Single-shot transverse coherence measurements with Young's double pinholes at FLASH2

Abstract

We measured the transverse coherence at FLASH2, a variable gap undulator line at the FLASH free-electron laser user facility at DESY in Hamburg. We demonstrate, theoretically and experimentally, a revised version of Young’s double pinhole approach to perform single-shot, repeatable and non-invasive transverse coherence measurements. At beamline FL24 of FLASH2, the transverse coherence of pulses was systematically characterized at wavelengths of 8, 13.5 and 18 nm for different FEL source settings. We determine degrees of coherence of 57% to 87% in the vertical and horizontal direction, respectively. These measurements can facilitate the planning of novel, coherence-based experiments at the FLASH facility.

From Femtoseconds to Hours—Measuring Dynamics over 18 Orders of Magnitude with Coherent X-rays

“…Due to the exceptional coherence obtained at these facilities, they are supposed to be perfectly suited for XPCS and XSVS experiments. Especially in the soft X-ray regime, their high degree of coherence was proven by double-slit experiments [60,[149][150][151]. For hard X-rays, coherence properties have been obtained from speckle patterns from amorphous samples as discussed above [59,[152][153][154][155].…”

X-ray Ptychographic Imaging and Spectroscopic Studies of Plasma-Treated Plastic Films

“…To reconstruct the surface morphology of the samples, an automatic differentiation ptychography algorithm was developed [26]. This ptychography algorithm has been devised to allow an analysis of the measured diffraction patterns despite the fact that FELs based on the self-amplified spontaneous emission process (SASE) [34] inherently exhibit pulse-to-pulse fluctuations of intensity, spectrum and pointing and have only a partial spatial coherence (typically 60-80%). At the same time, scanning imprecisions can be numerically integrated into the algorithm.…”