FEL experiments at SPARC: seeding with harmonics generated in gas

The SPARC FEL has been configured to test different cascaded FEL configurations with a seed generated in gas. In the framework of the DS4 EUROFEL collaboration, a research work plan at the SPARC FEL test facility 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, obtained as higher order harmonics generated in gases. We describe here the first experimental results, which were recently obtained.