Theoretical investigation of higher orders optimized Multilayer Laue Lens for hard x-ray nano-focusing

Abstract

The higher orders optimized Multilayer Laue Lens (MLL) was proposed in this paper to further improve the focusing resolution of hard x-rays. Based on the dynamical diffraction theory, the higher orders diffraction efficiency can be greatly improved through optimizing the thickness ratio (γ=dabsorp/Λ, Λ is the period of local gratings) and cross-section depth. For an optimized WSi2/Si MLL with an outmost layer period of 16nm and γ=0.3–0.25, the average efficiency of the -2nd and -3rd order diffractions are increased to 55.5% and 49.3%, respectively. The efficiencies are almost the same as the -1st order diffraction (55.9%). The focusing property of the optimized MLL with only 40% of the full structure was simulated. Compared to the -1st order, the focal line width of higher orders is decreased by a factor of k (k is the diffraction order) which is 9.0nm and 5.9nm for the -2nd and -3rd order, respectively. It is demonstrated that the higher orders optimized MLL can be used to further improve the focusing resolution of hard x-rays with high efficiency without fabricating ultra-thin outmost structures.