Technical feasibility of figuring optical surfaces by ion polishing

Procedures are described to figure optical surfaces by ion polishing. Fused silica, ULE, and Cer-Vit were employed as substrate materials. The sputtering yields for these materials were: 1.9 (150-keV(40) Ar(+)), 1.86 (150-keV (40)Ar(+)), and 3.7 (80-keV (126)Xe(+)) atoms/ion, respectively. The optical scatter, at lambda = 632.8 nm, was measured to be 0.06%, which is comparable to good surfaces prepared by conventional lap techniques. The rms surface error was reduced from 0.05lambda to 0.01lambda over the central 0.12-m aperture of a 0.2-m diam fused silica flat by ion polishing with 150-keV (40)Ar(+). Based on this experience, the design of a manufacturing facility is discussed.