Kerr-lens mode-locked 23-μm Tm^3+:YLF laser as a source of femtosecond pulses in the mid-infrared

We report what is to our knowledge a new source of femtosecond pulses in the mid-infrared, based on a Kerr-lens mode-locked (KLM) Tm3+:YLF laser at 2303 nm. An undoped ZnSe substrate was included in the resonator to provide enhanced nonlinear phase modulation during KLM operation. The Tm3+:YLF laser was end-pumped with a continuous-wave Ti3+ : sapphire laser at 780 nm. With 880 mW of pump power, we generated 514-fs pulses at a pulse repetition rate of 41.5 MHz with an average power of 14.4 mW. The spectral width (full width at half-maximum) was measured as 15.4 nm, giving a time-bandwidth product of 0.44. We foresee that the wide availability of this gain medium, as well as the straightforward pumping scheme near 800 nm, will make 2.3-μm, mode-locked Tm3+:YLF lasers versatile sources of ultrashort pulses in the mid-infrared.