20 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
Optically Active Metasurface with Non-Chiral Plasmonic Nanoantennas
We design, fabricate, and experimentally
demonstrate an optically
active metasurface of λ/50 thickness that rotates linearly polarized
light by 45° over a broadband wavelength range in the near IR
region. The rotation is achieved through the use of a planar array
of plasmonic nanoantennas, which generates a fixed phase-shift between
the left circular polarized and right circular polarized components
of the incident light. Our approach is built on a new supercell metasurface
design methodology: by judiciously designing the location and orientation
of individual antennas in the structural supercells, we achieve <i>an effective chiral metasurface</i> through <i>a collective
operation of nonchiral antennas</i>. This approach simplifies
the overall structure when compared to designs with chiral antennas
and also enables a chiral effect which <i>quantitatively</i> depends solely on the supercell geometry. This allows for greater
tolerance against fabrication and temperature effects
Broadband High-Efficiency Half-Wave Plate: A Supercell-Based Plasmonic Metasurface Approach
We design, fabricate, and experimentally demonstrate an ultrathin, broadband half-wave plate in the near-infrared range using a plasmonic metasurface. The simulated results show that the linear polarization conversion efficiency is over 97% with over 90% reflectance across an 800 nm bandwidth. Moreover, simulated and experimental results indicate that such broadband and high-efficiency performance is also sustained over a wide range of incident angles. To further obtain a background-free half-wave plate, we arrange such a plate as a periodic array of integrated supercells made of several plasmonic antennas with high linear polarization conversion efficiency, consequently achieving a reflection-phase gradient for the cross-polarized beam. In this design, the anomalous (cross-polarized) and the normal (copolarized) reflected beams become spatially separated, hence enabling highly efficient and robust, background-free polarization conversion along with broadband operation. Our results provide strategies for creating compact, integrated, and high-performance plasmonic circuits and devices
Wavelength-Tunable Spasing in the Visible
A SPASER,
short for surface plasmon amplification by stimulated
emission of radiation, is key to accessing coherent optical fields
at the nanoscale. Nevertheless, the realization of a SPASER in the
visible range still remains a great challenge because of strong dissipative
losses. Here, we demonstrate that room-temperature SPASER emission
can be achieved by amplifying longitudinal surface plasmon modes supported
in gold nanorods as plasmon nanocavities and utilizing laser dyes
to supply optical gain for compensation of plasmon losses. By choosing
a particular organic dye and adjusting the doping level, the resonant
wavelength of the SPASER emission can be tuned from 562 to 627 nm
with a spectral line width narrowed down to 5–11 nm. This work
provides a versatile route toward SPASERs at extended wavelength regimes
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 (∼90%)
for a wide wavelength window of incident illumination (∼1.55
μm) has been achieved
Efficient Light Bending with Isotropic Metamaterial Huygens’ Surfaces
Metamaterial Huygens’ surfaces
manipulate electromagnetic
wavefronts without reflection. A broadband Huygens’ surface
that efficiently refracts normally incident light at the telecommunication
wavelength of 1.5 μm 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
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 μm,
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
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 °C, in the wavelength
range of 330–2000 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
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
High-Resolution Large-Ensemble Nanoparticle Trapping with Multifunctional Thermoplasmonic Nanohole Metasurface
The
intrinsic loss in a plasmonic metasurface is usually considered
to be detrimental for device applications. Using plasmonic loss to
our advantage, we introduce a thermoplasmonic metasurface that enables
high-throughput large-ensemble nanoparticle assembly in a lab-on-a-chip
platform. In our work, an array of subwavelength nanoholes in a metal
film is used as a plasmonic metasurface that supports the excitation
of localized surface plasmon and Bloch surface plasmon polariton waves
upon optical illumination and provides a platform for molding both
optical and thermal landscapes to achieve a tunable many-particle
assembling process. The demonstrated many-particle trapping occurs
against gravity in an inverted configuration where the light beam
first passes through the nanoparticle suspension before illuminating
the thermoplasmonic metasurface, a feat previously thought to be impossible.
We also report an extraordinarily enhanced electrothermoplasmonic
flow in the region of the thermoplasmonic nanohole metasurface, with
comparatively larger transport velocities in comparison to the unpatterned
region. This thermoplasmonic metasurface could enable possibilities
for myriad applications in molecular analysis, quantum photonics,
and self-assembly and creates a versatile platform for exploring nonequilibrium
physics