Thermal Effects in End-Heated Laser Rods: A Time-Dependent Model and Diagnostic.

摘要

Unwanted heat generated in optically-pumped solid-state lasers causes thermal gradients, strain, and thermal expansion which in turn results in a nonuniform optical path difference (OPD) increase across the gain media. This ultimately results in poor beam quality. An interferometric based diagnostic for experimentally determining the time-dependent OPD change in an optically heated media was developed. This device is demonstrated by heating a glass (BK7) window with a CO sub 2 laser, effectively simulating high power end-pumping in a rod. Temporal OPD changes are measured by automated counting of interference fringes as they are generated by the thermal effects. A two-dimensional, time dependent model is developed to describe the radial temperature distribution in a cylinder, the stress and strain distributions, the thermal expansion, and the associated OPD change caused by a Gaussian heat source. This compared to the experimental data for the BK7 window to determine the validity of the approximations and its usefulness for other systems. Good agreement between the model and experiment, within 10 percent was observed.