Thermal lensing analysis of TGG and its effect on beam quality.

An analysis is presented of a TGG crystal rod under high power laser operation. A semianalytical thermal analysis is investigated to obtain the temperature profile and thermal lensing effect in a TGG crystal upon incidence of a high power laser light. By solving the heat transfer equation for the TGG crystal and taking the Gaussian beam transverse intensity profile as the heat source, the optical path difference due to induced thermal effects was obtained. Moreover, a detailed model for the dependence of thermal lensing and beam degradation which takes into account up to the fifth-order spherical aberration is presented. Based on this model, it is shown that up to a critical value of the beam power the degradation of the beam is not significant. The experimental results on thermal lensing and degradation on beam quality of a high power laser passing through a TGG crystal rod are in agreement with the main results from our model.