Mechanism of Surface Defects in Ultra-Precision Machining of Sesquioxide Laser Crystal Tm: GdScO3

It is well known that the surface quality of laser gain crystal elements is very high in or- 9der to ensure the stability of laser system and laser output quality. In the ultra-precision machin- 10ing process of a new sesquioxide laser crystal Tm: GdScO3, it is required to achieve very high sur- 11face shape and very low surface defects. In this paper, the molecular dynamics simulation model 12of single particle grinding is established. It is found that the normal load and tangential friction 13imposed by abrasive particles on the surface of components cause the spalling of atoms on the 14substrate surface, which constitutes the removal of materials at the macro-level. At the same time, 15it causes the displacement of the sub surface atoms, which constitutes the microscopic defects in 16the structure. Through the structural characterization of macro defects, it is confirmed that the es- 17sence of micro defects is the amorphous and distortion of surface structure, and the depth can 18reach 100 nm. The results of lapping and polishing experiments show that the adjustment of 19pressure has limited effect on the improvement of surface defects in the process of machining 20crystal elements with granular abrasive. 2