Short pulses and broadband measurement by autocorrelation with a sum-frequency generation setup

Generation of subpicosecond light pulses on the CLIO FEL has been reported previously, at a wavelength λ ≈ 9 μm. These results are especially striking when compared to the electron bunch, measured to be about 10 ps long. In this paper, we present experimental data giving us some clues to the understanding of this effect. Autocorrelation measurements are performed using two different systems, amongst which one is based on sum-frequency generation on surfaces. This allows broadband operation and study of the laser temporal characteristics with wavelength.