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Space-charge waves in photorefractive BSO crystals

Recent measurements revealing new aspects of the nature and physics of space-charge waves in photorefractive Bi12SiO20 crystals are presented. A Bessel-function family of space-charge wave resonances are shown to exist for excitation by a frequency modulated running interference pattern. It is also demonstrated that space-charge waves may continue into regions of the crystal not subjected to the driving light field. Subharmonic space-charge gratings are shown to have an internal structure that for running waves moves with a group velocity opposite the driving optical interference pattern, which is moving with the phase velocity of the space-charge field and the associated refractive-index grating. We also describe how the subharmonics evolve dynamically from a speckle-like pattern towards a regular wave structure. Finally, self-excitation of spontaneous scattered beams ins described, and it is demonstrated that space-charge waves with a long decay time and a high Q-factor are associated with this phenomenon.