Narrowband filters and broadband mirrors for the spectral rangefrom 50 to 200 nm

摘要

A summary of the optical coatings for the spectral range from 50 to 200 nm that can be prepared at Grupo de Optica deLaminas Delgadas is presented. This spectral range, named here far and extreme ultraviolet (FUV/EUV), is characterizedby the high absorption of almost all materials and the strong dependence of their optical properties on the depositionparameters and on the exposure of the samples to the atmosphere. Broadband mirrors and narrowband filters wereprepared in an ultra high vacuum system where in situ FUV/EUV reflectometry is available. In this work we summarizethe 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 120nm. An example is shown centered at 124 nm with a peak transmittance of 27% and a FWHM of 12 nm for a freshcoating. Below 115 nm, a research on reflectance filters has recently started with very promising results on filters peakedat –83 nm, close to the OB spectral line. Fresh filters with 27% peak reflectance at normal incidence and a FWHM of 14nm have been obtained. These novel reflectance filters based on Al, Yb and SiO must still demonstrate stability overtime. The developed coatings have a potential application in the field of astronomical observations.