Technological control tools for roughness and defect structure of the surface of ZnGeP ₂ single crystals using coherent optics methods

Subject of study. This study determines the surface-roughness parameters of polished infrared single-crystal materials by coherent-optics methods, using ZnGeP ₂ single crystals as an example. Aim of study. The aim of this study is to develop a method for estimating the surface roughness of ZnGeP ₂ zinc germanium phosphide crystals that can be integrated into the crystal-polishing process based on coherent-optics methods. Main results. A method for assessing the quality of crystal-surface finishing was developed using a spatial filter. An experimental setup was designed to evaluate the surface-polishing quality of ZnGeP ₂ crystals. The intensity of the radiation scattered by surface roughness and reflected from the crystal surface was measured using a lens system and spatial filter that suppressed the dc component in the radiation spectrum. A 532 nm, 20 mW solid-state laser was used as the radiation source. The scattered-radiation intensity was measured with an FD-24K photodiode connected to a V7-40/5 universal voltmeter. Intensity values were measured for six crystal samples with different facet-processing qualities. Practical significance. The experimental data were verified using an industrial profilometer, confirming the applicability of the developed method to the qualitative assessment of the surface roughness of infrared optical materials, including the possibility of integrating this method into the polishing process.