Author: Cucini, R.
Paper Title Page
Characterization of the Polarization of the First and Second Stage of FERMI FEL-2  
  • E. Roussel, E. Allaria, C. Callegari, M. Coreno, R. Cucini, S. Di Mitri, B. Diviacco, E. Ferrari, P. Finetti, D. Gauthier, L. Giannessi, G. Penco, L. Raimondi, C. Svetina, M. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • A. Beckmann
    XFEL. EU, Hamburg, Germany
  • L. Giannessi
    ENEA C.R. Frascati, Frascati (Roma), Italy
  • L. Glaser, G. Hartmann, F. Scholz, J. Seltmann, I. Shevchuk, J. Viefhaus
    DESY, Hamburg, Germany
  • M. Zangrando
    IOM-CNR, Trieste, Italy
  The FERMI free-electron laser (FEL) is nowadays the only user facility equipped with Apple-II type undulators that permit to produce either elliptical, circular or linearly polarized light within the extreme ultraviolet and soft x-ray wavelength range. The FERMI FEL-2 line is based on a two-stage "fresh-bunch" high-gain harmonic generation (HGHG) scheme, where the light emitted by a first HGHG stage seeds a fresh portion of the electron bunch in a second FEL stage. Both FEL lights, from the first and second stages, can be tuned separately to linear horizontal, vertical or circular left and right polarization. We report on a systematic characterization of the polarization state of the two stages of FERMI FEL-2 by using an electron Time-Of-Flight based polarimeter. Our results show a good independent control of the polarization of the two stages, with a high degree of polarization typically higher than 95%*
* E. Roussel et al., Polarization Characterization of Soft X-Ray Radiation at FERMI FEL-2. Photonics 2017, 4, 29.
Four-Wave Mixing Using Extreme Ultraviolet Transient Gratings at FERMI FEL  
  • F. Bencivenga, F. Capotondi, R. Cucini, L. Foglia, C. Masciovecchio, R. Mincigrucci, E. Pedersoli, E. Principi, A. Simoncig
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  Four-wave mixing (FWM) processes are exploited in the optical domain in a large array of scientific and technological applications. The extension of this approach to the XUV and X-ray range was theoretically conceived,* but not experimentally pursued because of the lack of photon sources with enough brightness and coherence. This situation has changed with the advent of FELs, in particular those stabilized by seeding processes. In this context, the XUV pulses delivered by FERMI have been used to experimentally demonstrate the FWM response stimulated by XUV transient gratings.** More recently the 'twin-seed' double-colour FEL mode of FERMI has been employed in a two-colour XUV FWM experiment.*** These results provide grounds to build up the sophisticated experiments envisioned by theoreticians,* which could provide access to high energy/high-wavevector excitations, with elemental selectivity and nano to atomic spatial resolution. Capabilities that can be exploited in different fields, ranging from thermal transport dynamics in nanoelectronic devices to charge transfer processes in molecules.
* S. Tanaka and S. Mukamel, Phys. Rev. Lett., 2002, 89, 043001
** F. Bencivenga et al., Nature, 2015, 520, 205
*** F. Bencivenga et al., Faraday Discuss., 2014, 171, 487