Abstract
The focusing and coherence properties of the NanoMAX Kirkpatrick-Baez mirror system at the fourth-generation MAX IV synchrotron in Lund have been characterized. The direct measurement of nano-focused X-ray beams is possible by scanning of an X-ray waveguide, serving basically as an ultra-thin slit. In quasi-coherent operation, beam sizes of down to 56 nm (FWHM, horizontal direction) can be achieved. Comparing measured Airy-like fringe patterns with simulations, the degree of coherence |μ| has been quantified as a function of the secondary source aperture (SSA); the coherence is larger than 50% for SSA sizes below 11 µm at hard X-ray energies of 14 keV. For an SSA size of 5 µm, the degree of coherence has been determined to be 87%.
Highlights
X-ray beams are a ubiquitous tool in many areas from biological physics and chemistry to material science and the semiconductor industry
The edge diffraction at slit d is quantitatively described with the formalism of the Cornu spiral; the fringe contrast from partial coherence is readily included by the degree of coherence between the slit edges, obtained from the van Cittert–Zernike theorem: for a slit of size s and two pinholes separated by distance d, the degree of spatial coherence ðs; dÞ is given as sd ðs; dÞ 1⁄4 sinc
We have quantified the X-ray focal spot size and its dependence on (i) KB mirror tilt angle, (ii) coherence properties defined by the secondary source aperture, and (iii) X-ray photon energy for the new NanoMAX beamline at the MAX IV synchrotron
Summary
X-ray beams are a ubiquitous tool in many areas from biological physics and chemistry to material science and the semiconductor industry. At the NanoMAX beamline of the MAX IV synchrotron, for example, diffraction, scattering and fluorescence are combined as imaging techniques to answer questions in material science, life and earth science, general physics, and chemistry and biology (Johansson et al, 2013). We present a characterization of focal spot size and coherence properties of the horizontally focused beam. The spot size and its dependence on (i) KB mirror tilt angle, (ii) coherence properties defined by a pair of slits defining the secondary source size, and (iii) X-ray photon energy are.
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