Terahertz permittivity parameters of monoclinic single crystal lutetium oxyorthosilicate

The anisotropic permittivity parameters of monoclinic single crystal lutetium oxyorthosilicate, Lu₂SiO₅ (LSO), have been determined in the terahertz spectral range. Using terahertz generalized spectroscopic ellipsometry (THz-GSE), we obtained the THz permittivities along the a, b, and c ⋆ crystal directions, which correspond to the ϵ a , ϵ b , and ϵ c ⋆ on-diagonal tensor elements. The associated off diagonal tensor element ϵ a c ⋆ was also determined experimentally, which is required to describe LSO's optical response in the monoclinic a-c crystallographic plane. From the four tensor elements obtained in the model fit, we calculate the direction of the principal dielectric axes in the a-c plane. We find good agreement when comparing THz-GSE permittivities to the static permittivity tensors from previous infrared and density functional theory studies.