Characterization of the optical constants of materials from the visible to the soft x-rays

A summary of the research performed on the optical characterization of Sc and of several lanthanides from the visible to the soft x-rays is presented. The low absorption of these materials mainly below the O2,3 edge (L 2,3 edge for Sc) turns them promising materials for the realization of multilayer mirrors in a spectral range in which most materials in nature absorb strongly. Thin-film samples with several thicknesses of the target material were deposited by evaporation over thin-film substrates in UHV, and their transmittance was measured in situ. A wide spectral range of direct characterization, along with extrapolations to longer and shorter wavelengths either using literature data (when available) or model predictions, enabled the development of consistent optical constants over the whole spectrum. An assortment of consistency sum rules has been used, and it was found that each of them highlights a given spectral range, which may help evaluate the consistency of each part of the combined spectrum.