“…The former problem is difficult to solve in principle, but the latter may be avoided by comparing a measured FRAC trace with a calculated trace by use of its spectrum. Nevertheless, the measured pulse duration tends to be evaluated to be shorter [2,3,4,5] than that obtained by other measurement methods, for example, frequency-resolved optical gating (FROG) [2,4,6] and spectral phase interferometry for direct electric-field reconstruction (SPIDER) [7,8,11]. In addition, the measured pulse duration is sometimes evaluated to be shorter than that of its Fourier-transform-limited (TL) pulses.…”