Generation, shaping, and characterization of intense femtosecond pulses tunable from 3 to 20 μm

We report on an intense mid-infrared light source that provides femtosecond pulses on a microjoule energy level, broadly tunable in the 3-20-mum wavelength range with pulse durations as short as 50 fs at 5 mum. The pulses are generated by phase-matched difference-frequency mixing in GaSe of near-infrared signal and idler pulses of a parametric device based on a 1-kHz Ti:sapphire amplifier system. Pulse durations are characterized with different techniques including autocorrelation measurements in AgGaS2, two-photon absorption in InSb, and cross-correlation measurements with near-infrared pulses in a thin GaSe crystal. A subsequent zero-dispersion stretcher of high transmission allows for optimum pulse compression, a more detailed amplitude and phase characterization and, ultimately, amplitude shaping of the mid-infrared pulses. (C) 2000 Optical Society of America [S0740-3224(00)00212-5] OCIS codes: 320.7110, 190.2620, 190.4970, 320.5540, 190.7220, 230.4320.