142 research outputs found
Non-Equilibrium Bose–Einstein Condensation of Exciton-Polaritons in Silicon Metasurfaces
Exciton-polaritons (EPs) are hybrid light–matter quasi-particles with bosonic character formed by the strong coupling between excitons in matter and photons in optical cavities. Their hybrid character offers promising prospects for the realization of non-equilibrium Bose–Einstein condensates (BECs), and room-temperature BECs are possible with organic materials. However, the thresholds required to create BECs of organic EPs remain still high to allow condensation with electrical injection of carriers. One of the factors behind these high thresholds is the very short cavity lifetimes, leading to a fast EP decay and the need to inject higher exciton densities in the reservoir to form the condensate. Here a BEC of EPs in organic dyes and all-dielectric metasurfaces at room temperature is demonstrated. By using dielectric metasurfaces that exhibit very low losses it is possible to achieve cavity lifetimes long enough to allow an efficient population of EP states via vibrational relaxation and radiative pumping. It is shown how polariton lasing or non-equilibrium Bose–Einstein condensation is achieved in several cavities, and one of the lowest reported thresholds for BECs in organic materials is observed.</p
Enhanced light emission by magnetic and electric resonances in dielectric metasurfaces
We demonstrate an enhanced emission of high quantum yield molecules coupled
to dielectric metasurfaces formed by periodic arrays of polycrystalline silicon
nanoparticles. Radiative coupling of the nanoparticles, mediated by in-plane
diffraction, leads to the formation of collective Mie scattering resonances or
Mie surface lattice resonances (M-SLRs), with remarkable narrow line widths.
These narrow line widths and the intrinsic electric and magnetic dipole moments
of the individual Si nanoparticles allow to resolve electric and magnetic
M-SLRs. Incidence angle- and polarization-dependent extinction measurements and
high-accuracy surface integral simulations show unambiguously that magnetic
M-SLRs arise from in- and out-of-plane magnetic dipoles, while electric M-SLRs
are due to in-plane electric dipoles. Pronounced changes in the emission
spectrum of the molecules are observed, with almost a 20-fold enhancement of
the emission in defined directions of molecules coupled to electric M-SLRs, and
a 5-fold enhancement of the emission of molecules coupled to magnetic M-SLRs.
These measurements demonstrate the potential of dielectric metasurfaces for
emission control and enhancement, and open new opportunities to induce
asymmetric scattering and emission using collective electric and magnetic
resonances.Comment: 27 pages with 9 figure
The Rise and Current Status of Polaritonic Photochemistry and Photophysics
The interaction between molecular electronic transitions and electromagnetic fields can be enlarged to the point where distinct hybrid light-matter states, polaritons, emerge. The photonic contribution to these states results in increased complexity as well as an opening to modify the photophysics and photochemistry beyond what normally can be seen in organic molecules. It is today evident that polaritons offer opportunities for molecular photochemistry and photophysics, which has caused an ever-rising interest in the field. Focusing on the experimental landmarks, this review takes its reader from the advent of the field of polaritonic chemistry, over the split into polariton chemistry and photochemistry, to present day status within polaritonic photochemistry and photophysics. To introduce the field, the review starts with a general description of light-matter interactions, how to enhance these, and what characterizes the coupling strength. Then the photochemistry and photophysics of strongly coupled systems using Fabry-Perot and plasmonic cavities are described. This is followed by a description of room-temperature Bose-Einstein condensation/polariton lasing in polaritonic systems. The review ends with a discussion on the benefits, limitations, and future developments of strong exciton-photon coupling using organic molecules
Inverse designed plasmonic metasurface with parts per billion optical hydrogen detection
Plasmonic sensors rely on optical resonances in metal nanoparticles and are typically limited by their broad spectral features. This constraint is particularly taxing for optical hydrogen sensors, in which hydrogen is absorbed inside optically-lossy Pd nanostructures and for which state-of-the-art detection limits are only at the low parts-per-million (ppm) range. Here, we overcome this limitation by inversely designing a plasmonic metasurface based on a periodic array of Pd nanoparticles. Guided by a particle swarm optimization algorithm, we numerically identify and experimentally demonstrate a sensor with an optimal balance between a narrow spectral linewidth and a large field enhancement inside the nanoparticles, enabling a measured hydrogen detection limit of 250 parts-per-billion (ppb). Our work significantly improves current plasmonic hydrogen sensor capabilities and, in a broader context, highlights the power of inverse design of plasmonic metasurfaces for ultrasensitive optical (gas) detection
Engineering bound states in the continuum at telecom wavelengths with non-Bravais lattices
Various optical phenomena can be induced in periodic arrays of nanoparticles
by the radiative coupling of the local dipoles in each particle. Probably the
most impressive example is bound states in the continuum (BICs), which are
electromagnetic modes with a dispersion inside the light cone but infinite
lifetime, i.e., modes that cannot leak to the continuum. Symmetry-protected
BICs appear at highly symmetric points in the dispersion of periodic systems.
Although the addition of nonequivalent lattice points in a unit cell is an easy
and straightforward way of tuning the symmetry, BICs in such particle lattice,
i.e., non-Bravais lattice, are less explored among periodic systems. Starting
from a periodic square lattice of Si nanodisks, we have prepared three
non-Bravais lattices by detuning size and position of the second disk in the
unit cell. Diffraction-induced coupling excites magnetic/electric dipoles in
each nanodisk, producing two surface lattice resonances at the point
with a band gap in between. %of 41 meV.
The high/low energy branch becomes a BIC for the size/position-detuned array,
respectively, while both branches are bright (or leaky) when both size and
position are detuned simultaneously. The role of magnetic and electric
resonances in dielectric nanoparticles and the change of BIC to bright
character of the modes is explained by the two different origins of BICs in the
detuned arrays, which is further discussed with the aid of a coupled electric
and magnetic dipole model. This study gives a simple way of tuning BICs at
telecom wavelengths in non-Bravais lattices, including both plasmonic and
dielectric systems, thus scalable to a wide range of frequencies.Comment: 26 pages, 5 figure
Room Temperature Exciton-Polariton Condensation in Silicon Metasurfaces Emerging from Bound States in the Continuum
We show the first experimental demonstration of room-temperature
exciton-polariton (EP) condensation from a bound state in the continuum (BIC).
This demonstration is achieved by strongly coupling stable excitons in an
organic perylene dye with the extremely long-lived BIC in a dielectric
metasurface of silicon nanoparticles. The long lifetime of the BIC, mainly due
to the suppression of radiation leakage, allows for EP thermalization to the
ground state before decaying. This property results in a condensation threshold
of less than 5 \mu J cm^{-2}, one order of magnitude lower that the lasing
threshold reported in similar systems in the weak coupling limit
Collective Mie Exciton-Polaritons in an Atomically Thin Semiconductor
Optically induced Mie resonances in dielectric nanoantennas feature low
dissipative losses and large resonant enhancement of both electric and magnetic
fields. They offer an alternative platform to plasmonic resonances to study
light-matter interactions from the weak to the strong coupling regimes. Here,
we experimentally demonstrate the strong coupling of bright excitons in
monolayer WS with Mie surface lattice resonances (Mie-SLRs). We resolve
both electric and magnetic Mie-SLRs of a Si nanoparticle array in angular
dispersion measurements. At the zero detuning condition, the dispersion of
electric Mie-SLRs (e-SLRs) exhibits a clear anti-crossing and a Rabi-splitting
of 32 meV between the upper and lower polariton bands. The magnetic Mie-SLRs
(m-SLRs) nearly cross the energy band of excitons. These results suggest that
the field of m-SLRs is dominated by out-of-plane components that do not
efficiently couple with the in-plane excitonic dipoles of the monolayer WS.
In contrast, e-SLRs in dielectric nanoparticle arrays with relatively high
quality factors (Q 120) facilitate the formation of collective Mie
exciton-polaritons, and may allow the development of novel polaritonic devices
which can tailor the optoelectronic properties of atomically thin
two-dimensional semiconductors.Comment: 27 pages, 7 figure
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Rarity of monodominance in hyperdiverse Amazonian forests.
Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such "monodominant" forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors
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