Multilayer Laue Lens: A Path Toward One Nanometer X-Ray Focusing

Abstract

The multilayer Laue lens (MLL) is a novel diffractive optic for hard X-ray nanofocusing, which is fabricated by thin film deposition techniques and takes advantage of the dynamical diffraction effect to achieve a high numerical aperture and efficiency. It overcomes two difficulties encountered in diffractive optics fabrication for focusing hard X-rays: (1) small outmost zone width and (2) high aspect ratio. Here, we will give a review on types, modeling approaches, properties, fabrication, and characterization methods of MLL optics. We show that a full-wave dynamical diffraction theory has been developed to describe the dynamical diffraction property of the MLL and has been employed to design the optimal shapes for nanofocusing. We also show a 16 nm line focus obtained by a partial MLL and several characterization methods. Experimental results show a good agreement with the theoretical calculations. With the continuing development of MLL optics, we believe that an MLL-based hard x-ray microscope with true nanometer resolution is on the horizon.

Influence of imperfections in a wedged multilayer Laue lens for the focusing of X-rays investigated by beam propagation method

“…Next, it is propagated in a free space to the entrance of the MLL. In the ideal wedged MLL the n-th zone radius x n fulfils equation [1]:…”

“…It is made by the thin layer deposition technique with layer thicknesses corresponding to the FZP equation [1]. A bar cut perpendicularly to the plane of the layers works as a one-dimensional (1D) lens.…”

Micro- and Nano-X-ray Beams

“…Their X-ray diffraction is similar to that from strained single crystals [64]. Finally, to follow exactly the Bragg condition everywhere, elliptical or parabolic zone profiles are necessary to ensure that the diffracted waves from each zone are in phase at the focus with size close to the wavelength [66]. By tilting the lens, however, a larger fraction of the structure contributes to the X-ray focusing.…”

Full-field X-ray microscopy with crossed partial multilayer Laue lenses

“…This effect is exploited in wedged and curved MLLs where each zone is placed in Bragg condition. In case of zone widths 20 nm, the diffraction efficiency exceeds the limit of 40 % that is given for first order focusing of a thin phase zone plate [7]. Furthermore, it is mandatory to fulfill the Bragg condition to focus X-rays to single nanometers since volume diffraction otherwise limits the resolution [8].…”