Effects of kinematics and groove parameters on the mid-spatial frequency error of optics induced during full aperture polishing

The mid-spatial frequency (MSF) error is a key controlled specification of optical elements for many important applications (e.g., high power laser systems, extreme ultraviolet lithography systems and other high-resolution imaging systems). However, the effective controlling of MSF error is one of the difficulties in high precision optical materials processing, especially in the full aperture polishing process. In this study, a theoretical model of optical element MSF error induced during full aperture polishing process was established. The effects of kinematics and groove parameters on workpiece surface MSF error were studied by numerical simulation. According to the theoretical analysis results, several process optimization measures for reducing workpiece MSF error during full aperture polishing process were proposed. The practical effects of these optimization measures were verified in the following polishing experiments. The theoretical analysis and polishing experimental results suggested that the period of MSF error is obviously influenced by the grooving spacing of the polishing pad, and the MSF error value (PSD-RMS) can be significantly reduced by optimizing the polishing speed and swing parameters.