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 Self-Amplified Spontaneous Emission (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 undulator 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.

中文翻译：

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欧洲 XFEL 的 Hanbury Brown 和 Twiss 干涉测量法揭示的高空间相干性和短脉冲持续时间

采用二阶强度干涉测量法研究欧洲 X 射线自由电子激光器 (EuXFEL) 的空间和时间特性。测量是在软 X 射线自放大自发发射 (SASE3) 波束线处以 1.2 keV 的光子能量在自放大自发发射 (SASE) 模式下进行的。详细研究了 SASE3 波荡器设置的两种高功率机制，即饱和时逐渐变细的线性和二次波荡器，并与线性增益机制进行了比较。统计分析表明，线性波动器锥形的空间相干度非常高，高达 90%。在我们的测量中，对光谱和空间域中测量数据的分析提供了大约 10 fs 的平均脉冲持续时间。