Potential and applicability of composite low-Z materials, such as the solid-state hydrides LiH, BeH2 and B10H14, are studied for their use in diffractive-refractive, space-based X-ray lenses for astronomy. Regardless technical challenges like their strong chemical reactivity, a low mass density, and the demand for a high elemental purity, the optical properties of the hydrides allow the design and construction of diffraction-limited focusing optics with an efficiency up to ≈ 1m2 × keV in the range (6 − 18) keV. If scaled to an aperture size of . 4.9m, an angular resolution . 1×10−3 arcsec is achieved. Three-fold lens stacking reduces the outer aspect ratio of the refractive component to 2.5 or less, at an – if combined with segmentation – focal length of no more than ≈ 5 × 102 km.
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