Ion-beam figuring of x-ray mirrors

Abstract

A significant portion toward understanding evolution of the universe comes from x-ray astronomy since many astronomical objects of interest, such as black holes, supernovae and distant galaxies, emit radiation in the x-ray band. As basically all materials have almost unity refractive index for x-rays focusing x-ray beams is only possible by reflection at grazing incidence. Due to the low photon flux of the objects under study (few photons per hour) each individual photon is of particular interest. Thus, the collective area of x-ray telescopes needs to be as large as possible which is achieved by a large amount of concentrically nested x-ray mirrors whose shape needs to be ideal fitting to the designed geometry for high image quality. Due to the mirrors curvature even state of the art mechanical machining and chemical mechanical polishing processes leave a residual surface error of several hundred nanometers. Those residual errors can be significantly reduced by ion beam figuring.