The formation and stability of the molten zone in single-crystal fiber growth by the LHPG method

We propose a new structure of the molten zone, which is formed during the pulling Bi12SiO20 and Bi12TiO20 single-crystal fibers by the LHPG method. According to the model, the hottest point of the molten zone corresponds to the focal point of the upper parabolic mirror used for the focusing of the laser beam. The influence of different parameters of the growth process (laser power, pulling and feeding rates etc.) on stability of the molten zone is discussed. The proposed model predicts the presence of high temperature gradients in the molten zone and explains the crystallization of metastable and incongruently melting compounds from stoichiometric melts by the LHPG method.