Assessing the quality of polished brittle optical crystal using quasi-Brewster angle technique

Abstract Polishing is a main process in achieving high-quality surfaces of optical components. However, effective assessing technique for rough stage in the polishing process is sparse so that hinders the study on the mechanism and optimization of polishing. In this study, we propose an inspection method for polishing quality based on quasi Brewster angle technology (qBAT). An equivalent medium layer theory and its model are developed to accurately describe the optical reflection characteristics of a rough surface. Hence both rough- and fine-polishing qualities can be evaluated by the qBAT approach. To demonstrate the newly proposed method, laser crystal, gadolinium gallium garnets, is studied by computational simulation and experiments. A high consistence is achieved between theoretical simulation and experimental results, which proves the robustness of the method to the rough surfaces. To our knowledge, it is the first time that the qBAT is developed to evaluate the polishing quality covering rough- and fine-polishing stages. This capability shows great potential in fundamental research and process optimization of polishing brittle-hard materials.