Contouring algorithm for ion figuring

Abstract

Ion beam figuring provides a highly deterministic method for the final precision figuring of optical components with advantages over conventional methods. The ion-figuring process involves bombarding a component with a stable beam of accelerated particles, which selectively removes material from the surface. The specific figure corrections are achieved by rastering the fixed-current beam across the workpiece at varying velocities. Unlike conventional methods, ion figuring is a noncontract technique that avoids such problems inherent in traditional fabrication processes as edge roll-off effects, tool wear, and force loading of the work piece. Other researchers have demonstrated that ion beam figuring is effective for correcting of large optical components. This work is directed toward the development of the precision ion-machining system (PIMS) at NASA's Marshall Space Flight Center (MSFC). This system is designed for processing small (≅ 10 cm diameter) optical components. The ion-figuring process involves obtaining an interferometric error map of the surface, choosing a raster pattern for the beam, and determining the velocities along that path. Because the material removed is the convolution of the fixed ion beam removal and the rastering velocity as a function of position, determining the appropriate velocities from the desired removal map and the known ion beam profile is a deconvolution process. A unique method of performing this deconvolution was developed for the project, which is also applicable to other mathematically similar processes, including computer-controlled polishing. This paper presents the deconvolution algorithm, a comparison of this technique with other methods, and a simulation analysis. Future research will implement this procedure at MSFC.