Structure of Lithium Niobate Crystals with Low Photorefractive Effect

Abstract

Stoichiometric and congruent single crystals of lithium niobate doped with cations (mass%) Mg2+ (0.078, 0.89), Zn2+ (0.03, 0.52, 0.62), Cu2+ (0.015), B3+ (0.12), Gd3+ (0.51), Y3+ (0.46), Gd3+ (0.23),Mg2+ (0.75), Mg2+ (0.86), Fe3+ (0.0036), Ta5+ (1.13):Mg2+ (0.011), Y3+ (0.24):Mg2+ (0.63) were investigated by photoinduced light scattering (PILS) and electron spectroscopy. It was found that the investigated samples could be divided into three groups depending on the type of PILS picture. The fi rst group included crystals with a relatively small photorefractive effect. The PILS indicatrix in such crystals was not evident even at laser power 160 mW. The second and third groups contained crystals that had a noticeable photorefractive response. The appearance of their indicatrices was accompanied by a PILS speckle pattern. The PILS indicatrix for the third group of crystals appeared quickly in the first few seconds after the laser irradiation began whereas the PILS indicatrix appeared in about a minute for the second group. The optical transmission edge of the first group was characterized by the steepest rise compared with the other crystals and indicated that the crystal composition was highly homogeneous. The transmission edge of LiNbO3:Cu (0.015 mass%) crystals typically behaved anomalously, indicating that it had high optical heterogeneity due obviously to an irregular distribution of defects and copper cations throughout the crystal volume. The position of the optical transmission edge of the third group [LiNbO3:Y (0.46 mass%) and LiNbO3:Y (0.24 mass%):Mg (0.63 mass%)] was similar to the transmission edge for crystals of the fi rst group. However, the slope of the transmission edge was substantially less.