Hardness and Young's modulus of BaGa4S7 and BaGa4Se7 nonlinear optical crystals

We report hardness and Young's modulus measurements of two recently developed non-chalcopyrite, non-centrosymmetric crystals, BaGa(4)S(7 )and BaGa4Se7 , which seem very promising for three-wave parametric interactions in the mid-IR part of the spectrum between 5 and 18 mu m. The obtained averaged values for the hardness from nanoindentation tests, converted into Vickers hardness number, are 556 kg/mm(2) for the sulphide and 336 kg/mm(2) for the selenide compound, respectively. Knowledge of these values will be essential for proper polishing and fabrication of optical elements, the wide use and commercialization of these novel non-oxide nonlinear crystals, which possess a number of other advantages over classical chalcopyrites operating in the same spectral window.