Agility of Felix Regarding Wavelength and Micropulse Shape

The user-facility FELIX employs two FELs together covering the spectral range from 6.5 to 110 mum. Adjustment of the undulator strength permits wavelength tuning over a factor of two within two minutes while continuously providing several kilowatts of output power. As FELIX combines short electron bunches with long wavelengths, short-pulse effects play an important role. A spectral analysis and intensity correlation measurements show that the micropulses are virtually transform limited. At small cavity desynchronisation, the duration can be much smaller than the electron-bunch duration (3 ps). Indications of the formation of subpulses within the micropulse have been observed.