FEMTOSECOND INFRARED PULSES TUNABLE FROM 9 TO 18 MU-M AT AN 88-MHZ REPETITION RATE

Femtosecond mid-infrared laser pulses that are continuously tunable in the wavelength range from 9 to 18 mu m are demonstrated. These nearly bandwidth-limited pulses are generated by phase-matched difference-fr equency mixing within the broad spectrum of 20-fs pulses from a mode-l ocked Ti:sapphire laser in GaSe. A direct determination of the pulse d uration at 11.5 mu m gives a value of 140 fs. The average mid-infrared power of 1 mu W is similar to 100 times greater than that for infrare d generation by non-phase-matched optical rectification. (C) 1998 Opti cal Society of America.