Plane wave excited vortices in photorefractive materials

The flow of spatially periodic current in a photorefractive film is investi gated under the conditions when two coherent plane waves are incident and a n electric field is applied. It is shown that in contrast to the usually ac cepted physical picture the major part of the current does not flow in a si mple manner from one boundary to the other boundary. Two examples are given : (i) transients in the perpendicular configuration (grating vector perpend icular to the direction of the applied field) with vertical diffusion negle cted and (ii) steady state in the parallel configuration (grating vector pa rallel with the applied electric field) with vertical diffusion included. T he flow of current is plotted with the aid of vector diagrams. It is clearl y shown that during transients current may flow from one point on the bound ary to another point on the same boundary, and that for the parallel config uration circular currents may flow in the steady state. (C) 2000 American I nstitute of Physics. [S0003-6951(00)00912-8].