Thermal runaway in germanium laser windows

A one-dimensional model is presented of thermal runaway in germanium induced by IR laser radiation. The model examines the effect of the temperature-dependent thermal conductivity. It is shown that the thermal runaway time prediction is changed by approximately 2%, thermal runaway being defined as a temperature rise to 500 K at the front surface of the sample. It is also shown that the inclusion of multiple internal reflections is a much more important factor. A discussion of the role of the numerical parameters is included. It is pointed out that the analysis given here can be generalized to include edge cooling effects, temporal and spatial beam profiles, and a stack of thick material plates (as encountered in IR transmission polarizers).