Influence of surroundings on photorefractive effect in lithium niobate crystals

摘要

In the paper results of the investigation of the influence of electric properties of the environment surrounding LiNbO _3 crystals on photorefractive effect induced in these crystals by Gaussian Ar laser beam with various intensities are presented. We show spatial and temporal dependences of changes of the refractive index obtained experimentally in LiNbO _3: Fe and LiNbO _3: Fe:Mn samples surrounded by media with different electric conductivities and different permittivities (water, air, water solution of CaCl _2). The space and time dependences of the refractive index changes induced by the Ar laser beam are observed by means of the Mach-Zehnder interferometer using light from HeNe laser. The experimentally obtained results are in a good agreement with those following from numerical calculations using the manifold mirroring method. The agreement between calculated and experimental results indicates that the polarization charge at the photorefractive crystal/surrounding medium boundary significantly influences the photorefractive process in the crystal. The experimentally observed slow spontaneous decrease of the refractive index change in a sample placed into a slightly conducting medium (air) after switching off the beam also indicates that the polarization charge in the sample's surroundings affects the photorefraction.