Two-photon excitation of NaI with femtosecond laser pulses

We have performed a quantum analysis of the two-pulse excitation of NaI, pertinent to the experiments of Rosker, Rose, and Zewail. The model for the NaI molecule is based on early work by Faist, Levine, Grice, and Herschbach. The quantum calculation uses a time-dependent fast Fourier transform method and is exact. We examine the dependence of the laser-induced fluorescence (LIF) signal on the properties of pump and probe pulses and on the dynamics of the excited molecule. Several important differences between the LIF method with ultrashort pulses and the cw case are pointed out.