Effect of thermal lensing on the mode matching between pump and laser beams in Cr4+: forsterite lasers: a numerical study

The numerical study presented in this paper investigates the role of therma l lensing on the mode matching between the pump beam and the cavity beam in continuous-wave end-pumped Cr4+:forsterite lasers. A suitable mode overlap function was first derived to calculate the degree of overlap between the pump beam and the fundamental mode of the resonator. The effect of thermal lensing on mode matching was then numerically investigated by calculating t he changes in the average value of the mode overlap function due to variati ons in pump power and crystal boundary temperature. Thermal lensing was tak en into account by calculating the pump-induced thermal gradients and by ap proximating the gain medium as a distributed quadratic lens. Finally, the m odel was used to offer guidelines about how one of the resonator lenses sho uld be readjusted in order to maintain optimum mode matching as the boundar y temperature and pump power are varied.