Multilayer optics for hard X-ray astronomy by means of replication techniques

In this paper we will report on an activity we have recently undertaken with the aim of setting up a method for the realization of hard X-ray (> 10 keV) multilayer mirror astronomical optics based on a replication process. Our approach foresees the direct deposition of the multilayer stack onto the mandrel by ion-beam sputtering followed by the deposition of the Nickel by means of an electrolytic bath. The Nickel gives the mechanical strength to the mirrors. All deposited materials are later on separated from the mandrel by cooling it. This is a natural extension of the method already successfully used for the production of the soft X-ray optics with Au monolayer coating for the SAX, JET-X and XMM telescopes. This method is particularly convenient because permits not only of keeping the mirror supports very thin (with a consequent gain in weight and shell filling factor) but also of achieving good imaging performances. Here we will present the main features of this method and the X-ray reflectivity and topographic results obtained from a first prototype flat sample we produced following this way.