Beam focus modifications by cropping partially coherent X-ray beams

European Synchrotron Radiation Facility - 71 Avenue des Martyrs, 38000 Grenoble, France

^(a) E-mail: srio@esrf.eu (corresponding author)

Received: 25 October 2022
Accepted: 22 November 2022

Abstract

We simulate the focusing of a partially coherent X-ray beam emitted by an undulator in a fourth-generation storage ring by performing a coherent mode decomposition and wave optics propagation. The focus position is shifted, and its size is enlarged when an entrance slit crops the beam. This is the usual case when a slit is used to select the coherent fraction. The pairing of two focusing elements (mirrors, lenses or transfocators) to ensure a fixed focal position is also analyzed. Our results show that the image of a partially coherent source, such an undulator in a low-emittance storage ring, is a non-trivial function of the aperture used to control the coherence fraction.