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 (10-10) arcsec over a field of view that is restricted by the available detector size. Coherently stepped achromatic lenses with diameters up to 5 m for compact apertures and 13 m in the case of segmentation provide an access to spectrally resolved imaging within keV-wide bands around the design energy between 10 and 30 keV. Within an integration time of 10 s, a photon-limited 5σ sensitivity down to (10-10) s cm keV 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.

Focusing diffraction optics for orbital telescopes

“…The equation for focal distance f = 4N(δr N ) 2 /mλ (11) demonstrates that if a certain reduction in angular resolution is permissible, the focal distance may be shortened in operation at a lower energy E by reducing the size of the outer FZP zone (δr N ) or the zone number (N). For example, segmented designs of Laue lenses have been proposed [236,237,242] to reduce the number of zones and simplify the retargeting of a telescope. A lens is divided into optically independent circular segments.…”

“…Note that a segmented FZP is similar in terms of design to a Laue lens. The concept of efficient simultaneous visualization in five energy ranges from 5 to 10 keV in a high-resolution X- ray telescope has been detailed in [237]. This design is optimized for a shortened focal distance (∼ 10 2 km).…”