The growth and characterization of Rb-doped $KNbO_3$ nonlinear optical crystals

We have successfully grown colorless and transparent Rb-doped potassium niobate (KRN) single crystals using the top seeded solution growth(TSSG) technique. In our crystal growth experiments, the Rb doping concentrations within the melt range from 2-15 mol% relative to that of Nb$_2$O5. Atomic absorption measurements indicate that the Rb content in the KRN solid solution is rather low; the Rb segregation coefficient is found to be on the order of 0.05. It is believed that this is due to the relatively much larger Rb+ ionic radius compared to that of K+, rendering it more difficult for Rb to replace K in the KNbO$_3$(KN) host lattice. Preliminary single-pass second harmonic generation (SHG) experimental results indicate that there exists marginal improvement in the phase-matching temperature tolerance of KRN compared to that of pure Kn single crystals.