Rice University

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Speaker: Ken Knappenberger
Associate Professor of Chemistry and Biochemistry
Florida State University

Structural Examined Through the Combined Lenses of Ultrafast and Magnetooptical Spectroscopy

Wednesday, March 1, 2017
4:00 PM  to 5:00 PM

180  Dell Butcher Hall
Rice University
6100 Main St
Houston, Texas, USA

Plasmonic nanoparticle assemblies offer unique opportunities for controlling energy at the nanoscale. Here, we describe experimental outcomes in three key areas critical to understanding nanoscale-structure-specific light-matter interactions: 1) selective amplification of specific light polarization states; 2) structure-dependent plasmon coherence times; and 3) plasmon-mode-specific 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-ratiodependent 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.

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