Laser Conoscopy and Photoinduced Light Scattering in a Lithium Niobate Crystal Doped with Y(0.24 wt %):Mg(0.63 wt %)

Abstract

The method of laser conoscopy and photoinduced light scattering was used to study the optical homogeneity and features of structural distortions when using laser radiation of low power P ~ 1 mW to minimize the possible influence of the photorefractive effect, as well as a power of 90 mW, the use of which made it possible to detect and study distortions arising from the action of light in a double-doped LiNbO₃:Y(0.24 wt %):Mg(0.63 wt %) crystal. The experiment showed that, at a laser radiation power of P ~ 1 mW, the conoscopic patterns of the samples under study correspond to the conoscopic patterns of uniaxial optically homogeneous crystals. Anomalous optical biaxiality manifests itself in conoscopic patterns with an increase in the laser radiation power up to ~90 mW. In this case, the black “Maltese cross” loses its correct shape, a significant gap appears in the center of the pattern, and the sharpness and contrast of the image are generally reduced in the conoscopic pattern. The distortions that appear in the conoscopic pattern correspond to the rapid opening of the photoinduced light scattering indicatrix with increasing laser radiation power. For the LiNbO₃:Y(0.24 wt %):Mg(0.63 wt %) crystal, a complex dynamics of the development of the PILS pattern over time is observed. In the first seconds of irradiation, a strongly elongated central layer appears, which does not divide into two halves with time, but remains intact. On the periphery, a smaller spot appears at the beginning, which gradually resolves. These changes are due to a complex redistribution of energy between ordinary and extraordinary rays.