High-repetition-rate ultrashort-pulse optical parametric oscillator continuously tunable from 2.8 to 6.8 μm

We describe a synchronously pumped femtosecond optical parametric oscillator based on periodically poled LiNbO3 that is broadly tunable in the mid infrared. A transmission window of periodically poled lithium niobate beyond the conventionally accepted infrared absorption edge of 5.4 mu m has been exploited to produce idler pulses that are tunable across a wavelength range of 4 mu m, with milliwatt-level output powers at wavelengths as long as 6.8 mu m. We also present experimental tuning results that are in good agreement with the theoretical phase matching predicted from published infrared-corrected Sellmeier equations for LiNbO3. (C) 1999 Optical Society of America OCIS codes: 190.0190, 190.2620, 190.4970, 190.4360, 320.2250, 320.7110.