Physical Review Accelerators and Beams (Apr 2022)

Single-shot transverse coherence in seeded and unseeded free-electron lasers: A comparison

  • M. Pop,
  • E. Allaria,
  • F. Curbis,
  • G. Geloni,
  • M. Manfredda,
  • S. Di Mitri,
  • L. Foglia,
  • D. Garzella,
  • L. Giannessi,
  • B. Mahieu,
  • N. Mahne,
  • N. Mirian,
  • G. Penco,
  • G. Perosa,
  • P. R. Ribič,
  • A. Simoncig,
  • S. Spampinati,
  • C. Spezzani,
  • M. Trovò,
  • S. Werin,
  • M. Zangrando,
  • G. De Ninno

DOI
https://doi.org/10.1103/PhysRevAccelBeams.25.040701
Journal volume & issue
Vol. 25, no. 4
p. 040701

Abstract

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The advent of x-ray free-electron lasers (FELs) drastically enhanced the capabilities of several analytical techniques, for which the degree of transverse (spatial) coherence of the source is essential. FELs can be operated in self-amplified spontaneous emission (SASE) or seeded configurations, which rely on a qualitatively different initialization of the amplification process leading to light emission. The degree of transverse coherence of SASE and seeded FELs has been characterized in the past, both experimentally and theoretically. However, a direct experimental comparison between the two regimes in similar operating conditions is missing, as well as an accurate study of the sensitivity of transverse coherence to key working parameters. In this paper, we carry out such a comparison, focusing in particular on the evolution of coherence during the light amplification process.