Dependence of Radiation Effects on System Configuration and Physical Properties in Bridgman Growth of Optical Crystals

Optical crystals, such as YAG, GGG, sapphire, CaF₂, are of high melting temperature. As a result, the radiative heat transfer during the crystal growth process is an important factor to influence the temperature distribution and hence the quality of as-grown crystals. However, the radiation effect is complicated in the optical crystal growth system. It depends on the system geometry and properties, such as the spectral transmittance of the oxide crystals, and the emissivity of the ampoule and the furnace inner wall. In this paper, the analysis of heat transfer coupled with radiation effect has been carried out using one-dimensional thermal resistance network method for optical crystals growth. The results show that radiation plays a significant role in the heat transfer and temperature distribution during growth, and the subsequent quality of the grown crystal. Two-dimensional numerical simulations have also been conducted and the simulation results have been compared with the one-dimensional results. Effects of system configuration and physical properties on crystal quality are also analyzed and discussed.