Measurement of two ultrashort pulses in a single shot: two-pulse frequency-resolved optical gating

Frequency-resolved optical gating (FROG) is a simple, intuitive, and powerful technique for measuring the amplitude and phase of a single arbitrary ultrashort pulse. A simple experimental setup generates a spectrogram of the pulse. The method of retrieving the complex pulse envelope from the spectrogram is intimately related to the phase-retrieval problem. The generation of the spectrogram requires that we gate the pulse using a nonlinear optical effect such as polarization rotation. Normally, the pulse is split into two replicas and a time-delayed version of the pulse itself serves as the gate pulse. However, it is possible to use a second (arbitrary) pulse to serve as a gate. This enables one to use FROG to measure pulses which are too low in energy to serve as an adequate gate for themselves