一种大口径平面镜支撑结构的仿真与实验

Simulation and Experiment of A Large Aperture Flat Mirror Support Structure

为提高600 mm大口径立式平面镜沿光轴旋转90°后的表面面型测量精度,对多孔支撑结构下5种不同材料的平面镜重力变形进行有限元仿真分析,并通过实验测量探究旋转后的静置时间对面型精度的影响等问题。结果表明,该多孔支撑结构下的平面镜表面由重力导致的轴向变形量不超过14 nm,满足精度要求。该多孔结构支撑的平面镜沿光轴旋转90°静置1 h后达到稳定状态,与静置2 h后的面型结果PV值仅相差0.337 nm,RMS值相差0.081 nm,实验探究了静置时间对面型结果的影响。研究发现,在至多去除6%外口径的条件下可以大幅降低平面镜表面面型PV值,PV值降低超过50 nm,由此提出一种制造大口径平面镜时通过设置支撑结构缓冲区以提高面型精度的方法,可以有效提高大口径平面镜的面型精度。

In order to improve the measurement accuracy of the surface profile of a 600 mm large diameter vertical plane mirror rotated 90°along the optical axis,the finite element simulation analysis of the gravity deformation of the plane mirror with five different materials under the porous support structure was carried out,and the influence of the standing time after rotation on the surface profile accuracy was explored through the experimental measurement.The results show that the axial deformation of the plane mirror surface caused by gravity under the po⁃rous support structure is less than 14 nm,which meets the accuracy requirements.The planar mirror supported by the porous structure rotated 90°along the optical axis and reached a stable state after standing for 1 h.The PV and RMS values of the planar mirror supported by the porous structure were only 0.337 nm and 0.081 nm different from the planar mirror results after standing for 2 h.The influence of the standing time on the planar mirror results was explored.Then,it is found that the PV value of the surface profile of the plane mirror can be greatly reduced under the condition of removing at most 6%of the outer diameter,and the PV value can be reduced by more than 50 nm.A method is proposed to im⁃prove the profile accuracy of the large diameter plane mirror by setting the buffer of the supporting structure,which can effectively improve the profile accuracy of the large diameter plane mirror.