Carbon-based Fresnel optics for hard x-ray astronomy.

Abstract

We investigate the potential of large-scale diffractive-refractive normal-incidence transmission lenses for the development of space-based hard x-ray telescopes with an angular resolution in the range of (10-6-10-3) arcsec over a field of view that is restricted by the available detector size. Coherently stepped achromatic lenses with diameters up to 5m for compact apertures and 13m in the case of segmentation provide an access to spectrally resolved imaging within keV-wide bands around the design energy between 10 and 30keV. Within an integration time of 106 s, a photon-limited 5σ sensitivity down to (10-9-10-7) s-1 cm-2 keV-1 can be achieved depending on the specific design. An appropriate fabrication strategy, feasible nowadays with micro-optical technologies, is considered and relies on the availability of high-purity carbon or polymer membranes. X-ray fluorescence measurements of various commercially available carbon-based materials prove for most of them the existence of a virtually negligible contamination by critical trace elements such as transition metals on the ppm level.