2,779 research outputs found
Gradient metasurfaces: a review of fundamentals and applications
In the wake of intense research on metamaterials the two-dimensional
analogue, known as metasurfaces, has attracted progressively increasing
attention in recent years due to the ease of fabrication and smaller insertion
losses, while enabling an unprecedented control over spatial distributions of
transmitted and reflected optical fields. Metasurfaces represent optically thin
planar arrays of resonant subwavelength elements that can be arranged in a
strictly or quasi periodic fashion, or even in an aperiodic manner, depending
on targeted optical wavefronts to be molded with their help. This paper reviews
a broad subclass of metasurfaces, viz. gradient metasurfaces, which are devised
to exhibit spatially varying optical responses resulting in spatially varying
amplitudes, phases and polarizations of scattered fields. Starting with
introducing the concept of gradient metasurfaces, we present classification of
different metasurfaces from the viewpoint of their responses, differentiating
electrical-dipole, geometric, reflective and Huygens' metasurfaces. The
fundamental building blocks essential for the realization of metasurfaces are
then discussed in order to elucidate the underlying physics of various physical
realizations of both plasmonic and purely dielectric metasurfaces. We then
overview the main applications of gradient metasurfaces, including waveplates,
flat lenses, spiral phase plates, broadband absorbers, color printing,
holograms, polarimeters and surface wave couplers. The review is terminated
with a short section on recently developed nonlinear metasurfaces, followed by
the outlook presenting our view on possible future developments and
perspectives for future applications.Comment: Accepted for publication in Reports on Progress in Physic
Tungsten disulfide-gold nanohole hybrid metasurfaces for nonlinear metalens in the visible region
Recently, nonlinear hybrid metasurface comes into an attractive new concept
in the research of nanophotonics and nanotechnology. It is composed of
semiconductors with an intrinsically large nonlinear susceptibility and
traditional plasmonic metasurfaces, offering opportunities for efficiently
generating and manipulating nonlinear optical responses. A high second-harmonic
generation (SHG) conversion efficiency has been demonstrated in the
mid-infrared region by using multi-quantum-well (MQW) based plasmonic
metasurfaces. However, it has yet to be demonstrated in the visible region.
Here we present a new type of nonlinear hybrid metasurfaces for the visible
region, which consists of a single layer of tungsten disulfide (WS2) and a
phased gold nanohole array. The results indicate that a large SHG
susceptibility of ~0.1 nm/V at 810 nm is achieved, which is 2~3 orders of
magnitude larger than that of typical plasmonic metasurfaces. Nonlinear
metalenses with the focal lengths of 30 {\mu}m, 50 {\mu}m and 100 {\mu}m are
demonstrated experimentally, providing a direct evidence for both generating
and manipulating SH signals based on the nonlinear hybrid metasurfaces. It
shows great potential applications in designing of integrated, ultra-thin,
compacted and efficient nonlinear optical devices, such as frequency
converters, nonlinear holography and generation of nonlinear optical vortex
beam
Holographic Resonant Laser Printing of metasurfaces using plasmonic template
Laser printing with a spatial light modulator (SLM) has several advantages
over conventional raster-writing and dot-matrix display (DMD) writing: multiple
pixel exposure, high power endurance and existing software for computer
generated holograms (CGH). We present a technique for the design and
manufacturing of plasmonic metasurfaces based on ultrafast laser printing with
an SLM. As a proof of principle, we have used this technique to laser print a
plasmonic metalens as well as high resolution plasmonic color decorations. The
high throughput holographic resonant laser printing (HRLP) approach enables
on-demand mass-production of customized metasurfaces.Comment: Supplementary information is available upon request to author
Maxwell-Hydrodynamic Model for Simulating Nonlinear Terahertz Generation from Plasmonic Metasurfaces
The interaction between the electromagnetic field and plasmonic
nanostructures leads to both the strong linear response and inherent nonlinear
behavior. In this paper, a time-domain hydrodynamic model for describing the
motion of electrons in plasmonic nanostructures is presented, in which both
surface and bulk contributions of nonlinearity are considered. A coupled
Maxwell-hydrodynamic system capturing full-wave physics and free electron
dynamics is numerically solved with the parallel finite-difference time-domain
(FDTD) method. The validation of the proposed method is presented to simulate
linear and nonlinear responses from a plasmonic metasurface. The linear
response is compared with the Drude dispersion model and the nonlinear
terahertz emission from a difference-frequency generation process is validated
with theoretical analyses. The proposed scheme is fundamentally important to
design nonlinear plasmonic nanodevices, especially for efficient and broadband
THz emitters.Comment: 8 pages, 7 figures, IEEE Journal on Multiscale and Multiphysics
Computational Techniques, 201
Fano collective resonance as complex mode in a two dimensional planar metasurface of plasmonic nanoparticles
Fano resonances are features in transmissivity/reflectivity/absorption that
owe their origin to the interaction between a bright resonance and a dark
(i.e., sub-radiant) narrower resonance, and may emerge in the optical
properties of planar two-dimensional (2D) periodic arrays (metasurfaces) of
plasmonic nanoparticles. In this Letter, we provide a thorough assessment of
their nature for the general case of normal and oblique plane wave incidence,
highlighting when a Fano resonance is affected by the mutual coupling in an
array and its capability to support free modal solutions. We analyze the
representative case of a metasurface of plasmonic nanoshells at ultraviolet
frequencies and compute its absorption under TE- and TM-polarized, oblique
plane-wave incidence. In particular, we find that plasmonic metasurfaces
display two distinct types of resonances observable as absorption peaks: one is
related to the Mie, dipolar resonance of each nanoparticle; the other is due to
the forced excitation of free modes with small attenuation constant, usually
found at oblique incidence. The latter is thus an array-induced collective Fano
resonance. This realization opens up to manifold flexible designs at optical
frequencies mixing individual and collective resonances. We explain the
physical origin of such Fano resonances using the modal analysis, which allows
to calculate the free modes with complex wavenumber supported by the
metasurface. We define equivalent array dipolar polarizabilities that are
directly related to the absorption physics at oblique incidence and show a
direct dependence between array modal phase and attenuation constant and Fano
resonances. We thus provide a more complete picture of Fano resonances that may
lead to the design of filters, energy-harvesting devices, photodetectors, and
sensors at ultraviolet frequencies.Comment: 6 pages, 5 figure
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