Study On Thermal Distortion Control Of Deformable Mirror For Large Aperture Telescope Adaptive Optical System

Adaptive optical system is a key technology to correct the imaging error of a largeaperture telescope.To high-resolution and high signal-to-noise ratio images,improving the thermal distortion of deformable mirrors is an effective means to improve the correction accuracy of an adaptive optical system,so it becomes the focus of adaptive optical system design.Based on the 39-unit drive deformable mirror developed by the Institute of Optics and Electronics,Chinese Academy of Sciences,this thesis studies the control of thermal distortion of the deformable mirror.In order to reduce the interference of traditional thermal control devices on optical systems and reduce the difficulty of optical-mechanical-thermal integrated optimization.Inspired by the research status of porous and fractal structures,which have better improvement on the thermal characteristics of objects,it was proposed to introduce these two self-cooling microstructures into deformable mirrors,respectively.The effects of these two microstructures on the heat transfer characteristics of deformable mirrors were discussed,and the self-cooling microstructures suitable for deformable mirrors were obtained by comparative analysis.Firstly,the thermal-mechanical coupling simulation was carried out for the deformable mirror with a porous structure.The results showed that due to the thin size of the deformable mirror,the closed-hole structure has a limited ability to optimize the temperature control of the deformable mirror.The half-through-hole structure could greatly optimize the thermal distortion of the mirror,and the optimization ability increased with the decrease of the aperture.Based on the calculation of grey correlation analysis,the distribution of porous structure has the greatest influence on the thermal distortion of the mirror surface of the deformable mirror,followed by the aperture,and finally the aperture.However,the porous structure will have a great impact on the overall structure of the deformable mirror,and the introduction of large new distortion was not recommended.Secondly,the thermal-mechanical coupling simulation was carried out for the deformable mirror with fractal micro-convex structure.The results showed that the uniform distribution of fractal structure was the best way to improve the thermal distortion of the deformable mirror.The thermal distortion of the mirror surface of the deformable mirror changes linearly with the specific surface area of the fractal structure;increasing the thickness of the fractal structure can effectively reduce the thermal distortion of the deformable mirror.Based on the grey correlation analysis,the specific surface area of the structure has the greatest impact on the thermal distortion of the mirror,followed by the thickness,and finally the distribution.At the same time,the introduction of fractal structure has little effect on the overall structure of the deformable mirror.Finally,compared the effects of two microstructures on the thermal characteristics of the deformable mirror,it was concluded that the fractal self-cooling microstructure was suitable for the thermal control microstructure design of the deformable mirror.Therefore,combined with the existing test conditions,the numerical simulation method of the thermal characteristic of the fractal structures deformable mirror in this paper was verified.The results showed that the relative error between the measured point temperature of each group of the test model and the simulation results was within 3.2 %-6.7 %,which verifies the accuracy of the simulation results of the thermal characteristics of the fractal structure deformable mirror.The surface measuring point temperature of the test model with fractal structure was 3 ? – 4 ? lower than that of the model without fractal structure,which was close to the simulation results.It was verified that the fractal structure can enhance the heat dissipation capacity of the deformation mirror and reduce the thermal distortion of the mirror.In this thesis,the research method of introducing microstructure into the deformable mirror and improving the heat dissipation characteristics of the mirror by designing the microstructure parameters of the deformable mirror was proposed,which can effectively reduce the deformation of the mirror surface of the deformable mirror.The additional heat dissipation device is not needed,which is conducive to reducing the thermal control difficulty of the deformable mirror and provides a new idea and theoretical reference for the thermal control design of the deformable mirror.