65 research outputs found
Slow-light plasmonic metamaterial based on dressed-state analog of electromagnetically-induced transparency
We consider a simple configuration for realizing one-dimensional slow-light
metamaterials with large bandwidth-delay products using stub-shaped Fabry-Perot
resonators as building blocks. Each metaatom gives rise to large group indices
due to a classical analog of the dressed-state picture of
electromagnetically-induced transparency. By connecting up to eight metaatoms,
we find bandwidth-delay products over unity and group indices approaching 100.
Our approach is quite general and can be applied to any type of Fabry-Perot
resonators and tuned to different operating wavelengths
Nonlocal study of ultimate plasmon hybridization
Within our recently proposed generalized nonlocal optical response (GNOR)
model, we revisit the fundamental problem of an optically excited plasmonic
dimer. The dimer consists of two identical cylinders separated by a
nanometre-sized gap. We consider the transition from separated dimers via
touching dimers to finally overlapping dimers. In particular, we focus on the
touching case, showing a fundamental limit on the hybridization of the bonding
plasmon modes due to nonlocality. Using transformation optics we determine a
simple analytical equation for the resonance energies of the bonding plasmon
modes of the touching dimer
Nonlocal optical response in metallic nanostructures
This review provides a broad overview of the studies and effects of nonlocal
response in metallic nanostructures. In particular, we thoroughly present the
nonlocal hydrodynamic model and the recently introduced generalized nonlocal
optical response (GNOR) model. The influence of nonlocal response on plasmonic
excitations is studied in key metallic geometries, such as spheres and dimers,
and we derive new consequences due to the GNOR model. Finally, we propose
several trajectories for future work on nonlocal response, including
experimental setups that may unveil further effects of nonlocal response
Generalized nonlocal optical response in nanoplasmonics
Metallic nanostructures exhibit a multitude of optical resonances associated
with localized surface plasmon excitations. Recent observations of plasmonic
phenomena at the sub-nanometer to atomic scale have stimulated the development
of various sophisticated theoretical approaches for their description. Here
instead we present a comparatively simple semiclassical generalized nonlocal
optical response (GNOR) theory that unifies quantum-pressure convection effects
and induced-charge diffusion kinetics, with a concomitant complex-valued GNOR
parameter. Our theory explains surprisingly well both the frequency shifts and
size-dependent damping in individual metallic nanoparticles (MNPs) as well as
the observed broadening of the cross-over regime from bonding-dipole plasmons
to charge-transfer plasmons in MNP dimers, thus unraveling a classical
broadening mechanism that even dominates the widely anticipated
short-circuiting by quantum tunneling. We anticipate that the GNOR theory can
be successfully applied in plasmonics to a wide class of conducting media,
including doped semiconductors and low-dimensional materials such as graphene.Comment: 7 pages, including 3 figures. Supplementary information is available
upon request to author
Resonant laser printing of bi-material metasurfaces: from plasmonic to photonic optical response
Metasurfaces are nanostructured surfaces with engineered optical properties - currently impacting many branches of optics, from miniaturization of optical components to realizing high-resolution structural colors. The optical properties of metasurfaces can be traced to the individual meta-atoms, which set the nature of the optical response, e.g., plasmonic for metallic meta-atoms or photonic for dielectric meta-atoms. Combining multiple types of responses opens up new horizons in design of optical materials, but has so far been avoided due to the fabrication difficulties associated with constructing a metasurface composed of several meta-atom materials. Here, we present a multi-material design approach by optically post-processing a metasurface constructed from self-assembled polystyrene spheres coated with silver. Using our concept of resonant laser printing, we locally alter the initial plasmonic response of the meta-atoms to a pure photonic response. Our work constitutes a conceptually different way of designing metasurfaces and can pave the way for realizing multi-material metasurfaces on large areas while being cost effective.Independent Research Funding Denmark (7026-00117B); VILLUM FONDEN (17400).Peer reviewe
Non-imaging metasurface design for collimated beam shaping
Metasurfaces provide a versatile platform for realizing ultrathin flat optics
for use in a wide variety of optical applications. The design process involves
defining or calculating the phase profile of the metasurface that will yield
the desired optical output. Here, we present an inverse design method for
determining the phase profile for shaping the intensity profile of a collimated
incident beam. The model is based on the concept of optimal transport from
non-imaging optics and enables a collimated beam with an arbitrary intensity
profile to be redistributed to a desired output intensity profile. We derive
the model from the generalized law of refraction and numerically solve the
resulting differential equation using a finite-difference scheme. Through a
variety of examples, we show that our approach accommodates a range of
different input and output intensity profiles, and discuss its feasibility as a
design platform for non-imaging optics
Blueshift of the surface plasmon resonance in silver nanoparticles: substrate effects
We study the blueshift of the surface plasmon (SP) resonance energy of
isolated Ag nanoparticles with decreasing particle diameter, which we recently
measured using electron energy loss spectroscopy (EELS). As the particle
diameter decreases from 26 down to 3.5 nm, a large blueshift of 0.5 eV of the
SP resonance energy is observed. In this paper, we base our theoretical
interpretation of our experimental findings on the nonlocal hydrodynamic model,
and compare the effect of the substrate on the SP resonance energy to the
approach of an effective homogeneous background permittivity. We derive the
nonlocal polarizability of a small metal sphere embedded in a homogeneous
dielectric environment, leading to the nonlocal generalization of the classical
Clausius-Mossotti factor. We also present an exact formalism based on multipole
expansions and scattering matrices to determine the optical response of a metal
sphere on a dielectric substrate of finite thickness, taking into account
retardation and nonlocal effects. We find that the substrate-based calculations
show a similar-sized blueshift as calculations based on a sphere in a
homogeneous environment, and that they both agree qualitatively with the EELS
measurements.Comment: Invited paper for SPP6 special issue to be published in Opt. Expres
Unusual resonances in nanoplasmonic structures due to nonlocal response
We study the nonlocal response of a confined electron gas within the
hydrodynamical Drude model. We address the question whether plasmonic
nanostructures exhibit nonlocal resonances that have no counterpart in the
local-response Drude model. Avoiding the usual quasi-static approximation, we
find that such resonances do indeed occur, but only above the plasma frequency.
Thus the recently found nonlocal resonances at optical frequencies for very
small structures, obtained within quasi-static approximation, are unphysical.
As a specific example we consider nanosized metallic cylinders, for which
extinction cross sections and field distributions can be calculated
analytically.Comment: 5 pages, 2 figures. Accepted as a PRB Rapid Communication, revised
title, minor changes to the tex
- …