21 research outputs found
Lasing Action with Gold Nanorod Hyperbolic Metamaterials
Coherent nanoscale photon sources are of paramount importance to achieving
all-optical communication. Several nanolasers smaller than the diffraction
limit have been theoretically proposed and experimentally demonstrated using
plasmonic cavities to confine optical fields. Such compact cavities exhibit
large Purcell factors, thereby enhancing spontaneous emission, which feeds into
the lasing mode. However, most plasmonic nanolasers reported so far have
employed resonant nanostructures and therefore had the lasing restricted to the
proximity of the resonance wavelength. Here, we report on an approach based on
gold nanorod hyperbolic metamaterials for lasing. Hyperbolic metamaterials
provide broadband Purcell enhancement due to large photonic density of optical
states, while also supporting surface plasmon modes to deliver optical feedback
for lasing due to nonlocal effects in nanorod media. We experimentally
demonstrate the advantage of hyperbolic metamaterials in achieving lasing
action by its comparison with that obtained in a metamaterial with elliptic
dispersion. The conclusions from the experimental results are supported with
numerical simulations comparing the Purcell factors and surface plasmon modes
for the metamaterials with different dispersions. We show that although the
metamaterials of both types support lasing, emission with hyperbolic samples is
about twice as strong with 35% lower threshold vs. the elliptic ones. Hence,
hyperbolic metamaterials can serve as a convenient platform of choice for
nanoscale coherent photon sources in a broad wavelength range
Zinc Oxide Based Plasmonic Multilayer Resonator: Localized and Gap Surface Plasmon in the Infrared
Using alternative plasmonic materials,
we experimentally demonstrate
gap plasmon resonances in metalāinsulatorāmetal nanostructures
in the near- and mid-infrared wavelength regions utilizing gallium
doped zinc oxide as the metallic component and undoped zinc oxide
as the dielectric. We show that similar to metalāinsulatorāmetal
resonators previously demonstrated with noble metals, the layered
transparent conducting oxide nanodisks support gap surface plasmon
resonances characterized by highly confined electromagnetic fields
in the dielectric gap. Such resonances can be tailored to desired
values by varying the dielectric-layer thickness. Utilizing these
observed gap plasmon resonance, we examine the potential of our structure
for sensing applications by measuring the surface enhanced infrared
absorption of an octadecanethiol layer. The layered nanostructure
can detect very weak absorption resonances in nanoscale volumes of
absorbing material deposited over the nanodisk resonator
Highly Broadband Absorber Using Plasmonic Titanium Carbide (MXene)
Control of light transmission and
reflection through nanostructured
materials has led to demonstration of metamaterial absorbers that
have augmented the performance of energy harvesting applications of
several optoelectronic and nanophotonic systems. Here, for the first
time, a broadband plasmonic metamaterial absorber is fabricated using
two-dimensional titanium carbide (Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub>) MXene. Arrays of nanodisks made of Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> exhibit strong
localized surface plasmon resonances at near-infrared frequencies.
By exploiting the scattering enhancement at the resonances and the
optical losses inherent to Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> MXene, high-efficiency absorption (ā¼90%)
for a wide wavelength window of incident illumination (ā¼1.55
Ī¼m) has been achieved
Efficient Light Bending with Isotropic Metamaterial Huygensā Surfaces
Metamaterial Huygensā surfaces
manipulate electromagnetic
wavefronts without reflection. A broadband Huygensā surface
that efficiently refracts normally incident light at the telecommunication
wavelength of 1.5 Ī¼m is reported. The electric and magnetic
responses of the surface are independently controlled by cascading
three patterned, metallic sheets with a subwavelength overall thickness
of 430 nm. The peak efficiency of the device is significantly enhanced
by reducing the polarization and reflection losses that are inherent
to earlier single-layer designs
Photothermal Heating Enabled by Plasmonic Nanostructures for Electrokinetic Manipulation and Sorting of Particles
Plasmonic nanostructures support strong electromagnetic field enhancement or optical āhot spotsā that are accompanied by local heat generation. This heating effect is generally seen as an obstacle to stable trapping of particles on a plasmonic substrate. In this work, instead of treating the heating effect as a hindrance, we utilized the collective photoinduced heating of the nanostructure array for high-throughput trapping of particles on a plasmonic nanostructured substrate. The photoinduced heating of the nanostructures is combined with an ac electric field of less than 100 kHz, which results in creation of a strong electrothermal microfluidic flow. This flow rapidly transports suspended particles toward the plasmonic substrate, where they are captured by local electric field effects. This work is envisioned to have application in biosensing and surface-enhanced spectroscopies such as SERS
Photothermal Heating Enabled by Plasmonic Nanostructures for Electrokinetic Manipulation and Sorting of Particles
Plasmonic nanostructures support strong electromagnetic field enhancement or optical āhot spotsā that are accompanied by local heat generation. This heating effect is generally seen as an obstacle to stable trapping of particles on a plasmonic substrate. In this work, instead of treating the heating effect as a hindrance, we utilized the collective photoinduced heating of the nanostructure array for high-throughput trapping of particles on a plasmonic nanostructured substrate. The photoinduced heating of the nanostructures is combined with an ac electric field of less than 100 kHz, which results in creation of a strong electrothermal microfluidic flow. This flow rapidly transports suspended particles toward the plasmonic substrate, where they are captured by local electric field effects. This work is envisioned to have application in biosensing and surface-enhanced spectroscopies such as SERS
Temperature-Dependent Optical Properties of Single Crystalline and Polycrystalline Silver Thin Films
Silver
holds a unique place in plasmonics compared to other noble
metals owing to its low losses in the visible and near-IR wavelength
ranges. With a growing interest in local heating and high temperature
applications of plasmonics, it is becoming critical to characterize
the dielectric function of nanometer-scale thin silver films at higher
temperatures, especially near the breakdown temperature, which depends
on the film thickness and crystallinity. So far, such a comprehensive
study has been missing. Here we report the in situ high temperature
ellipsometry measurements of ultrasmooth and epitaxial quality crystalline
silver films, along with electron beam evaporated polycrystalline
silver films at temperatures up to 700 Ā°C, in the wavelength
range of 330ā2000 nm. Our findings show that the dielectric
function of all the films changes remarkably at elevated temperatures
with larger relative changes observed in polycrystalline films. In
addition, low-loss epitaxial films were found to be thermally more
stable at elevated temperatures. We demonstrate the importance of
our findings for high temperature applications with a numerical simulation
of field enhancement in a bow-tie nanoantenna, a near field transducer
commonly used for heat-assisted magnetic recording. The simulated
field profiles at elevated temperatures showed significant deviations
compared to those at room temperature, clearly suggesting that the
use of room temperature optical properties in modeling elevated temperature
applications can be misleading due to the thermal deviations in the
Ag dielectric function. We also provide causal analytical models describing
the elevated temperature Ag dielectric functions
Electrical Modulation of Fano Resonance in Plasmonic Nanostructures Using Graphene
Pauli
blocking of interband transistions gives rise to
tunable
optical properties in single layer graphene (SLG). This effect is
exploited in a graphene-nanoantenna hybrid device where Fano resonant
plasmonic nanostructures are fabricated on top of a graphene sheet.
The use of Fano resonant elements enhances the interaction of incident
radiation with the graphene sheet and enables efficient electrical
modulation of the plasmonic resonance. We observe electrically controlled
damping in the Fano resonances occurring at approximately 2 Ī¼m,
and the results are verified by full-wave 3D finite-element simulations.
Our approach can be used for development of next generation of tunable
plasmonic and hybrid nanophotonic devices
Shape-Dependent Plasmonic Response and Directed Self-Assembly in a New Semiconductor Building Block, Indium-Doped Cadmium Oxide (ICO)
The influence of particle shape on
plasmonic response and local
electric field strength is well-documented in metallic nanoparticles.
Morphologies such as rods, plates, and octahedra are readily synthesized
and exhibit drastically different extinction spectra than spherical
particles. Despite this fact, the influence of composition and shape
on the optical properties of plasmonic semiconductor nanocrystals,
in which free electrons result from heavy doping, has not been well-studied.
Here, we report the first observation of plasmonic resonance in indium-doped
cadmium oxide (ICO) nanocrystals, which exhibit the highest quality
factors reported for semiconductor nanocrystals. Furthermore, we are
able to independently control the shape and free electron concentration
in ICO nanocrystals, allowing for the influence of shape on the optical
response of a plasmonic semiconductor to be conclusively demonstrated.
The highly uniform particles may be self-assembled into ordered single
component and binary nanocrystal superlattices, and in thin films,
exhibit negative permittivity in the near infrared (NIR) region, validating
their use as a new class of tunable low-loss plasmonic building blocks
for 3-D optical metamaterials
Quantum Emitters in Aluminum Nitride Induced by Zirconium Ion Implantation
The integration of solid-state single-photon sources with foundry-compatible photonic platforms is crucial for practical and scalable quantum photonic applications. This study investigates aluminum nitride (AlN) as a material with properties highly suitable for integrated on-chip photonics specifically due to AlN capacity to host defect-center related single-photon emitters. We conduct a comprehensive study of the creation and photophysical properties of single-photon emitters in AlN utilizing Zirconium (Zr) and Krypton (Kr) heavy ion implantation and thermal annealing techniques. Guided by theoretical predictions, we assess the potential of Zr ions to create optically addressable spin-defects and employ Kr ions as an alternative approach that targets lattice defects without inducing chemical doping effects. With the 532 nm excitation wavelength, we found that single-photon emitters induced by ion implantation are primarily associated with vacancy-type defects in the AlN lattice for both Zr and Kr ions. The emitter density increases with the ion fluence, and there is an optimal value for the high density of emitters with low AlN background fluorescence. Additionally, under shorter excitation wavelength of 405 nm, Zr-implanted AlN exhibits isolated point-like emitters, which can be related to Zr-based defect complexes. This study provides important insights into the formation and properties of single-photon emitters in aluminum nitride induced by heavy ion implantation, contributing to the advancement of the aluminum nitride platform for on-chip quantum photonic applications