Thermal deformation on a crystal measured with speckle based at-wavelength metrology

Abstract The development of diffraction-limited storage rings and X-ray free electron lasers has put forward higher requirements for the quality and performance of X-ray optics. To preserve the X-ray wavefront of coherent X-ray beams, the standard deviation of the height error should be sub-nm for mirrors and lesser for crystal monochromators. However, the average power of X-ray free electron lasers can reach a few hundred watts. In this case, the impact of thermal deformation is more prominent. In this paper, the heat bump of a single crystal and the crystal of an X-ray monochromator have been measured using the speckle tracking technique. At the same time, the temperature of the crystal surface was measured by infrared thermography. The experiment shows that the temperature on the crystal surface increased by 10 degrees centigrade, resulting in an overall increase of 5 μrad in the wavefront slope error. This method directly relates temperature to changes in the wavefront, which is beneficial for the design and improvement of beamlines.