Transmittance and optical constants of Eu films from 8.3 to 1400 eV

The optical constants of Eu films were obtained in the 8.3–1400 eV range from transmittance measurements performed at room temperature. Thin films of Eu were deposited by evaporation in ultrahigh vacuum conditions and their transmittance was measured in situ. Eu films were deposited onto grids coated with a thin C support film. The refractive index n of Eu was calculated using the Kramers-Kronig analysis. Data were extrapolated both on the high- and low-energy sides by using experimental and calculated extinction coefficient values available in the literature. Eu, similar to other lanthanides, has a low-absorption band just below the O2,3 edge onset; the lowest absorption was measured at about 16.7 eV. Therefore, Eu is a promising material for filters and multilayer coatings in the energy range below the O2,3 edge in which materials typically have a strong absorption. The consistency of the composite optical constants was tested with the f and inertial sum rules and found to be good.