3,110 research outputs found
Second-harmonic generation in subwavelength graphene waveguides
We suggest a novel approach for generating second-harmonic radiation in
subwavelength graphene waveguides. We demonstrate that quadratic phase matching
between the plasmonic guided modes of different symmetries can be achieved in a
planar double-layer geometry when conductivity of one of the layers becomes
spatially modulated. We predict theoretically that, owing to graphene nonlocal
conductivity, the second-order nonlinear processes can be actualized for
interacting plasmonic modes with an effective grating coupler to allow external
pumping of the structure and output of the radiation at the double frequency.Comment: 5 pages, 3 figure
Trapping and guiding surface plasmons in curved graphene landscapes
We demonstrate that graphene placed on top of structured substrates offers a
novel approach for trapping and guiding surface plasmons. A monolayer graphene
with a spatially varying curvature exhibits an effective trapping potential for
graphene plasmons near curved areas such as bumps, humps and wells. We derive
the governing equation for describing such localized channel plasmons guided by
curved graphene and validate our theory by the first-principle numerical
simulations. The proposed confinement mechanism enables plasmon guiding by the
regions of maximal curvature, and it offers a versatile platform for
manipulating light in planar landscapes. In addition, isolated deformations of
graphene such as bumps are shown to support localized surface modes and
resonances suggesting a new way to engineer plasmonic metasurfaces.Comment: 6 pages, 4 figure
What Do Students Value? Exploring Instructor Behaviors In Face-To-Face And Online Higher Education Classrooms
Understanding Perceptions of Problematic Facebook Use: When People Experience Negative Life Impact and a Lack of Control
While many people use social network sites to connect with friends and
family, some feel that their use is problematic, seriously affecting their
sleep, work, or life. Pairing a survey of 20,000 Facebook users measuring
perceptions of problematic use with behavioral and demographic data, we
examined Facebook activities associated with problematic use as well as the
kinds of people most likely to experience it. People who feel their use is
problematic are more likely to be younger, male, and going through a major life
event such as a breakup. They spend more time on the platform, particularly at
night, and spend proportionally more time looking at profiles and less time
browsing their News Feeds. They also message their friends more frequently.
While they are more likely to respond to notifications, they are also more
likely to deactivate their accounts, perhaps in an effort to better manage
their time. Further, they are more likely to have seen content about social
media or phone addiction. Notably, people reporting problematic use rate the
site as more valuable to them, highlighting the complex relationship between
technology use and well-being. A better understanding of problematic Facebook
use can inform the design of context-appropriate and supportive tools to help
people become more in control.Comment: CHI 201
Tunable nonlinear graphene metasurfaces
We introduce the concept of nonlinear graphene metasurfaces employing the
controllable interaction between a graphene layer and a planar metamaterial.
Such hybrid metasurfaces support two types of subradiant resonant modes,
asymmetric modes of structured metamaterial elements ("metamolecules") and
graphene plasmons exhibiting strong mutual coupling and avoided dispersion
crossing. High tunability of graphene plasmons facilitates strong interaction
between the subradiant modes, modifying the spectral position and lifetime of
the associated Fano resonances. We demonstrate that strong resonant
interaction, combined with the subwavelength localization of plasmons, leads to
the enhanced nonlinear response and high efficiency of the second-harmonic
generation.Comment: 6 pages, 5 figure
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