Remote multi-color excitation using femtosecond propagating surface plasmon polaritons in gold films.

We demonstrate dual-color nonlinear excitation of quantum dots positioned onto a gold film at distances up to 40 μm away from a micrometer sized focused laser spot. We attribute the observed remote nonlinear signal to the excitation of two independent surface plasmon polariton (SPP) modes excited at the laser spot in the gold film, which subsequently propagate in a collinear fashion to a distant site and provide the surface field required for nonlinear excitation of the target. This scheme decouples the illuminating photon flux from surface plasmon mediated nonlinear excitation of the target, which provides more control of unwanted heating effects at the target site and represents an attractive approach for surface-mediated femtosecond nonlinear examinations of molecules.