Anisotropic bubble defects and stress distribution in LuAG single-crystal fibers grown by the laser-heated pedestal growth method

Abstract

Bubble defects severely affect the optical properties of single-crystal fibers (SCFs), so it is necessary to avoid the incorporation of bubbles during crystal growth. The process of bubbles entering a crystal was observed during pulling of Lu₃Al₅O₁₂ (LuAG) SCFs from ceramic pedestals by the laser-heated pedestal growth (LHPG) method. The effects of orientation and growth chamber pressure on the density and size of bubbles as well as on stress distribution were fully studied. <111>-oriented LuAG crystal fibers are likely to incorporate more and larger bubbles than <100>-oriented fibers. The low pressure in the growth chamber can limit the formation and transport of bubbles, and the bubble densities are decreased by nearly 50% with a chamber pressure of 0.3 atm. Notably, the <111>-oriented LuAG crystal fibers are more sensitive to pressure with an almost 40% decrease in the average bubble size and stress.