Phase-matching property optimization using birefringence tuning in solid solutions of KTiOPO₄ isomorphs

We report here the linear and nonlinear optical properties of the solid-solutions KTiOP_xAs_1-xO₄ and Cs _1-xK_xTiOAsO₄. Single domain crystals of these solid solutions were grown using a high temperature solution growth technique. By varying the compositional parameter x, the optical birefringence of these crystals was tuned to achieve noncritically phase-matched type II frequency doubling of the 1.064 and 1.32 μm lines of Nd:YAG. Near optimal compositions for these two applications, and their associated phase-matching angles, temperature bandwidths and angular acceptances are presented. The birefringence of KTiOP_xAs_1-xO₄ exhibits a Vegard dependence on x, and the phase-matching property optimization amounts to an accurate determination of the partition coefficients for P and As suitable for crystal growth. For the Cs_1-xK_xTiOAsO₄ solid solution, a non-Vegard dependence of the crystal birefringence and the cell constants was observed. This is believed to be due to the preferential occupation of the larger K(2) site by Cs.