Plasmonic nanoparticle transducers offer unique opportunities for using light amplification to improve optical microscopy measurements. Here, experimental outcomes in key areas critical to understanding nanoscale-structure-specific light-matter interactions are described, including structure-dependent plasmon coherence times and plasmon-mode-specific 3-D spatial localization of electromagnetic energy to nanoscale volumes. Interferometric single-particle second harmonic generation (SHG) and two-photon photoluminescence (TPPL) imaging techniques developed in our lab provide high spatial accuracy and precision along with femtosecond time resolution for examining nanoparticle assemblies. Femtosecond time-resolution is achieved by employing a sequence of phase-locked laser pulses to examine the nanostructures. These imaging methods have been employed to quantify plasmon coherence times for assemblies of nanospheres and nanorods. Determination of plasmon coherence times provides a quantitative measurement of mode-specific quality factors, which are important for assessing the efficiency of nanostructures for using electromagnetic energy. Based on our coherence data, one-dimensional nanorods are promising building blocks of nanoparticle networks for using electromagnetic energy at the nanoscale. The effectiveness of the nanorods results from the inherent length-to-diameter aspect-ratio-dependent tunability of the longitudinal plasmon resonance (LSPR) frequency. The LSPR of high aspect ratio nanorods can be energetically decoupled from interband relaxation channels, which are a major source plasmon decoherence, thus explaining the experimental results. Indeed, preliminary interferometric nonlinear optical studies of nanorod trimers indicate the plasmon coherence time can be increased by approximately 100% for nanoparticle networks of specific symmetries. Translation of these coherence time increases to improved 3-D spatial accuracy will be demonstrated.

Structural plasmonics studied using ultrafast spectroscopy beyond the diffraction limit

253rd National Meeting (2017)

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