Nonlinear Optical Properties of Potassium-Lithium Niobates

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.