Effects of Surface Polishing on the Microstrain Behavior of Telescope Mirror Materials

摘要

Rough ground silicic mirror substrate materials were found in previous investigations to exhibit significant surface yield. This effect was removed by surface etching, a procedure not normally employed in the finishing of optical telescope mirrors. The effects of fine grinding and polishing techniques as well as graded etching are investigated. Torsional shear measurements of yield strain versus stress are made on four candidate mirror substrate materials: polycrystalline silicon, ULE silica 7971, CER-VIT 101, and fused silica 7940. Commonly employed fine grinding and polishing practices are shown to remove a major portion of the surface yield found in rough ground mirror substrate materials. (Author)