Using χ(3) to measure the intensity and phase of an ultrashort laser pulse: frequency-resolved optical gating

We have developed a simple, intuitive, self-contained, and general technique for measuring the intensity and phase of a single arbitrary ultrashort pulse. We use a novel arrangement and reduce the mathematics of the problem to a two-dimensional phase-retrieval problem - a well-known, solved problem from image science. Our technique, frequency-resolved optical gating (FROG), requires splitting the pulse into two variably delayed replicas, which then cross in any instantaneously responding nonlinear-optical medium. A single-shot optical-gate arrangement yields a signal-pulse electric field. The signal-pulse spectrum is then measured vs. the delay