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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) Tm:YLF laser at 2303 nm. An undoped ZnSe substrate was included in the resonator to provide enhanced nonlinear phase modulation during KLM operation. The Tm:YLF laser was end-pumped with a continuous-wave Ti : 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 Tm:YLF lasers versatile sources of ultrashort pulses in the mid-infrared.

We report, what is to our knowledge, the first passively Q-switched operation of a 2.3-μm Tm³⁺:YLF laser by using a Cr²⁺:ZnSe saturable absorber. In the experiments, a tunable Ti³⁺:sapphire laser was used to end pump the Tm³⁺:YLF gain medium inside an x cavity. A Cr²⁺:ZnSe saturable absorber was also included in the cavity to initiate passive Q switching. At all pump power levels above lasing threshold, passively Q-switched operation of the Tm³⁺:YLF laser could be obtained at 2309 nm with pulse durations and repetition frequencies in the ranges of 1.2-1.4 μs and 0.3-2.1 kHz, respectively. Analysis of power dependent repetition rate data further gave an estimated value of 3.1% for the round-trip saturable loss of the Cr²⁺:ZnSe saturable absorber.

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