Growth and Evaluation of Nonlinear Optical Materials for Laser Applications: Barium Borate, Lithium Borate and Silver Gallium Selenide

A major goal of this program is to develop processes that industry can use to grow large high quality B-barium borate BBO and lithium triborate LBO crystals with good yield. High optical quality single crystals of both are currently being grown by modified top-seeded solution growth TSSG methods using sodium oxide and boric oxide, respectively, as solvents. This advanced TSSG growth technology has been transferred to both INRAD, Inc. and Cleveland Crystals, Inc. during the course of the program. The development of a phenomenological model which accurately predicts the growth rate in these systems has allowed us to grow cylindrical boules of both in multi-centimeter lengths, which has not previously been possible by the TSSG method. The crystal growth process is also being monitored by a high resolution weight sensing system which verifies system parameters. Development of a control algorithm using the growth rate model and real time weight sensing is being pursued in order to develop a totally automatic diameter control process. Additional research has focused on reducing the density of solvent inclusions in flux-grown barium borate by optimizing forced convective stirring in the melts and by understanding the effects of melt chemistry. Computer-controlled periodic reversals in seed rotation have demonstrated that the density of solvent inclusions can be reduced by forced convection, but the underlying causes for solvent incorporation on the growth interface have never been clearly understood. Evidence of carbonate impurities in BBO crystals and solidified charges has recently been discovered, reinforcing previous suspicions of insoluble particulate contamination in the melts, and additional experiments are underway to elucidate the role of carbonate ions that are introduced during the melt synthesis process.