Photorefractive properties of lithium niobate single crystals doped with copper

Raman scattering with excitation in the ultraviolet, visible, and near infrared and electron paramagnetic resonance are used to study the photorefractive properties of nominally pure, stoichiometric (R = Li/Nb = 1) single crystals of lithium niobate grown from a melt with 58.6 mol% Li2O (LiNbO3stoich), nominally pure crystals with a congruent composition (LiNbO3congr, R = 0.946), and Cu-doped crystals with a congruent composition (LiNbO3:Cu, [Cu] = 0.015 mass%). Optical irradiation is found to cause charge exchange of copper cations, Ca2+ → Cu, in the LiNbO3:Cu ([Cu] = 0.015 mass%) crystals. Thus, crystalline LiNbO3:Cu ([Cu] = 0.015 mass%) manifests photorefractive properties as a result of charge exchange of copper ions during laser irradiation, in addition to the contribution from intrinsic defects with localized electrons previously observed in LiNbO3stoich and LiNbO3congr.