| Abstract: | Deformation of the first crystal of an X‐ray monochromator under the heat load of a high‐power beam, commonly referred to as `heat bump', is a challenge frequently faced at synchrotron beamlines. Here, quantitative measurements of the deformations of an externally water‐cooled silicon (111) double‐crystal monochromator tuned to a photon energy of 17.6 keV are reported. These measurements were made using two‐dimensional hard X‐ray grating interferometry, a technique that enables in situ at‐wavelength wavefront investigations with high angular sensitivity. The observed crystal deformations were of the order of 100 nm in the meridional and 5 nm in the sagittal direction, which lead to wavefront slope errors of up to 4 µrad in the meridional and a few hundred nanoradians in the sagittal direction. |
