Gain optimization of a Kerr-lens mode-locked Cr:forsterite laser in the CW regime: Theory and experiments

We present a parametric study of the optimisation of a longitudinally pumped astigmatically-compensated Cr4+:forsterite laser and compare with experimental results. The gain medium is characterized by a low figure of merit and an upper state life time which is sensitive to temperature, and therefore to pump power. The objective is the optimisation in the CW regime in order to get the highest circulating intensity, thereby making self mode-locking easier. We solve the rate equations of a two-level vibronic laser to obtain the CW laser output and show that there exits an optimum crystal length, weakly dependent on pump power, output coupler and upper state life time. The model is shown to agree well with experiment when the pump power induced thermal effects are taken into account.