Circling vortices and pattern dynamics in a unidirectional photorefractivering oscillator

We report results on unidirectional oscillation in a photorefractive oscill ator implemented with BaTiO3 that is actively stabilized. Dynamic spatial p atterns and pattern competition were observed, depending strongly on the Fr esnel number of the system. As the origin for spontaneous pattern alternati on we identified variations in the cavity length that are in turn mainly du e to temperature fluctuations. By varying the cavity length, we were able t o adjust stable patterns of different mode families and control pattern dyn amics as mode beats, optical vortices and their rotations and more complete pattern dynamics for higher Fresnel numbers. (C) 1999 Elsevier Science Ltd . Ail rights reserved.