Abstract
We generated synchronized sub-200-fs pulses between 3 and 4.4 mm at a 1-kHz repetition rate by pumping a KNbO3 optical parametric amplifier with a femtosecond Ti:sapphire regenerative amplifier and seeding it by narrow-band quasi-cw radiation. Output idler energies as high as 7 μJ at 4 μm are reported from this extremely simple single-stage device, which correspond to amplification factors as high as 3 × 105 and a conversion efficiency of 15.