Measurement of the Spatial Coherence Function of Undulator Radiation using a Phase Mask

A measurement of the horizontal coherence function of 7.9 keV radiation from an undulator beam line at the Advanced Photon Source is reported. X-ray diffraction from a phase-shifting mask was used, and the coherence function was measured as a function of the width of beam-conditioning slits in the beam line. The coherence distribution is found to be best described by a Lorentzian function.

Figure 1

Optical microscope image of the URA. The overall width is $700\mu \mathrm{m}$.

Figure 2

The upper image shows a calculated fully coherent diffraction pattern. The lower image shows the pattern obtained with a nominal beam-conditioning slit width of $170\mu \mathrm{m}$.

Figure 3

Measured complex coherence factor and Lorentzian fit for a beam conditioning slit width of (a) $10\mu \mathrm{m}$, (b) $50\mu \mathrm{m}$, (c) $90\mu \mathrm{m}$, and (d) $170\mu \mathrm{m}$. The uncertainty in each data point is indicated by the height of the symbol.