Single crystals LiGaX 2 (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, LiGaS 2 and LiGaSe 2 , have a wurtzite-type structure whereas LiGaTe 2 is tetragonal (chalcopyrite lattice). The three refractive indices were measured in the whole transparency ranges of LiGaS 2 and LiGaSe 2 and n a and n c were found to be very close (quasi-uniaxial optical anisotropy) with a crosspoint at 6.5 µm (LiGaS 2 ) and 8 µm (LiGaSe 2 ). 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 LiGaS 2 and LiGaSe 2 .
Lithium thioindate (LiInS2) is a new nonlinear chalcogenide biaxial material transparent from 0.4 to 12 µm, that has been successfully grown in large sizes and good optical quality. We report on new physical properties that are relevant for laser and nonlinear optics applications. With respect to AgGaS(e)2 ternary chalcopyrite materials, LiInS2 displays a nearly-isotropic thermal expansion behavior, a 5-times larger thermal conductivity associated with high optical damage thresholds, and an extremely low intensity-dependent absorption allowing direct high-power downconversion from the near-IR to the deep mid-IR. Continuous-wave difference-frequency generation (5-11 µm) of Ti:sapphire laser sources is reported for the first time.
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