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.
Highlights
X-ray techniques have found numerous applications in life science, materials science, chemistry, medicine, and environmental science utilizing the unique properties of X-rays, such as penetration capability and sensitivity to structural and chemical information
With the assumption that the multilayer Laue lens (MLL) can be locally decomposed into periodic gratings, their approach is limited to cases of w f with a relatively small numerical aperture (NA) corresponding to a resolution of 2 nm
To overcome the limitation of these approaches and to provide a model that is valid to a spatial resolution on the order of the wavelength of radiation used, we developed a modeling method that is analogous to Takagi-Taupin equations in crystallography by realizing the similarities of X-ray diffraction between an MLL and a single crystal [18]
Summary
X-ray techniques have found numerous applications in life science, materials science, chemistry, medicine, and environmental science utilizing the unique properties of X-rays, such as penetration capability and sensitivity to structural and chemical information. Because of the weak refractive interaction of materials for X-rays (the difference of the refractive index from unity is typically 10−5–10−6 for hard X-rays), it is very difficult to fabricate X-ray nanofocusing optics This difficulty is the major obstacle preventing current X-ray microscopy from achieving nanometer resolution. Recent progress in mirrors [2], zone plates (ZPs) [3], and refractive lenses [4] has pushed the frontiers of X-ray nanofocusing well below 50 nm. Many of these optics may be close to their practical limits for focusing. Because an MLL is operated in transmission geometry and the size of the lens is on the order of tens of microns, assembling two MLLs to produce a 2D focus is feasible
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