• D. Garzella
  CEA/Saclay, Gif-sur-Yvette
• C. Bruni
  PhLAM/CERCLA, Villeneuve d'Ascq Cedex
• M.-E. Couprie
  CEA/DSM/DRECAM/SPAM, Gif-sur-Yvette
• G. De Ninno, B. Diviacco, M. Marsi, M. Trovo
  ELETTRA, Basovizza, Trieste

The ELETTRA Storage Ring FEL succeded in operating in the Ultraviolet range, around 350 nm, with an etalon Fabry Perot inserted in the optical cavity. The high vacuum vessel, integrating a totally motorized control system for the principal degrees of freedom of the silica plate, allowed to obtain the laser oscillation, showing a reduction of the spectral linewidth by more than an order of magnitude. Temporal analysis by a double sweep streak camera showed also a broadening of the temporal pulse width. These major results are here exposed and compared with a numerical analysis and the Storage Ring FEL dynamics theory.

• G. De Ninno, E. Allaria, F. Curbis, M.B. Danailov, B. Diviacco, M. Marsi, M. Trovo
  ELETTRA, Basovizza, Trieste
• M. Coreno
  CNR - IMIP, Trieste
• S. Günster, D. Ristau
  Laser Zentrum Hannover, Hannover

Thanks to an intensive technological effort in the framework of the EEC Contract HPRI CT-2001-50025 (EUFELE), the European FEL at ELETTRA was able to break the previous record for the shortest wavelength of an FEL oscillator. Novel solutions were adopted for multilayer mirrors to allow FEL operation in the wavelength region between 160 and 190 nm, which is one of the main targets of the project. The characteristics of the FEL pulses measured at 176 nm (spectral profiles, high intensity, meV bandpass, MHz repetition rate) make it a competitive light source for spectroscopy, in particular for fluorescence studies in the VUV spectral range. Proof of principle experiments have been performed on different types of silica glasses, yielding information on the mechanisms of light absorption in this material.

• W. Graves, F.O. Ilday, F.X. Kaertner, T. Zwart
  MIT, Middleton, Massachusetts
• M.B. Danailov, B. Diviacco, M. Ferianis, M. Marsi
  ELETTRA, Basovizza, Trieste
• Z. Huang
  SLAC, Menlo Park, California
• S.M. Lidia
  LBNL, Berkeley, California

The optical properties of an FEL amplifier are sensitively dependent on the electron beam current profile, energy spread, and transverse emittance. In this paper we consider using a short FEL amplifier operating on a low harmonic of a visible-IR input seed as a mildly destructive electron beam diagnostic able to measure these properties for sub-ps time slices. The optical methods are described as well as a planned implementation of the device for the FERMI@Elettra XUV FEL under construction at Sincrotrone Trieste, including its fiber-based seed laser closely coupled with the facility timing system, undulator parameters, and requirements on the electron and FEL pulses. This diagnostic is conveniently integrated with a "laser heater" designed to increase the very low electron beam energy spread produced by a photoinjector in order to avoid space charge and coherent synchrotron radiation instabilities.