Thermal gradient control at the solid-liquid interface in the laser-heated pedestal growth technique

The laser-heated pedestal growth technique, which is used for preparing single crystal fibers, involves very large temperature gradients at the growth interface. While this is often useful, it can also be problematic for some material systems. By introducing an additional optical component into the laser beam path, we were able to substantially decrease the axial temperature gradients. In this new configuration, the CO2 laser beam divergence was altered by using a ZnSe beam expander, This created an optical aberration at the laser focal point, thereby redistributing the thermal energy over a larger melt surface area. With this modification the thermal gradients were decreased from (3800+/-100)degreesC/cm to (2700+/-100)degreesC/cm during the growth of Bi-Sr-Ca-Cu-O (2212) single crystal fibers, showing that it is possible to control the thermal gradients by manipulating the laser beam, before it enters the growth chamber. (C) 2002 Elsevier Science B.V. All rights reserved.