Nanometer focusing of X-rays with modified reflection zone plates

Transmission Fresnel zone plates and x-ray waveguides are presently the best high-resolution optical elements used in x-ray microscopy and micro-probing. The spatial resolution of zone plates is defined not only by the technological limit of about 10 nm but also by the effects of volume diffraction, even for high-order zone plates. The physical nature of a waveguide limits the theoretical spatial resolution to 10 nm, corresponding to the minimum thickness of film able to fulfil the conditions necessary for optical mode formation. Here, we show that reflection zone plates and Bragg-Fresnel lenses can overcame the resolution limit of transmission zone plates and waveguides and make it possible to achieve spatial resolution into the sub-nanometer range, subject to source size limitations. Such optics can be used with existing third-generation synchrotron radiation sources, as well as with x-ray laser sources, e.g., free-electron lasers.