Laser-dressed photoemission spectroscopy has established itself as the gold standard of attosecond temporal metrology. In this technique, the attosecond structure of an extreme-ultraviolet pulse is retrieved from the wave function of the electron wave packet released during photoionization. Here, we show that this electron wave packet should rather be described using the density matrix formalism, thus allowing one to account for all processes that can affect its coherence, from the attosecond pulse generation to the photoemission and the measurement processes. Using this approach, we reconstruct experimentally a partially coherent electron wave packet with a purity of 0.11 (1 for full coherence). Comparison with theoretical models then allows us to identify the origins of this decoherence and to overcome several limitations such as beam-line instabilities or spectrometer resolution. Furthermore, we show numerically how this method gives access to the coherence and eigencomponents of complex photoelectron wave packets. It thus goes beyond the current measurement of photoionization time delays and provides a general framework for the analysis and understanding of complex photoemission processes.

中文翻译：

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量化阿秒计量学中的退相干

激光穿戴式光发射光谱仪已成为阿秒时间计量学的金标准。在该技术中，从在光电离期间释放的电子波包的波函数中检索出极紫外脉冲的阿秒结构。在这里，我们表明应该使用密度矩阵形式描述这种电子波包，从而使人们能够考虑可能影响其相干性的所有过程，从阿秒脉冲的产生到光发射和测量过程。使用这种方法，我们通过实验重建了部分相干的电子波包，其纯度为0.11（全相干为1）。然后与理论模型进行比较，使我们能够确定这种退相干的根源，并克服了一些局限性，例如束线不稳定性或光谱仪分辨率。此外，我们在数值上显示了该方法如何访问复杂光电子波包的相干性和本征分量。因此，它超越了目前对光电离时延的测量范围，并为分析和理解复杂的光发射过程提供了一个通用框架。