Evaluation of the surface and subsurface evolution of single-crystal yttrium aluminum garnet during polishing

Yttrium aluminum garnet (Y3Al5O12/YAG) has attracted extensive research and application interest in the field of optoelectronics. However, the evolution mechanism of the surface and subsurface of YAG single crystals during polishing have not been elucidated, thus hindering the in-depth understanding of the processing mechanism of brittle solids. Herein, rough and fine polished YAG crystals were obtained by designing a processing scheme, and the surface and subsurface were expeditiously evaluated simultaneously by angle-resolved ellipsometry. The dependence between the ellipsometric parameter near the Brewster angle and the surface and subsurface quality was determined by modeling the polished surface and subsurface damage optics. The monotonicity of the quasi -Brewster angle shift (qBAS) reveals the diminishing feature of subsurface damage, and the oscillation of the slope unveils the atomic-level topography evolution of the polished planes. The results were validated using data from surface and subsurface damage tests, thereby proving the feasibility and reliability of the method. Furthermore, the refractive indices (210-1690 nm) of YAG were identified based on the spectroscopic ellipsometry data of the fine polished crystal. These findings provide a promising paradigm for predicting and evaluating the surface and subsurface microstructures and optical properties of brittle solids in material-removal-based surface engineering.