Chirp and self-phase modulation in induced-grating autocorrelation measurements of ultrashort pulses

We show that induced-grating/four-wave-mixing ultrashort-pulse autocorrelation techniques that use slowly responding media offer the same phase information as interferometric second-harmonic generation. We also show that autocorrelation traces from nearly all possible induced-grating/four-wave-mixing beam geometries provide this information, with all yielding the same theoretical result, an integral of a fourth-order electric-field coherence function. Such traces clearly reveal chirp and self-phase-modulation effects without high-frequency fringes. Experiments using a two-beam-coupling arrangement in photorefractive media illustrate these effects.