<title>Optical performance of bimetallic mirrors under thermal environment</title>

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 environment used in this study is a unit thermal soak. 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 polating material, plating thickness, and the mirror substrate shapes materials. The optimum plating thickness combinations were determined based on plating material and mirror substrate with temperature difference. The results were compared with the optical surface errors and the corrected surface errors. The results indicate that there does not exist a definitive common rule for the optimum, but a detailed analysis such as presented herein is generally needed to design bimetallic mirrors in a thermal environment.