Nonoxidized Al-overcoated Ir bilayers with high reflectance in the extreme ultraviolet above 50 nm

Bilayers of a thin, nonoxidized Al film over an Ir film are prepared.The bilayers are intended to enhance the reflectance of Al below the Al plasma wavelength ( p ϳ83 nm).Above p the bilayers have a high reflectance comparable to that of single Al films.Ir films were deposited by electron gun evaporation on a heated substrate.Al films of various thicknesses are deposited by evaporation from a thermal source on the Ir film once it is cooled to room temperature.The bilayers are prepared under ultra-high-vacuum (UHV) conditions and their reflectance is measured in situ.Accelerated aging processes, which are performed by annealing the bilayers in UHV, show that the bilayers are stable after 1 h annealing at temperatures up to 540Ϯ25 K.The bilayers show no observable deterioration after long-term storage under normal atmosphere.The optical constants of Ir films are also obtained.In-orbit coating of optical surfaces with Ir/Al bilayers is proposed for extreme UV astronomy.