Transmittance and optical constants of Er films in the 3.25-1,580 eV

Juan I. Larruquert, Fabio Frassetto, Sergio García-Cortés, Manuela Vidal-Dasilva, Mónica Fernández-Perea, José A. Aznárez, José A. Méndez, Luca Poletto, A. Marco Malvezzi, Angelo Giglia, and Stefano Nannarone

Abstract

The optical constants of erbium (Er) films were obtained in the 3.25–1580 eV range from transmittance measurements performed at room temperature. Thin films of Er were deposited by evaporation in ultra high vacuum conditions and their transmittance was measured in situ. Substrates consisted of a thin C film supported on a grid. Transmittance measurements were used to obtain the extinction coefficient k of the Er films. The refractive index n of Er was calculated using the Kramers–Krönig analysis. k data were extrapolated both on the high- and low-energy parts of the spectrum by using experimental data and calculated k values available in the literature. Er, similar to other lanthanides, has a low-absorption band below the O2,3 edge onset; the smallest absorption was measured at ~22.5 eV. Therefore, Er is a promising material for filters and multilayer coatings in the energy range below the O2,3 edge, in which materials typically have an absorption stronger than at other energies. Good consistency of the data resulted from the application of f and inertial sum rules.