Generation of high-repetition-rate femtosecond pulses from 8 to 18 mu m

We generated subpicosecond pulses from 8 to 18 mu m by difference-frequency mixing in a 1-mm-thick AgGaSe2 crystal, the 130- and 180-fs output pulses (1.45 < lambda < 1.85 mu m) 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 mu m, respectively. By cross correlation (upconversion) of 10.5-mu m pulses with 90-fs, 810-nm pulses in AgGaS2, the pulse length was measured to be 310 fs in good agreement with simulations. (C) 1997 Optical Society of America.