Externally seeded free electron laser invading the x-ray region

The FERMI facility has provided over the last decade pulses characterized by a high degree of coherence over the spectral range from 100 nm down to 4 nm. Thanks to the use of an external seed to initiate the FEL process, FERMI pulses are characterized by unique characteristics very much appreciated by the user community. The extraordinary degree of coherence but also the flexible temporal or spectral properties of the photon pulses combined with a high reproducibility and low temporal jitter has supported important scientific experiment in various fields. Recently experiments have been conducted extending the tuning range to wavelengths shorter than 2 nm accessing important spectral resonances. Current operations at such a high photon energy rely on the use of undulator harmonics which limit the FEL performances. A project has been initiated to upgrade the FEL facility with new accelerator modules and new FEL configurations to access this important spectral range in nominal operation at the fundamental resonance of the FEL amplifier and with full control of polarization and other photon properties currently available.