Selection of Optimal Phase Matching Conditions for Semiconductor Nonlinear Crystals Under Cascade Pumping at 2 μm

Model studies of the optimal phase matching conditions are performed for the implementation of an optical parametric oscillator (OPO) in the mid-infrared range (IR) based on promising nonlinear crystals, such as: cadmium selenide CdSe, barium selenogallates BaGa 4 Se 7 and BaGa 2 GeSe 6 , mercury thiogallate HgGa 2 S 4 and zinc germanium phosphide ZnGeP 2 (ZGP). To pump OPOs, it is necessary to use a laser source with a wavelength in the spectral range of 1.9–2.2 μm, since for the combination of physical properties of the listed above nonlinear crystals, it is optimal for achieving the maximum efficiency of parametric frequency conversion. Despite the high values of the effective nonlinear susceptibility and thermal conductivity, the transparency range of the ZGP crystal in the mid-IR range does not exceed 10.4 μm, and the achieved OPO generation wavelength range does not exceed 9 μm in the nanosecond mode. The HgGa 2 S 4 and BaGa 4 Se 7 crystals have lower values of nonlinear coefficients and thermal conductivity and wider transparency ranges and, as a consequence, make it possible to obtain lasing up to a wavelength of 12 μm. When using a BaGa 4 Se 7 crystal, the lasing range can be extended up to 17 μm. The CdSe crystal has the widest transparency range. However, its other parameters do not allow solving the set tasks.