Aspheric optics: smoothing the ripples with semiflexible tools

A well-known fabrication problem with aspheric optical surfaces lies in high-frequency surface irregularities inherent in the figuring process. Optical grinding and polishing tools can smooth these ripples, yet retain the flexibility required to fit the aspheric surface. An f/0.52, paraboloidal, 17-in. convex surface is produced with conventional rigid tools. A transmission ronchigram is obtained showing high-spatial-frequency errors of large magnitude. After four hours of grinding with a semi-flexible multiple-segment ring tool, almost all high-frequency error is removed. This shows good potential for smoothing finished aspheric optics. Flexible tools can also be involved in the figuring process itself. (C) 2002 Society of Photo-Optical Instrumentation Engineers.