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Observation of Synchrotron Radiation Spikes for Transverse Electron Beam Size Measurements at a Free-Electron Laser

Andrei Trebushinin*,†, Svitozar Serkez†, Wolfgang Freund, Andreas Koch, Jan Grünert, and Gianluca Geloni

Weilun Qin‡,§ and Sergey Tomin

  • *Contact author: andrei.trebushinin@xfel.eu
  • †These authors contributed equally to this work.
  • ‡Present address: Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China.
  • §Present address: Spallation Neutron Source Science Center, Dongguan 523803, China.
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Phys. Rev. Lett. 135, 215001 – Published 20 November, 2025

DOI: https://doi.org/10.1103/z89g-f7j6

Abstract

We report the observation of transverse intensity fluctuations—spikes—in synchrotron radiation from a single undulator cell at the European XFEL after monochromatization. Autocorrelation analysis of the recorded events confirms that these fluctuations originate from the partial transverse coherence of the radiation. By calculating the second-order autocorrelation function, we determined the averaged transverse slice size of the electron beam along the SASE1 undulator. The measurements were performed with 5.49 keV x-ray photons using a commissioning silicon monochromator with (111) Bragg reflection and an x-ray imager. This technique enables undulator cell-by-cell diagnostics of the transverse electron beam size at free-electron laser facilities.

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Corrections

4 February, 2026

Correction: The title has been amended to more accurately reflect the scope of the research.

See Also

Noninterferometric method for transverse electron beam size diagnostic with synchrotron radiation at a free-electron laser

Andrei Trebushinin, Svitozar Serkez, Wolfgang Freund, Giovanni Perosa, Andreas Koch, Jan Grünert, Gianluca Geloni, Weilun Qin, and Sergey Tomin
Phys. Rev. Accel. Beams 28, 112801 (2025)

Article Text

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Phys. Rev. Lett. 135, 215001– Published 20 November, 2025
  • Received 14 May 2025
  • Accepted 2 September 2025
  • Corrected 4 February 2026
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