Abstract
We have used a combined optical system of a high gain elliptic Kirkpatrick-Baez mirror system (KB) and a multilayer Laue lens (MLL) positioned in the focal plane of the KB for hard x-rays nano-focusing. The two-step focusing scheme is based on a high acceptance and high gain elliptical mirror with moderate focal length and a MLL with ultra-short focal length. Importantly, fabrication constraints, i.e. in mirror polishing and bending, as well as MLL deposition can be significantly relaxed, since (a) the mirror focus in the range of 200-500 nm is sufficient, and (b) the number of layers of the MLL can be correspondingly small. First demonstrations of this setup at the coherence beamline of the PETRA III storage ring yield a highly divergent far-field diffraction pattern, from which the autocorrelation function of the near-field intensity distribution was obtained. The results show that the approach is well suited to reach smallest spot sizes in the sub-10nm range at high flux.
Highlights
Coherent x-ray imaging as a lensless technique holds the promise to overcome the resolution limits of x-ray objective lenses.[1,2] In this context, ‘lensless’ means that no optical element is placed between sample and detector
Fabrication of wedged zones will be much easier, since all constraints in fabrication favor small multilayer Laue lens (MLL) apertures. (ii) If small N MLLs are required without compromising high flux, an optimized focusing system has to be devised based on high gain pre-focusing
The simulated intensity distribution behind the OA-MLL with parameters fixed to the experimental design is visualized in (c) for an ideal exit wave as calculated based on the ‘projection approximation’, and in (d) for the actual thickness of OA-MLL D = 3.26 μm based on a multislice algorithm
Summary
Coherent x-ray imaging as a lensless technique holds the promise to overcome the resolution limits of x-ray objective lenses.[1,2] In this context, ‘lensless’ means that no optical element is placed between sample and detector.
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