Browsing by Author "Zhen, Yu-Rong"

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    Coherent Fano resonances in a plasmonic nanocluster enhance optical four-wave mixing
    (National Academy of Sciences, 2013) Zhang, Yu; Wen, Fangfang; Zhen, Yu-Rong; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
    Plasmonic nanoclusters, an ordered assembly of coupled metallic nanoparticles, support unique spectral features known as Fano resonances due to the coupling between their subradiant and superradiant plasmon modes. Within the Fano resonance, absorption is significantly enhanced, giving rise to highly localized, intense near fields with the potential to enhance nonlinear optical processes. Here, we report a structure supporting the coherent oscillation of two distinct Fano resonances within an individual plasmonic nanocluster. We show how this coherence enhances the optical four-wave mixing process in comparison with other doubleresonant plasmonic clusters that lack this property. A model that explains the observed four-wave mixing features is proposed, which is generally applicable to any third-order process in plasmonic nanostructures. With a larger effective susceptibility χ (3) relative to existing nonlinear optical materials, this coherent double-resonant nanocluster offers a strategy for designing high-performance thirdorder nonlinear optical media.
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    Dye-Assisted Gain of Strongly Confined Surface Plasmon Polaritons in Silver Nanowires
    (American Chemical Society, 2014) Paul, Aniruddha; Zhen, Yu-Rong; Wang, Yi; Chang, Wei-Shun; Xia, Younan; Nordlander, Peter; Link, Stephan; Laboratory for Nanophotonics
    Subwavelength confinement and active control of light is essential for nanoscale communication devices at visible frequencies that support large bandwidths.[1-5] Noble-metal nanostructures present an excellent platform for strongly confined optical waveguides [6-13] because of their ability to support surface plasmon polaritons (SPPs).[14] However, SPP propagation suffers from losses that seriously limit their application potential. [9] Although significant progress toward SPP loss compensation has been reported for various planar 2D waveguide structures,[15-20] as well as lasing involving strongly localized plasmon modes,[21,22] SPP gain in 1D nanoscale waveguides at visible frequencies is yet to be accomplished. Here, we report the first demonstration of gain for deep subwavelength confined SPPs (mode area = λ2/40) in chemically prepared silver nanowires (Ag NWs). We measured a gain coefficient of 270 cm-1 resulting in 14% loss compensation using a continuous-wave (cw) pump laser. These results are an important step toward total loss compensation for highly confined nanowire SPPs.
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    Evolution of light-induced vapor generation at a liquid-immersed metallic nanoparticle
    (American Chemical Society, 2013) Fang, Zheyu; Zhen, Yu-Rong; Neumann, Oara; Polman, Albert; de Abajo, F. Javier García; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics
    When an Au nanoparticle in a liquid medium is illuminated with resonant light of sufficient intensity, a nanometer scale envelope of vapor -a “nanobubble”- surrounding the particle, is formed. This is the nanoscale onset of the well-known process of liquid boiling, occurring at a single nanoparticle nucleation site, resulting from the photothermal response of the nanoparticle. Here we examine bubble formation at an individual metallic nanoparticle in detail. Incipient nanobubble formation is observed by monitoring the plasmon resonance shift of an individual, illuminated Au nanoparticle, when its local environment changes from liquid to vapor. The temperature on the nanoparticle surface is monitored during this process, where a dramatic temperature jump is observed as the nanoscale vapor layer thermally decouples the nanoparticle from the surrounding liquid. By increasing the intensity of the incident light or decreasing the interparticle separation, we observe the formation of micron sized bubbles resulting from the coalescence of nanoparticle-“bound” vapor envelopes. These studies provide the first direct and quantitative analysis of the evolution of light-induced steam generation by nanoparticles from the nanoscale to the macroscale, a process that is of fundamental interest for a growing number of applications.