Composition-dependent electro-optic and nonlinear optical properties of KTP-family crystals

A series of single crystals of KTP (KTiOPO4) and its isomorphs (KTiOAsO4, RbTiOPO4 and RTiOAsO4) has been grown from self-fluxes at different concentrations of the solute in the high-temperature solutions. The ferroelectric transition (Curie) temperature of each crystal has been measured by the standard dielectric technique, and the Curie temperatures have been found to increase with the decrease in the initial solute concentration. This phenomenon is explained in terms of the dependence of crystal stoichiometry on the solution chemical composition. Its main consequence is the experimentally observed compositional variation of large KTP-type crystals and the associated variation of the refractive indices. We have shown that the top-seeded solution growth method with pulling on X-oriented seeds assures the smallest variation in the values of the refractive indices. Calculations based on the experimental results for KTP show that such crystals exhibit sufficient optical uniformity for the most important electro-optic and nonlinear optical applications.