Surface ripple suppression in subaperture polishing with fragment-type tool paths.

In order to reduce the ripple-induced effect in subaperture polishing of high-power laser optics, the tool paths are investigated and optimized in this study. Various fragment-type curves (i.e., fractal and fractal-like unicursal curves) are designed as tool paths, and most importantly, a novel algorithm for generating a random fractal-like tool path is proposed in detail. Compared with scanning paths, fragment-type paths possess multi-directionality during multiple polishing iterations, which could better smooth the surface texture and restrain the polishing-induced surface ripples. In particular, the random fractal-like path exhibits high randomness, boundary adaption, and step-length arbitrariness, which make it more flexible and powerful for iterative polishing. Experiments were conducted on a computer numerical control machine, with conclusions that during iterative polishing, (1) the repetitive usage of a single fractal path would aggravate surface ripples; (2) the combination of multiple fractal paths or using the random fractal-like path can restrain surface ripples efficiently; and (3) pitch pads exhibit a better ripple-smoothing effect than polyurethane. The proposed random fractal-like path is a good prospect for the manufacture of high-power laser optics, which demands very low surface ripples.