Beam fanning used to study thermal disorder and decay of polar structures in the ferroelectric relaxor

A new photorefractive approach using the temperature evolution of beam fanning to study the polar structure of the ferroelectric relaxor strontium-barium-niobate (SBN) undergoing the ferroelectric-paraelectric phase transition is proposed. A strong temperature dispersion of the decay of polar structures of different sizes is observed. We compare our results with those obtained by other measurement methods to show their dependence on the size distribution of the polar structures

Holographic light scattering in photorefractive crystals with local response

Strong polarization-isotropic wide-angle light scattering in photorefractive crystals with dominating photovoltaic response is explained referring to different experimental results obtained for LiTaO 3 :Fe crystals. It is shown experimentally that the steady-state amplification of the light scattering results from a nonzero shift in the temporal frequency between the coherent optical noise and the pump beam. Competition of photovoltaic and diffusion contributions in the photorefractive effect leads to a spatial and temporal asymmetry of nonlinear scattering. Contributions of ''hot'' electrons in the diffusion process have to be assumed