Barium gallium sulfide, BaGa4S7 (BGS) is an attractive nonlinear optical (NLO) crystal notable for the rare combination of wide band gap (2.64 eV), long phonon cut-off wavelength (13.7 m), and relative ease of growth from stoichiometric melts. BGS is ideal for shifting widely-available Ti:sapphire and Yb-doped femtosecond laser sources deep into the mid-IR. However, BGS is plagued by severe cracking during cool-down and post-growth processing. To overcome these difficulties, we fabricated oriented single crystal BGS cubes with faces normal to the principal axes, and determined the thermal expansion coefficient along each axis via temperature-dependent x-ray diffraction as well as dilatometry.

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Peter G. Schunemann, Michael A. Susner, and Kevin T. Zawilski, "Crystal growth and anisotropic thermal expansion of BaGa4S7," Proc. SPIE PC12405, Nonlinear Frequency Generation and Conversion: Materials and Devices XXII, PC124050L (Presented at SPIE LASE: February 01, 2023; Published: 17 March 2023); https://doi.org/10.1117/12.2655196.6321500025112.