An atomic-level picture of molecular and bulk processes, such as chemical bonding and charge transfer, necessitates an understanding of the dynamical evolution of these systems. On the ultrafast timescales associated with nuclear and electronic motion, the temporal behaviour of a system is often interrogated in a ‘pump–probe’ scheme. Here, an initial ‘pump’ pulse triggers dynamics through photoexcitation, and after a carefully controlled delay a ‘probe’ pulse initiates projection of the instantaneous state of the evolving system onto an informative measurable quantity, such as electron binding energy. In this paper, we apply spectral ghost imaging to a pump–probe time-resolved experiment at an X-ray free-electron laser (XFEL) facility, where the observable is spectral absorption in the X-ray regime. By exploiting the correlation present in the shot-to-shot fluctuations in the incoming X-ray pulses and measured electron kinetic energies, we show that spectral ghost imaging can be applied to time-resolved pump–probe measurements. In the experiment presented, interpretation of the measurement is simplified because spectral ghost imaging separates the overlapping contributions to the photoelectron spectrum from the pump and probe pulse.

中文翻译：

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具有光谱域重影成像的时间分辨泵浦探针光谱

原子级的分子过程和整体过程（例如化学键和电荷转移）需要了解这些系统的动态演化。在与核运动和电子运动相关的超快速时标上，通常以“泵－探针”方案来询问系统的时间行为。在这里，初始的“泵浦”脉冲通过光激发触发动力学，在经过仔细控制的延迟后，“探测”脉冲启动正在演化的系统的瞬时状态到信息量如电子结合能的投影。在本文中，我们将光谱重影成像应用于X射线自由电子激光（XFEL）设施的泵浦时间分辨实验，其中可观察到的是X射线状态下的光谱吸收。通过利用入射X射线脉冲的逐次波动和测得的电子动能中存在的相关性，我们表明光谱重影成像可应用于时间分辨的泵浦探针测量。在提出的实验中，简化了测量的解释，因为频谱重影成像将泵浦和探测脉冲对光电子谱的重叠贡献分开了。