Generation of high-repetition-rate femtosecond pulses from 8 to 18 microm.

We generated subpicosecond pulses from 8 to 18 mum by difference-frequency mixing in a 1-mm-thick AgGaSe(2) crystal, the 130- and 180-fs output pulses (1.45 < lambda < 1.85 mum) from an 84-MHz-repetition-rate optical parametric oscillator. Numerical simulations show that intrapulse and interpulse group velocity dispersion determine minimum pulse duration above and below 15 mum, respectively. By cross correlation (upconversion) of 10.5-mum pulses with 90-fs, 810-nm pulses in AgGaS(2), the pulse length was measured to be 310 fs in good agreement with simulations.