Generation of high-power femtosecond light pulses at 1 kHz in the mid-infrared spectral range between 3 and 12 mu m by second-order nonlinear processes in optical crystals

We review methods for frequency conversion of amplified femtosecond laser p ulses from the near- to the mid-infrared. The potential of all commercially available optical crystals is evaluated on the basis of the specific requi rements in the high-power femtosecond regime. A comparative experimental st udy of a number of materials (birefringent and quasi-phase-matched) employe d in a seeded optical parametric amplifier pumped near 800 nm is presented, where the generated idler is tunable between 3 and 4 mum. Internal convers ion efficiencies as high as 40% and pulse energies as high as 20 muJ are ac hieved in this spectral range. Wavelength tunability up to 12 mum with ener gies exceeding 1 muJ is demonstrated by pumping optical parametric amplifie rs and generators near 1.25 and 2 mum, as well as by difference frequency g eneration with a quantum efficiency of 40-80%. In all cases the generated m id-infrared pulses are almost bandwidth limited with a duration of 100-200 fs.