Anomalous erasure of photorefractive holograms in LiNbO3

The Kuktarev band transport equations predict exponential decay in the space charge field associated with photorefractive holograms erased with uniform illumination. We have found, in contrast, that in certain conditions the amplitude of the space charge field, monitored via the diffraction efficiency, can increase dramatically before eventually decaying when a hologram is erased by uniform Bragg mismatched light. This effect can be explained using the multiple active trap model proposed by Valley in 1983. We describe experiments demonstrating this effect in LiNbO3. We analyze the effect in the context of the multiple trap model and consider its effect on the recording process. The use of volume holographic media for high density information storage requires multiple exposures. We consider the difficulties the multiple trap model creates for multiple exposure recording in photorefractive materials.