Fabrication of double-sided Fresnel zone plates and absolute measurements of their diffraction efficiency in an X-ray-tube-based setup

Abstract

Diffractive lenses for X-rays, so-called Fresnel zone plates (FZPs), are used as focusing elements in X-ray imaging applications in synchrotrons all over the world. One of the main characteristics of FZPs is their diffraction efficiency. Measurements of the absolute diffraction efficiency as a function of the X-ray energy can reliably be done using synchrotron radiation, but require beamtime at synchrotrons which is not available on a routine basis. Here, the design, construction and characterization of an in-lab X-ray-tube-based setup for measuring the absolute diffraction efficiency of single- and double-sided FZPs is presented. The broad spectrum from the Xray tube is monochromatized using a set of copper- and nickel filters, giving an approximate X-ray energy of 8.4 keV; the spectrum is simulated and confirmed through spectrometer measurements. Single- and double-sided line-doubled Fresnel zone plates with different characteristics have been fabricated and measured using the setup, yielding absolute diffraction efficiencies of up to 6.4%. Diffraction efficiency maps, showing the spatial distribution of the diffraction efficiency, have been obtained for each zone plate. The measurements have given important information regarding issues with the fabrication process related to the alignment between the two halves of double-sided zone plates, and these issues have been investigated further. Finally, measurements have been performed where the misalignment in double-sided zone plates has been determined by employing a functionality of the setup where the measured zone plates can be tilted around two different axes.