Characterization Methods of Subsurface Cracks in Grinding of Optical Elements

In this paper, the subsurface cracks of fused silica introduced in grinding were detected by taper polishing method, and then characterized by the maximum depth, the cluster depth, and the density of cracks. The quantitative relationship between maximum depth and cluster depth of subsurface cracks was determined, and the distribution of subsurface crack density along the depth was studied. The results showed that the abrasive grain size had a great influence on maximum depth and cluster depth of subsurface cracks, while the grinding fluid concentration had little effect on them. The different processing parameters changed maximum depth and cluster depth, but their ratio was almost unchanged. The subsurface crack density decreased exponentially along the depth, and the decrease trend had slowed down significantly at the half of cluster depth.