Large Aperture and Wedged Multilayer Laue Lens for X-ray Nanofocusing.

Diffraction optics fabricated from multilayers offer an intriguing alternative to lithography-based zone plates due to their advantages of virtually limitless aspect ratio and extremely small feature size. However, other issues, intrinsic to thin-film deposition, such as film stress and deposition rate instability, for example, limit the total achievable aperture. Over the last decade, Multilayer Laue Lens (MLLs) have progressed from a mere curiosity with initial aperture sizes in the 3-10 m range, to real beamline-deployed optics with apertures in the 40-50 m range (X. Huang, et al., 3, 3562 (2013); E. Nazaretski, et al., 85, 033707 (2014); E. Nazaretski, et al., 24, 1113 (2017)). By optimizing deposition conditions and incorporating new materials, MLLs have now broken the 100 m thickness milestone. A flat WSi₂/Al-Si MLL with a deposition thickness of 102 m, the largest MLL to date, is reviewed. New large aperture wedged MLLs (wMLL), which were first fabricated by APS in 2006 using the WSi2/Si material system, are presented which demonstrate high focusing efficiency across a broad energy range. These results confirm findings by other groups who have also independently fabricated wMLL (A. J. Morgan, et al., 5, 9892 (2015); S. Bajt, et al., 7, 17162 (2017)) based on a similar material system.