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High-resolution attosecond interferometry reveals spin-orbit and electron-correlation effects in photoionization delays

Thomas Berglitsch1, C. Leon M. Petersson2, Daniel Hammerland1, Kiyoshi Ueda1,3, Eva Lindroth2,*, and Hans Jakob Wörner1,†

  • 1Laboratorium für Physikalische Chemie, ETH Zürich, CH-8093 Zürich, Switzerland
  • 2Department of Physics, Stockholm University, AlbaNova University Center, SE-106 91 Stockholm, Sweden
  • 3Department of Chemistry, Tohoku University, Sendai 980-8578, Japan

  • *Contact author: eva.lindroth@fysik.su.se
  • †Contact author: hwoerner@ethz.ch
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Phys. Rev. Research 8, 043065 – Published 16 October, 2026

DOI: https://doi.org/10.1103/9j4f-mw66

Abstract

We introduce an experimental technique for achieving an unprecedented energy resolution in attosecond interferometry. Using a second-harmonic bandwidth compressor, we create narrow-band (<1nm), tunable femtosecond pulses that generate high harmonics with a bandwidth of 50–73 meV, achieving the highest energy resolution in any attosecond time-resolved measurement, sufficient to resolve the spin-orbit splitting of the P2 ground state of Ar+. The fine tunability of these pulses resolves a 10-as variation of the spin-orbit photoionization delay across the [Ne]3s13p65p resonance of neutral Ar. Calculations based on the relativistic random-phase approximation with exchange, with qualitative inclusion of shakeup configurations, reveal the importance of spin-orbit and electron-correlation effects to accurately reproduce and interpret photoionization delays.

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Phys. Rev. Research 8, 043065– Published 16 October, 2026
  • Received 25 March 2026
  • Accepted 11 September 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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