Structure optimization and fabricating capability analysis of an ion-beam machine for a subnanometer optical surface.

Abstract

Ultraprecise and ultrasmooth surfaces become critical requirements for some high-performance optical systems. Ion-beam figuring (IBF) is a good and highly deterministic method for the final precision optical figuring. However, the uniform convergences of all spatial frequency surface errors are strongly dependent on the dynamic performance and ion-beam stability of the IBF machine. In this paper, only the dynamic performance is discussed, which is limited by the acceleration and velocity of the motion system. So we discuss these problems and their influences on figuring optical surfaces in detail. The structure optimization principle is based on the fabricating capability of ultraprecise surface errors in all spatial frequency ranges. With this requirement, the structure optimization of a quick-response platform is performed to improve its dynamic performance. Manufacturing experiments on a fused silica spherical concave surface (Φ135.7 mm, radius of curvature 340.5 mm) are accomplished, and the IBF machine can effectively correct the figure errors and improve the surface quality simultaneously. The IBF process realizes the uniform convergence of surface errors in all spatial frequency ranges, which is reduced down to 0.368 nm RMS, 0.204 nm RMS, and 0.087 nm RMS, respectively. The final results indicate that the performance of the new designed IBF machine meets the requirements well for the fabrication of a subnanometer optical surface.