Investigate Material Systems for Mirrors Used in High Power Co and C 02 Lasers

This report and the two preceding semiannual reports present the results of eighteen months of research aimed at demonstrating the viability of a mirror structure concept formed by sputter deposited materials. The mirror concept would be used in high energy CO, C0?, and other infrared laser systems at the infrared wave length of 10.6 m. Briefly, the mirror concept consisted of a support with sequential layers of a highly polishable sputtered deposit, a high reflectivity metal overlayer, and a minimum number of quarter-wavelength reflectivity enhancement coatings. Sputtered deposits of Cu-1 vol% SiC on a variety of metal substrates provided surfaces that could be reproducibly polished using conventional techniques to an rms roughness of 20 8 or less. Although the desired reflectivity of 99.5% in the sputter deposited silver overlayer was not achieved, values of ^99.258 were obtained. Sputter-deposited germanium and CdTe were found to have optical properties near those of bulk material. Sputter deposition of quarter-wavelength reflectivity enhancement coatings therefore appears feasible. The results of limited laser damage testing were exceptional considering that there was not time to optimize material , roperties. The laser damage threshold as measured by BNW for a superpolished Cu-1 vol% SiC deposit was between 35 and 2 2 136 joules/cm ; and was 44 joules/cm for a sputtered silver overlayer.