High-energy astrophysics at the diffraction limit

We discuss various astrophysical science drivers for upcoming high-resolution X-ray instruments on the mas scale. Even more than current missions like Chandra and XMM-Newton, planned diffraction-limited telescopes would provide unprecedented insights into hottest-ever physical processes in the universe. We apply an efficient and simple Fresnel lens design to samples of well-known targets like stellar coronae, X-ray binaries, AGN, ultraluminous X-ray sources and supernova remnants. The cosmological impact of deep observations is discussed as well as potential applications to low-mass gravitational lenses.