Advanced techniques for improving laser optical surfaces

This program is a study of surface-finishing techniques considered to be capable of improving the surface quality of laser optical materials. A variety of conventional and superpolishing techniques will be developed for single-crystal and polycrystalline potassium chloride and calcium fluoride, and crystalline zinc selenide. Acceptable conventional polishing techniques for polycrystalline calcium fluoride and zinc selenide were developed, and preliminary grinding steps of the process were identified as requiring further study. Bowl-feed superpolishing was shown to improve the surface quality of conventionally polished zinc selenide and calcium fluoride substantially. Zinc sulfide powders were evaluated as infrared-transparent abrasives for potassium chloride and found to be inferior to alumina. Light scattering measurements demonstrated that ion milling could be used to clean surfaces prior to deposition of optical coatings without seriously degrading them, but that more extensive material removal sharply increased scattering at angles close to the specular direction. (Modified author abstract)