Browsing by Author "Li, Yang"

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    Angle- and Spectral-Dependent Light Scattering from Plasmonic Nanocups
    (2013-06-05) Li, Yang; Nordlander, Peter J.; Halas, Naomi J.; Link, Stephan
    The interaction of light with small designed particles and structures gives rise to an increasing number of phenomena of potentially dramatic technological importance, such as metamaterials, superlens focusing, and enhanced spectroscopy. Metallic nanostructures with their geometry-dependent optical resonances are a topic of intense current interest due to their ability to manipulate light in ways not possible with conventional optical materials. A particularly fascinating aspect of these systems is the recently realized possibility of creating optical frequency “magnetic plasmon” responses of comparable magnitude to the “electric plasmon” response. Au nanocups at their magnetoinductive resonance have the unique ability to redirect scattered light in a direction dependent on cup orientation, as a true three-dimensional nanoantenna. As optical frequency nanoantennas, reduced-symmetry plasmonic nanoparticles have light-scattering properties that depend strongly on geometry, orientation, and variations in dielectric environment. Here we investigate how these factors influence the spectral and angular dependence of light scattered by Au nanocups. A simple dielectric substrate causes the axial, electric dipole mode of the nanocup to deviate substantially from its characteristic cos square free space scattering profile, while the transverse, magnetic dipole mode remains remarkably insensitive to the presence of the substrate. Nanoscale irregularities of the nanocup rim and the local substrate permittivity have a surprisingly large effect on the spectral- and angle-dependent light-scattering properties of these structures. The different angular scattering and wavelength response from the axial and transverse nanocup modes make the nanocup an interesting particle for the nanoscale manipulation of light in three dimensions. The sensitivity of this system to geometric and environmental factors may present opportunities for active, substrate-mediated control of light scattering.
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    Binary and analog variation of synapses between cortical pyramidal neurons
    (eLife Sciences Publications Ltd., 2022) Dorkenwald, Sven; Turner, Nicholas L.; Macrina, Thomas; Lee, Kisuk; Lu, Ran; Wu, Jingpeng; Bodor, Agnes L.; Bleckert, Adam A.; Brittain, Derrick; Kemnitz, Nico; Silversmith, William M.; Ih, Dodam; Zung, Jonathan; Zlateski, Aleksandar; Tartavull, Ignacio; Yu, Szi-Chieh; Popovych, Sergiy; Wong, William; Castro, Manuel; Jordan, Chris S.; Wilson, Alyssa M.; Froudarakis, Emmanouil; Buchanan, JoAnn; Takeno, Marc M.; Torres, Russel; Mahalingam, Gayathri; Collman, Forrest; Schneider-Mizell, Casey M.; Bumbarger, Daniel J.; Li, Yang; Becker, Lynne; Suckow, Shelby; Reimer, Jacob; Tolias, Andreas S.; Macarico da Costa, Nuno; Reid, R. Clay; Seung, H. Sebastian
    Learning from experience depends at least in part on changes in neuronal connections. We present the largest map of connectivity to date between cortical neurons of a defined type (layer 2/3 [L2/3] pyramidal cells in mouse primary visual cortex), which was enabled by automated analysis of serial section electron microscopy images with improved handling of image defects (250 × 140 × 90 μm3 volume). We used the map to identify constraints on the learning algorithms employed by the cortex. Previous cortical studies modeled a continuum of synapse sizes by a log-normal distribution. A continuum is consistent with most neural network models of learning, in which synaptic strength is a continuously graded analog variable. Here, we show that synapse size, when restricted to synapses between L2/3 pyramidal cells, is well modeled by the sum of a binary variable and an analog variable drawn from a log-normal distribution. Two synapses sharing the same presynaptic and postsynaptic cells are known to be correlated in size. We show that the binary variables of the two synapses are highly correlated, while the analog variables are not. Binary variation could be the outcome of a Hebbian or other synaptic plasticity rule depending on activity signals that are relatively uniform across neuronal arbors, while analog variation may be dominated by other influences such as spontaneous dynamical fluctuations. We discuss the implications for the longstanding hypothesis that activity-dependent plasticity switches synapses between bistable states.
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    Efficient Second Harmonic Generation in a Hybrid Plasmonic Waveguide by Mode Interactions
    (American Chemical Society, 2019) Shi, Junjun; Li, Yang; Kang, Meng; He, Xiaobo; Halas, Naomi J.; Nordlander, Peter; Zhang, Shunping; Xu, Hongxing; Laboratory for Nanophotonics
    Developing highly efficient nanoscale coherent light sources is essential for advances in technological applications such as integrated photonic circuits, bioimaging, and sensing. An on-chip wavelength convertor based on second harmonic generation (SHG) would be a crucial step toward this goal, but the light-conversion efficiency would be low for small device dimensions. Here we demonstrate strongly enhanced SHG with a high conversion efficiency of 4 × 10–5 W–1 from a hybrid plasmonic waveguide consisting of a CdSe nanowire coupled with a Au film. The strong spatial overlap of the waveguide mode with the nonlinear material and momentum conservation between the incident and reflected modes are the key factors resulting in such high efficiency. The SHG emission angles vary linearly with excitation wavelength, indicating a nonlinear steering of coherent light emission at the subwavelength scale. Our work is promising for the realization of efficient and tunable nonlinear coherent sources and opens new approaches for efficient integrated nonlinear nanophotonic devices.
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    Manipulation of Energy Propagation, Redirection, and Dissipation by Tunable Plasmonic Nanostructures
    (2013-07-24) Li, Yang; Nordlander, Peter J.; Halas, Naomi J.; Link, Stephan
    Plasmons, the collective electronic oscillations of metallic nanoparticles and nanostructures, are at the forefront of the development of nanoscale optics. Metallic nanostructures with their geometry-dependent optical resonances are a topic of intense current interest due to their ability to manipulate light in ways not possible with conventional optical materials. As optical frequency nanoantennas, reduced-symmetry plasmonic nanoparticles have light-scattering properties that depend strongly on geometry, orientation, and variations in dielectric environment. Particularly fascinating aspect of these systems is the recently realized possibility of creating optical frequency “magnetic plasmon” responses of comparable magnitude to the “electric plasmon” response. It is of our central interest to understand better the plasmonic system so as to manipulate the energy transport mechanism. With the much more advanced numerical calculations, and based on the Finite Element Method (FEM) and Finite-Difference Time-Domain (FDTD) method, we are now able to study various kinds of nanostructures for different interesting optical properties. With the help of FDTD, we show the geometry dependent dissipation rate in different nanosystems. We brought up a new damped harmonic oscillator model to account for the observed difference. We show that our new model better completes the full map of the energy dissipation mechanism, and the predicted outcome agreed very well with the FDTD calculations. Elliptical nanorings were investigated by applying both FEM and FDTD methods. The mulitiple plasmonic resonaces exhibited by elliptical nanorings and the well tunability of the nanosystem make elliptical nanorings very interesting. Different features can be realized by controlling the aspect ratios of the elliptical nanorings. We show another interesting nanostructures, light bending nanocup as well. Due to its unique light scattering properties, nanocup is a very promising candidate in solar cell applications. We studied more about its light redirection properties with the presence of a dielectric substrate and its sensitivity to the subtle geometry differences. Plasmonic heptamer has been shown to possess an intriguing Fano resonance due to the interference of its hybridized subradiant and super-radiant modes. Neighboring fused heptamers can support magnetic plasmons due to the generation of antiphase ring currents in the metallic nanoclusters. We use such artificial plasmonic molecules as basic elements to construct low-loss plasmonic waveguides and devices. The manipulation of magnetic plasmons in heptamer interconnects can further be expanded to more complex systems, for example, by integrating more optical paths to achieve multiple input and output plasmonic networks. With their compact dimensions, outstanding low-loss propagation characteristics, and range of functionalities, magnetic plasmon-based devices based on these structures should be key to the further development of high- performance energy transport components in informa- tion processing and data storage applications.
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    Structure and function of axo-axonic inhibition
    (eLife Sciences Publications Ltd, 2021) Schneider-Mizell, Casey M.; Bodor, Agnes L.; Collman, Forrest; Brittain, Derrick; Bleckert, Adam; Dorkenwald, Sven; Turner, Nicholas L.; Macrina, Thomas; Lee, Kisuk; Lu, Ran; Wu, Jingpeng; Zhuang, Jun; Nandi, Anirban; Hu, Brian; Buchanan, JoAnn; Takeno, Marc M.; Torres, Russel; Mahalingam, Gayathri; Bumbarger, Daniel J.; Li, Yang; Chartrand, Thomas; Kemnitz, Nico; Silversmith, William M.; Ih, Dodam; Zung, Jonathan; Zlateski, Aleksandar; Tartavull, Ignacio; Popovych, Sergiy; Wong, William; Castro, Manuel; Jordan, Chris S.; Froudarakis, Emmanouil; Becker, Lynne; Suckow, Shelby; Reimer, Jacob; Tolias, Andreas S.; Anastassiou, Costas A.; Seung, H. Sebastian; Reid, R. Clay; Costa, Nuno Maçarico da
    Inhibitory neurons in mammalian cortex exhibit diverse physiological, morphological, molecular, and connectivity signatures. While considerable work has measured the average connectivity of several interneuron classes, there remains a fundamental lack of understanding of the connectivity distribution of distinct inhibitory cell types with synaptic resolution, how it relates to properties of target cells, and how it affects function. Here, we used large-scale electron microscopy and functional imaging to address these questions for chandelier cells in layer 2/3 of the mouse visual cortex. With dense reconstructions from electron microscopy, we mapped the complete chandelier input onto 153 pyramidal neurons. We found that synapse number is highly variable across the population and is correlated with several structural features of the target neuron. This variability in the number of axo-axonic ChC synapses is higher than the variability seen in perisomatic inhibition. Biophysical simulations show that the observed pattern of axo-axonic inhibition is particularly effective in controlling excitatory output when excitation and inhibition are co-active. Finally, we measured chandelier cell activity in awake animals using a cell-type-specific calcium imaging approach and saw highly correlated activity across chandelier cells. In the same experiments, in vivo chandelier population activity correlated with pupil dilation, a proxy for arousal. Together, these results suggest that chandelier cells provide a circuit-wide signal whose strength is adjusted relative to the properties of target neurons.