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  • Letter
  • Open Access

Emergence of pseudoresonance in high-intensity resonant inelastic x-ray scattering

Sang-Kil Son (손상길)1,*,†, Thomas M. Baumann2,*,‡, Jacob Pedersen3,4, Laura Budewig1,5, Kai Li6,7, Hans Ågren8, Olle Björneholm8, Rebecca Boll2, John Bozek9 et al.

Carl Caleman1,8, Sebastian Cardoch8, Lucas M. Cornetta10, Alberto De Fanis2, Emiliano De Santis11,8, Simon Dold2, Gilles Doumy7, Ulrich Eichmann12, Xiaochun Gong13, Johan Gråsjö14,8, Alice E. Green15,16,2, Iyas Ismail17, Ludvig Kjellsson18, Eva Lindroth19, Tommaso Mazza2, Jacobo Montaño2, Terry Mullins1, Christian Ott20, Yevheniy Ovcharenko2, Thomas Pfeifer20, Maria Novella Piancastelli17, Ralph Püttner21, Nils Rennhack2, Nina Rohringer1,5, Cecilia Sánchez-Hanke22, Conny Såthe18, Philipp Schmidt2, Björn Senfftleben2, Marc Simon17, Nicuşor Tîmneanu8, Moto Togawa2, Kiyoshi Ueda23,24, Sergey Usenko2, Hans Jakob Wörner25, Weiqing Xu26,27, Zhong Yin28, Linda Young6,7, Joseph Nordgren8, Marcus Agåker18,8, Johan Söderström8, Sonia Coriani3, Michael Meyer2, Robin Santra1,5, and Jan-Erik Rubensson8,§

  • *These authors contributed equally to this work.
  • †Contact author: sangkil.son@cfel.de
  • ‡Contact author: thomas.baumann@xfel.eu
  • §Contact author: jan-erik.rubensson@physics.uu.se
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Phys. Rev. A 112, L051101 – Published 7 November, 2025

DOI: https://doi.org/10.1103/drmh-vmgk

Abstract

We report resonant inelastic x-ray scattering (RIXS) spectra of neon atoms interacting with intense x-ray pulses generated using an x-ray free-electron laser (XFEL). We find that an unexpected peak emerges near the Kα line of Ne, which does not coincide with any physical resonances of neon ions. We perform theoretical calculations based on a quantum-state-resolved rate-equation approach with x-ray-induced processes including possible resonant excitations. Our dynamics simulations demonstrate that a sequence of multiple resonant photoabsorption events are involved and the interplay of those multiple resonances in combination with the relatively large spectral bandwidth of XFEL radiation leads to the emergent resonance-like structure at a position where no resonances exist. Our finding offers critical guidance for future applications of high-intensity RIXS at XFEL facilities.

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Phys. Rev. A 112, L051101– Published 7 November, 2025
  • Received 18 June 2025
  • Accepted 1 October 2025
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