Growth of β-BaB 2 O 3 single crystals for frequency converters of optical radiation

Single crystals (beta) -BaB2O4 (BBO) are new perspective nonlinear-optical material used for development of laser sources tunable in wide spectral range from near IR to UV. It is well known that BBO single crystals cannot be grown from their own melt because of formation of (alpha) - phase of BaB2O4 at melting point of 1095 degree(s)C. Therefore the solution-melt (flux) technique is used for growth of low-temperature (beta) -BaB2O4 phase (temperature of (alpha) yields (beta) phase transition is 925 degree(s)C). This method is applied still quite seldom because of high labor-consuming. BBO single crystals were grown by top-seeded solution growth technique with high temperature gradient with simultaneous decrease of temperature. The main difficulties of the growth of BBO single crystals are related to high viscosity, tendency to stratifying and vitreous formation, incongruent evaporation of solution-melt, and possibility of simultaneous co- crystallization both (alpha) - and (beta) -phases from the supercooled solution-melt. Any of them result in formation of various growth defects with concentrations depended on peculiarities of technological conditions.