Structured slope errors on real x-ray mirrors: Ray-tracing versus Experiment

R. Signorato and M. Sanchez del Rio

European Synchrotron Radiation Facility
BP 220, 38043 Grenoble-Cedex 9, France

ABSTRACT

Ray-tracing plays an essential role for the design of a synchrotron radiation beamline optics. Nevertheless, it can
also be extremely useful during the commissioning phase of a beamline. At that moment, it is possible to include
real surface figure errors in the computer simulation of the optical devices. The resulting focal spot size and photon
ux values are the final targets for the experimental optimization and alignment of the optics setup. We report
on extensive ray-tracing of the mirror systems of the two beamlines placed at the ESRF insertion device 12. Slope
errors measured after mirror delivery are included in the calculations. It is demonstrated how slope errors with
characteristic periodicity between 1 and ca. 1/20 of the mirror length can affect the focal spot shape, size and
position. In particular, they can create structures or satellites in the focal spot. The distortions from the ideal shape
are generated by the polishing process itself and are intrinsic to each single mirror. Comparison between the effects
of slope errors in ray-tracing using either real (measured) surfaces or numerically generated ones are also reported.

Keywords: ray-tracing, slope error, x-ray mirror, synchrotron radiation beamline, PSD, mirror metrology