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The Purcell effect is usually described as a modification of the spontaneous decay rate in the presence of a resonator. In plasmonics, this effect is commonly associated with a large local-field enhancement in "hot spots" due to the excitation of surface plasmons. However, high-index dielectric nanostructures, which become the basis of all-dielectric nanophotonics, can not provide high values of the local-field enhancement due to larger radiation losses. Here, we demonstrate how to achieve a strong Purcell effect in all-dielectric nanostructures, and show theoretically that the Purcell factor can be increased by two orders of magnitude in a finite chain of silicon nanoparticles. Using the eigenmode analysis for an infinite chain, we demonstrate that the high Purcell factor regime is associated with a Van Hove singularity. We perform a proof-of-concept experiment for microwave frequencies and observe the 65-fold enhancement of the Purcell factor in a chain of 10 dielectric particles.

Robert Czaplicki, Antti Kiviniemi, Janne Laukkanen, Joonas Lehtolahti, Markku Kuittinen, Martti Kauranen
We investigate the role of surface-lattice resonances (SLRs) in second-harmonic generation (SHG) from arrays of metal nanoparticles. The SLRs affect the generated signal when the sample is rotated away from normal incidence. The adjustment of the incident angle tunes the SLRs to the fundamental ... [Opt. Lett. 41, 2684-2687 (2016)]

Nature Photonics 10, 361 (2016). doi:10.1038/nphoton.2016.97

Authors: Tianyu Liu & Yat Li

The sustainability of many existing desalination technologies is questionable. Plasmon-mediated solar desalination has now been demonstrated for the first time, using an aluminium structure that absorbs photons spanning the 200 nm to 2,500 nm wavelength range, and is both cheap and 'clean'.

Author(s): Cristian Della Giovampaola and Nader Engheta

Some of the plasmonic phenomena can be imitated by exploiting the structural dispersion of parallel-plate waveguides filled with positive dielectrics. This synthetic platform, as a test bed for exploring plasmonic features, is more suitable for longer-wavelength regimes and may exhibit lower loss, since positive dielectric materials are utilized.

[Phys. Rev. B 93, 195152] Published Tue May 24, 2016

The magneto-optical activity, namely the polarization conversion capabilities of high-index, non-absorbing, core-shell dielectric nanospheres is theoretically analyzed. We show that, in analogy with their plasmonic counterparts, the polarization conversion in resonant dielectric particles is linked to the amount of electromagnetic field probing the magneto-optical material in the system. However, in strong contrast with plasmon nanoparticles, due to the peculiar distribution of the internal fields in resonant dielectric spheres, the magneto-optical response is fully governed by the magnetic (dipolar and quadrupolar) resonances with little effect of the electric ones.

The optical properties of metallic nanoparticles with plasmon resonances have been studied extensively, typically by measuring the transmission of light, as a function of wavelength, through a nanoparticle suspension. One question that has not yet been addressed, however, is how an image is transmitted through such a suspension of absorber-scatterers,...

Nanoactuators and nanomachines have long been sought after, but key bottlenecks remain. Forces at submicrometer scales are weak and slow, control is hard to achieve, and power cannot be reliably supplied. Despite the increasing complexity of nanodevices such as DNA origami and molecular machines, rapid mechanical operations are not yet...

Strong interaction between light and a single quantum emitter is essential to a great number of applications, including single photon sources. Microcavities and plasmonic antennas have been used frequently to enhance these interactions through the Purcell effect. Both can provide large emission enhancements: the cavity typically through long photon lifetimes (high $Q$), and the antenna mostly through strong field enhancement (low mode volume $V$). In this work, we demonstrate that a hybrid system, which combines a cavity and a dipolar antenna, can achieve stronger emission enhancements than the cavity or antenna alone. We show that such systems can be used as a versatile platform to tune the bandwidth of enhancement to any desired value, while simultaneously boosting emission enhancement. Our fully consistent analytical model allows to identify the underlying mechanisms of boosted emission enhancement in hybrid systems, which include radiation damping and constructive interference between multiple-scattering paths. Additionally, we find excellent agreement between strongly boosted enhancement spectra from our analytical model and from finite-element simulations on a realistic cavity-antenna system. Finally, we demonstrate that hybrid systems can simultaneously boost emission enhancement and maintain a near-unity outcoupling efficiency into a single cavity decay channel, such as a waveguide.

Nanophotonics investigates the processing of light at the nanoscale, with the promise of transforming the telecommunication, biomedical, and computation industries. Advances in nanophotonics have traditionally been boosted but also limited by our capabilities of fabricating complex structures at the nanoscale. On page 805 of this issue, Ren et al. (1) try to break free of these limitations with their experimental demonstration of a simple nanostructure that can separate and process complex light modes carrying angular momentum. Thus, instead of processing light fields with complex nanostructures, the idea is to use comparatively simpler structures and push the complexity to the light fields themselves. Author: Gabriel Molina-Terriza

Substituting noble metals for high-index dielectrics has recently been proposed as an alternative strategy in nanophotonics to design broadband optical resonators and circumvent the ohmic losses of plasmonic materials. In this report, we demonstrate that subwavelength silicon nanoantennas can manipulate the photon emission dynamics of fluorescent molecules. In practice, it is showed that dielectric nanoantennas can both increase and decrease the local density of optical states (LDOS) at room temperature, a process that is inaccessible with noble metals at the nanoscale. Using scanning probe microscopy, we analyze quantitatively, in three dimensions, the near-field interaction between a 100 nm fluorescent nanosphere and silicon nanoantennas with diameters ranging between 170 nm and 250 nm. Associated to numerical simulations, these measurements indicate increased or decreased total spontaneous decay rates by up to 15 % and a gain in the collection efficiency of emitted photons by up to 85 %. Our study demonstrates the potential of silicon-based nanoantennas for the low-loss manipulation of solid-state emitters at the nanoscale and at room temperature.

Machine-learning-assisted materials discovery using failed experiments

Nature 533, 7601 (2016). doi:10.1038/nature17439

Authors: Paul Raccuglia, Katherine C. Elbert, Philip D. F. Adler, Casey Falk, Malia B. Wenny, Aurelio Mollo, Matthias Zeller, Sorelle A. Friedler, Joshua Schrier & Alexander J. Norquist

Inorganic–organic hybrid materials such as organically templated metal oxides, metal–organic frameworks (MOFs) and organohalide perovskites have been studied for decades, and hydrothermal and (non-aqueous) solvothermal syntheses have produced thousands of new materials that collectively contain nearly all the metals in the periodic table. Nevertheless, the formation of these compounds is not fully understood, and development of new compounds relies primarily on exploratory syntheses. Simulation- and data-driven approaches (promoted by efforts such as the Materials Genome Initiative) provide an alternative to experimental trial-and-error. Three major strategies are: simulation-based predictions of physical properties (for example, charge mobility, photovoltaic properties, gas adsorption capacity or lithium-ion intercalation) to identify promising target candidates for synthetic efforts; determination of the structure–property relationship from large bodies of experimental data, enabled by integration with high-throughput synthesis and measurement tools; and clustering on the basis of similar crystallographic structure (for example, zeolite structure classification or gas adsorption properties). Here we demonstrate an alternative approach that uses machine-learning algorithms trained on reaction data to predict reaction outcomes for the crystallization of templated vanadium selenites. We used information on ‘dark’ reactions—failed or unsuccessful hydrothermal syntheses—collected from archived laboratory notebooks from our laboratory, and added physicochemical property descriptions to the raw notebook information using cheminformatics techniques. We used the resulting data to train a machine-learning model to predict reaction success. When carrying out hydrothermal synthesis experiments using previously untested, commercially available organic building blocks, our machine-learning model outperformed traditional human strategies, and successfully predicted conditions for new organically templated inorganic product formation with a success rate of 89 per cent. Inverting the machine-learning model reveals new hypotheses regarding the conditions for successful product formation.

Riceviamo e pubblichiamo da Gherardo Vita, dottorando in Fisica al MIT

“Il governo si prepara a stanziare oltre 16 milioni di euro per un programma di inserimento nel mondo del lavoro di chi è in possesso di un PhD, ossia un dottorato di ricerca.

Anticipating artificial intelligence

Nature 532, 7600 (2016). doi:10.1038/532413a

Concerns over AI are not simply fear-mongering. Progress in the field will affect society profoundly, and it is important to make sure that the changes benefit everyone.

Nature Photonics 10, 285 (2016). doi:10.1038/nphoton.2016.88

Author: Noriaki Horiuchi

An AI learning to walk through a Doom-inspired maze by sight is one thing, but how can it handle live multiplayer mayhem? That's what the "Visual Doom AI" competition this September hopes to discover. The first set of matches are limited to a dozen 1...

Author: John Assad

Article

Sensors based on localized surface plasmon resonance suffer from low figures of merit. Here, the authors achieve high refractive index sensitivities and figures of merit by introducing a chiral shape and the idea of engineering the material dispersion function.

Nature Communications doi: 10.1038/ncomms11331

Authors: Hyeon-Ho Jeong, Andrew G. Mark, Mariana Alarcón-Correa, Insook Kim, Peter Oswald, Tung-Chun Lee, Peer Fischer

Article

The ability to control both electric and magnetic dispersion of light allows a novel type of hyperbolic material with impedance matched to air. Here, the authors show experimentally a topological transition between elliptic and magnetic hyperbolic dispersions in a metamaterial for control of thermal radiation.

Nature Communications doi: 10.1038/ncomms11329

Authors: Sergey S. Kruk, Zi Jing Wong, Ekaterina Pshenay-Severin, Kevin O'Brien, Dragomir N. Neshev, Yuri S. Kivshar, Xiang Zhang

Nature Nanotechnology 11, 325 (2016). doi:10.1038/nnano.2015.285

Authors: Xiaolong Zhu, Christoph Vannahme, Emil Højlund-Nielsen, N. Asger Mortensen & Anders Kristensen

Colour generation by plasmonic nanostructures and metasurfaces has several advantages over dye technology: reduced pixel area, sub-wavelength resolution and the production of bright and non-fading colours. However, plasmonic colour patterns need to be pre-designed and printed either by e-beam lithography (EBL) or focused ion beam (FIB), both expensive and not scalable processes that are not suitable for post-processing customization. Here we show a method of colour printing on nanoimprinted plasmonic metasurfaces using laser post-writing. Laser pulses induce transient local heat generation that leads to melting and reshaping of the imprinted nanostructures. Depending on the laser pulse energy density, different surface morphologies that support different plasmonic resonances leading to different colour appearances can be created. Using this technique we can print all primary colours with a speed of 1 ns per pixel, resolution up to 127,000 dots per inch (DPI) and power consumption down to 0.3 nJ per pixel.