Wide spectral range optical characterization of terbium gallium garnet (TGG) single crystal by universal dispersion model

Terbium gallium garnet (TGG – ${\mathrm{Tb}}_3{\mathrm{Ga}}_5{O}_{12}$) single crystal was optically characterized using the multi-sample and multi-instrument method across a wide spectral range with the help of the universal dispersion model. The obtained optical constants cover the spectral range from the far-IR region ($25{\mathrm{cm}}^{-1}$) to the vacuum-UV region (10.3 eV). The applied dispersion model includes all elementary absorption processes occurring within the spectral range that affect the dielectric response, including phonons and valence electron excitations. The primary objective was to accurately determine the optical constants with the highest possible precision. The optical results were compared with ab initio density functional theory calculations to gain insight into the nature of the absorption edge and the distribution of the f-electron excitations.