Barium chalcogenides for nonlinear optics in the mid-IR: Properties and applications

The essential properties of BaGa4S7 (BGS), BaGa4Se7 (BGSe), BaGa2GeS6 (BGGS), BaGa2GeSе6 (BGGSe), and Ba2Ga8GeS16 (B2GGS) are reviewed, together with all nonlinear optical applications of these non-centrosymmetric crystals realized so far. •Essential properties of five Ba chalcogenide crystals are reviewed useful for nonlinear frequency conversion in the mid-IR.•All realizations of such nonlinear optical frequency conversion processes are briefly documented.•Ambiguities in the literature due to different conventions are explained.•The advantages of these novel nonlinear materials compared to existing commercially available materials are outlined.