD value of the high-pass filter can improve the signal-to-noise ratio of Raman scattered light, but the difficulty of coating the high-pass filter will increase significantly.

[0173] Since the high-pass filter is located in the parallel light path, increasing the number of high-pass filters will not affect the focusing and collection effects of the optical system. Multiple high-pass filters can be stacked together for use, 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 cone constant is continuously adjusted in the optical design software, and the surface parameters are optimized by the cone constant and the spot radius that minimize the RMS value of the spot radius, including:

[0175] In the optical design software, the cone constant when the convex surface of the plano-convex lens is spherical is taken as the center and increases or decreases in sequence with a preset interval as the step size.

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

[0177] In the embodiment of the present 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 numerical aperture of the collimating fiber is 0.22, the numerical aperture of the collecting fiber is 0.22, the numerical aperture of the laser focusing and the Raman scattered light collection are both 0.22; the working distance of the collimating lens is 9.5mm, and the working distance of the converging lens is 9.5mm; the wavelength of the excitation light emitted by the laser is 785nm, and the wavelength band of the Raman scattered signal light is 795nm-1145nm, and the wave number range of the corresponding Raman frequency shift is 160cm -1 -4005cm -1 ; The total length of the optical part in the Raman probe optical system is 100 mm, that is, the straight-line length between the end of the transmitting optical fiber close to the collimating lens and the end of the substance to be measured close to the sealing window is 100 mm; the diameter of the optical part in the Raman probe optical system does not exceed 25.4 mm; 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, it is known that the refractive index of fused silica is n=1.45, and the center thickness of the plano-convex lens is t=3 mm. According to formula (2), the specific value of the distance d′ between the image side principal point and the rear surface of the plano-convex lens can be calculated.

[0180] Specifically,

[0181] It is known that the working distance WD′ of the convex surface of the plano-convex lens is 9.5, and 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′=11.57 mm.

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

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

[0185] After obtaining that the effective aperture of the convex surface of the plano-convex lens is 5.22 mm, an assembly margin of the structural parts is reserved and the plano-convex lens is set to 6 mm.

[0186] When k=0, the value of the curvature radius 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 the effective light aperture of the narrowband filter and the high-pass filter are set to be the same as those of the plano-convex lens; and the thickness of the narrowband filter and the high-pass filter is set to 2 mm.

[0189] When setting the initial structural parameters of the dichroic mirror and the reflector, the rectangular apertures of the dichroic mirror and the reflector are calculated to be 6 mm × 8.5 mm according to D × 1.414 D. The thickness of the dichroic mirror and the reflector are both set to 2 mm, 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, the specific value of the effective light semi-aperture a of the focusing lens plane is calculated according to formula (10).

[0192] Specifically,

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

[0194] Specifically,

[0195] After determining that the effective semi-aperture of the sealed window is 1.69 mm, according to The effective aperture of the sealing window is calculated, the assembly margin of the structural parts is reserved, and the outer diameter of the sealing window is set to 4.5 mm and the thickness of the sealing window is set to 2 mm.

[0196] Finally, the working distance of the sealing window is determined according to formula (7) and formula (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. The OD value of the currently more mature commercial high-pass filter in this embodiment can be greater than 3 for the band corresponding to the Raman scattered signal light. Therefore, in this embodiment, two high-pass filters with the same optical parameters are selected for superposition and the spacing between the high-pass filters is set to 1 mm.

[0199] In this embodiment, it is known that the total length of the optical part is 100 mm, the spacing from the focusing lens to the dichroic mirror is 55 mm, the spacing from the dichroic mirror to the first high-pass filter is 10 mm, and the spacing from the reflector to the narrow-band filter is 15 mm.

[0200] It is known 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 spacing from the dichroic mirror to the reflector is given to be 12 mm.

[0201] According to the above initial structural parameters, a simulation model of the Raman probe optical system is built in the ZEMAX optical design software. In the ZEMAX optical design software, the total length of the optical part 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 actual design scenario requirements.

[0202] like Fig. 9 As shown, when optimizing the surface parameters of the convex surface of the plano-convex lens, a value of k is given each time, and it is increased or decreased in steps of 0.1 with 0 as the center;

[0203] Taking the minimum RMS value of the spot radius output by the simulation model as the goal, and the convex curvature radius R of the plano-convex lens as the variable, the R value and RMS value corresponding to each k are obtained;

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

[0205] In this embodiment, according to Fig. 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 curvature radius R is 5.29 mm, and the RMS value of the spot radius is 9.979 μm.

[0206] After the surface parameter optimization is completed, the final structure of the Raman probe optical system is as follows: Fig.10 As shown, the overall spatial size of its optical part is less than 7.5mm (X) × 21.5mm (Y) × 100mm (Z).

[0207] Further, in an embodiment of the present invention, if Fig.11 As shown, at room temperature of 20°C, according to the spot diagram of the laser focused spot, it can be obtained that the RMS value of the spot radius is 9.979 μm.

[0208] like Fig.12 As shown, at room temperature of 20°C, the spot diagram of the light spot collected according to the Raman scattering signal can be obtained, and the RMS value of the spot radius is 20.02μm.

[0209] like Fig.13As shown, 4J32 alloy is used as the optical element support structure of the Raman probe. At a low temperature of -180°C, according to the point diagram of the laser focused spot, it can be obtained that the RMS value of the spot radius is 11.847 μm.

[0210] like Fig.14 As shown, 4J32 alloy is used as the optical element support structure of the Raman probe. At a low temperature of -180°C, the spot diagram of the light spot collected according to the Raman scattering signal can be obtained, and the RMS value of the spot radius is 23.602μm.

[0211] Therefore, the Raman probe uses the same lens material and matches the structural material with a similar thermal expansion coefficient, which can achieve athermalization over a wide temperature range, and the optical performance of the Raman probe hardly changes.

[0212] Therefore, in addition to being usable in a wide temperature range, the Raman probe optical system of the present invention can also be directly placed in a low-temperature environment for use after the Raman probe is assembled and adjusted at room temperature, eliminating the trouble 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 through Gaussian optical formulas.

[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, thereby facilitating adaptation with different emission or collection optical fibers and improving 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 element can be freely set within a certain range, which is helpful to match different application scenarios.

[0216] The number of high-pass filters in 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 work stably within a wide temperature range, and after being assembled and adjusted at room temperature, it can be directly placed for use at low temperature without any adjustment.

[0218] In the Raman probe optical system of the present invention, the collimating lens, the converging lens and the focusing lens adopt plano-convex lenses with completely identical optical parameters, which has advantages in cycle and cost in batch processing.

[0219] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function according to the embodiment of the present invention is generated in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable devices. The computer instructions can be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions can be transmitted from a website site, a computer, a server or a data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode to another website site, computer, server or data center. 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 a data center that includes one or more available media integration. The available medium can be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid-state hard disk Solid State Disk (SSD)), etc.

[0220] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for designing a Raman probe optical system, characterized in that: The Raman probe optical system comprises a sealed tube shell, one end of which is embedded with a sealed window, and the other end of which is penetrated by a transmitting optical fiber and a collecting optical fiber; it also comprises a transmitting optical path formed by a collimating lens, a narrow-band filter and a reflector arranged in sequence inside the sealed tube shell and cooperating with the transmitting optical fiber; and a dichroic mirror coaxial for transmitting and receiving, 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 sealed window and the dichroic mirror; Based on the Gaussian optical formula, the initial structural parameters of each optical element in the Raman probe optical system are determined according to the 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 include the surface parameters of the convex surface of the plano-convex lens, the effective aperture of each optical element, and the distance between two adjacent optical elements; the plano-convex lens includes the collimating lens, the converging lens and the focusing lens; the surface parameters include the radius of curvature and the cone constant when the convex surface of the plano-convex lens is spherical; Building a simulation model of the Raman probe optical system in optical design software according to the initial structural parameters; Taking the minimum RMS value of the spot radius output by the simulation model as the goal, the cone constant is continuously adjusted in the optical design software, and the surface parameters are optimized by the cone constant and the curvature radius that minimize the RMS value of the spot radius; The initial structural parameters are updated according to the optimized surface parameters to obtain the final structural parameters of the Raman probe optical system.

2. The method for designing a 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 angle of the incident angle and / or the exit angle of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector; 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, the initial structural parameters of each optical element in the Raman probe optical system are determined, specifically including: Determine the effective aperture and surface parameters of the convex surface of the plano-convex lens according to the obtained numerical aperture, working distance, lens center thickness and refractive index of the plano-convex lens; Determine the effective light-clearance semi-aperture of the sealing window and the working distance of the sealing window according to 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-clearance aperture of the convex surface of the plano-convex lens; Determining the lateral displacement of the dichroic mirror / reflector according to the angle of incidence and / or emission angle of the dichroic mirror / reflector, the thickness of the dichroic mirror / reflector, and the refractive index of the dichroic mirror / reflector; Determine the effective light apertures of the narrowband filter and the high-pass filter according to the effective light aperture of the convex surface of the plano-convex lens; The spacing between two adjacent optical elements is determined according to the size of the probe, the working distance of the plano-convex lens, the gap distance between the sealing window and the focusing lens, and the thickness of each of the optical elements.

3. The method for designing a Raman probe optical system according to claim 2, characterized in that: According to the obtained numerical aperture, working distance, lens center thickness and refractive index of the plano-convex lens, the effective aperture and surface parameters of the convex surface of the plano-convex lens are determined, specifically including: Determining the distance between the image-side principal point and the rear surface of the plano-convex lens according to the ratio of the center thickness of the plano-convex lens to the refractive index of the plano-convex lens; Determine the image-side focal length of the plano-convex lens according to the sum of the distance between the image-side principal point and the rear surface and the working distance of the plano-convex lens; Determine the effective aperture of the convex surface of the plano-convex lens according to the product of twice the image-side focal length and 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; Combined with the vector height equation of the quadratic surface, the curvature radius and the cone constant are used to represent the surface shape of the convex surface of the plano-convex lens. When the convex surface of the plano-convex lens is spherical, the curvature radius and the cone constant are used as the surface shape parameters of the convex surface of the plano-convex lens.

4. The method for designing a Raman probe optical system according to claim 3, characterized in that: According to 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 clearance aperture of the convex surface of the plano-convex lens, the effective light clearance semi-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, wherein the first formula is specifically: <h2 style=";text-align:left;direction:ltr">WD′<h2 style=";text-align:left;direction:ltr"> W <h2 style=";text-align:left;direction:ltr"> =WD′+L3-L1-L2; Among them, WD′ W represents the working distance of the sealing window, WD′ represents the working distance of the focusing lens, L3 represents the back focus distance before and after the sealing window is set, L1 represents the gap distance between the sealing window and the focusing lens, and L2 represents the thickness of the sealing window; The back focus distance before and after the sealing window is determined according to a second formula, wherein the second formula is specifically: Among them, n W represents the refractive index of the sealing window; The effective semi-aperture of the sealing window is determined according to the third formula, and the third formula is specifically: Among them, a W represents the effective semi-aperture of the sealing window, and a represents the effective semi-aperture of the focusing lens plane; The effective semi-aperture of the focusing lens plane is determined according to the fourth formula, and the fourth formula is specifically: 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.

5. The method for designing a Raman probe optical system according to claim 2, characterized in that: The incident angle is equal to the exit angle; and according to the incident angle and / or the exit angle 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 comprising: The lateral displacement of the dichroic mirror / reflector is determined according to the fifth formula, which is specifically: Wherein, Δ represents the lateral displacement of the dichroic mirror / reflector, τ represents the thickness of the dichroic mirror / reflector, represents the angle of incidence of the dichroic mirror / mirror, n p represents the refractive index of the dichroic mirror / mirror.

6. The method for designing a Raman probe optical system according to claim 2, characterized in that: According to the effective aperture of the convex surface of the plano-convex lens, the effective apertures of the narrow-band filter and the high-pass filter are determined, specifically: The effective light apertures of the narrowband filter and the high-pass filter are set to be the same as the effective light aperture of the convex surface of the plano-convex lens.

7. The method for designing a 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 set; Determining the initial structural parameters of each optical element in the Raman probe optical system also includes: The number of high-pass filters to be set is determined according to the optical density value of the acquired Raman scattered light and the transmittance of the single high-pass filter within the Raman scattered light band.

8. The method for designing a Raman probe optical system according to claim 1, characterized in that: Taking the minimum RMS value of the spot radius output by the simulation model as the goal, the cone constant is continuously adjusted in the optical design software, and the surface parameters are optimized by the cone constant and the curvature radius that minimize the RMS value of the spot radius, specifically including: In the optical design software, the cone constant when the convex surface of the plano-convex lens is spherical is taken as the center, and the preset interval is used as the step length to increase or decrease in sequence; A cone constant that minimizes the RMS value of the spot radius output by the simulation model is determined, the cone constant is used as the optimized cone constant, and the curvature radius corresponding to the cone constant is used as the optimized curvature radius.

9. A Raman probe optical system, characterized in that: It comprises a sealed tube shell, one end of which is embedded with a sealed window, and the other end of which is penetrated by a transmitting optical fiber and a collecting optical fiber; it also comprises a transmitting optical path formed by a collimating lens, a narrow-band filter and a reflector arranged in sequence inside the sealed tube shell and cooperating with the transmitting optical fiber; and a dichroic mirror coaxial for transmitting and receiving, 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 sealed window and the dichroic mirror; The sealing window is made of sapphire; The collimating lens, the narrow-band filter, the reflector, the dichroic mirror, the high-pass filter and the converging lens are all made of fused quartz; 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 plano-convex lenses of the same model.

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