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Defect structure and optical damage resistance of In:Fe:Cu:LiNbO3 crystals

The threshold concentration for In3+ ions was found in In:Fe:Cu:LiNbO3 crystals by measurements of the infrared absorption spectra and the Curie temperature of the crystals. The optical damage resistance of In:Fe:Cu:LiNbO3 crystals was characterized by changes in light-induced birefringence as well as by distortion of the transmitted beam pattern. The resistance of In:Fe:Cu:LiNbO3 crystals to optical damage increases remarkably when the concentration of In3+ ions exceeds its threshold concentration. The resistance to optical damage of In(3.0 mol.%):Fe:Cu:LiNbO3 crystals is two orders of magnitude higher than that of Fe:Cu:LiNbO3 crystals. The change in light-induced birefringence also decreases with increasing concentration of In3+ ions. The dependence of the optical damage resistance on the defect structure of In:Fe:Cu:LiNbO3 crystals is discussed in detail.