• R. Bachelard, F. Briquez, M.-E. Couprie, A. Loulergue
  SOLEIL, Gif-sur-Yvette
• A. Ben Ismail, S. Corde, J. Faure, G. Lambert, O. Lundh, V. Malka, A. Rousse, K. Ta Phuoc
  LOA, Palaiseau
• G. De Ninno
  ELETTRA, Basovizza
• M. Labat
  ENEA C.R. Frascati, Frascati (Roma)

In the quest for compact FEL ultra-compact sources, a test experiment is under preparation, to couple an electron beam from a laser driven plasma accelerator, stable and tunable in energy, to an undulator. The electron beam is generated in the colliding laser pulses scheme, by focusing two short and intense laser pulse in an underdense plasma plume. The electron bunch has an energy tunable in up to a few hundreds MeV with 1% energy spread, a length 10 fs, a charge in the 10 pC range, while its radius and divergence are respectively 1μm and 3 mrad. As a first step toward a FEL experiment, the transport and radiation through an undulator of this short and compact electron beam is studied. The spontaneous emission through a 60 cm undulator in the 40-120 nm range is presented, and criteria to reach the threshold of Self-Amplified Spontaneous Emission are discussed.

• M. Labat, F. Ciocci, G. Dattoli, M. Del Franco, A. Doria, G.P. Gallerano, L. Giannessi, E. Giovenale, A. Petralia, M. Quattromini, C. Ronsivalle, E. Sabia, I.P. Spassovsky, V. Surrenti
  ENEA C.R. Frascati, Frascati (Roma)
• D. Alesini, M. Bellaveglia, R. Boni, M. Boscolo, M. Castellano, E. Chiadroni, A. Clozza, L. Cultrera, G. Di Pirro, A. Drago, M. Ferrario, L. Ficcadenti, D. Filippetto, V. Fusco, A. Gallo, G. Gatti, A. Mostacci, E. Pace, L. Palumbo, B. Spataro, C. Vaccarezza
  INFN/LNF, Frascati (Roma)
• A. Bacci, V. Petrillo, A.R. Rossi, L. Serafini
  Istituto Nazionale di Fisica Nucleare, Milano
• F. Briquez, M.-E. Couprie
  SOLEIL, Gif-sur-Yvette
• B. Carré, D. Garzella
  CEA, Gif-sur-Yvette
• A. Cianchi, B. Marchetti
  INFN-Roma II, Roma
• G. Marcus, J.B. Rosenzweig
  UCLA, Los Angeles, California
• M. Mattioli, M. Serluca
  INFN-Roma, Roma

The SPARC FEL can be operated in both SASE and seeded modes. A major part of the second stage of the commissioning, currently in progress, is dedicated to the characterization of the SASE radiation. Simultaneously, we are finalizing the experimental setup for seeding. We present an in-situ characterization of the two input seeds that are foreseen: both are obtained via harmonic generation, the first one in crystal (400 and 266 nm) and the second in rare gas (Argon). We also describe the specific diagnostics implemented for the electron-seed overlap in the undulator, together with the diagnostics for radiation analysis (2D spectrometer and FROG). The seeding will enable the operation of the SPARC FEL in original cascaded configurations.