Femtosecond measurement of fluorescence by two-photon interference

We show that the coherence time and the pulse envelope of ultrashort fluorescence can be measured with two-photon interference. We have performed these measurements in a solution of Nile Blue in N,N-dimethylaniline in the femtosecond regime. The coherence time and the envelope contribute two components to a dip in the coincidence count rate. We have verified that these components can be measured separately at will. This technique provides the means to measure the pulse envelope of ultrashort pulses over a wide range of wavelengths and intensities.