The random nature of self-amplified spontaneous emission (SASE) is a well-known challenge for x-ray core level spectroscopy at SASE free-electron lasers (FELs). Especially in time-resolved experiments that require a combination of good temporal and spectral resolution the jitter and drifts in the spectral characteristics, relative arrival time as well as power fluctuations can smear out spectral-temporal features. We present a combination of methods for the analysis of time-resolved photoelectron spectra based on power and time corrections as well as self-referencing of a strong photoelectron line. Based on sulfur 2p photoelectron spectra of 2-thiouracil taken at the SASE FEL FLASH2, we show that it is possible to correct for some of the photon energy drift and jitter even when reliable shot-to-shot photon energy data is not available. The quality of pump–probe difference spectra improves as random jumps in energy between delay points reduce significantly. The data analysis allows to identify coherent oscillations of 1 eV shift on the mean photoelectron line of 4 eV width with an error of less than 0.1 eV.

中文翻译：

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SASE 自由电子激光器时间分辨 X 射线光电子能谱的数据分析程序

自放大自发辐射 (SASE) 的随机性是 SASE 自由电子激光器 (FEL) 中 X 射线核心能级光谱的众所周知的挑战。特别是在需要良好的时间和光谱分辨率组合的时间分辨实验中，光谱特性中的抖动和漂移、相对到达时间以及功率波动会模糊光谱时间特征。我们提出了一种基于功率和时间校正以及强光电子线自参考的时间分辨光电子能谱分析方法组合。基于在 SASE FEL FLASH2 上拍摄的 2-硫氧嘧啶的硫 2p 光电子能谱，我们表明即使没有可靠的逐次发射光子能量数据，也可以校正一些光子能量漂移和抖动。随着延迟点之间能量的随机跳跃显着减少，泵浦-探针差异光谱的质量得到改善。数据分析允许识别 4 eV 宽度的平均光电子线上 1 eV 偏移的相干振荡，误差小于 0.1 eV。