Origin and distribution of redeposition layer in polished fused silica

Subsurface damage, especially photoactive impurities embedded in the redeposition layer, degrades the performance of high-energy optics in UV or high-power laser systems. The features and distributions of the redeposition layer in classical and magnetorheological finishing polished fused silica were detected and evaluated by a variety of measurements, such as secondary ion mass spectroanalyzer, atomic force microscope, scanning electron microscope, and x-ray photoelectron spectroscopy. Then, a critical particle Reynolds number approach and chemical contribution were applied to interpret the deposition mechanism of impurities, on the basis of which a comprehensive redeposition model of polished optics was presented. Eventually, the relationship between distributions of redeposition materials in depth and freshly polished surface structure was investigated. Results show that the redeposition process of nanoparticles is dominated with the particle Reynolds number and the formation of a Ce-O-Si bond. The impurities in the redeposition layer are mixed with removed glass and present as a uniform dopant. Furthermore, there exists explicit correlation between redeposition layer and subsurface defected layer; so it is easy to achieve planarized surface in the polishing process. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)