Defect structure and optical damage resistance of In:Mg:Fe:LiNbO3 crystals with various Li/Nb ratios

In:Mg:Fe:LiNbO3 crystals were grown by the Czochralski technique with various ratios of Li/Nb=0.85, 0.94, 1.05, 1.20 and 1.38 in the melt. The crystal composition and defect structure were analyzed by the UV–vis and IR spectroscopy. A new narrow OH−-associated vibrational peak at 3518 cm−1 was revealed in In:Mg:Fe:LiNbO3 crystals with the ratio of Li/Nb=1.38. It was attributed to a (InNb)2−–OH−–(MgNb)3− defect center. The optical damage resistance of In:Mg:Fe:LiNbO3 crystals was studied by the transmitted beam pattern distortion method. The results show that when both the In2O3 threshold and the “In–Mg threshold” concentrations are reached, as for the Li/Nb ratio of 1.38, the optical damage resistance of In:Mg:Fe:LiNbO3 crystals is the highest.