Nonlinear Optical Properties of Potassium-Lithium Niobates

Abstract

Crystals of composition (K₂O)_0.3(Li₂O)_0.7‐x (Nb₂O₅)_x with x in the range 0.515 to 0.55 have useful and unique nonlinear optical properties. These are transparent ferroelectric crystals having the tetragonal tungsten‐bronze structure. Thus, they do not have to be detwinned, as does NaBa₂Nb₅O₁₅. The dc halfwave voltage is about 1350 V at 6328 A, and the nonlinear constant d₃₁ is 1.7d₃₁ (LiNbO₃). For x=0.515 the birefringence is very large. Thus, the phase‐matching temperatures for harmonic generation without double refraction with the Nd‐YAG laser is 450°C. For x=0.55, 140°C is obtained. With these crystals the GaAs injection laser emitting 0.90 μ can be phase matched above room temperature for the first time without double refraction.