Instituto de Óptica «Daza de Valdés»

M. Fernández-Perea; M. Vidal-Dasilva; J. I. Larruquert; J. A. Méndez; J. A. Aznárez


A summary of the optical coatings for the spectral range from 50 to 200 nm that can be prepared at GOLD is presented. This spectral range, named here far and extreme ultraviolet (FUV/EUV), is characterized by the high absorption of almost all materials and the strong dependence of their optical properties on the deposition parameters and on the exposure of the samples to the atmosphere. Broadband mirrors and narrowband filters were prepared in an ultra high vacuum system where in situ FUV/EUV reflectometry is available. In this work we summarize the main aspects concerning in situ performance and ageing of these coatings. Broadband mirrors composed of Al/MgF2, SiC, B and Al/MgF2/SiC cover the FUV/EUV spectral range from 50 to 200 nm. Above the transparency cutoff of MgF2 (115 nm), transmittance filters based on Al/MgF2 multilayers have been developed peaked at wavelengths as short as 120 nm. An example is shown centered at 124 nm with a peak transmittance of 27% and a FWHM of 12 nm for a fresh coating. Below 115 nm, a research on reflectance filters has recently started with very promising results on filters peaked at ~83 nm, close to the OII spectral line. Fresh filters with 27% peak reflectance at normal incidence and a FWHM of 14 nm have been obtained. These novel reflectance filters based on Al, Yb and SiO must still demonstrate stability over time. The developed coatings have a potential application in the field of astronomical observations.