Single-shot measurement of the intensity and phase of an arbitrary ultrashort pulse by using frequency-resolved optical gating

We introduce a new technique, frequency-resolved optical gating, for measuring the intensity I(t) and the phase ø(t) of an individual arbitrary ultrashort pulse. Using an instantaneous nonlinear-optical interaction of two variably delayed replicas of the pulse, frequency-resolved optical gating involves measuring the spectrum of the signal pulse versus relative delay. The resulting trace, a spectrogram, yields an intuitive full-information display of the pulse. Inversion of this trace to obtain the pulse intensity and phase is equivalent to the well-known two-dimensional phase-retrieval problem and thus yields essentially unambiguous results for I(t) and ø(t).