Effects of light polarization and crystal orientation on the holographic recording efficiency in doped LiNbO3 crystals

Abstract

The holographic recording efficiency in doped LiNbO3 crystals has been studied both experimentally and theoretically depending on the type of dope, on the recording geometry and on the polarizations of the recording and readout light.. The studied crystals can be arranged in the following order by their efficiency: LiNbO3:Cu, LiNbO3:Fe (yet having a smaller thickness and donor concentration than LiNbO3:Cu), LiNbO3:Fe+Cu, LiNbO3:Fe+Ti, LiNbO3:Ti. It was found that the recording geometry with the holographic grating vector along the optical axis is much more efficient than in the perpendicular configuration.This fact is in accordance with the photorefraction theory based on photogalvanic and linear electro-optic effects (PGE-LEO theory). Other recording mechanisms are active, too, but much less eficient. The recording efficiency polarization dependence is mainly determined by dopes.It is different in the cases of Fe and Cu impurities. It also follows from our studies that photoconductivity along the optical axis is much larger than in the perpendicular direction.