Influence of thermal effects in Kerr-lens modelocked femtosecond Cr4+:forsterite lasers

We report the characterization of a synchronously-pumped Kerr-lens mode-locked (KLM) femtosecond Cr4+:forsterite laser, generating 66 fs pulses at 1240 nm, with 200 mW output power. The influence of the induced thermal lensing on the fast Kerr modulation is analysed by a simple model, which shows that the conventional criteria employed for KLM optimization of Ti:sapphire must be revised when considering the strong thermal effects induced in the Cr4+:forsterite crystal. Indications from our simple model agree with the experimental results.