Equal-pulse correlation technique for measuring femtosecond excited state relaxation times

A new technique for measuring extremely fast excited state relaxation times, on the order of or less than the laser pulse width, in the presence of a longer relaxation time is described. The difficulties involved in using the conventional pump-and-probe technique and the corresponding advantages of the new technique are illustrated with numerical examples for specific three-level systems. Qualitative experimental results on semiconductors and organic dye molecules substantiating the results are shown.