Development of mechanical polishing methods for multilayer Laue lens fabrication

Abstract

Multilayer Laue lenses (MLLs) are diffractive optics to achieve nanometer-scale hard x-ray focusing. Flat and wedged MLLs are fabricated by sectioning multilayer films made of thousands of planar or laterally graded and depth-graded layers. The total thickness of the films could extend to over 100 micrometers. The outmost zone width of an MLL is one to a few nanometers. After the deposition of multilayers, the films are sectioned to an appropriate thickness targeting the optimal focusing efficiency over the operating x-ray energy range. Wedged MLLs are candidates to achieve higher efficiency and sub-10 nm hard x-ray focusing, which are more complex optics to produce. In particular, wedged MLL fabrication brings additional critical requirements on section(s) extraction. At the National Synchrotron Light Source II (NSLSII) of Brookhaven National Laboratory (BNL), we made evolutions in MLL fabrication by mechanical polishing methods over the last decade. We started with conventional polishing and then developed the polish-on-diamond and the combined polishing with focused ion beam (FIB) methods. The introduction of new techniques has proven effective in improving our MLL fabrication efficiency. In this paper, the current progress of each method is discussed in detail.