• M. Labat, M.-E. Couprie
  SOLEIL, Gif-sur-Yvette
• S. Bielawski, C. Szwaj
  PhLAM/CERCLA, Villeneuve d'Ascq Cedex
• C. Bruni
  LAL, Orsay
• N. Joly
  University of Erlangen-Nuremberg, Erlangen-Nuremberg

We investigate a dynamical behaviors occurring in single-pass free electron lasers (FELs), depending on the electron beam, undulator and seed laser parameters. We put in evidence a complex spatiotemporal deformation of the amplified pulse, leading ultimately to a pulse splitting effect with two sub-pulses. This phenomenon has been first observed in PERSEO simulations in the case of ARC-EN-CIEL project studies, and then been analyzed more in details with the Colson-Bonifacio FEL equations. This studies reveal that slippage length as well as the seed laser pulse wings are the main ingredients of this dynamics [1]. We show that the splitting results from the nonhomogeneous saturation of the gain by the optical field copropagating with the electron beam.

M.Labat et al. “Pulse-splitting in short wavelength seeded free electron laser,” Phys. Rev. Lett. {10}3, 264801 (2009)

Slides

• L. Giannessi, F. Ciocci, G. Dattoli, M. Del Franco, A. Petralia, M. Quattromini, C. Ronsivalle, E. Sabia, I.P. Spassovsky, V. Surrenti
  ENEA C.R. Frascati, Frascati (Roma)
• D. Alesini, M. Bellaveglia, M. Castellano, E. Chiadroni, L. Cultrera, G. Di Pirro, M. Ferrario, L. Ficcadenti, D. Filippetto, A. Gallo, G. Gatti, E. Pace, B. Spataro, C. Vaccarezza, C. Vicario
  INFN/LNF, Frascati (Roma)
• A. Bacci, V. Petrillo, A.R. Rossi, L. Serafini
  Istituto Nazionale di Fisica Nucleare, Milano
• M. Bougeard, B. Carré
  CEA, Gif-sur-Yvette
• F. Briquez, M.-E. Couprie, M. Labat
  SOLEIL, Gif-sur-Yvette
• A. Cianchi
  Università di Roma II Tor Vergata, Roma
• F. Frassetto, L. P. Poletto
  LUXOR, Padova
• G. Lambert
  LOA, Palaiseau
• G. Marcus, J.B. Rosenzweig
  UCLA, Los Angeles, California
• M. Moreno, M. Serluca
  INFN-Roma, Roma
• A. Mostacci
  Rome University La Sapienza, Roma
• J.V. Rau, V. Rossi Albertini
  ISM-CNR, Rome

SPARC is a single pass free electron laser test facility realized in collaboration between the main Italian research institutions and devoted to experiments of light amplification in different beam conditions. While the laser was commissioned in self amplified spontaneous emission (SASE) mode during the last year, the operation in seeded mode has been recently demonstrated. The amplifier has been seeded with the second harmonic of the Ti:Sa driver laser generated in a crystal and with higher order VUV harmonics generated in a gas cell. The comparison between seeded and unseeded FEL emission will be discussed. The laser has been also operated in a new SASE configuration with a strongly chirped longitudinal e-beam phase space resulting from the RF compression. The chirp has been compensated by accordingly tapering the undulator gaps. Spectra with and without taper have been collected. An increase of about a factor 5 of the pulse energy in combination with spectra with a single longitudinal coherence region have been detected in presence of the taper. The combination of the chirp with the input seed is under study.