Parametric Down-Conversion of Near-IR Laser Radiation into the Mid-IR Range Using Nonlinear LiGaSe2 and LiGaS2 Crystals with Antireflection Microstructures

Abstract

The LiGaSe₂ and LiGaS₂ crystals with antireflection microstructures are comparatively tested as frequency down-converters into the mid-infrared range (4874 nm) in a two-stage optical parametric oscillator with a single cavity under intracavity pumping with a Nd:YLF laser with a wavelength of 1047 nm and a pulse duration of 25 ns. The first stage of optical parametric oscillation in the KTiOAsO₄ crystal produces two-micron radiation with wavelengths of 1724 and 2668 nm at a pulse energy of up to 2 mJ. In the second stage of conversion, the LiGaS₂ crystal with antireflection microstructures compared to LiGaSe₂ with antireflection microstructures proves to be more efficient despite the lower effective nonlinearity coefficient, which can be explained by the higher optical quality of the crystal. The energy of the radiation pulse with a wavelength of 4874 nm reaches the level of 100 nJ.