Effect of dimensions on thermal deformation of high reflectance sapphire mirrors under high power laser irradiation
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摘要: 为了进一步减小白宝石（Al2O3）高反镜在强光辐照下的热变形，提高光束质量，研究了白宝石高反镜厚度、直径尺寸对热变形的影响。采用以极坐标表示的热传导方程和热变形公式来描述白宝石高反镜的温度场分布和位移场分布；在有限元分析软件中建立数值计算模型，并计算了不同厚度、直径尺寸下的温度场和位移场，得到了热变形随厚度尺寸和直径尺寸变化的规律。结果表明，影响白宝石高反镜反射面峰谷值变化的主要因素是温度，而尺寸变化对温度和刚度均有影响；选择合适的高反镜直径和厚度尺寸，可以有效降低镜面温升，同时得到合适的轴向结构刚度，从而减小反射镜镜面热变形。该研究结果对强光辐照下白宝石高反镜尺寸设计和选择具有一定的参考价值。Abstract: In order to reduce thermal deformation of high reflectance sapphire mirrors under high power laser irradiation and improve the beam quality, effect of the diameter and thickness on thermal deformation of the high reflectance mirror was studied. The heat conduction equation expressed in polar coordinate and the thermal deformation formula were used to describe the distribution of the temperature field and the displacement field of the sapphire mirror. Then, the numerical calculation model was built with the finite element analysis software and the temperature field and displacement field in different thickness and diameter was calculated. The thermal deformation with respect to the thickness and diameter was obtained. The results indicate that the main factors affecting the PV value of the sapphire mirror surface is the temperature variation and the change of the size has effect on both temperature and stiffness. Appropriate size and thickness effectively reduce the rise of mirror's temperature and keep suitable axial structural stiffness, and thus the thermal deformation of the reflective mirror is decreased. The study results are useful for the size determination and selection of high reflectance sapphire mirrors under high power laser irradiation.
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