Infrared optical properties of calcium lanthanum sulfide

The fundamental infrared optical properties of CaLa₂S₄ were determined by specular reflectance measurements from theoretically dense, optically transparent, polycrystalline ceramics. Kramers-Kronig transformation of the reflectance spectra permitted the extraction of refractive index, and transverse and longitudinal optic modes. Five transverse modes predicted by factor group analysis were observed with the intense high wavenumber mode occurring at 142 and 205 cm^− 1. The other three modes are weak and occur at 37, 59, and 86 cm^− 1. The two high wavenumber intense modes have identifiable longitudinal modes at l51 and 318 cm^− 1.