# UVSOR synchrotron pulse pairs time-resolve xenon 4d core-hole decay of about 6 femtoseconds - Published: 2026-11-11 04:53 UTC - Section: Science › Physics - Tags: xenon 4d core hole, inner-shell vacancy decay, phase-coherent pulse pairs, photoelectron wave-packet interferometry, UVSOR synchrotron, extreme ultraviolet pulses, Auger decay, femtosecond dynamics, spin-orbit splitting - URL: https://realtech.media/news/rt-e227c0d069d2e2d617a7eb8e_uvsor_synchrotron_pulse/ **Researchers at UVSOR used phase-coherent extreme ultraviolet pulse pairs and watched interference fringe contrast fall over a few femtoseconds, tracking an inner-shell vacancy in xenon atoms.** ![UVSOR synchrotron pulse pairs time-resolve xenon 4d core-hole decay of about 6 femtoseconds](https://realtech.media/media/2026/11/516eea5296e5f19b.jpg) *CLS Research Office from Saskatoon, Canada, Wikimedia Commons, CC BY-SA 2.0* Researchers at the UVSOR Synchrotron Facility (Institute for Molecular Science, Japan) and partner institutions have observed the decay of a xenon 4d core hole, an inner-shell vacancy, directly in the time domain, EurekAlert reports. They used pairs of phase-coherent extreme ultraviolet pulses from a synchrotron. The pulses released photoelectron wave packets that interfered with each other. The contrast of the interference fringes decreased over a few femtoseconds as the delay between the pulses increased. The results appeared in Physical Review A on 6 October 2026. [1] A model that used literature core-hole lifetimes of 5.9 and 6.3 femtoseconds reproduced the rapid decay of the fringe contrast. The decay of the xenon 4d hole is dominated by Auger decay, in which a valence electron fills the vacancy and another electron is ejected. [1] ## Interferometry with coherent pulse pairs Until the mid-2000s, such dynamics were mostly inferred from the spectral widths of photoelectron lines. Attosecond streaking later made time-domain observation possible. The team introduces an alternative based on coherent pulse pairs and extends photoelectron wave-packet interferometry to core holes created by photoionization. [1] At beamline BL1U of the UVSOR-III synchrotron, two undulators in tandem, separated by a phase-shifter magnet, emitted the phase-coherent pulse pairs. The photon energy was 93.4 eV, with a bandwidth of about 3%. The phase-shifter magnet set the delay between pulses with attosecond resolution. A hemispherical analyzer recorded photoelectron spectra as a function of delay. [1] ## Xenon against a helium reference Helium, which has no comparable decay, served as a reference, and its fringe contrast showed the instrument's own contrast loss. Both gases showed fringes spaced 40 attoseconds apart, matching the optical cycle of the light. In helium the contrast decreased slowly, which the authors attribute mainly to the energy spread and emittance of the electron beam. Imperfect overlap and intensity imbalance between the undulators also contributed. In xenon the contrast decreased much faster, which the authors attribute to the femtosecond lifetime of the core hole. [1] The xenon contrast also oscillated with a period of about 2 femtoseconds. According to the authors, this beat comes from the coherent excitation of the spin-orbit splitting. Model calculations with the reported lifetimes reproduced both the decay and the beat and gave a spin-orbit splitting in excellent agreement with established values. [1] The authors describe this as the first application of photoelectron wave-packet interference to a short-lived core-hole state. They propose extending the approach to molecules and condensed matter, and suggest that shorter wavelengths could be reached with ultralow-emittance synchrotrons. [1] ## Sources 1. [EurekAlert](https://www.eurekalert.org/news-releases/1150975) --- Source: RealTech, realtech.media — https://realtech.media/news/rt-e227c0d069d2e2d617a7eb8e_uvsor_synchrotron_pulse/