70 MW-Level Picosecond Mid-Infrared Radiation Generation by Difference Frequency Generation in AgGaS₂, BaGa₄Se₇, LiGaSe₂, and LiGaS₂

Abstract

Comparative study of nonlinear crystals for picosecond difference frequency generation in mid-IR is presented. Nonlinear crystals of AgGaS2, BaGa4 Se7, LiGaSe2, and LiGaS2 were studied. In order to investigate the dependence of efficiency on the crystal length, three sets of crystals with lengths of 2, 4, or 8 mm were tested. The developed tunable DFG system was driven by the 1.03 µm, 1.8 ps, Yb:YAG thin-disk laser system operated at the repetition rate of 10 or 100 Hz. As the best result, picosecond mid-IR pulses at a wavelength of $\sim$7 µm with the energy up to 130 µJ corresponding to the peak power of $\sim$72 MW were generated using the 8 mm long LiGaS2 crystal. Using the BaGa4 Se7 crystal, DFG tunability in the wavelength range from 6 up to 13 µm was achieved.

Keywords

• Difference frequency generation
• mid-infrared radiation
• nonlinear optics
• picosecond lasers