阅读说明：本技术 一种用于抽运激光系统光束整形的自由曲面透镜的优化设计方法 (Optimization design method of free-form surface lens for beam shaping of pumping laser system ) 是由 郝剑 翟跃阳 韩邦成 唐照建 刘颖 黄梓嫄 于 2020-08-26 设计创作，主要内容包括：本发明提出了一种用于抽运激光系统光束整形的自由曲面透镜的优化设计方法,基于光束质量分析仪采集的数据和Tracepro软件表面光源生成器功能的综合运用,建立模拟仿真光源,使其无限接近抽运激光光源的真实特性,在实现抽运激光系统模拟仿真的同时,可避免后续对激光的偏振状态、光束整形系统(自由曲面透镜、准直透镜)模拟仿真和优化设计时引入的误差；同时综合使用Tracepro软件中的Scheme宏语言和优化引擎After-scheme宏语言的功能,以优化变量(自由曲面透镜各控制点)为桥梁,建立优化通道,可实现对自由曲面透镜的自动优化设计,避免了模型导入导出的麻烦和复杂的计算过程。(The invention has proposed the optimization design method of the free-form surface lens used for pumping the laser system beam shaping, on the basis of the data that the quality analyzer of light beam gathers and comprehensive application of the function of the surface light source generator of the Tracepro software, set up the light source of analog simulation, make it infinitely close to the true characteristic of pumping the laser light source, while realizing the analog simulation of pumping the laser system, can avoid the error introduced while simulating simulation and optimizing the design to the polarization state, light beam shaping system (free-form surface lens, collimating lens) of the laser subsequently; meanwhile, the functions of the Scheme macro language in the Tracepro software and the optimization engine After-Scheme macro language are comprehensively used, optimization variables (control points of the free-form-surface lens) are used as bridges, an optimization channel is established, automatic optimization design of the free-form-surface lens can be realized, and the trouble of model import and export and the complex calculation process are avoided.)

1. A method for optimally designing a free-form surface lens for beam shaping of a pump laser system is characterized by comprising the following steps of: the method comprises the following specific steps:

(1) testing the pumping laser by adopting a beam quality analyzer to obtain the size, shape, central position, azimuth angle and power intensity distribution information of a light spot, and performing analog simulation on the laser light source based on Scheme macro language of Tracepro software and the function of a surface light source generator;

(2) introducing a designed free-form surface lens plan by an optimization engine (interactive Optimizer) function based on Tracepro software, adding segmentation points (segmentation points) to a designed free-form surface by utilizing a Toolbox function in the optimization engine, setting the segmentation points as optimization variables, setting an optimization range, setting a lens material based on the Optimizer function in the software, taking illumination uniform distribution as an optimization target, and performing first-step optimization design on the free-form surface lens;

(3) storing the result with the uniformity of more than 80% after the first-step optimization design, deriving discrete points of the free-form surface, extracting control points of the free-form surface, and finally fitting the extracted control points into a form of a quadratic B spline curve;

(4) writing a Scheme program of the structure, material and size of the free-form surface lens based on a Tracepro software Scheme macro language, setting control points of the free-form surface as variables, taking the values of the control points extracted in the step (3) as initial values of the variables, writing a program for optimizing the size, polarization characteristics and spacing of a target surface, and taking the curvature radius of the collimating lens as an optimization variable;

(5) based on an optimization engine in Tracepro software, the method also takes uniform illumination distribution as an optimization target, an After-Scheme program which takes a control point of a free-form surface as a variable is written in an Optimizer, a whole optimization channel is established with a Scheme macro language program by using the same optimization variable, automatic optimization of a free-form surface lens is realized, the optimization variable can be reduced for a part of the free-form surface corresponding to the uniformity of less than 90%, local optimization of the corresponding surface is carried out, and uniform shaping of a laser beam is finally realized.

(6) And (4) selecting a plano-convex lens as the collimating lens, placing the plano-convex lens at the position of the target surface in the step (5), deleting the target surface, and calculating the focal length of the convex lens to ensure that the uniformly shaped light rays can be emitted to the alkali metal air chamber in parallel through the collimating lens.

2. The method of claim 1, wherein the free-form lens for beam shaping in the pump laser system comprises: in the step (1), a Gaussian beam is not directly selected as an ideal light source to design a subsequent system, but a beam quality analyzer is adopted to test and collect the size, shape, central position, azimuth angle and power intensity distribution information of a light spot; secondly, inputting the acquired data based on the function of a Tracepro software surface light source generator, and operating to obtain a simulated laser light source; and then, rotating the laser light source, and adjusting parameters such as the size and the azimuth angle of a light spot to enable the light spot to be consistent with the tested light spot.

3. The method of claim 1, wherein the free-form lens for beam shaping in the pump laser system comprises: in the step (2), the surface type of the free-form surface lens plane diagram is designed according to the application requirement, and then optimization is realized by means of the optimization engine function of Tracepro software.

4. The method of claim 1, wherein the free-form lens for beam shaping in the pump laser system comprises: in the step (2) and the step (5), in order to avoid the step phenomenon of the optimized free-form surface, the variation range of the optimized variable does not exceed 0.1mm, and the segmentation point is extracted as the initial data of the automatic optimization of the system.

5. The method of claim 1, wherein the free-form lens for beam shaping in the pump laser system comprises: in the step (5), the functions of the project macro language in the Tracepro software and the optimization engine After-project macro language are comprehensively used, optimization variables (each control point of the free-form surface lens and the curvature radius of the collimating lens) are used as bridges, an optimization channel is established, and the optimization design of the free-form surface lens and the collimating lens can be realized.

6. The method of claim 1, wherein the free-form lens for beam shaping in the pump laser system comprises: in the step (5), the pumping laser system has a requirement on the size of light spots with uniformity higher than 90% and energy, and when an optimization target is set, illumination distribution curves (at least 6) and energy utilization rates at different positions are simultaneously used as optimization target values.

7. The method of claim 1, wherein the free-form lens for beam shaping in the pump laser system comprises: in the step (6), the design of a collimating mirror is aligned, a plano-convex lens is selected, after collimation optimization, light beam polarized atoms with the middle uniformity higher than 90% are selected, and peripheral light spots are abandoned.

Technical Field

The invention relates to the field of weak magnetic detection, in particular to an optimal design method of a free-form surface lens for shaping a laser beam of a pumping laser system, which can realize efficient and uniform distribution of the laser beam.

Background

The ultrahigh-sensitivity inertial measurement device based on the Serf state atoms can realize ultrahigh-sensitivity inertial measurement, greatly surpasses the sensitivity realized by the existing related measurement means, challenges the magnetic field and sensitivity limit, and enables people to obtain a new tool for knowing the world. The method mainly utilizes a pumping light system to polarize atoms, so that atomic spin is in a state capable of sensing angular velocity, the atomic spin state can be changed along with the atomic spin state under the action of external angular velocity, and angular velocity information is extracted by detecting the atomic spin state. In the system, parameters such as uniformity of light intensity distribution of pumping light, light efficiency and the like can influence the polarization efficiency of atoms and the sensitivity of the system, so that the research on a high-uniformity and high-efficiency pumping light shaping system is one of core problems of the device for improving the atomic polarization rate.

Currently, typical laser beam shaping methods are: diffractive optical elements, aspherical lens groups, birefringent lens groups, microlens arrays, liquid crystal spatial light modulators, free-form surface optical systems, and the like. And some methods have mature products of beam expanding and shaping systems on sale, but all the methods are ideal laser sources, and the light sources of a plurality of semiconductor lasers applied in the field are irregular, so that the light beam shaping design is required. The free-form surface lens has higher design freedom, and can realize the shaping design of uniform laser beams under the condition of only using a single lens, so the free-form surface lens has the advantages of simple system structure, high-efficiency light output, uniform radiation illumination and the like. With the improvement of the processing technology, particularly the rapid development of the 3D printing technology, the method has wide application prospect in the aspect of laser shaping. However, the design of the free-form surface lens is realized by combining methods such as calculation, fitting, modeling, simulation, optimization and the like at present, the process is complex and tedious, and the trouble of importing and exporting the model cannot be avoided; and the shaping system of the pumping laser system mainly adopts a mode of a lens group, so that the system is long and difficult to debug. Therefore, the patent provides an optimal design method of a free-form surface lens for shaping a pumping laser system, which avoids the traditional complex processes of calculation and model introduction and export during the design of the free-form surface lens and the difficult debugging condition, can realize the efficient and uniform shaping of the laser beam system by combining the optimization engine of Tracepro software and Scheme macro language, and simultaneously provides the optimal structural design of the pumping laser system by optimizing the alignment straight lens.

Disclosure of Invention

The invention aims to provide a method for optimally designing a free-form surface lens for realizing laser shaping aiming at the defects of the prior art, so as to realize efficient and uniform shaping of laser.

The purpose of the invention is realized by the following technical scheme: an optimal design method of a free-form surface lens for beam shaping of a pumping laser system comprises the following specific steps:

(1) testing the pumping laser by adopting a beam quality analyzer to obtain the size, shape, central position, azimuth angle and power intensity distribution information of a light spot, and performing analog simulation on the laser light source based on Scheme macro language of Tracepro software and the function of a surface light source generator;

(2) introducing a designed free-form surface lens plan by an optimization engine (interactive Optimizer) function based on Tracepro software, adding segmentation points (segment points) to a designed free-form surface by utilizing a Toolbox function in the optimization engine, setting the segmentation points as optimization variables, setting an optimization range, and performing first-step optimization design on the free-form surface lens by taking uniform illumination distribution as an optimization target and setting a lens material simultaneously on the basis of the Optimizer function in the software;

(3) storing the result with the uniformity of more than 80% after the first-step optimization design, deriving discrete points of the free-form surface, extracting control points of the free-form surface, and finally fitting the extracted control points into a form of a quadratic B spline curve;

(4) writing a Scheme program of the structure, material and size of the free-form surface lens based on a Tracepro software Scheme macro language, setting control points of the free-form surface as variables, taking the values of the control points extracted in the step (3) as initial values of the variables, writing a program for optimizing the size, polarization characteristics and spacing of a target surface, and taking the curvature radius of the collimating lens as an optimization variable;

(5) based on an optimization engine in Tracepro software, the method also takes uniform illumination distribution as an optimization target, an After-Scheme program which takes a control point of a free-form surface as a variable is written in an Optimizer, a whole optimization channel is established with a Scheme macro language program by using the same optimization variable, automatic optimization of a free-form surface lens is realized, the optimization variable can be reduced for a part of the free-form surface corresponding to the uniformity of less than 90%, local optimization of the corresponding surface is carried out, and uniform shaping of a laser beam is finally realized.

(6) And (4) selecting a plano-convex lens as the collimating lens, placing the plano-convex lens at the position of the target surface in the step (5), deleting the target surface, and calculating the focal length of the convex lens to ensure that the uniformly shaped light rays can be emitted to the alkali metal air chamber in parallel through the collimating lens.

Further, in the step (1), a Gaussian beam is not directly selected as an ideal light source to design a subsequent system, but a beam quality analyzer is adopted to test and collect the size, shape, central position, azimuth angle and power intensity distribution information of a light spot; secondly, inputting the acquired data based on the function of a Tracepro software surface light source generator, and operating to obtain a simulated laser light source; and then, rotating the laser light source, and adjusting parameters such as the size and the azimuth angle of a light spot to enable the light spot to be consistent with the tested light spot.

Further, in the step (2), the surface shape of the free-form surface lens plan is designed according to the application requirement, and then optimization is realized by means of the optimization engine function of the Tracepro software.

Further, in the step (2) and the step (5), in order to avoid the step phenomenon of the optimized free-form surface, the variation range of the optimized variable does not exceed 0.1mm, and the segmentation point (segment point) is extracted as the initial data of the automatic optimization of the system.

Further, in the step (5), the functions of the project macro language in the Tracepro software and the optimization engine After-project macro language are used comprehensively, optimization variables (each control point of the free-form-surface lens and the curvature radius of the collimating lens) are used as bridges, an optimization channel is established, and the optimization design of the free-form-surface lens and the collimating lens can be realized.

Further, in the step (5), the pump laser system has a requirement for the size of the light spot and the energy with uniformity higher than 90%, and when the optimization target is set, the illuminance distribution curves (at least 6) and the energy utilization rate at different positions are simultaneously used as the optimization target values.

Further, in the step (6), a plano-convex lens is selected according to the design of a collimating mirror, and after collimation optimization, light beam polarized atoms with the middle uniformity higher than 90% are selected, and peripheral light spots are abandoned.

Compared with the prior art, the method has the following advantages:

1. the laser light source simulation method of the free-form surface lens suitable for shaping the light beam of the pumping laser system can lead the simulation light source to be infinitely close to the real characteristic of the pumping laser light source, and avoids the error in the design of the subsequent optical system (the free-form surface lens and the collimating lens) while realizing the simulation of the pumping laser system.

2. The invention provides an optimal design method of a free-form surface lens suitable for shaping a light beam of a pumping laser system, which can realize efficient and uniform shaping of the light beam by using a single lens, simplify the system and realize large-size and efficient uniform illumination of the pumping laser system at a short distance.

3. The invention provides an optimization design method of a free-form surface lens suitable for shaping a beam of a pumping laser system, wherein the two-step optimization method avoids the complex processes of calculation, simulation, import and export, optimization and the like of the traditional design method.

Drawings

FIG. 1 is a flow chart of an optimal design method of the present invention;

FIG. 2 is a schematic diagram of control point extraction;

FIG. 3 is a schematic diagram of beam shaping extraction; in the figure: a is a free-form surface lens, and B is a collimating lens.

FIG. 4 is a free-form lens construction;

FIG. 5 is a diagram of a system structure and simulation (a) a system structure and (b) an optical simulation system; in the figure: 1-laser, 2-unit for adjusting polarization state, 3-beam shaping system, 4-target surface (alkali metal air chamber)

FIG. 6 is a graph of the optimized illuminance distribution at different positions;

fig. 7 is a diagram of light polarization analysis.

Detailed Description

The invention is further described in the following operational sequence in accordance with the flow chart in conjunction with the drawings:

as shown in fig. 1, the method for optimally designing a free-form surface lens for beam shaping of a pump laser system provided by the present invention comprises the following specific steps:

(1) testing the pumping laser by adopting a beam quality analyzer to obtain the size, shape, central position, azimuth angle and power intensity distribution information of a light spot, and performing analog simulation on the laser light source based on Scheme macro language of Tracepro software and the function of a surface light source generator; in the step, a Gaussian beam is not directly selected as an ideal light source to design a subsequent system, but a beam quality analyzer is adopted to test and collect the size, shape, central position, azimuth angle and power intensity distribution information of a light spot; secondly, inputting the acquired data based on the function of a Tracepro software surface light source generator, and operating to obtain a simulated laser light source; and then, rotating the laser light source, and adjusting parameters such as the size and the azimuth angle of a light spot to enable the light spot to be consistent with the tested light spot.

(2) The method comprises the steps that a free-form surface lens plan designed according to application needs is imported by an optimization engine (interactive Optimizer) function based on Tracepro software, a Toolbox function in the optimization engine is utilized, segmentation points (segment points) are added to a designed free-form surface and set as optimization variables, an optimization range is given, the variation range of the optimization variables does not exceed 0.1mm, the segmentation points (segment points) are extracted as initial data for automatic optimization of a system, the phenomenon that the optimized free-form surface has step is avoided, illumination is uniformly distributed as an optimization target based on the optimization engine (interactive Optimizer) function in the software, lens materials are set at the same time, and the free-form surface lens is subjected to first-step optimization design; the optimization method is a downhill simplex method, the optimization variables are points on the free-form surface, and the points on the free-form surface are fitted by a spline method inside the optimization method.

(3) Storing the result with the uniformity of more than 80% after the first-step optimization design, deriving discrete points of the free-form surface, extracting control points of the free-form surface, and finally fitting the extracted control points into a form of a quadratic B spline curve; the quadratic B-spline is closer to the same characteristic polygon than the cubic B-spline curve, and local optimization is easier to perform, so that the quadratic B-spline curve is selected to fit the extracted discrete points of the free-form surface for the requirements of Scheme programming. The fitting process is divided into two steps, firstly, the control point of the free-form surface is extracted from the discrete point, the schematic diagram is shown in figure 2, the first two data points are selected, and the two points are connected to form a straight line l₁Taking two more data points at k points apart and drawing a straight line l₂Taking a straight line l₁And l₂Point of intersection b₁Sequentially taking points b in the same way₂,b₃,…b_mIn 1, is_lUpper fetching point b₀So that the first data point is exactly the line segment b₀,b₁The middle point of (1), the following, and so on;

next, the control points are fitted to the form p (t) of a quadratic B-spline, i.e.:

p_n-1(t)＝0.5×(b_n-1+b_n+1-2b_n)t²+(b_n-b_n-1)t+0.5×(b_n-1+b_n)

wherein t is more than or equal to 0 and less than or equal to 1; p is a radical of_n(t) is the quadratic curve to be optimized, p_n-1(t) isp (t) an nth segment of quadratic B-spline curve, n is more than or equal to 1 and less than or equal to l, l is the number of quadratic B-spline curves and is an arbitrary integer more than or equal to 1, B_n-1，b_n+1，b_nIs a curve p _n-13 control points on (t).

And finally, writing a Scheme macro language program of the free-form surface lens in Tracepro software, writing attributes such as materials and the like, setting the control points as optimization variables, and taking the extracted control points as initial values so as to facilitate subsequent optimization iteration.

(4) Writing a Scheme program of the structure, material and size of the free-form surface lens based on a Tracepro software Scheme macro language, setting control points of the free-form surface as variables, taking the values of the control points extracted in the step (3) as initial values of the variables, writing a program for optimizing the size, polarization characteristics and spacing of a target surface, and taking the curvature radius of the collimating lens as an optimization variable; the simulation of the polarization beam splitter prism needs to add a plurality of layers of film materials which are alternately coated into the materials in advance, the film materials are ZnS and MgF2, the film materials are simulated into the effect of the polarization beam splitter prism in a mode of alternately coating a plurality of films, and finally the space between instruments is set as a variable and the variation range is set in consideration of the actual application requirement.

(5) Based on an optimization engine in Tracepro software, an After-Scheme program taking the control points of the free-form surface as variables is written in an Optimizer and combined with a Scheme macro language program, the optimization variables (the control points of the free-form surface lens and the curvature radius of the collimating lens) are used as bridges, a whole optimization channel is established, automatic optimization of the free-form surface lens is realized, the optimization variables can be reduced for the part of the free-form surface with the uniformity lower than 90%, the local optimization of the corresponding surface is carried out, and the uniform shaping of the laser beam is finally realized. The pumping laser system has requirements on light spots with uniformity higher than 90% and energy, and when an optimization target is set, illumination distribution curves (at least 6) and energy utilization rates at different positions are simultaneously used as optimization target values.

(6) As shown in fig. 3, a is a free-form surface lens, and B is a collimating lens; and (3) selecting a plano-convex lens as the collimating lens, placing the plano-convex lens at the position of the target surface in the step (5), deleting the target surface, aligning the design of the plano-convex lens, selecting light beam polarization atoms with the middle uniformity higher than 90% after collimation optimization, and discarding peripheral light spots. And meanwhile, calculating the focal length of the convex lens, reversely prolonging the incident beam, and regarding the focal length of the convex lens and the focal point of the optical axis as the focal point of the convex lens so as to ensure that the uniformly shaped light can be emitted to the alkali metal gas chamber in parallel through the collimating lens. The alkali metal gas cell can be arranged with a target surface on its upper surface, middle and lower surfaces respectively to detect the collimation of the light beam.

One specific application example of the present invention is as follows: a laser with a wavelength of 770nm of UligrainTeco is selected as a light source, the size of a polarization splitting prism is 25.4mm when a is b and c, the aperture D of a 1/4 wave plate is 25.4mm, the material of a free-form surface lens and a collimating lens is BK7, and an atomic gas cell is a 14mm alkali metal gas cell.

(1) The simulated light spots are elliptical light spots, the major axis is 3mm, and the minor axis is 2.5 mm;

(2) finally, 4 control points are extracted from the two free-form surfaces respectively;

(3) the designed free-form surface lens structure is shown in fig. 4, wherein the surface 1 and the surface 2 are both free-form surfaces, separate optimization is proposed during optimization, and the size after optimization is about 10mm by 4 mm;

(4) when the optimization target is set, the illuminance distribution curves (6) and the energy utilization rate at different positions are respectively used as target values of the free-form surface lens and the collimating lens, and based on the target values, the optimal design of the two lenses is realized. As shown in fig. 5, (a) is a structure diagram of an optical system, and (b) is a diagram of an optical analog simulation system, wherein a laser 1, a polarization state adjusting unit 2, a beam shaping system 3 and a target surface (an alkali metal gas chamber) 4 are connected in sequence; wherein, the position of the collimating lens is provided with full absorption at the rest positions for convenient observation, and the size of the collimating lens is about 16mm by 16mm through design;

(5) after the system simulation, the illuminance distribution at different positions is shown in fig. 6, and the calculation formula of the uniformity is as follows:

through calculation, the uniformity at different positions is larger than 90%, and the polarization analysis can realize the elliptical polarization state as shown in FIG. 7.

In summary, the present invention establishes an analog simulation light source based on the data collected by the beam quality analyzer and the comprehensive application of the function of the Tracepro software surface light source generator, so that the analog simulation light source can be infinitely close to the real characteristic of the pumping laser light source, and the analog simulation of the pumping laser system can be realized while the errors in the design of the subsequent optical system (free-form surface lens and collimating lens) can be avoided; meanwhile, the functions of a schema macro language in Tracepro software and an optimization engine After-schema macro language are comprehensively used, optimization variables (each control point of the free-form-surface lens and the curvature radius of the collimating lens) are used as bridges, an optimization channel is established, automatic optimization design of the control point of the free-form-surface lens and the curvature radius of the collimating lens can be realized, and the trouble of model import and export is avoided. The designed free-form surface lens can realize large-size and high-efficiency uniform illumination of the pumping laser system at a short distance.

The above-described embodiments are intended to illustrate rather than to limit the invention, and any modifications and variations of the present invention are within the spirit of the invention and the scope of the appended claims.