Development of multilayers for hard X-ray optics

We have been studying multilayers in the view point of developing X-ray optical instrument mainly for X-ray astronomy. Recently we successfully made hard X-ray telescope using platinum carbon multilayer supermirror with effective energy band up to several tens of keV for the first balloon experiment. In this telescope, we use a few hundred nested thin foil mirrors with radii of 60 - 200 mm, which correspond to grazing incidence angles of 0.11 - 0.36 degree for 8 m focal length. On the surface of each mirror, we deposited Pt/C depth graded multilayes, so-called supermirror by DC magnetron sputtering system. Multilayer parameters, such as d-spacing, ratio of Pt thickness to d-spacing, total number of layer pairs were searched in order to maximize integrated reflectivity in the given energy band. Evaluation of the X-ray reflection performance was done by X-ray beam line in our laboratory and synchrotron facility SPRING8. From these measurements, we found that the basic performance was as expected and especially the averaged interfacial roughness was 0.4 nm. In this paper, we will discuss general design of multilayer supermirror for hard X-rays, fabrication and evaluation of such multilayers and future applications.