gevero

We propose and experimentally test a method to fabricate patterns of steep, sharp features on surfaces, by exploiting the nonlinear dynamics of uniformly ion-bombarded surfaces. We show via theory, simulation, and experiment that the steepest parts of the surface evolve as one-dimensional curves that move in the normal direction at...

The dream to create novel computing hardware that captures aspects of brain computation has occupied the minds of researchers for over 50 y. Driving goals are to carry both the astounding energy efficiency of computations in neural networks of the brain and their learning capability into future generations of electronic...

Can we open the black box of AI?

Nature 538, 7623 (2016). http://www.nature.com/doifinder/10.1038/538020a

Author: Davide Castelvecchi

Artificial intelligence is everywhere. But before scientists trust it, they first need to understand how machines learn.

Prospects of using metal hole arrays for the enhanced optical detection of molecular chirality in nanosize volumes are investigated. Light transmission through the holes filled with an optically active material is modeled and the activity enhancement by more than an order of magnitude is demonstrated. The spatial resolution of the chirality detection is shown to be of a few tens of nanometers. From comparing the effect in arrays of cylindrical holes and holes of complex chiral shape, it is concluded that the detection sensitivity is determined by the plasmonic near field enhancement. The intrinsic chirality of the arrays due to their shape appears to be less important.

Nature Photonics 10, 681 (2016). doi:10.1038/nphoton.2016.162

Authors: Drew Morrill, Dongfang Li & Domenico Pacifici

Nature Photonics 10, 667 (2016). doi:10.1038/nphoton.2016.174

Authors: Tobias Rybka, Markus Ludwig, Michael F. Schmalz, Vanessa Knittel, Daniele Brida & Alfred Leitenstorfer

The high peak electric fields provided by single-cycle light pulses can be harnessed to manipulate and control charge motion in solid-state systems, resulting in electron emission out of metals and semiconductors or high harmonics generation in dielectrics. These processes are of a non-perturbative character and require precise reproducibility of the electric-field profile. Here, we vary the carrier-envelope phase of 6-fs-long near-infrared pulses with pJ-level energy to control electronic transport in a laterally confined nanoantenna with an 8 nm gap. Peak current densities of 50 MA cm–2 are achieved, corresponding to the transfer of individual electrons in a half-cycle period of 2 fs. The observed behaviours are made possible by the strong distortion of the effective tunnelling barrier due to the extreme electric fields that the nanostructure provides and sustains under sub-cycle optical biasing. Operating at room temperature and in a standard atmosphere, the performed experiments demonstrate a robust class of nanoelectronic switches gated by phase-locked optical transients of minute energy content.

Nature Photonics 10, 647 (2016). doi:10.1038/nphoton.2016.184

Authors: Yushin Kim, Soo-Young Lee, Jung-Wan Ryu, Inbo Kim, Jae-Hyung Han, Heung-Sik Tae, Muhan Choi & Bumki Min

In dielectric cavities with a rotational symmetry, whispering gallery modes (WGMs) with an extremely long lifetime (that is, a very high Q factor) can be formed by total internal reflection of light around the rim of the cavities. The ultrahigh Q factor of WGMs has enabled a variety of impressive photonic systems, such as ultralow threshold microlasers, bio-sensors with unprecedented sensitivity and cavity optomechanical devices. However, the isotropic emission of WGMs, which is due to the rotational symmetry, is a serious drawback in applications that require directional light sources. Considerable efforts have thus been devoted to achieving directional emission by intentionally breaking the rotational symmetry. However, all of the methods proposed so far have suffered from substantial Q-spoiling. Here, we show how the mode properties of dielectric whispering gallery cavities, such as the Q factor and emission directionality, can be tailored at will using transformation optics. The proposed scheme will open a new horizon of applications beyond the conventional WGMs.

Nature Photonics. doi:10.1038/nphoton.2016.184

Authors: Yushin Kim, Soo-Young Lee, Jung-Wan Ryu, Inbo Kim, Jae-Hyung Han, Heung-Sik Tae, Muhan Choi & Bumki Min

In dielectric cavities with a rotational symmetry, whispering gallery modes (WGMs) with an extremely long lifetime (that is, a very high Q factor) can be formed by total internal reflection of light around the rim of the cavities. The ultrahigh Q factor of WGMs has enabled a variety of impressive photonic systems, such as ultralow threshold microlasers, bio-sensors with unprecedented sensitivity and cavity optomechanical devices. However, the isotropic emission of WGMs, which is due to the rotational symmetry, is a serious drawback in applications that require directional light sources. Considerable efforts have thus been devoted to achieving directional emission by intentionally breaking the rotational symmetry. However, all of the methods proposed so far have suffered from substantial Q-spoiling. Here, we show how the mode properties of dielectric whispering gallery cavities, such as the Q factor and emission directionality, can be tailored at will using transformation optics. The proposed scheme will open a new horizon of applications beyond the conventional WGMs.

Nature Materials 15, 1100 (2016). doi:10.1038/nmat4694

Authors: Xiaoyu Zheng, William Smith, Julie Jackson, Bryan Moran, Huachen Cui, Da Chen, Jianchao Ye, Nicholas Fang, Nicholas Rodriguez, Todd Weisgraber & Christopher M. Spadaccini

Localized cavity resonances due to nanostructures at material surfaces can greatly enhance radiative heat transfer (RHT) between two closely placed bodies owing to stretching of cavity states in momentum space beyond light line. Based on such understanding, we numerically demonstrate the possibility of ultra-broadband super-Planckian RHT between two plates patterned with trapezoidal-shaped hyperbolic metamaterial (HMM) arrays. The phenomenon is rooted not only in HMM's high effective index for creating sub-wavelength resonators, but also its extremely anisotropic isofrequency contour. The two properties enable one to create photonic bands with a high spectral density to populate a desired thermal radiation window. At sub-micron gap sizes between such two plates, the artificial continuum states extend outside light cone, tremendously increasing overall RHT. Our study reveals that structured HMM offers unprecedented potential in achieving a controllable super-Planckian radiative heat transfer for thermal management at nanoscale.

One-dimensional photonic crystals with slowly varying, i.e. "chirped", lattice period are responsible for broadband light reflectance in many diverse biological contexts, ranging from the shiny coatings of various beetles to the eyes of certain butterflies. We present a quantum scattering analogy for light reflection from these adiabatically chirped photonic crystals (ACPCs) and apply a WKB-type approximation to obtain a closed-form expression for the reflectance. From this expression we infer several design principles, including a differential equation for the chirp pattern required to elicit a given reflectance spectrum and the minimal number of bilayers required to exceed a desired reflectance threshold. Comparison of the number of bilayers found in ACPCs throughout nature and our predicted minimal required number also gives a quantitative measure of the optimality of chirped biological reflectors. Together these results elucidate the design principles of chirped reflectors in nature and their possible application to future optical technologies.

Author(s): Jacopo Frigerio, Andrea Ballabio, Giovanni Isella, Emilie Sakat, Giovanni Pellegrini, Paolo Biagioni, Monica Bollani, Enrico Napolitani, Costanza Manganelli, Michele Virgilio, Alexander Grupp, Marco P. Fischer, Daniele Brida, Kevin Gallacher, Douglas J. Paul, Leonetta Baldassarre, Paolo Calvani, Valeria Giliberti, Alessandro Nucara, and Michele Ortolani

Mid-infrared plasmonics has the potential to revolutionize molecular sensing technology, if integrated into optoelectronic chips. Recently,several groups working on plasmonics have substituted metals with heavily doped semiconductors for the sake of integration, also opening up the possibility of tuning the device response via the doping level. In this work, the authors analyze the relevant case of heavily doped Ge films by combining transport measurements with infrared spectroscopy. They demonstrate a broad tunability of the screened plasma frequency up to the mid-infrared range. The main loss channels are identified through comparison of the experimental scattering rates with quantum calculations and pump-probe measurements. Heavily doped Ge is highlighted as a viable route for the integration of mid-infrared plasmonics into silicon optoelectronic platforms.

[Phys. Rev. B 94, 085202] Published Mon Aug 15, 2016

Monumental proof to torment mathematicians for years to come

Nature 536, 7614 (2016). http://www.nature.com/doifinder/10.1038/nature.2016.20342

Author: Davide Castelvecchi

Conference on Shinichi Mochizuki’s work inspires cautious optimism.

Author(s): Dominik Floess, Thomas Weiss, Sergei Tikhodeev, and Harald Giessen

Using localized surface plasmons, the magneto-optical response of dielectric thin films can be resonantly amplified and spectrally tailored. While the experimental realization and numerical simulation of such systems received considerable attention, so far, there is no analytical theoretical descrip…

[Phys. Rev. Lett. 117, 063901] Published Mon Aug 01, 2016

Author(s): Ivan Fernandez-Corbaton, Martin Fruhnert, and Carsten Rockstuhl

A chiral object cannot be superimposed onto its mirror image—a geometric definition of chirality. A new theoretical study introduces a definition of electromagnetic chirality.

[Phys. Rev. X 6, 031013] Published Thu Jul 28, 2016