Inversion of Frequency-Resolved Optical Gating (FROG) Spectrograms in Real-Time: A Femtosecond Oscilloscope

Abstract

Frequency-resolved optical gating (FROG) is a technique used to measure the intensity and phase of ultrashort laser pulses. The pulse to be measured is split into probe and gate pulses. The gate and probe pulses are combined in a non-linear optical medium to temporally select portions of the probe. The resulting signal is spectrally resolved at various time delays to produce a spectrogram of the probe.1-3 All the time and frequency information about the pulse (probe) is contained in its spectrogram (“FROG trace”). An iterative 2-dimensional phase retrieval algorithm is used to determine the phase of the FROG trace, and hence, the intensity and phase of the pulse.1,2