Correction masks for large-area ion beam etching and figuring of optics

Abstract

Broad beam ion sources, which produce a Gaussian distribution of the ion current density, are considered in designing correction masks to achieve uniform etching and to impart a deterministic shape or figure to large-area rotating optically polished substrates. Phase-shifting optical interferometry is used to obtain digitized maps of the test surfaces before and after etching. The maps are then used to determine the experimental etch rate and the surface figure of the optical substrate, and to test for convergence of the etched surface to some end figure.