Sem-analysis of fracture features formed in excimer-laser induced surface damage of CaF₂

Abstract

Abstract The fracture damage of bulk (111)-CaF2 crystals induced by pulsed irradiation in single shot mode with 248 nm laser light in air is investigated. The irradiated spots are studied with a scanning electron microscope (SEM) using different operational modes. An analysis of the fracture features yields evidence for defect induced absorption, thermal stress and shock wave generation as the main cause of damage. Fracturing is preferentially aligned along the (111)-directions resulting in a triangular shape for the tile fragments. The thickness of the fragments shows a clear dependence on incident laser fluence, what can be explained assuming an enhanced surface absorption in the CaF2 crystal.