The seeded FEL FERMI has completed the commissioning of both the FEL lines, and it is now providing the user community with a coherent and tunable UV radiation (from 100 nm to 4 nm) in a number of different configurations. These also include original FEL-pump - FEL-probe schemes with twin-seeded FEL pulses. Among the key systems for the operation of FERMI, there is the femtosecond optical timing system and dedicated longitudinal diagnostics, specifically developed for FERMI. In this paper, after a short review of the FERMI optical timing system and of its routinely achieved performances, we focus on the results obtained from the suite of longitudinal diagnostics (Bunch Arrival Monitor, Electro Optical sampling station and RF deflectors) all operating in single shot and with 10s fs resolution which demonstrate the FERMI achieved performances. The longitudinal diagnostics measurements are compared between these device and other device on shot-to-shot basis, looking for correlations between machine parameters. Finally future challenges in terms of improvement of existing diagnostics, planned installations and possible upgrades are discussed.
FERMI@Elettra is the first seeded VUV/soft X-ray FEL source. It is composed of two undulatory chains: the low energy branch (FELl) covering the wavelength range from 20 nm up to 100 nm, and the high energy branch (FEL2, employing a double stage cascade), covering the wavelength range from 4 nm up to 20 nm. At the end of 2012 FELl has been opened to external users while FEL2 has been turned on for the first time having demonstrated that a double cascade scheme is suitable for generating high intensity coherent FEL radiation. In this paper we will share our experience and will show our most recent results for both FERMI FELl and FEL2 sources. We will also present a brand new machine scheme that allows to perform two-colour pump and probe experiments as well as the first experimental results.
The techniques for synchronizing ultra fast lasers to external radio frequency reference sources are well established and characterized in the literature. However, there is little data on the actual light-to-light jitter that can be achieved in different synchrotron operation modes when an external laser is locked to the storage ring master clock. Here we present first results of the synchronization of an ultra fast Cr:LiSAF laser with synchrotron radiation generated by the ELETTRA storage ring in different filling modes. In addition, data on the synchronization of the same laser with the ELETTRA FEL pulses, both in free running and Q-switching regimes, are reported. In our experiments, laser-to-RF locking was continuously monitored using built-in phase detection. The laser light to storage ring light locking was characterized by simultaneous acquisition of the two/three pulse trains by a streak camera. In addition, pulse jitter was determined by processing of the signal of fast photodiodes monitoring the different light beams.