Study of operability of a nonlinear converter based on a LiGaSe$_2$ crystal with surface antireflection microstructures under nanosecond laser excitation

Laser-induced damage threshold for LiGaSe$_2$ with different antireflection microstructures and without it by 1-on-1 method using a nanosecond YAG:Nd$^{3+}$ laser with intracavity optical parametric oscillation at a wavelength of 2.1 $\mu$m is investigated. A two-stage optical parametric oscillator based on KTiOPO$_4$ and LiGaSe$_2$ crystals with antireflection microstructures pumped by a nanosecond YAG:Nd$^{3+}$ laser is developed. The results of a numerical and physical experiment on testing a LiGaSe$_2$ crystal with antireflection microstructures as an active nonlinear medium for the parametric conversion of laser radiation into the mid-infrared range are presented.