Sub-picosecond laser pulse generation on the CLIO FEL

Laser pulse length measurements have been carried out on the CLIO infrared free-electron laser using a Michelson interferometer with a Te crystal as a second order autocorrelation device. Simultaneously spectral measurements have been carried out showing that the laser pulse is close to the Fourier transform limit. A minimum laser pulse length of δt = 400 fs, and a line width of δ;λ = 500 nm have been found for λ = 9.2 μm, giving a peak power of 70 MW in the full spectral bandpass. We also examine, in this paper, the laser spectral brightness as a function of the cavity length detuning, and the laser pulse length with the linac operating off the crest of the accelerating wave.