Beamlines specifically designed for coherent X-ray methods are enhancing these studies (Chubar et al., 2011 Fluerasu et al., 2011 Rau et al., 2011 Winarski et al., 2012 ). Likewise, coherent diffractive imaging methods (Abbey, 2013 ) are revealing strain distributions and dislocations by using Bragg scattering (Yau et al., 2017 ) and surface steps by using crystal truncation-rod scattering (Zhu et al., 2015 ). For example, X-ray photon correlation spectroscopy (XPCS) (Stephenson et al., 2009 Shpyrko, 2014 ) has revealed the dynamics of atomic diffusion in crystals (Leitner et al., 2009 ) and glasses (Ruta et al., 2014 ) and atomic steps on electrode/electrolyte interfaces (Karl et al., 2015 ). The methods described herein should be widely applicable for measuring the X-ray coherence properties of synchrotron beamlines.Ĭoherent X-ray methods are providing revolutionary new capabilities for observing nanoscale dynamics and imaging atomic structure in materials. While the brightness and coherent flux obtained without a monochromator (`pink beam') agree well with those calculated for the source, those measured with the monochromator were a factor of three to six lower than the source, primarily because of vertical divergence introduced by the monochromator. Imaging of the source using a compound refractive lens was found to be the most accurate method for determining the vertical divergence. Diffraction patterns from slits as a function of slit width are analyzed using wave propagation theory to obtain the beam divergence and thus coherence length. The measured X-ray divergence, beam size, brightness and coherent flux at energies up to 26 keV are compared with the calculated values from the undulator source, and the effects of beamline optics such as a mirror, monochromator and compound refractive lenses are evaluated. In anticipation of the increased use of coherent X-ray methods and the need to upgrade beamlines to match improved source quality, here the coherence properties of the X-rays delivered by beamline 12ID-D at the Advanced Photon Source have been characterized.
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