Carbon coatings for soft-x-ray reflectivity enhancement

In X-ray astronomical telescopes, the focalization of the radiation is achieved by means of grazing incidence Wolter I (parabola + hyperbola) optics in total reflection regime. In general, high density materials (e.g. Au, Pt, Ir, W) are used as reflecting coatings, in order to increase as much as possible the cut-off angles and energies for total reflection. However these materials present an important reduction of the reflectivity between 0.2 and 5 keV, due to the photoabsorption, and this phenomenon is particularly enhanced in correspondence of the M absorption edges (between 2 and 3.5 keV). In general, this determines a strong decrease of the telescope effective area. To overcome the pro…