Optical constants of Yb films in the 23-1700 eV range. 
The optical constants of Yb films have been determined in the 23-1700 eV spectral range from transmittance measurements performed in situ on Yb films deposited by evaporation in ultrahigh vacuum conditions.  Yb films were deposited over grids coated with a thin carbon film.  Transmittance measurements were used to obtain the extinction coefficient of Yb films at each individual photon energy investigated.  The energy range investigated encompasses Yb edges from M(4,5) to O(2,3).  The current results, along with data in the literature, show that Yb has an interesting low-absorption band in the approximately 12-24 eV range, which may be useful for the development of transmittance filters and multilayer coatings.  The current data along with literature data and extrapolations were used to obtain n, the real part of the complex refractive index, using a Kramers-Krönig analysis.  The application of the sum rules showed a good consistency of the results.