  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.
