Polishing of supersmooth metal mirrors

This work has resulted in clarifying the fabrication technology that is required for high energy 10.6-microm laser programs now underway. Polishing and coating techniques for metallic substrates were developed, and the deposition of metallic coatings to reproducibly create metal mirror surfaces with low absorptance at a wavelength of 10.6 microm was investigated. The basic task was one of expanding and transferring to metal substrates the technology developed by Bennett and Ashley for fused silica substrates. Metal substrates of molybdenum, TZM, and beryllium-copper were polished to a surface roughness of from 12 A to 15 A rms and overcoated with ultrahigh vacuum silver and gold. Absorption coefficients obtained were as low as 0.0064. The basic finishing techniques that are now employed are acid etch stress relieving and controlled grinding, modified conventional polishing techniques, sputtering of similar metallic film, and modified conventional polishing. Quantitative evaluations of the substrates were made with t e total integrated scatterometer (6328 A), photomicrograph studies, the newly developed fringes of equal chromatic order (FECO) interferometer, and the absolute calorimeter measurement.