DYNAMIC SPATIAL STRUCTURE OF SPONTANEOUS BEAMS IN PHOTOREFRACTIVE BISMUTH SILICON-OXIDE

We report the domain structure of spontaneously occurring beams (subha rmonics) in photorefractive bismuth silicon oxide with an applied elec tric field from 1 to 6 kV/cm and a running grating. The subharmonic be ams are generated in a pattern of domains that evolve dynamically as t hey move through the crystal. We find that the domains move as a whole with a speed approximately equal to that of the primary grating, but in the opposite direction. The domains are separated by narrow boundar y regions, where the phase of the subharmonic waves changes by pi. The domain motion is consistent with the group velocity for running space -charge waves. (C) 1996 Optical Society of America.