Free Electron Laser Seeding Experiments at SPARC

We report on the recent activity at SPARC, which has successfully been operated in seeded mode. In the framework of the DS4 EUROFEL collaboration, a research work plan aiming at the investigation of seeded and cascaded FEL configurations was implemented. The main goal of the collaboration was to study the amplification and the harmonic generation process of an input seed signal. We describe here the first experimental results, with the observation of harmonics up to the 11th of the fundamental and the operation of the FEL in cascaded mode, driven both by seed generated in crystal and in gas (Ar).