Stress-free overclad tuning method for tunable off-axis beam expander system

Abstract

The application discloses a stress-free assembly method for an adjustable focus off-axis beam expanding system, which comprises the following steps: aging treatment during structure processing, glue injection and solidification of the structure and optical components, stress release, structure mounting surface covering and constant force fastening, etc. The application realizes stress-free assembly of the adjustable focus off-axis beam expanding system which comprises two plane mirrors, one secondary mirror, one primary mirror and a mirror frame, and a truss structure, wherein the system wavefront RMS change is less than 10% after environmental test, meanwhile, the assembly process is controllable, and the efficiency of optical mechanical system assembly is improved.

Description

Technical Field

[0001] This invention relates to the assembly and adjustment of optomechanical systems, and in particular to a stress-free assembly and adjustment method for an adjustable focus off-axis beam expander system, which is mainly used for rapid assembly and adjustment of optomechanical systems such as tracking, aiming and emission under different operating conditions. Background Technology

[0002] A typical laser beam emitted by a laser has a certain divergence angle. In fields such as laser transmission systems, it is necessary to expand the laser beam to obtain a large-aperture output spot. Off-axis beam expanders have the advantages of no central obstruction and high light energy utilization efficiency. They can expand the beam of powerful lasers, increase the effective range of the laser beam on the target, and also compress the laser divergence angle, improving the efficiency of the laser beam. Compared with coaxial systems, off-axis beam expanders have the advantages of no central obstruction and high light energy utilization efficiency. However, during the assembly and adjustment process of off-axis beam expanders, under extreme operating conditions, the accuracy and consistency of the spatial pose error of optical components may be affected, leading to changes in image quality. Furthermore, the assembly and adjustment cycle is long. Summary of the Invention

[0003] This invention addresses the problems of poor stability and long adjustment cycles in existing multi-reflector off-axis beam expanders under different operating conditions. It provides a stress-free bonding and adjustment method for an adjustable-focus off-axis beam expander, aiming to improve the stability of the off-axis beam expander under different operating conditions, increase the assembly and adjustment efficiency, and thus improve the laser beam transmission quality and focusing capability.

[0004] The technical solution adopted in this invention is as follows:

[0005] A stress-free assembly and adjustment method for an adjustable-focus off-axis beam expander system, wherein the structural components of the adjustable-focus off-axis beam expander system include a first plane mirror, a second plane mirror, a secondary mirror, a primary mirror, a focusing mechanism, and a truss. The components are sequentially arranged along the incident light direction, consisting of the first plane mirror, the second plane mirror, the secondary mirror, and the primary mirror. The secondary mirror is laterally fixed to the focusing mechanism. All components are fixed by a mirror frame and a truss, wherein the mirror frame and truss are made of a low-expansion metal material. The method is characterized by the following steps:

[0006] 1) Aging treatment during structural component processing: To release the stress introduced by structural component processing, screw tightening, and welding, sufficient aging treatment is required as follows:

[0007] First, perform deep cryogenic treatment to improve grain uniformity and reduce deformation. Depending on the material, use either the "immersion method" at approximately -190°C or the "air cooling method" at approximately -150°C for 0.5 hours.

[0008] Then, rapid high-temperature treatment was performed at 200℃ for 1 hour.

[0009] Finally, the stabilization treatment was carried out at 98℃ for 10-12 hours.

[0010] 2) Structural and optical components are glued and cured: In a high-cleanliness environment, after the optical component axis is aligned with the lens frame axis, it is installed in the lens mount and fixed by glue injection. There are 8 glue injection points evenly distributed on the side of the lens frame, and each glue injection point has 3 glue injection holes, for a total of 24 glue injection holes. Ensure that the glue injection amount is consistent at each point, totaling 50g. During the glue injection process, it must not overflow above the lens surface.

[0011] 3) Stress relief during assembly: The entire component undergoes temperature cycling and vibration treatment. Test conditions:

[0012] Temperature cycle: -45℃~75℃, time: 24h, heating rate not greater than 3℃ / h;

[0013] According to the installation method during use, drive a truck on a gravel road for 1000-1200km at a speed of not less than 30km / h;

[0014] 4) Structural component mounting surface mating, i.e., grinding the mounting surface, on the one hand, removes residual singularities from the mounting surface to ensure a better fit; on the other hand, by grinding the mounting surface, the spatial pose error of the optical components during assembly is adjusted to obtain the best image quality. The method of adding shims must not be adopted.

[0015] 5) Constant force fastening: The frame and truss are fastened with screws. There are 3 mounting surfaces evenly distributed on the end face of the frame, with 2 screw holes on each mounting surface. Use a calibrated torque wrench to tighten. Tighten to the specified torque according to the bolt specifications and installation requirements to ensure that the tightening force is consistent at each point, and mark the points for inspection.

[0016] The surface shape error RMS accuracy of the two plane mirrors, one secondary mirror and one primary mirror is required to be better than 0.03λ, and the system wavefront RMS is better than 0.2λ; λ = 632.8nm.

[0017] The technical effects of this invention are as follows:

[0018] This invention effectively ensures the stability of assembly and adjustment by effectively releasing the stress generated during the manufacturing and assembly of each component before precision assembly and by ensuring consistent stress through constant force fastening after assembly, as well as by adjusting the position and orientation errors of optical components through surface finishing. This reduces the rework rate of the system after environmental testing and improves the system assembly and adjustment efficiency. Attached Figure Description

[0019] Figure 1 Schematic diagram of an adjustable focus off-axis beam expander system

[0020] Figure 2 Schematic diagram of the layout of the adjustable focus off-axis beam expander system

[0021] Figure 3 The main process of the stress-free bonding and assembly method provided by the present invention

[0022] Figure 4 Schematic diagram of the glue injection hole structure for the eyeglass frame

[0023] Figure 5 Schematic diagram of the mounting surface structure

[0024] Figure 6 RMS waveform of the system wavefront based on this method.

[0025] Figure 7 The wavefront RMS plot of the system after environmental testing based on this method. Detailed Implementation

[0026] To make the implementation scheme of the present invention clearer, it will be described clearly and completely below with reference to the accompanying drawings. The embodiments described are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, without making any inventive step, all other embodiments fall within the scope of protection of the present invention.

[0027] Example

[0028] A stress-free bonding and adjustment method for an adjustable-focus off-axis beam expander system, please refer to [link / reference]. Figure 1 The adjustable-focus off-axis beam expander system comprises a first plane mirror 1, a second plane mirror 2, a secondary mirror, a primary mirror, a focusing mechanism, and a truss. Along the incident light direction, the components are sequentially arranged as the first plane mirror 1, the second plane mirror 2, the secondary mirror, and the primary mirror. The secondary mirror is laterally fixed to the focusing mechanism. All components are secured by a frame and a truss, which are made of low-expansion metal. The method includes the following steps:

[0029] 1) Aging treatment during structural component manufacturing: The surface shape error RMS accuracy of the two plane mirrors, one secondary mirror, and one primary mirror is required to be better than 0.03λ, and the system wavefront RMS is required to be better than 0.2λ; λ = 632.8nm. See also Figure 2 ,

[0030] To release the stress introduced by structural component machining, screw tightening, and welding, sufficient aging treatment is required as follows:

[0031] First, perform deep cryogenic treatment to improve grain uniformity and reduce deformation. Depending on the material, use either the "immersion method" at approximately -190°C or the "air cooling method" at approximately -150°C for 0.5 hours.

[0032] Then, rapid high-temperature treatment was performed at 200℃ for 1 hour.

[0033] Finally, the stabilization treatment was carried out at 98℃ for 10-12 hours.

[0034] 2) Adhesive injection and curing of structural and optical components: See Figure 4 In a high-cleanliness environment, after the optical element axis is aligned with the lens frame axis, it is installed in the lens mount and fixed by glue injection. There are 8 glue injection points evenly distributed on the side of the lens frame, and each glue injection point has 3 glue injection holes, for a total of 24 glue injection holes, to ensure that the glue injection amount at each point is consistent, totaling 50g. During the glue injection process, it must not overflow above the mirror surface.

[0035] 3) Stress relief during assembly: The entire component undergoes temperature cycling and vibration treatment. Test conditions:

[0036] Temperature cycle: -45℃~75℃, time: 24h, heating rate not greater than 3℃ / h;

[0037] According to the installation method during use, drive a truck on a gravel road for 1000-1200km at a speed of not less than 30km / h;

[0038] 4) The mounting surface of structural components is fitted, i.e., the mounting surface is ground. This serves two purposes: firstly, to remove any residual singularities from the machining process on the mounting surface, ensuring a closer fit; secondly, by grinding the mounting surface, the spatial pose error of the optical components during assembly is adjusted to obtain optimal image quality. Adding shims is not permitted. See [link / reference]. Figure 5 ;

[0039] 5) Constant force fastening: The frame and truss are fastened with screws. There are 3 mounting surfaces evenly distributed on the end face of the frame, with 2 screw holes on each mounting surface. Use a calibrated torque wrench to tighten. Tighten to the specified torque according to the bolt specifications and installation requirements to ensure that the tightening force is consistent at each point, and mark the points for inspection.

[0040] In this embodiment, the specific layout and parameters are as follows: the primary mirror is an off-axis parabolic mirror with a radius of 1290 mm and a light-transmitting diameter of 320 mm; the secondary mirror is a convex off-axis hyperboloid mirror with a radius of 322.5 mm and a light-transmitting diameter of 82 mm; the distance between the primary and secondary mirrors is 506.22 mm. The light-transmitting diameters of plane mirror 1 and plane mirror 2 are 90 mm.

[0041] After system assembly, the system wavefront RMS was performed. (Participants...) Figure 6 .

[0042] Environmental testing was then conducted. After the tests, the RMS value of the system wavefront was measured using an interferometer. The change in RMS value compared to before the tests was less than 10%. (See appendix) Figure 7 .

[0043] Experiments show that the stress-free bonding and adjustment method of the adjustable focus off-axis beam expander system of the present invention can effectively ensure the stability of the assembly and adjustment by effectively releasing the stress generated during the manufacturing and assembly of each component before precision assembly and by ensuring consistent force after assembly through constant force fastening, as well as adjusting the position and orientation error of optical components by grinding the mounting surface. This reduces the rework rate of the system after environmental testing and improves the system assembly and adjustment efficiency.

Claims

1. A stress-free assembly and adjustment method for an adjustable-focus off-axis beam expander system, wherein the structural components of the adjustable-focus off-axis beam expander system include a first plane mirror (1), a second plane mirror (2), a secondary mirror, a primary mirror, a focusing mechanism, and a truss, which are sequentially arranged along the incident light direction, the secondary mirror being fixed to the focusing mechanism by a lateral fixing method, and all parts being fixed by a mirror frame and a truss, wherein the mirror frame and truss are made of a low-expansion metal material, characterized in that... The method includes the following steps: 1) Aging treatment during structural component processing: To release the stress introduced by structural component processing, screw tightening, and welding, sufficient aging treatment is required as follows: First, perform deep cryogenic treatment to improve grain uniformity and reduce deformation. Depending on the material, use either the "immersion method" at a temperature of approximately -190℃ or the "air cooling method" at a temperature of approximately -150℃, and maintain the treatment time for 0.5 hours. Then, rapid high-temperature treatment was performed at 200℃ for 1 hour. Finally, the stabilization treatment was carried out at 98℃ for 10-12 hours. 2) Structural and optical components are glued and cured: In a high-cleanliness environment, after the optical component axis is aligned with the lens frame axis, it is installed in the lens mount and fixed by glue injection. There are 8 glue injection points evenly distributed on the side of the lens frame, and each glue injection point has 3 glue injection holes, for a total of 24 glue injection holes. Ensure that the glue injection amount is consistent at each point, totaling 50g. During the glue injection process, it must not overflow above the lens surface. 3) Stress relief during assembly: The entire component is subjected to temperature cycling and vibration treatment. Test conditions: temperature cycling: -45℃~75℃, time: 24h, heating rate not greater than 3℃ / h; according to the installation method during use, drive a truck on a gravel road for 1000-1200km at a speed of not less than 30km / h. 4) Structural component mounting surface mating, i.e., grinding the mounting surface, on the one hand, removes residual singularities from the mounting surface to ensure a better fit; on the other hand, by grinding the mounting surface, the spatial pose error of the optical components during assembly is adjusted to obtain the best image quality. The method of adding shims must not be adopted. 5) Constant force fastening: The frame and truss are fastened with screws. There are 3 mounting surfaces evenly distributed on the end face of the frame, with 2 screw holes on each mounting surface. Use a calibrated torque wrench to tighten. Tighten to the specified torque according to the bolt specifications and installation requirements to ensure that the tightening force is consistent at each point, and mark the points for inspection.

2. The stress-free bonding and assembly method for the adjustable focus off-axis beam expander system according to claim 1, characterized in that: The surface shape error RMS accuracy of the two plane mirrors, one secondary mirror and one primary mirror is required to be better than 0.03λ, and the system wavefront RMS is required to be better than 0.2λ; λ=632.8nm.

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