Photorefractive hologram fixing by a 4 K cooldown to the phase transition in K1− x Li x Ta1− y Nb y O3

A fixing process of photorefractive holograms is reported. The process is based on the formation of an ionic space charge which becomes mobile at the phase transition temperature. A fixed grating was formed in paraelectric potassium lithium niobate tantalate by a 4 K cooldown to Tc, and a warmup back to the paraelectric phase. The diffraction efficiency of the fixed grating was 66% of the original photorefractive space charge grating.