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High-power attosecond x-ray free-electron lasers: Physics and design strategy

Chenzhi Xu1,2,3, Jiawei Yan4,*, Ye Chen4, Winfried Decking4, Marc Guetg4, Tianyun Long4, Bingyang Yan1,2, and Haixiao Deng5,†

  • *Contact author: jiawei.yan@desy.de
  • †Contact author: denghx@sari.ac.cn
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Phys. Rev. Accel. Beams 29, 103406 – Published 21 October, 2026

DOI: https://doi.org/10.1103/hqjn-r9k9

Abstract

Attosecond pulses from x-ray free-electron lasers (XFELs) have opened new opportunities for probing ultrafast electronic dynamics on the Ångstrom-attosecond spatiotemporal scale. Most attosecond XFEL concepts rely on generating an ultrashort high-current spike through either external laser modulation or accelerator-based beam manipulation. Despite their different implementations, these approaches share the same essential physics, namely, that the XFEL amplification is confined to a short effective lasing window within the electron beam. However, existing studies are often scheme-specific and do not yet provide a unified quantitative picture of how fundamental electron-beam properties constrain high-power attosecond performance. In this work, we investigate the general physics and scheme-independent requirements for generating high-power attosecond x-ray pulses from a short current spike. From the perspective of postsaturation superradiant evolution, we show that the electron-beam length governs both the attainable peak power and the pulse duration. We further examine the distinct roles of slice energy spread, slice emittance, energy chirp, and transverse beam tilt. Our results reveal the trade-off between peak power, pulse shortening, and single-spike probability, and provide facility-independent guidelines for optimizing electron-beam phase-space manipulation toward terawatt-class attosecond XFEL operation.

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Phys. Rev. Accel. Beams 29, 103406– Published 21 October, 2026
  • Received 23 April 2026
  • Accepted 16 September 2026
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