Reading and optical erasure of holograms stored by the photorefractive effect in lithium niobate

Abstract

The reading and optical erasure (on and off the Bragg angle) of holograms stored in lithium niobate and similar materials by the photorefractive effect have been modeled using numerical methods for the case of a single trapping level and with the further restrictions of uniformly and completely illuminated crystals, short transport lengths, and constant applied voltage. For the first time, the model allowed simultaneously for finite dark conductivity, feedback effects due to space charge on the redistribution of photoliberated electrons, writing of a new hologram by interference between the reconstructed and the reading waves (causing enhancement or disenhancement of the original hologram according to the conditions), and nonuniformity of the hologram through the thickness of the crystal. The model generates all the reported types of behavior, and it is believed to be accurate enough for a meaningful comparison with experiment. Excluded are those effects due to the large scale field associated with the envelope of the illumination when this is nonuniform.