Multilayer Laue lens focuses hard x-rays

While the X-FELO, which is located at the Argonne National Laboratory, will enable new science, focusing optics for it and other hard-x-ray sources are difficult to create—especially optics that are efficient and can focus at near the diffraction limit. Argonne scientists have developed and tested a new multilayer lens (MLL) design, having a geometry like the Laue geometry in crystal diffraction (in which stacked diffracting surfaces are oriented almost parallel with the optical axis), that produced a 16 nm line focus at a 0.064 nm x-ray wavelength, with an efficiency of 31%.

The lens was fabricated of alternating planar multilayers of pure silicon and tungsten silicide; the layers decreased in thickness from the bottom to the top of the 13.25 µm structure, with the thinnest layer being 5 nm. A single 15-µm-thick section sliced from the structure became the test lens, with the aspect ratio of the outermost (thinnest) layer being 3000. A synchrotron and monochromator produced the 0.064 nm (19.5 keV) light for testing; the test lens had a numerical aperture of about 0.005. Future MLL structures may focus to sizes below 1 nm. Contact Jörg Maser at [email protected].