A nondiffusion mechanism for writing shifted holograms in LiNbO3

This paper attempts to explain the experimental facts that the resolution of LiNbO3 crystals in writing holograms is poor, and that large discrepancies exist between the measured characteristics of diffraction efficiency and predictions based on current and widely used models. A new model for charge transport is proposed that takes into account macro-and mesoscopic nonuniformities. It is shown that the electric fields arising from modulation of the spontaneous polarization by defects lead to asymmetric diffusion of photoexcited electrons, which makes it highly unlikely that the writing of shifted components of holograms is via a diffusion mechanism. Possible characteristics of shifted and non-shifted holograms written via photogalvanic currents are discussed. (C) 1997 American Institute of Physics.