Efficient full-aperture mirror polishing method with variable orbital radius in computer-controlled optical surfacing

Abstract

Optical systems in astronomy have extremely high requirements on the full-aperture surface precision and fabrication efficiency of aspherical mirrors. However, the current full-aperture optics fabrication method suffers from both fabrication and computation inefficiency. The former is caused by the isolated polishing strategy for the inner and edge regions of the mirror with different tools, while the latter is caused by the global computation strategy for the two regions. In this paper, a full-aperture mirror polishing method with the reversed strategy is proposed to solve this problem. Firstly, the dwell time of inner/edge regions are respectively calculated by the deconvolution method and the linear equations method based on the space-variant tool influence function. Therefore, both the computation cost and the edge polishing error can be reduced. Then, a fused tool path is developed to achieve variable orbital radius in the inner/edge region so the full aperture can be polished in one round. Simulations and experiments using a SiC aspherical mirror and large segmented mirrors demonstrate that the surface error can converge quickly in the full aperture. As a consequence, the full-aperture fabrication accuracy and efficiency can be greatly improved through the proposed method.