A novel technique for ultrafast pulse measurement is presented. This technique involves only the measurement of the fundamental, second harmonic, and third harmonic (or other third-order nonlinear) spectra of an ultrafast pulse. An algorithm is employed to generate trial SHG and THG spectra based on the measured fundmental spectrum and a trial phase. The phase is adjusted iteratively until the best match between the trial and measured SHG and THG spectra is obtained. The technique is experimentally simple, not subject to delicate temporal alignments, and potentially insensitive to wavefront quality
