Growth and properties of LiGaX2 (X = S, Se, Te) single crystals for nonlinear optical applications in the mid-IR

Single crystals LiGaX2 (X = S, Se, Te) of optical quality were grown, with transparency ranges at 5 cm‐1 absorption level of 0.32‐11.6 μm, 0.37‐13.2 μm and 0.54‐14.2 μm, respectively. The first two, LiGaS2 and LiGaSe2, have a wurtzite‐type structure whereas LiGaTe2 is tetragonal (chalcopyrite lattice). The three refractive indices were measured in the whole transparency ranges of LiGaS2 and LiGaSe2 and na and nc were found to be very close (quasi‐uniaxial optical anisotropy) with a crosspoint at 6.5 μm (LiGaS2) and 8 μm (LiGaSe2). Sellmeier equations were fitted and phase‐matching conditions for second harmonic generation (SHG) were calculated: the 1.467‐11.72 μm spectral range for the fundamental is covered by LiGaS2 and LiGaSe2.