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In this work the coherence properties of the synchrotron radiation beam from an X-ray undulator in a fourth-generation storage ring are analyzed. A slightly focused X-ray beam is simulated using a wavefront propagation through a non-redundant array of slits and the mutual coherence function is directly obtained and compared with the Gaussian-Schell approximation. The numerical wave propagation and the approximate analytical approaches are shown to agree qualitatively, and it is also shown that, when the coherent fraction is selected by a finite aperture before the focusing element, even achromatic focusing systems like total reflection mirrors become slightly chromatic. This effect is also well accounted for in the Gaussian-Schell model. The wavefront propagation simulation through the non-redundant array was repeated with an imperfect mirror demonstrating that, although the wavefront is distorted, its coherent length is practically unchanged.

Cateretê, the coherent X-ray scattering beamline at the new Brazilian synchrotron 5bent-achromat source, Sirius [1] is dedicated to coherent diffraction imaging (CDI) as well as X-ray photon correlation spectroscopy (XPCS) studies. Making the most of the coherence properties of the ultra-low emittance of the Sirius accelerator, will enable to perform 3D imaging of micrometer sized specimen down to few nanometers spatial resolution.

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