• G. Gatti, M. Bellaveglia, E. Chiadroni, L. Cultrera, M. Ferrario, D. Filippetto, C. Vicario
  INFN/LNF, Frascati (Roma)
• A. Bacci, A.R. Rossi
  Istituto Nazionale di Fisica Nucleare, Milano
• P. Musumeci
  UCLA, Los Angeles
• H. Tomizawa
  JASRI/SPring-8, Hyogo-ken

Shining a photocathode at the same time with an UV laser able to extract electrons and an IR laser properly tuned could influence the way the electron beam is generated. Such a process is under investigation at SPARC, through direct measurements, as much as through computer codes assessment studies.

• M. Ferrario, D. Alesini, F. A. Anelli, M. Bellaveglia, M. Boscolo, L. Cacciotti, M. Castellano, E. Chiadroni, L. Cultrera, G. Di Pirro, L. Ficcadenti, D. Filippetto, S. Fioravanti, A. Gallo, G. Gatti, A. Mostacci, E. Pace, R.S. Sorchetti, C. Vaccarezza
  INFN/LNF, Frascati (Roma)
• A. Bacci, V. Petrillo, A.R. Rossi, L. Serafini
  Istituto Nazionale di Fisica Nucleare, Milano
• A. Cianchi, B. Marchetti
  INFN-Roma II, Roma
• L. Giannessi, A. Petralia, C. Ronsivalle
  ENEA C.R. Frascati, Frascati (Roma)
• O. Limaj
  University of Rome La Sapienza, Rome
• M. Moreno, M. Serluca
  INFN-Roma, Roma
• J.B. Rosenzweig
  UCLA, Los Angeles, California
• H. Tomizawa
  JASRI/SPring-8, Hyogo-ken
• C. Vicario
  PSI, Villigen

The primary goal of the SPARC project is the commissioning of the SASE FEL operating at 500 nm driven by a 150-200 MeV high brightness photoinjector. Additional experiments are foreseen also in the HHG Seeded configuration at 266, 160 and 114 nm. A second beam line hosting a THz source has been recently commissioned. The recent successful operation of the SPARC injector in the Velocity Bunching (VB) mode has opened new perspectives to conduct advanced beam dynamics experiments with ultra-short electron pulses able to extend the THz spectrum and to drive the FEL in the SASE Single Spike mode. Moreover a new technique called Laser Comb, able to generate a train of short pulses with high repetition rate, as the one required to drive coherent plasma wake field excitation, has been tested in the VB configuration. The energy/density modulation produced by an infrared laser pulse interacting with the electron beam near the cathode has been also investigated. In this paper we report the experimental results obtained so far and the comparison with simulations.

• C.P. Hauri, B. Beutner, H.-H. Braun, R. Ganter, C.H. Gough, R. Ischebeck, F. Le Pimpec, M. Paraliev, M. Pedrozzi, C. Ruchert, T. Schietinger, B. Steffen, A. Trisorio, C. Vicario
  PSI, Villigen PSI

In the framework of the SwissFEL activities at PSI we developed a powerful UV laser system delivering wavelength-tunable pulses at a central wavelength varying from 260 to 283 nm. The laser system based on a ultra-stable frequency-trippled Ti:sapphire amplifier delivers mJ pulse energy within a duration of 1-10 ps with 1.5 nm spectral width. Temporal flattop pulses are achieved by direct UV shaping with a UV Dazzler and a prism-based stretcher. The system is used to explore thermal emittance and quantum efficiency dependence on photon energy from metallic photo-cathode (Cu and Mo). With pepperpot techniques we have measured the predicted theoretical limit for thermal emittance (0.4 mm.mrad / mm rms laser spot size at 283 nm and 0.6 mm.mrad / mm at 263 nm) for metallic photocathodes.