Abstract: A method for measuring an ultrashort optical pulse, in which third order autocorrelation of femtosecond (10−15 second) optical pulses was realized based on third-harmonic-generation (THG). A THG signal with three fundamental frequency photon contributed from three different split pulses of the ultrashort optical pulse is first generated. The three split pulses have time delays &tgr;1 and &tgr;2 in between. Then, the intensity of the THG signal is detected while varying the time delays &tgr;1 and &tgr;2 between the split pulses to obtain a triple correlation of the ultrashort optical pulse. The triple correlation and its Fourier transform are used to obtain the magnitude |Ĩ(&ngr;)| and the phase &agr;(&ngr;) of the ultrashort optical pulse intensity in the frequency domain, and the intensity of the ultrashort optical pulse in the time domain I(t) is determined using the magnitude |Ĩ(&ngr;)| and the phase &agr;(&ngr;) by inverse Fourier Transform.

Abstract: A method for measuring an ultrashort optical pulse, in which third order autocorrelation of femtosecond (10−15 second) optical pulses was realized based on third-harmonic-generation (THG). A THG signal with three fundamental frequency photon contributed from three different split pulses of the ultrashort optical pulse is first generated. The three split pulses have time delays &tgr;1 and &tgr;2 in between. Then, the intensity of the THG signal is detected while varying the time delays &tgr;1 and &tgr;2 between the split pulses to obtain a triple correlation of the ultrashort optical pulse. The triple correlation and its Fourier transform are used to obtain the magnitude |Ĩ(&ngr;)| and the phase &agr;(&ngr;) of the ultrashort optical pulse intensity in the frequency domain, and the intensity of the ultrashort optical pulse in the time domain I(t) is determined using the magnitude |Ĩ(&ngr;)| and the phase &agr;(&ngr;) by inverse Fourier Transform.