AI Summary

Researchers at Japan’s UVSOR Synchrotron Facility and collaborators directly observed the femtosecond decay of a xenon 4d core hole using pairs of phase‑coherent extreme ultraviolet pulses. By creating interfering photoelectron wave packets, they measured a rapid drop in fringe contrast as the pulse delay increased, indicating a decay time of roughly six femtoseconds. A model based on literature core‑hole lifetimes reproduced this behavior, confirming that Auger decay—where a valence electron fills the vacancy and another electron is emitted—dominates the process. The work offers a coherent‑pulse‑pair alternative to attosecond streaking for time‑domain studies of inner‑shell dynamics.

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