7 research outputs found
Underpinning Hybridization Intuition for Complex Nanoantennas by Magnetoelectric Quadrupolar Polarizability Retrieval
A central idea in plasmonics and
metamaterials is to interpret
scattering resonances as resulting from hybridization of electric
dipoles. Recent developments in metamaterials as well as in plasmonic
Fano systems have further included magnetic dipoles and electric quadrupoles
in this reasoning. We derive a method to retrieve dipole and quadrupole
polarizability tensors of nano scatterers from full-wave simulations,
which allows us to underpin this intuitive reasoning by quantifying
the existent modes and their strengths in complex nano antennas. By
application to a dolmen plasmon structure, we show how the retrieval
sheds new light on plasmon induced transparency. Further, we show
how to implement radiative corrections to a dipole–quadrupole
model applicable when scatterers are placed near a surface, sphere,
or stratified medium, similar to the known correction of dipole polarizabilities
by the local density of optical states. We demonstrate how this model
allows us to interpret near field excitation data taken on plasmon
antennas deposited on a high-index substrate
Supplement 1: Direct imaging of hybridized eigenmodes in coupled silicon nanoparticles
Supplemental document Originally published in Optica on 20 January 2016 (optica-3-1-93
Angle-Resolved Cathodoluminescence Imaging Polarimetry
Cathodoluminescence
spectroscopy (CL) allows characterizing light
emission in bulk and nanostructured materials and is a key tool in
fields ranging from materials science to nanophotonics. Previously,
CL measurements focused on the spectral content and angular distribution
of emission, while the polarization was not fully determined. Here
we demonstrate a technique to access the full polarization state of
the cathodoluminescence emission, that is the Stokes parameters as
a function of the emission angle. Using this technique, we measure
the emission of metallic bullseye nanostructures and show that the
handedness of the structure as well as nanoscale changes in excitation
position induce large changes in polarization ellipticity and helicity.
Furthermore, by exploiting the ability of polarimetry to distinguish
polarized from unpolarized light, we quantify the contributions of
different types of coherent and incoherent radiation to the emission
of a gold surface, silicon and gallium arsenide bulk semiconductors.
This technique paves the way for in-depth analysis of the emission
mechanisms of nanostructured devices as well as macroscopic media
Nanoscale Relative Emission Efficiency Mapping Using Cathodoluminescence g<sup>(2)</sup> Imaging
Cathodoluminescence
(CL) imaging spectroscopy provides two-dimensional
optical excitation images of photonic nanostructures with a deep-subwavelength
spatial resolution. So far, CL imaging was unable to provide a direct
measurement of the excitation and emission probabilities of photonic
nanostructures in a spatially resolved manner. Here, we demonstrate
that by mapping the cathodoluminescence autocorrelation function g<sup>(2)</sup> together with the CL spectral distribution the excitation
and emission rates can be disentangled at every excitation position.
We use InGaN/GaN quantum wells in GaN nanowires with diameters in
the range 200–500 nm as a model system to test our new g<sup>(2)</sup> mapping methodology and find characteristic differences
in excitation and emission rates both between wires and within wires.
Strong differences in the average CL intensity between the wires are
the result of differences in the emission efficiencies. At the highest
spatial resolution, intensity variations observed within wires are
the result of excitation rates that vary with the nanoscale geometry
of the structures. The fact that strong spatial variations observed
in the CL intensity are not only uniquely linked to variations in
emission efficiency but also linked to excitation efficiency has profound
implications for the interpretation of the CL data for nanostructured
geometries in general
The Planar Parabolic Optical Antenna
One of the simplest and most common structures used for
directing
light in macroscale applications is the parabolic reflector. Parabolic
reflectors are ubiquitous in many technologies, from satellite dishes
to hand-held flashlights. Today, there is a growing interest in the
use of ultracompact metallic structures for manipulating light on
the wavelength scale. Significant progress has been made in scaling
radiowave antennas to the nanoscale for operation in the visible range,
but similar scaling of parabolic reflectors employing ray-optics concepts
has not yet been accomplished because of the difficulty in fabricating
nanoscale three-dimensional surfaces. Here, we demonstrate that plasmon
physics can be employed to realize a resonant elliptical cavity functioning
as an essentially planar nanometallic structure that serves as a broadband
unidirectional parabolic antenna at optical frequencies
Gallium Plasmonics: Deep Subwavelength Spectroscopic Imaging of Single and Interacting Gallium Nanoparticles
Gallium has recently been demonstrated as a phase-change plasmonic material offering UV tunability, facile synthesis, and a remarkable stability due to its thin, self-terminating native oxide. However, the dense irregular nanoparticle (NP) ensembles fabricated by molecular-beam epitaxy make optical measurements of individual particles challenging. Here we employ hyperspectral cathodoluminescence (CL) microscopy to characterize the response of single Ga NPs of various sizes within an irregular ensemble by spatially and spectrally resolving both in-plane and out-of-plane plasmonic modes. These modes, which include hybridized dipolar and higher-order terms due to phase retardation and substrate interactions, are correlated with finite difference time domain (FDTD) electrodynamics calculations that consider the Ga NP contact angle, substrate, and native Ga/Si surface oxidation. This study experimentally confirms previous theoretical predictions of plasmonic size-tunability in single Ga NPs and demonstrates that the plasmonic modes of interacting Ga nanoparticles can hybridize to produce strong hot spots in the ultraviolet. The controlled, robust UV plasmonic resonances of gallium nanoparticles are applicable to energy- and phase-specific applications such as optical memory, environmental remediation, and simultaneous fluorescence and surface-enhanced Raman spectroscopies
Nanoscale Spatial Coherent Control over the Modal Excitation of a Coupled Plasmonic Resonator System
We demonstrate coherent control over
the optical response of a coupled plasmonic resonator by high-energy
electron beam excitation. We spatially control the position of an
electron beam on a gold dolmen and record the cathodoluminescence
and electron energy loss spectra. By selective coherent excitation
of the dolmen elements in the near field, we are able to manipulate
modal amplitudes of bonding and antibonding eigenmodes. We employ
a combination of CL and EELS to gain detailed insight in the power
dissipation of these modes at the nanoscale as CL selectively probes
the radiative response and EELS probes the combined effect of Ohmic
dissipation and radiation