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

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Abstract
We review methods for frequency conversion of amplified femtosecond laser pulses from the near- to the mid-infrared. The potential of all commercially available optical crystals is evaluated on the basis of the specific requirements in the high-power femtosecond regime. A comparative experimental study of a number of materials (birefringent and quasi-phase-matched) employed in a seeded optical parametric amplifier pumped near 800 nm is presented, where the generated idler is tunable between 3 and 4 µm. Internal conversion efficiencies as high as 40% and pulse energies as high as 20 µJ are achieved in this spectral range. Wavelength tunability up to 12 µm with energies exceeding 1 µJ is demonstrated by pumping optical parametric amplifiers and generators near 1.25 and 2 µm, as well as by difference frequency generation with a quantum efficiency of 40-80%. In all cases the generated mid-infrared pulses are almost bandwidth limited with a duration of 100-200 fs.