FEL experiments at SPARC: operation in seeded and chirped mode

We report on the recent activity at SPARC, which has successfully been operated both SASE and seeded mode. Full SASE has been achieved by combining the velocity bunching compression technique, to increase the peak current, with an undulator tapering, to compensate the chirp in the longitudinal phase space[1]. The seeded mode operation has been accomplished, both as a single amplifier and as a single stage cascade doubling the frequency of the input seed at 400nm. We report on the main results obtained in both the configurations.