• 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.