A method for evaluating the spatial coherence of an X-ray beam

Professors T. Narayanan (ESRF, Grenoble, France), M. Giglio (XFEL, Hamburg, Germany) and their collaborators have recently published an interesting paper on a novel method to map the two-dimensional transverse coherence of an X-ray beam. The technique uses the dynamical near-field speckles formed by scattering from colloidal particles, which are executing Brownian motions. It is possible to measure the change of the interference fringes, and consequently the fluctuation of speckles. It was found that the coherence properties of synchrotron radiation from an undulator source are obtained with high accuracy. For more information, see the paper, "Probing the transverse coherence of an undulator X-ray beam using Brownian particles", M. D. Alaimo et al., Phys. Rev. Lett., 103, 194805 (2009).