Characterization of the X-ray Coherence Properties of an Undulator Beamline at the Advanced Photon Source

TL;DR

This paper characterizes the coherence properties of an X-ray beamline at the Advanced Photon Source, comparing measurements with theoretical calculations and evaluating the effects of beamline optics on coherence and flux.

Contribution

It provides a comprehensive methodology for measuring X-ray coherence properties and assesses the impact of beamline components on coherence and flux.

Findings

Measured coherence properties match source calculations without monochromator.

Monochromator reduces flux and coherence due to added divergence.

Source imaging with refractive lenses is effective for divergence measurement.

Abstract

In anticipation of the increased use of coherent x-ray methods and the need to upgrade beamlines to match improved source quality, we have characterized the coherence properties of the x-rays delivered by beamline 12ID-D at the Advanced Photon Source. We compare the measured x-ray divergence, beam size, brightness, and coherent flux at energies up to 26 keV to the calculated values from the undulator source, and evaluate the effects of beamline optics such as a mirror, monochromator, and compound refractive lenses. 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. Imaging of the source using a compound refractive lens was found to be the most accurate method for determining the vertical divergence. 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 3 to 6 lower than the source, primarily because of vertical divergence introduced by the monochromator. The methods we describe should be widely applicable for measuring the x-ray coherence properties of synchrotron beamlines.