Research on key technology of compound polishing of off-axis parabolic mirror

Off-axis aspherical surface have the advantages of excellent optical performance and simplified system structure. In order to satisfy the requirements of high-precision off-axis aspheric mirror in the telescopic system of some equipment, the research on ultra-precision manufacturing technology of off-axis aspheric mirror is carried out, and a composite polishing and detection technology based on robot-controlled optical surfacing and ion beam figuring is proposed. In the processing stage, the robotic flexible polishing and gadget polishing are used to quickly grind and polish the aspheric surface, and then the pitch lap is used to smooth the mid-spatial-frequency errors. Finally the aspheric surface is machined to the final requirement by ion beam figuring. In the detection stage, the coordinate measuring machine is used to detect the surface shape in the grinding stage, and the stigmatic null test is used to detect the aspheric shape in the fine polishing stage. Using the proposed method, the off-axis aspheric surface of a caliber 408mm is machined and tested, and the final surface figure error was 0.015 λ (λ = 632.8nm), which meets the requirements of the index.