Tracking Ultrashort Electron Processes in Matter With X‐Ray Chronoscopy

ABSTRACT The development of X‐ray Free Electron Lasers (XFELs) unlocked new possibilities in many areas of science. These facilities routinely produce femtosecond X‐ray pulses with extremely high peak brilliance, enabling time‐resolved X‐ray spectroscopy experiments to study ultrashort phenomena in matter. However, many fundamental electron processes in atoms, molecules, and clusters are still unreachable by the XFEL‐based time‐resolved methods. Recently, an innovative methodology called X‐ray Chronoscopy was introduced to address some current time resolution limits typically encountered at XFEL. Herein, we assess the ability of X‐ray Chronoscopy to track electron dynamics in an optical pump/X‐ray probe XFEL experiment. By employing numerical simulations, we showed that the proposed method could determine femtosecond relaxation rates in matter while mitigating the main issues related to optical pump/X‐ray probe experiments at XFELs, such as pump–probe arrival time jitter. We anticipate that with the ongoing advent of temporal diagnostic tools, the implementation of X‐ray Chronoscopy at XFEL would complement the information obtained from X‐ray spectroscopy, providing a complete picture of the sample's electronic structure.