50-µJ level, 20-picosecond, narrowband difference-frequency generation at 4.6, 5.4, 7.5, 9.2, and 10.8 µm in LiGaS2 and LiGaSe2 at Nd:YAG laser pumping and various crystalline Raman laser seedings

A comparative study of picosecond mid-IR difference frequency generation in a wide wavelength range of 4.6-10.8 µm in a simple down-converter based on the 8-mm long, high-damage-threshold crystals of LiGaS 2 or LiGaSe 2 under the 5-mJ, 20-ps, 1.064-µm Nd:YAG laser pumping and the single-pass crystalline (CaCO 3 , BaWO 4 , CVD-diamond) Raman laser seeding was presented. 10-µJ-level, narrowband (<2 cm −1 ) generation at discrete wavelengths of 4.6, 5.4, 7.5, and 9.2 µm with the optical frequencies equal to the vibrational Raman frequency or its second harmonic of various crystalline Raman seeders was demonstrated. Optimization of the pump spot and mode-matching between the pump and signal spots allowed to increase the output pulse energy up to 50 µJ in the case of LiGaSe 2 .