How to measure femtosecond pulses

We discuss techniques allowing to measure the duration of ultrashort laser pulses. In particular, a new method is described, which recovers the phase, amplitude and absolute intensity of femtosecond pulses, allowing to reconstruct the temporal pulse profile with femtosecond resolution. It is based on the spectral analysis, at different time delays, of a probe pulse experiencing cross-phase modulation induced by a pump pulse.