Exploiting the Feller Coupling for the Ewens Sampling Formula

This is the final version of the article. It first appeared from the Institute of Mathematical Statistics via http://dx.doi.org/10.1214/15-STS53

A bimetallic nanoantenna for directional colour routing

Recent progress in nanophotonics includes demonstrations of meta-materials displaying negative refraction at optical frequencies, directional single photon sources, plasmonic analogies of electromagnetically induced transparency and spectacular Fano resonances. The physics behind these intriguing effects is to a large extent governed by the same single parameter—optical phase. Here we describe a nanophotonic structure built from pairs of closely spaced gold and silver disks that show phase accumulation through material-dependent plasmon resonances. The bimetallic dimers show exotic optical properties, in particular scattering of red and blue light in opposite directions, in spite of being as compact as ∼λ3/100. These spectral and spatial photon-sorting nanodevices can be fabricated on a wafer scale and offer a versatile platform for manipulating optical response through polarization, choice of materials and geometrical parameters, thereby opening possibilities for a wide range of practical applications

Magnetoplasmonic design rules for active magneto-optics

Light polarization rotators and non-reciprocal optical isolators are essential building blocks in photonics technology. These macroscopic passive devices are commonly based on magneto-optical Faraday and Kerr polarization rotation. Magnetoplasmonics - the combination of magnetism and plasmonics - is a promising route to bring these devices to the nanoscale. We introduce design rules for highly tunable active magnetoplasmonic elements in which we can tailor the amplitude and sign of the Kerr response over a broad spectral range

3D optical Yagi–Uda nanoantenna array

Future photonic circuits with the capability of high-speed data processing at optical frequencies will rely on the implementation of efficient emitters and detectors on the nanoscale. Towards this goal, bridging the size mismatch between optical radiation and subwavelength emitters or detectors by optical nanoantennas is a subject of current research in the field of plasmonics. Here we introduce an array of three-dimensional optical Yagi–Uda antennas, fabricated using top-down fabrication techniques combined with layer-by-layer processing. We show that the concepts of radiofrequency antenna arrays can be applied to the optical regime proving superior directional properties compared with a single planar optical antenna, particularly for emission and reception into the third dimension. Measuring the optical properties of the structure reveals that impinging light on the array is efficiently absorbed on the subwavelength scale because of the high directivity. Moreover, we show in simulations that combining the array with suitable feeding circuits gives rise to the prospect of beam steering at optical wavelengths

Magnetic hot spots in closely spaced thick gold nanorings

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/page/policy/articlesonrequest/index.htmlLigh-matter interaction at optical frequencies is mostly mediated by the electric component of the electromagnetic field, with the magnetic component usually being considered negligible. Recently, it has been shown that properly engineered metallic nanostructures can provide a magnetic response at optical frequencies originated from real or virtual flows of electric current in the structure. In this work, we demonstrate a magnetic plasmonic mode which emerges in closely spaced thick gold nanorings. The plasmonic resonance obtains a magnetic dipole character by sufficiently increasing the height of the nanorings. Numerical simulations show that a virtual current loop appears at resonance for sufficiently thick nanorings, resulting in a strong concentration of the magnetic field in the gap region (magnetic hot spot). We find that there is an optimum thickness that provides the maximum magnetic intensity enhancement (over 200-fold enhancement) and give an explanation of this observation. This strong magnetic resonance, observed both experimentally and theoretically, can be used to build new metamaterials and resonant loop nanoantennas at optical frequencies.This work has been supported by Spanish Government and European Union (EU) funds under contracts CSD2008-00066 and TEC2011-28664-C02-02 and Universitat Politecnica de Valencia (program INNOVA 2011). The authors extend special thanks to Mr. J. Ross Aitken for his contribution to this work.Lorente Crespo, M.; Wang, L.; Ortuño Molinero, R.; García Meca, C.; Ekinci, Y.; Martínez Abietar, AJ. (2013). Magnetic hot spots in closely spaced thick gold nanorings. Nano Letters. 13(6):2654-2661. https://doi.org/10.1021/nl400798sS2654266113

Absorption Enhancement in Lossy Transition Metal Elements of Plasmonic Nanosandwiches

Combination of catalytically active transition metals and surface plasmons offers a promising way to drive chemical reactions by converting incident visible light into energetic electron-hole pairs acting as a mediator. In such a reaction enhancement scheme, the conversion efficiency is dependent on light absorption in the metal. Hence, increasing absorption in the plasmonic structure is expected to increase generation of electron-hole pairs and, consequently, the reaction rate. Furthermore, the abundance of energetic electrons might facilitate new reaction pathways. In this work we discuss optical properties of homo- and heterometallic plasmonic nanosandwiches consisting of two parallel disks made of gold and palladium. We show how near-field coupling between the sandwich elements can be used to enhance absorption in one of them. The limits of this enhancement are investigated using finite-difference time-domain simulations. Physical insight is gained through a simple coupled dipole analysis of the nanostructure. For small palladium disks (compared to the gold disk), total absorption enhancement integrated over the near visible solar AM 1.5 spectrum is 8-fold, while for large palladium disks, similar in size to the gold one, it exceeds three

Polyimide hollow fiber membranes for CO2 separation from wet gas mixtures

Matrimid®5218 hollow fiber membranes were prepared using the dry-wet spinning process. The transport properties were measured with pure gases (H2, CO2, N2, CH4 and O2) and with a mixture (30% CO2 and 70% N2) in dry and wet conditions at 25 ºC, 50 ºC, 60 ºC and 75 ºC and up to 600 kPa. Interesting values of single gas selectivity up to 60 ºC (between 31 and 28 for CO2/N2 and between 33 and 30 for CO2/CH4) in dry condition were obtained. The separation factor measured for the mixture was 20% lower compared to the single gas selectivity, in the whole temperature range analyzed. In saturation conditions the data showed that water influences the performance of the membranes, inducing a reduction of the permeance of all gases. Moreover, the presence of water caused a decrease of single gas selectivity and separation factor, although not so significant, highlighting the very high water resistance of hollow fiber membrane modules

Designer Magnetoplasmonics with Nickel Nanoferromagnets

We introduce a new perspective on magnetoplasmonics in nickel nanoferromagnets by exploiting the phase tunability of the optical polarizability due to localized surface plasmons and simultaneous magneto-optical activity. We demonstrate how the concerted action of nanoplasmonics and magnetization can manipulate the sign of rotation of the reflected light’s polarization (i.e., to produce Kerr rotation reversal) in ferromagnetic nanomaterials and, further, how this effect can be dynamically controlled and employed to devise conceptually new schemes for biochemosensing. © 2011 American Chemical Society.A.D. and Z.P. acknowledge support from the Swedish Research Council and Swedish Foundation for Strategic Research (Framework program Functional Electromagnetic Metamaterials, project RMA08). J.Å. acknowledges support from the Swedish Research Council, the Swedish Foundation for Strategic Research (Future Research Leader Programme), and the G€oran Gustafsson Foundation. J.Å. is a Royal Swedish Academy of Sciences Research Fellow supported by a grant from the Knut and Alice Wallenberg Foundation. V.B. acknowledges the G€oran Gustafsson Foundation and the Blanceflor Boncompagni-Ludovisi Foundation. P.V. acknowledges funding from the Basque Government through the ETORGAI Program, Project No. ER- 2010/00032 and Program No. PI2009-17, the Spanish Ministry of Science and Education under Projects No. CSD2006-53 and No. MAT2009-07980. J.N. acknowledges funding for the Generalitat de Catalunya and the Spanish Ministry of Science and Education through No. 2009-SGR-1292 and No. MAT2010-20616-C02 projects.Peer Reviewe