Recording and fixing dynamics of nonvolatile photorefractive holograms in LiNbO_3 :Fe:Mn crystals

Abstract

A theoretical explanation of nonvolatile holographic recording in LiNbO3:Fe:Mn crystals is given based on jointly solving the two-center material equations and the coupled-wave equations. The nonuniformity of the dynamics of the photorefractive grating can be effectively described and analyzed by using this method. The time–space evolution, including the space-charge field, the diffraction efficiency, the light modulation depth, the phases of the space-charge field and the interference field, as well as the relative spatial phase shift between them, is studied for both oxidized and reduced crystals. The optimal conditions for material prescriptions and oxidation–reduction processing are discussed in detail. The bending isophase of the fringe pattern and the redistributed intensities of the two-coupled beams inside the crystal are presented. The theoretical results can confirm and predict experimental results. Some new effects are also discovered, such as: The fixed diffraction efficiency can exceed the saturation diffraction efficiency for strongly recorded gratings; the energy transfer direction between two-coupled beams can be reversed with crystal thickness; and the holographic readout in reduced crystal is always accompanied by fast phase changes, which results in the slow deterioration of the recorded holograms as a result of the production of homogeneous distributions of electrons.