Direct temporal intensity measurement of ultrashort optical pulses using third-harmonic-generation based triple correlation

Summary form only given. Because electronic devices (streak camera etc.) are too slow to measure temporal evolution of ultrashort optical pulses, many techniques were developed to retrieve temporal pulse shape. Most of them extract the temporal intensity either by assuming an analytic pulse shape (autocorrelation) or with the help of spectral measurements (including FROG and SPIDER.) All, of these techniques rely on either interference or various nonlinear effect including second harmonic generation and optical Kerr effect. However, in the later 1960s it was shown,that a triple correlation is sufficient to determine the temporal intensity of, a laser pulse with a direct mathematical calculation. In this report, we demonstrate direct temporal intensity measurement of ultrashort optical pulses using a novel third-harmonic-generation (THG) based triple correlation method. Using THG process in a single GaN thin film, the optical pulse intensity profile, from a mode-locked Cr:forsterite laser was directly obtained with the background free triple correlation trace without any spectral information and pulseshape assumption. This is different from the previous demonstration where triple correlation was obtained through a complex combination of second-harmonic generation and sum-frequency-generation. In order to retrieve the corresponding phase information, a simple genetic algorithm was also developed for the first time based on, the direct optical spectrum measurement with improved O(n) complexity than O(n/sup 2/) in.