Advanced Fresnel X-ray telescopes for spectroscopic imaging

We present an effective achromatic imaging technique for diffraction-limited X-ray telescopes. For a common focal length, independent optical sections of the aperture are dedicated to two or more spectral bands and optimized with respect to their efficiency. For this purpose, we introduce the “achromatic gain” of an X-ray hybrid lens. Large-scale segmented and nested apertures provide a promising implementation of that scheme. An optimized numerical example and astrophysical simulations prove its capabilities for an energy range between 6 and 16 keV.