Study of the Reflectivity in the XUV Domain of the Normal-Incidence Multilayer Mirrors

The development of multilayer optics has profound inplicationos for soft ray/UV astronomy, since it allows to extend the use of normal incidence telescopes to covee th XUV region where the lines are formed at grately different temperatures. A multilayer mirror consist of alternating thi layers of suitable materials deposited on a substrate and its performance depends not only on the optical properties of the materials but also on the design of the multilayer. In this study we have computed the reflectivity of multilayer mirrors to select both the materials and the multilayer design to achieve the best performance in the wevelength range from 30 to 350 A. Our calculations show that high theoretical reflectivities, from 0.2 to 0.8 and relatively narrow bandpasses, rom 1 A to 30 A can be obtained, in the wavelength range from 30 to 350 , by a suitable choice of the materials and of the multilayer design