The generation of attosecond pulse trains at free-electron lasers opens new opportunities in ultrafast science, as it gives access, for the first time, to reproducible, programmable, extreme ultraviolet (XUV) waveforms with high intensity. In this work, we present a detailed analysis of the theoretical model underlying the temporal characterization of the attosecond pulse trains recently generated at the free-electron laser FERMI. In particular, the validity of the approximations used for the correlated analysis of the photoelectron spectra generated in the two-color photoionization experiments are thoroughly discussed. The ranges of validity of the assumptions, in connection with the main experimental parameters, are derived.

在自由电子激光器中产生阿秒脉冲序列为超快科学开辟了新的机遇，因为它第一次提供了可重复的、可编程的、高强度的极紫外 (XUV) 波形。在这项工作中，我们详细分析了最近在自由电子激光器 FERMI 上产生的阿秒脉冲序列的时间特征的理论模型。特别是，彻底讨论了用于对双色光电离实验中产生的光电子光谱进行相关分析的近似值的有效性。推导出与主要实验参数相关的假设的有效性范围。