The FREAG gives complete recovery of spectral and temporal information on ultrafast laser pulses in real time, and is similar to, but far more sensitive than, Frequency Resolved Optical Gating (FROG). It works by linear transmission through a modulated gate, contrasting with the non-linear crystal required for second-harmonic generation autocorrelators. The result is the same, accurate recovery of real and imaginary parts of the electric field but without requiring high intensity input.

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