Femtosecond noncollinear optical parametric amplification in the mid-infrared range with 1.25 mu m pumping

Abstract

We study noncollinear three-wave interaction in a traveling wave optical parametric amplifier operating in the mid-infrared spectral range between 6 and 8 mum using HgGa2S4 and AgGaS2 as nonlinear optical crystals. Calculations reveal that matching of the group velocities in both crystals is possible in a wider spectral (or angular) region for type-I interaction. High-power femtosecond pulses at 1.25 mum from a Cr:forsterite regenerative amplifier are used for pumping the optical parametric amplifier at a repetition rate of 1 kHz. Experimentally we verify the advantages of noncollinear interaction by increasing the conversion efficiency approximately sixfold in the saturation regime as compared to the collinear case. The maximum idler energy measured near 6 mum exceeds 4 muJ and typical pulse durations are about 300 fs