Optical performance of bimetallic mirrors in thermal environments

Abstract

Evaluation of the optical performances of bimetallic mirrors with various substrate shapes was conducted using the finite element analysis program, SDRC-IDEAS. In these analyses, two different plating materials, nickel and aluminum were considered for an aluminum and a beryllium mirror substrate. Thermal environments used in this study are: a unit thermal soak (temperature difference), an axial temperature distribution, and radial temperature distributions on the mirror substrate. The goal of this study is to optimize the optical surface quality for various plating thicknessess. Surface errors, individual aberration terms, such as piston, tilts, focus and other aberrations were obtained by the program PCFRINGE. It was found that the optical performances of bimetallic mirrors depend on the plating material, plating thickness, and the mirror substrate materials. The optimum plating thickness combinations were determined based on plating material and mirror substrate with variation of temperature distributions. The results were compared with the optical surface errors and the corrected surface errors. The results indicate that there does not exist a definite common rule for the optimum, but a detailed analysis such as presented herein is generally needed to design bimetallic mirrors in a thermal environment.