Dynamic halo scattering in photorefractive crystals

The theoretical description of the 'dynamic halo' -- the specific scattering cone is presented. This effect was found in LiTaO3 crystals doped with Cr under steady-state laser illumination. The main distinctive features of the scattering, namely the conic spatial structure and temporal evolution have been successfully considered within the framework of the theory. Our approach is based on the linearization of equations for wave-coupling in photorefractive media with linear electro-optic effect and local (photovoltaic) response. We take into account interactions between two waves: the strong pumping wave and the weak forward-scattering wave. The random inhomogeneities of refractive index occurred due to the small dynamic fluctuations in the photovoltaic impurity distribution were considered as the scattering seeds. The temporal evolution of the halo amplification exists due to the photovoltaic current. The weak scattering wave arises near the front plane of the crystal and reinforces inside its depth. We have obtained qualitatively agreement of our theory with the experiments for the thick crystals.