Elastically induced birefringence in a cubic acousto-optic crystal KRS-5

This research is related to analysis of acoustic, optic and acousto-optic properties of the single crystal KRS-5. The material is considered as a medium for applications in the infrared acousto-optic devices providing laser beam control. The crystal belongs to the cubic class m3m of crystalline compounds and it is optically isotropic. Absence in the crystal of optical birefringence restricts applications of the material and is impeding its exploitation in acousto-optic devices operating in the middle and long infrared region of electromagnetic spectrum. In order to overcome the difficulty, we have artificially induced birefringence in the crystal artificially by applying external static pressure. Varying the pressure, we controlled the birefringence and obtained changes in magnitude of the refraction indexes up to Δn = 3.5 · 10−4. Velocities of longitudinal and shear acoustic waves in the KRS-5 crystal were calculated. Theoretical predictions were confirmed by experiments including laser probing of acoustic beams and analysis of Schaefer-Bergmann diagrams. Different regimes of anisotropic acousto-optic interaction in the birefringent medium were experimentally assessed. The theoretical and experimental investigation confirms the potential of using single crystal KRS-5 in acousto-optic devices operating in the middle and long infrared region of electromagnetic spectrum.