The dynamical theory of spectroscopy with ultrashort pulse excitation is developed to simulate the femtosecond time-resolved fluorescence depletion with the bielectron system. The double exponential decay curve and hollow of fluorescence depletion on the experiment are recurred. The microdynamical causation of these is explained. It is found that the stimulated emission of excited molecules on vibrational ground and higher vibrational level by probe pulse respectively leads to the double exponential decay curve and the hollow of fluorescence depletion.

Key words: fluorescence depletion, femtosecond pulse, vibrational relaxation