Adaptive fringe-locked running hologram in photorefractive crystals

We have recorded running holograms in a photorefractive crystal with an applied electric field, using a 90 degrees phase-shift fringe-locked interference pattern of light. This method provides a simple way to obtain optimal conditions for nonstationary holographic recording. The experiment that we describe allows us to calculate the crystal diffusion length L(D) and provides direct evidence of the occurrence of running holograms in photorefractive crystals. Experimental results for a Bi(12)SiO(20) sample are reported.