Transmittance and optical constants of Lu films in the 3–1800 eV spectral range

The optical constants n and k of lutetium (Lu) films were obtained in the 3-1800 eV range from transmittance measurements performed at room temperature. These are the first experimental optical constant data of Lu in the whole range. Thin films of Lu with various thicknesses were deposited by evaporation in ultrahigh vacuum conditions and their transmittance was measured in situ. Lu films were deposited onto grids coated with a thin, C support film. Transmittance measurements were used to obtain the extinction coefficient k of Lu films. The refractive index n of Lu was calculated with Kramers-Krönig analysis. k data were extrapolated both on the high and on the low-energy sides by using experimental and calculated k values available in the literature. Lu, similar to other lanthanides, has a low-absorption band below the O 2,3 edge onset; the lowest absorption was measured at ∼25.1 eV. Therefore, Lu is a promising material for filters and multilayer coatings in the energy range below the O 2,3 edge in which most materials have a large absorption. Good consistency of the data was obtained through f and inertial sum rules.