Abstract
The CoSAXS beamline at the MAX IV Laboratory is a modern multi-purpose (coherent) small-angle X-ray scattering (CoSAXS) instrument, designed to provide intense and optionally coherent illumination at the sample position, enabling coherent imaging and speckle contrast techniques. X-ray tracing simulations used to design the beamline optics have predicted a total photon flux of 1012-1013 photons s-1 and a degree of coherence of up to 10% at 7.1 keV. The normalized degree of coherence and the coherent flux of this instrument were experimentally determined using the separability of a ptychographic reconstruction into multiple mutually incoherent modes and thus the Coherence in the name CoSAXS was verified. How the beamline can be used both for coherent imaging and XPCS measurements, which both heavily rely on the degree of coherence of the beam, was demonstrated. These results are the first experimental quantification of coherence properties in a SAXS instrument at a fourth-generation synchrotron light source.
Highlights
Fourth-generation synchrotron light sources have been developed to reduce the emittance of the storage rings and increase the brilliance of the provided X-ray beams
We show by exemp- horizontal cuts of the reconstructed beam intensity profile lary measurements that the high-quality beam at the CoSAXS were fitted with Gaussians to extract full width at halfbeamline can be successfully used for coherent imaging and maximum (FWHM) beam sizes of 13.4 mm and 31.8 mm, X-ray photon correlation spectroscopy (XPCS) measurements respectively
Adding more divergence to the beam by using additional focusing optics would allow using the full flux as well as creating a small enough beam profile to inherently fulfill the over-sampling criterion for ptychographic measurements. This would enable a wide range of imaging methods at the CoSAXS beamline
Summary
Fourth-generation synchrotron light sources have been developed to reduce the emittance of the storage rings and increase the brilliance of the provided X-ray beams. The CoSAXS beamline at the MAX IV Laboratory, the first of this new generation of synchrotron light sources, recently came online It is a multi-purpose small-angle X-ray scattering (SAXS) instrument, designed to provide a high-intensity X-ray probe with a selectable degree of transverse coherence (Plivelic et al, 2019). All other optical elements are apertures to collimate the beam or reduce the parasitic scattering The performance of this X-ray optical setup has been simulated using a hybrid ray-tracing and fieldpropagation approach (Klementiev & Chernikov, 2014). In tele-ptychography experiments with a sample, the reconstructed wavefront is usually numerically propagated upstream to the position of the sample In this case we did not use a sample, but instead placed the analyzer pinhole right where normally a sample would be placed in the beam.
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