Nonlinear thermal distortion in YAG rod amplifiers

Yttrium aluminum garnet (YAG) has thermal, mechanical, and optical properties that vary strongly with temperature. In this paper, we show that when such properties are taken into account the resulting thermally induced distortions in rod amplifiers cannot be described as quadratically varying with rod radius, and thus cannot be completely corrected using a simple spherical lens. In addition, we show that for operation with a coolant temperature at 77 K, thermally induced distortion is minimal and birefringence is substantially reduced when compared to that during operation with a coolant at room temperature.