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Study on the destructive measurement of subsurface damage for fused silica mirror

During the course of super smooth surface processing, grinding procedure is a very important link, for one thing the subsurface damage induced by cutting can be removed, for another its quality determines the subsurface damage depth of the mirror which influences some important index such as strength, stability, coating quality and so on. Therefore, the accurate measurement of subsurface damage depth is the prerequisite to ensure the removal amount in the subsequent processing and make sure that the subsurface damage is removed completely. In this paper, based on fused silica mirror as the experimental object, free abrasives of W28 size are used to grind the mirror blank, then two destructive measurement methods are adopted respectively. The result shows that, comparing with angle polishing method, differential chemical etching method could describe the subsurface damage depth accurately.