Physical Review X (Dec 2014)

Control of the Polarization of a Vacuum-Ultraviolet, High-Gain, Free-Electron Laser

  • Enrico Allaria,
  • Bruno Diviacco,
  • Carlo Callegari,
  • Paola Finetti,
  • Benoît Mahieu,
  • Jens Viefhaus,
  • Marco Zangrando,
  • Giovanni De Ninno,
  • Guillaume Lambert,
  • Eugenio Ferrari,
  • Jens Buck,
  • Markus Ilchen,
  • Boris Vodungbo,
  • Nicola Mahne,
  • Cristian Svetina,
  • Carlo Spezzani,
  • Simone Di Mitri,
  • Giuseppe Penco,
  • Mauro Trovó,
  • William M. Fawley,
  • Primoz R. Rebernik,
  • David Gauthier,
  • Cesare Grazioli,
  • Marcello Coreno,
  • Barbara Ressel,
  • Antti Kivimäki,
  • Tommaso Mazza,
  • Leif Glaser,
  • Frank Scholz,
  • Joern Seltmann,
  • Patrick Gessler,
  • Jan Grünert,
  • Alberto De Fanis,
  • Michael Meyer,
  • André Knie,
  • Stefan P. Moeller,
  • Lorenzo Raimondi,
  • Flavio Capotondi,
  • Emanuele Pedersoli,
  • Oksana Plekan,
  • Miltcho B. Danailov,
  • Alexander Demidovich,
  • Ivaylo Nikolov,
  • Alessandro Abrami,
  • Julien Gautier,
  • Jan Lüning,
  • Philippe Zeitoun,
  • Luca Giannessi

DOI
https://doi.org/10.1103/PhysRevX.4.041040
Journal volume & issue
Vol. 4, no. 4
p. 041040

Abstract

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The two single-pass, externally seeded free-electron lasers (FELs) of the FERMI user facility are designed around Apple-II-type undulators that can operate at arbitrary polarization in the vacuum ultraviolet-to-soft x-ray spectral range. Furthermore, within each FEL tuning range, any output wavelength and polarization can be set in less than a minute of routine operations. We report the first demonstration of the full output polarization capabilities of FERMI FEL-1 in a campaign of experiments where the wavelength and nominal polarization are set to a series of representative values, and the polarization of the emitted intense pulses is thoroughly characterized by three independent instruments and methods, expressly developed for the task. The measured radiation polarization is consistently >90% and is not significantly spoiled by the transport optics; differing, relative transport losses for horizontal and vertical polarization become more prominent at longer wavelengths and lead to a non-negligible ellipticity for an originally circularly polarized state. The results from the different polarimeter setups validate each other, allow a cross-calibration of the instruments, and constitute a benchmark for user experiments.