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  • Letter
  • Open Access

Enhanced generation of single-spike hard x-ray free-electron laser pulses with lower charge and shorter electron beams in the injector

Eduard Prat1,*, Alexander Malyzhenkov2,3, Gian Luca Orlandi1, Tobias Weilbach1, and Sven Reiche1

  • 1PSI Center for Accelerator Science and Engineering, Paul Scherrer Institute, 5232 Villigen, Switzerland
  • 2CERN, 1211 Geneva, Switzerland
  • 3Swiss International Institute Lausanne, 1008 Prilly, Switzerland

  • *Contact author: eduard.prat@psi.ch
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Phys. Rev. Research 7, L042060 – Published 10 December, 2025

DOI: https://doi.org/10.1103/t8qq-h31p

Abstract

Standard x-ray free-electron lasers (FELs) produce pulses with total durations of tens of femtoseconds and with time and spectral profiles consisting of multiple randomly distributed spikes. Strongly compressing an electron beam is a typical approach to produce shorter and coherent FEL pulses. We have advanced this method by starting at the injector of the FEL facility with electron beams with lower charges and shorter durations than in standard configurations. This leads to shorter electron beams with reduced energy spread after full compression and, consequently, to shorter and higher-quality FEL pulses. By operating with electron beams at the injector with charges of a few pC and rms durations of 360 fs, we show the generation of hard x-ray FEL radiation with practically all pulses having a single spike and a duration estimated from spectral measurements of about 300 as (full-width-at-half-maximum values). The demonstration was conducted at SwissFEL, the FEL at the Paul Scherrer Institute in Switzerland. Our work represents a simple way to enhance the production of single-spike events in x-ray FEL facilities, paving the way to achieve fully coherent hard x-ray FEL pulses with unprecedented durations.

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Phys. Rev. Research 7, L042060– Published 10 December, 2025
  • Received 14 August 2025
  • Accepted 11 November 2025
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