Femtosecond incoherent second-order nonlinear light scattering: opportunities for molecular and device characterization

We now demonstrate a novel technique in the frequency-domain for the suppression of the multi-photon fluorescence contribution in hyper-Rayleigh scattering experiments. The technique takes advantages of the demodulation and the phase-shift in the frequency-domain of the time-delayed (multi-photon) fluorescence in the time-domain. For this technique, we use the improved temporal resolution offered by the femtosecond pulse versus the nanosecond pulse. We demonstrate the effectiveness of the demodulation of the fluorescence at high modulation frequencies of the fundamental laser beam by determining the molecular second-order nonlinear polarizability for a reference molecule under fluorescent conditions