Kramers-Kronig-constrained variational dielectric fitting and the reflectance of a thin film on a substrate

A test was made of the ability of Kramers-Kronig-constrained variational dielectric fitting to extract the optical conductivity of a thin film from reflectance data containing structure due to both thin film and substrate. The reflectance of a series of well-characterized thin films of SrRu(x)Mg(1-x)O(3) and SrRu(x)O(3) with a variety of thicknesses (approximately 56-300 nm) and dc resistivities (approximately 250-2200 micro Omega cm) was measured. The low frequency values of the extracted optical conductivities agree with the dc measurements, however, removal of features due to the substrate improves with increasing film thickness.