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Plasmonic cavities represent a promising platform for controlling light–matter interaction due to their exceptionally small mode volume and high density of photonic states. Using plasmonic cavities for enhancing light’s coupling to individual two-level systems, such as single semiconductor quantum dots (QD), is particularly desirable for exploring cavity quantum electrodynamic (QED)...

Paper folding is found across cultures for both aesthetic and functional purposes, with its most widely recognized exponent being the ancient art form of origami. More recently, there has been an upsurge of interest for translating origami designs into mathematics, natural sciences, engineering, and architecture. Across these different fields, origami...

Nature Nanotechnology 10, 878 (2015). doi:10.1038/nnano.2015.178

Authors: Francesco Meinardi, Hunter McDaniel, Francesco Carulli, Annalisa Colombo, Kirill A. Velizhanin, Nikolay S. Makarov, Roberto Simonutti, Victor I. Klimov & Sergio Brovelli

Author(s): Srikanth Toppaladoddi and J. S. Wettlaufer

A new solution to an old equation will make it easier to model the evolution of sea-ice thickness.

[Phys. Rev. Lett. 115, 148501] Published Fri Oct 02, 2015

We demonstrate a broadband, polarization independent, omnidirectional absorber based on a metallic metasurface architecture, which accomplishes greater than 90% absorptance in the visible and near-infrared range of the solar spectrum, and exhibits low emissivity at mid- and far-infrared wavelengths. The complex unit cell of the metasurface solar absorber consists of eight pairs of gold nano-resonators that are separated from a gold ground plane by a thin silicon dioxide spacer. Our experimental measurements reveal high-performance absorption over a wide range of incidence angles for both s- and p-polarizations. We also investigate numerically the frequency-dependent field and current distributions to elucidate how the absorption occurs within the metasurface structure. Furthermore, we discuss the potential use of our metasurface absorber design in solar thermophotovoltaics by exploiting refractory plasmonic materials.

Nature Materials 14, 962 (2015). doi:10.1038/nmat4441

Author: Maria Maragkou

Article

Analysis and detection of circularly polarized light involves the use of multiple optical elements. Here, the authors demonstrate an ultracompact circularly polarized light detector using chiral plasmonic metamaterials with hot electron injection, realizing its implementation on an integrated photonic platform.

Nature Communications doi: 10.1038/ncomms9379

Authors: Wei Li, Zachary J. Coppens, Lucas V. Besteiro, Wenyi Wang, Alexander O. Govorov, Jason Valentine

Metasurfaces are planar structures that locally modify the polarization, phase, and amplitude of light in reflection or transmission, thus enabling lithographically patterned flat optical components with functionalities controlled by design. Transmissive metasurfaces are especially important, as most optical systems used in practice operate in transmission. Several types of transmissive metasurfaces have been realized, but with either low transmission efficiencies or limited control over polarization and phase. Here we show a metasurface platform based on high-contrast dielectric elliptical nano-posts which provides complete control of polarization and phase with sub-wavelength spatial resolution and experimentally measured efficiency ranging from 72% to 97%, depending on the exact design. Such complete control enables the realization of most free-space transmissive optical elements such as lenses, phase-plates, wave-plates, polarizers, beam-splitters, as well as polarization switchable phase holograms and arbitrary vector beam generators using the same metamaterial platform.

Author(s): Matthias Kraft, Yu Luo, S. A. Maier, and J. B. Pendry

Solar cell technology benefits from increased photocurrents. New research uses transformation optics to preferentially concentrate light in hotspots in a metal grating.

[Phys. Rev. X 5, 031029] Published Tue Sep 08, 2015

Materials in nature are characterized by structural order over multiple length scales have evolved for maximum performance and multifunctionality, and are often produced by self-assembly processes. A striking example of this design principle is structural coloration, where interference, diffraction, and absorption effects result in vivid colors. Mimicking this emergence of...

The covariance matrix adaptation evolutionary strategy (CMA-ES) is explored here as an improved alternative to well-established algorithms used in electromagnetic (EM) optimization. In the past, methods such as the genetic algorithm (GA), particle swarm optimization (PSO), and differential evolution (DE) have commonly been used for EM design. In this article, we examine and compare the performance of CMA-ES, PSO, and DE when applied to test functions and several challenging EM design problems. Of particular interest is demonstrating the ability of the relatively new CMA-ES to more quickly and more reliably find acceptable solutions compared with those of the more classical optimization strategies. In addition, it will be shown that due to its self-adaptive scheme, CMA-ES is a more user-friendly algorithm that requires less knowledge of the problem for preoptimization configuration.

Plasmon-induced hot-electron transfer from metal nanostructures is a potential new paradigm for solar energy conversion; however, the reported efficiencies of devices based on this concept are often low because of the loss of hot electrons via ultrafast electron-electron scattering. We propose a pathway, called the plasmon-induced interfacial charge-transfer transition (PICTT), that enables the decay of a plasmon by directly exciting an electron from the metal to a strongly coupled acceptor. We demonstrated this concept in cadmium selenide nanorods with gold tips, in which the gold plasmon was strongly damped by cadmium selenide through interfacial electron transfer. The quantum efficiency of the PICTT process was high (>24%), independent of excitation photon energy over a ~1–electron volt range, and dependent on the excitation polarization. Authors: K. Wu, J. Chen, J. R. McBride, T. Lian

Absorption of photons by solid materials is critical for applications such as photovoltaics (1), photocatalysis (2), and sensors (3). Fundamental to these technologies is the design of materials that can efficiently absorb photons of desired wavelengths and direct the separation and transport of the generated charge carriers [electrons (negative) and holes (positive)] to their respective collectors. Materials with high concentrations of free conducting electrons, such as coinage metals (Ag, Au, and Cu), have attracted attention for these applications because of their tunable ability to strongly concentrate a light flux in small volumes via the excitation of resonant surface plasmons. However, the lifetime of useful electrons and holes generated in metals upon the decay of surface plasmons is on the order of 1 ps, which limits their efficient collection. On page 632 of this issue, Wu et al. (4) overcome this limitation by demonstrating a direct, instantaneous transfer of plasmon-derived electrons into interfacial semiconductors that allows for efficient solar energy harvesting across a broad range of photon energies. Authors: Matthew J. Kale, Phillip Christopher

Nature Nanotechnology 10, 676 (2015). doi:10.1038/nnano.2015.118

Authors: Young Duck Kim, Hakseong Kim, Yujin Cho, Ji Hoon Ryoo, Cheol-Hwan Park, Pilkwang Kim, Yong Seung Kim, Sunwoo Lee, Yilei Li, Seung-Nam Park, Yong Shim Yoo, Duhee Yoon, Vincent E. Dorgan, Eric Pop, Tony F. Heinz, James Hone, Seung-Hyun Chun, Hyeonsik Cheong, Sang Wook Lee, Myung-Ho Bae & Yun Daniel Park

Graphene and related two-dimensional materials are promising candidates for atomically thin, flexible and transparent optoelectronics. In particular, the strong light–matter interaction in graphene has allowed for the development of state-of-the-art photodetectors, optical modulators and plasmonic devices. In addition, electrically biased graphene on SiO2 substrates can be used as a low-efficiency emitter in the mid-infrared range. However, emission in the visible range has remained elusive. Here, we report the observation of bright visible light emission from electrically biased suspended graphene devices. In these devices, heat transport is greatly reduced. Hot electrons (∼2,800 K) therefore become spatially localized at the centre of the graphene layer, resulting in a 1,000-fold enhancement in thermal radiation efficiency. Moreover, strong optical interference between the suspended graphene and substrate can be used to tune the emission spectrum. We also demonstrate the scalability of this technique by realizing arrays of chemical-vapour-deposited graphene light emitters. These results pave the way towards the realization of commercially viable large-scale, atomically thin, flexible and transparent light emitters and displays with low operation voltage and graphene-based on-chip ultrafast optical communications.

Author(s): A. Goban, C.-L. Hung, J. D. Hood, S.-P. Yu, J. A. Muniz, O. Painter, and H. J. Kimble

Trapping atoms near a photonic crystal waveguide produces strong atom-photon coupling that results in enhanced atomic emission of light.

[Phys. Rev. Lett. 115, 063601] Published Wed Aug 05, 2015

Chiral fields with large optical chirality are very important in chiral molecules analysis, sensing and other measurements. Plasmonic nanostructures have been proposed to realize such super chiral fields for enhancing weak chiral signals. However, most of them cannot provide uniform chiral near-fields close to the structures, which makes these nanostructures not so efficient for applications. Plasmonic helical nanostructures and blocked squares have been proved to provide uniform chiral near-fields, but structure fabrication is a challenge. In this paper, we show that very simple plasmonic dimer structures can provide uniform chiral fields in the gaps with large enhancement of both near electric fields and chiral fields under linearly polarized light illumination with polarization off the dimer axis at dipole resonance. 30 times of volume averaged chiral field enhancement is gotten in the whole gap. Chiral fields with opposite handedness can be obtained simply by changing the polarization to the other side of the dimer axis. It is especially useful in Raman optical activity measurement and chiral sensing of small quantity of chiral molecule.

Here we propose a route to the high-Q perfect absorption of light by introducing the concept of a Fano anti-laser. Based on the drastic spectral variation of the optical phase in a Fano-resonant system, a spectral singularity for scatter-free perfect absorption can be achieved with an order of magnitude smaller material loss. By applying temporal coupled mode theory to a Fano-resonant waveguide platform, we reveal that the required material loss and following absorption Q-factor are ultimately determined by the degree of Fano spectral asymmetry. The feasibility of the Fano anti-laser is confirmed using a photonic crystal platform, to demonstrate spatio-spectrally selective heating. Our results utilizing the phase-dependent control of device bandwidths derive a counterintuitive realization of high-Q perfect conversion of light into internal energy, and thus pave the way for a new regime of absorption-based devices, including switches, sensors, thermal imaging, and opto-thermal emitters.

Saharan silver ants, Cataglyphis bombycina, forage under extreme temperature conditions in the African desert. We show that the ants’ conspicuous silvery appearance is created by a dense array of triangular hairs with two thermoregulatory effects. They enhance not only the reflectivity of the ant’s body surface in the visible and near-infrared range of the spectrum, where solar radiation culminates, but also the emissivity of the ant in the mid-infrared. The latter effect enables the animals to efficiently dissipate heat back to the surroundings via blackbody radiation under full daylight conditions. This biological solution for a thermoregulatory problem may lead to the development of biomimetic coatings for passive radiative cooling of objects. Authors: Norman Nan Shi, Cheng-Chia Tsai, Fernando Camino, Gary D. Bernard, Nanfang Yu, Rüdiger Wehner

Machine learning addresses the question of how to build computers that improve automatically through experience. It is one of today’s most rapidly growing technical fields, lying at the intersection of computer science and statistics, and at the core of artificial intelligence and data science. Recent progress in machine learning has been driven both by the development of new learning algorithms and theory and by the ongoing explosion in the availability of online data and low-cost computation. The adoption of data-intensive machine-learning methods can be found throughout science, technology and commerce, leading to more evidence-based decision-making across many walks of life, including health care, manufacturing, education, financial modeling, policing, and marketing. Authors: M. I. Jordan, T. M. Mitchell