<p>Chalcogenide glass samples shaped as thin discs of the Ga₃Ge₂₅As₁₅Se₅₇ composition, undoped and doped with samarium ions (Sm³⁺) at concentrations of 0, 750 and 1700 ppmw, were illuminated with S- or P-polarized light in the range of wavelengths of 0.5–1.8&#xa0;μm near the fundamental absorption band edge. The transmittance and reflectance measurements were validated by comparison with a theoretical model example that takes into account the refractive index dispersion, polarization-dependent Fresnel reflections, and an absorption band at a specific frequency. Based on the measurement results, spectral dependences of the attenuation coefficients and refractive indices of the doped and undoped glasses were calculated. The scattering coefficients corresponding to the “gray” losses, estimated by analyzing the microstructure studied in the bulk of glass samples using IR 3D microscopy, were subtracted from the attenuation coefficients to obtain the absorption coefficients at the edge of the fundamental absorption band and to estimate the bandgap energy and the Urbach tail parameter of the glasses. It was found that the scattering coefficients decrease with increasing Sm³⁺concentration. The absorption coefficients depend on the ion concentration at the low-frequency edge of the Urbach tail and at the weak absorption tail between the absorption bands of Sm³⁺. A slight separation of the spectral dependences of the refractive indices and absorption coefficients measured at different light polarizations was obtained for both undoped and doped glasses. It was found that the glass doping with such Sm³⁺concentrations does not affect zone-zone transitions in the glass, but changes the density of localized states in the bandgap.</p>