Coherence properties of hard x-ray synchrotron sources and x-ray free-electron lasers

TLDR

The authors employ a statistical‑optics framework, using a Gaussian Schell‑model source and transverse‑mode decomposition, to calculate the transverse coherence of PETRA III and the SASE1 undulator at the European XFEL. The analysis shows that only a handful of transverse modes dominate the radiation field of the SASE1 XFEL source.

Abstract

A general theoretical approach based on the results of statistical optics is used for the analysis of the transverse coherence properties of 3-rd generation synchrotron sources and x-ray free-electron lasers (XFEL). Correlation properties of the wavefields are calculated at different distances from an equivalent Gaussian Schell-model source. This model is used to describe coherence properties of the five meter undulator source at the synchrotron storage ring PETRA III. In the case of XFEL sources the decomposition of the statistical fields into a sum of independently propagating transverse modes is used for the analysis of the coherence properties of these new sources. A detailed calculation is performed for the parameters of the SASE1 undulator at the European XFEL. It is demonstrated that only a few modes contribute significantly to the total radiation field of that source.