The Satisloh plasma polisher: plasma surface figuring ultra precision optics

The next generation of ultra-precision optics requires rapid and cost effective surface figuring technology. Different manufacturing technologies exist: magnetorheological finishing, chemical mechanical polishing, and ion beam figuring; however, these technologies are slow and lead to expensive optics. Plasma figuring, operating at atmospheric pressure, is a cost effective method for figure correction of ultra-precision optical surfaces. In this presentation, fast figure correction of optical surfaces is reported using the Satisloh Plasma Polisher (SPP). The technology uses a reactive plasma jet to surface figure flats of fused silica. The plasma jet is powered by a solid state microwave generator, which operates in pulse mode to reduce the plasma temperature hence increasing the repeatability of the etched trenches. The trenches are characterised using an interferometer. Each trench follows a Gaussian function. Material removal rates can range from nm³ to a mm³ per minute, which can result in surface form error reductions of 90% in a single iteration. The surface roughness is measured using a white light interferometer and shows no degradation in the surface finish.