Resolution limits of transmission optics for x-ray astronomy

We report on recent theoretical and experimental results on diffractive-refractive transmission lenses as promising candidates for next-generation X-ray telescopes with an ultra-high angular resolution. This feature is especially analyzed for elementary refractive, diffractive and dispersion-corrected hybrid lenses and a fundamental limit to the angular resolution for optics of the latter type is identified. An inherent flexibility in adjusting the image sharpness is obtained from the segmentation of an aperture into small partitions, whose degree of coherence can be controlled continuously. Successfully realized monolithic phase zone plates from a spin-coated polymer show the way to the practical implementation of large-scale objectives. Based on these concepts, an arrangement for enhanced and variable high-throughput imaging around the Fe-K_α line at 6.4 keV is finally proposed.