High spatial coherence and short pulse duration revealed by the Hanbury Brown and Twiss interferometry at the European XFEL

TL;DR

This study used second-order intensity interferometry to analyze the spatial coherence and pulse duration of the European XFEL, revealing high coherence up to 90% and an average pulse duration of about 10 femtoseconds.

Contribution

It demonstrates the high spatial coherence and short pulse duration of the EuXFEL using Hanbury Brown and Twiss interferometry, providing valuable insights for future experiments.

Findings

Spatial coherence up to 90% in linear undulator tapering

Average pulse duration of about 10 femtoseconds

Comparison of different SASE regimes

Abstract

Second-order intensity interferometry was employed to study the spatial and temporal properties of the European X-ray Free-Electron Laser (EuXFEL). Measurements were performed at the soft X-ray SASE3 undulator beamline at a photon energy of 1.2 keV in the Self-Amplified Spontaneous Emission (SASE) mode. Two high-power regimes of the SASE3 undulator settings, i.e. linear and quadratic tapering at saturation, were studied in detail and compared with the linear gain regime. The statistical analysis showed an exceptionally high degree of spatial coherence up to 90% for the linear undulator tapering. Analysis of the measured data in spectral and spatial domains provided an average pulse duration of about 10 fs in our measurements. The obtained results will be valuable for the experiments requiring and exploiting short pulse duration and utilizing high coherence properties of the EuXFEL.