Kerr-lens mode-locked femtosecond Cr2+:ZnSe laser at 2420 nm

We describe a cw Kerr-lens mode-locked Cr2+:ZnSe laser pumped by a 1800 nm thulium fiber laser. The astigmatically compensated asymmetric x cavity contained a 2.4-mm-long Cr2+:ZnSe sample with a pump absorption coefficient of 11.6 cm(-1) and was operated with a 1% output coupler. The dispersion compensation was achieved by using a MgF2 prism pair. During Kerr-lens mode-locked operation, we could generate 95 fs pulses at a pulse repetition rate of 94.3 MHz and with 40 mW of output power. The center wavelength of the pulses was 2420 nm. The pulses had a spectral width of 69 nm and a time-bandwidth product of 0.335, which is close to the transform limit for hyperbolic secant pulses. (C) 2009 Optical Society of America