Three-Dimensional Surface Error Reconstruction and Ion Beam Figuring of Optical Hemisphere

This research is aiming at exploring a feasible machining method for ultra-high slope surface with deterministic figuring technology. We first successfully realize the nanometer-precision machining of optical hemispherical surface by using ion beam figuring (IBF) under the guidance of the reconstructed three-dimensional (3D) surface error. For figuring such a high-slope surface, we proposed some technical details, the modified algorithm for dwell time, the nonlinear developing method of surface error and the stitching machining technology, to address some important problems in process. Simultaneity a fused silica hemispherical surface is figured with our proposed method on the experimental installation IBF700-5V developed by ourselves. The root-mean-square (RMS) surface error of this sample is reduced from 19.6 nm to 9.6 nm after four iterations and about 37.8min. The experimental results indicate that IBF is a technique of high efficiency for the nanometer-precision machining of high-slope surface.