Nonlinear Near-Field Dynamics of Plasmonic Nanostructures
Davidson, Roderick Belden II
We present three experiments designed to explore the physics of nanostructured materials in nonlinear optics. We utilize both photon and electron-beam excitations on systems with local densities of states specifically designed to generate small mode volumes. The first experiment uses planar arrays of gold Archimedean nanospirals to create asymmetric electric-field profiles for efficient second-harmonic generation (SHG). This nanostructure exhibits two-dimensional chirality and record SHG efficiency per unit volume. In the optical-field-induced second harmonic experiment, we employ an array of serrated gold nanogaps coupled to a polymer film to temporally resolve the change in the second-order nonlinear susceptibility of the polymer with 100 attosecond time resolution while separaing the nonlinear signals from the polymer and plasmonic emission using a spatial light modulator. Finally, we report the first demonstration of a quantum emitter in a dressed state using an electron beam to excite neutral nitrogen-vacancy (NV0) centers in a diamond nanocrystal. We deduce the presence of Rabi oscillations from the ensemble of NV0 centers at room temperature by measuring the second-order autocorrelation function of the cathodoluminescence signal that arises from the beam-induced plasmon interaction with the NV0 centers. The effects of phonon scattering on the autocorrelation amplitudes are revealed by subtracting the zero-phonon contribution to the cathodoluminescence spectrum. In summary, we have demonstrated three unique approaches for generating strong nonlinearities in nanoscale systems by manipulating the local density of states and following the dynamical evolution of these states in the time domain.