Oxyfluoride glass for high-energy laser windows: Thermal lensing issue

摘要

Recently, a glass composition identified as oxyfluoride glass (OFG™) has stimulated great expectations in terms of creating "athermal" high-energy laser (HEL) windows. A proper evalution of the two thermal lensing coefficients, however, indicates that (a) the intrinsic stress birefringence cannot be ignored (χ_=-2.88 X 10~(-7) K~(-1)), and (b) the evaluation of χ_+ (χ_+=5.87 X 10~(-7) K~(-1)) must include the stress-optic contribution. Strehl-ratio calculations demonstrate that, in the absence of stress-driven failure modes, HEL windows made of OFG outperform fused-silica windows but may not match the capability of windows made of fusion-cast CaF_2.