Efficient laser frequency converters made of nonphotorefractive lithium niobate

A systematic investigation was made of photorefractive and nonlinear optical properties of LiNbO₃:Mg, LiNbO₃:Fe, LiNbO₃:Mg:Fe and LiNbO₃:Mg:Nd crystals grown from congruent melts with a wide range of dopant concentrations. The nonlinear optical properties depended nonmonotonically on the impurity concentration and strong suppression of photorefraction was observed when the magnesium concentration was more than 1%. Crystals containing 2.6% Mg were used for second harmonic generation of radiation emitted by a YAG:Nd³⁺ laser at room temperature with a conversion efficiency of 25%.