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-freq uency mixing in a 1-mm-thick AgGaSe2 crystal, the 130- and 180-fs outp ut pulses (1.45 < lambda < 1.85 mu m) from an 84-MHz-repetition-rate o ptical parametric oscillator. Numerical simulations show that intrapul se and interpulse group velocity dispersion determine minimum pulse du ration above and below 15 mu m, respectively. By cross correlation (up conversion) of 10.5-mu m pulses with 90-fs, 810-nm pulses in AgGaS2, t he pulse length was measured to be 310 fs in good agreement with simul ations. (C) 1997 Optical Society of America.