Quantum Conductivity for Metal-Insulator-Metal Nanostructures

We present a methodology based on quantum mechanics for assigning quantum conductivity when an ac field is applied across a variable gap between two plasmonic nanoparticles with an insulator sandwiched between them. The quantum tunneling effect is portrayed by a set of quantum conductivity coefficients describing the linear ac conductivity responding at the frequency of the applied field and nonlinear coefficients that modulate the field amplitude at the fundamental frequency and its harmonics. The quantum conductivity, determined with no fit parameters, has both frequency and gap dependence that can be applied to determine the nonlinear quantum effects of strong applied electromagnetic fields even when the system is composed of dissimilar metal nanostructures. Our methodology compares well to results on quantum tunneling effects reported in the literature and it is simple to extend it to a number of systems with different metals and different insulators between them

Jenseits von Souveränität und Territorialität: Überlegungen zu einer politischen Theorie der Stadt

Zusammenfassung: Seit jeher dienen Städte als Projektionsfläche sowohl für die Identifikation von problematischen Tendenzen der (modernen) Gesellschaft als auch für die Entwicklung erstrebenswerter gesellschaftlicher Zukünfte. Als Kristallisationspunkt und Triebkraft soziopolitischer Entwicklungen nimmt die Stadt eine zentrale Stellung in Praktiken des Regierens und deren Beobachtung ein – und doch tut sich die Politische Theorie traditionell schwer damit, ein Verständnis von Stadt zu entwickeln, das diesem Status und den damit verbundenen Ambivalenzen gerecht wird. Allzu oft verbleiben entsprechende Debatten dem Souveränitätsparadigma verhaftet, sodass die Stadt primär in Relation zum Prinzip territorialstaatlicher Souveränität begriffen wird. Unser Beitrag argumentiert, dass eine Auflösung dieser konzeptionellen Verwicklung dazu beitragen kann, das Verhältnis zwischen dem Städtischen und dem Politischen als ein konstitutionslogisches, das sich von anderen Konstitutionslogiken des Politischen unterscheidet, sichtbar zu machen. Dazu greifen wir auf eine raumtheoretische Perspektive der Moderne zurück, die Stadt und Territorialstaat nicht als „Kleines“ und „Großes“, sondern als zwei eigenständige, zugleich komplementäre und konfligierende Modi der räumlichen Vergesellschaftung begreift. Unser Beitrag zeigt auf, dass Verdichtung und Heterogenisierung, als die beiden wesentlichen raumstrukturellen Merkmale des Städtischen, mit einer spezifischen Konstitution des Politischen im Sinne einer Erzeugung von kollektiver Macht und gesellschaftlicher Ordnung verbunden sind. Die Stadt tritt damit nicht bloß als (austauschbarer) Ort der Materialisierung übergreifender soziopolitischer Phänomene in den Blick, sondern als räumliches Prinzip, das Möglichkeiten für gemeinsames Sprechen und Handeln sowie für Praktiken der konfliktiven Infragestellung hegemonialer Projekte erst hervorbringt. Eine dergestalt angelegte politische Theorie der Stadt erlaubt es, politische Praktiken nicht nur in der Stadt zu lokalisieren, sondern als genuin städtische Phänomene zu erfassen und sowohl die Komplementaritäten als auch die Widersprüche zwischen den Raumprinzipien der Stadt und des souveränen Territorialstaats herauszuarbeiten

Nonlocal and Quantum Tunneling Contributions to Harmonic Generation in Nanostructures: Electron Cloud Screening Effects

Our theoretical examination of second and third harmonic generation from metal-based nanostructures predicts that nonlocal and quantum tunneling phenomena can significantly exceed expectations based solely on local, classical electromagnetism. Mindful that the diameter of typical transition metal atoms is approximately 3{\AA}, we adopt a theoretical model that treats nanometer-size features and/or sub-nanometer size gaps or spacers by taking into account: (i) the limits imposed by atomic size to fulfill the requirements of continuum electrodynamics; (ii) spillage of the nearly-free electron cloud into the surrounding vacuum; and (iii) the increased probability of quantum tunneling as objects are placed in close proximity. Our approach also includes the treatment of bound charges, which add crucial, dynamical components to the dielectric constant that are neglected in the conventional hydrodynamic model, especially in the visible and UV ranges, where interband transitions are important. The model attempts to inject into the classical electrodynamic picture a simple, perhaps more realistic description of the metal surface by incorporating a thin patina of free-electrons that screens an internal, polarizable medium.Comment: Submitted to PR

Thermal noises and noise compensation in high-reflection multilayer coating

Thermal fluctuations of different origin in the substrate and in the coating of optical mirrors produce phase noise in the reflected wave. This noise determines the ultimate stabilization capability of high-Q cavities used as a reference system. In particular this noise is significant in interferometric laser gravitational wave antennas. It is shown that simple alteration of a mirror multilayer coating may provide suppression of phase noise produced by thermorefractive, thermoelastic, photothermal and thermoradiation induced fluctuations in the coating.Comment: 10 pages, 5 figure

Enhanced Cerenkov Second-Harmonic Generation in Patterned Lithium Niobate

We present experimental results of second harmonic generation enhancement through the resonance of the band edge in a photonic crystal based on lithium niobate. Proton exchange technique was used to fabricate a waveguide near the surface of the lithium niobate substrate. The photonic crystal structure over the waveguide was made by UV laser interferometry. Subsequently experiments were designed to quantify the Cerenkov second-harmonic generation (CSHG) radiated into the substrate. The SHG radiated inside the waveguides was also experimentally investigated. In our experiments, the second guided mode of the waveguide was tuned to the band edge resonance to enhance the second harmonic generation. The highest conversion efficiency of CSHG using photonic band gap (PBG) was around 50 times compared to SHG emission from non-patterned lithium niobate. A numerical model was used to corroborate the experimental result. It was also found that the SHG signal in the waveguides is quenched compared to the CSHG signal

Role of Antenna Modes and Field Enhancement in Second Harmonic Generation from Dipole Nanoantennas

We study optical second harmonic generation from metallic dipole antennas with narrow gaps. Enhancement of the fundamental-frequency field in the gap region plays a marginal role on conversion efficiency. In the symmetric configuration, i.e., with the gap located at the center of the antenna axis, reducing gap size induces a significant red-shift of the maximum conversion efficiency peak. Either enhancement or inhibition of second-harmonic emission may be observed as gap size is decreased, depending on the antenna mode excited at the harmonic frequency. The second-harmonic signal is extremely sensitive to the asymmetry introduced by gap’s displacements with respect to the antenna center. In this situation, second-harmonic light can couple to all the available antenna modes. We perform a multipolar analysis that allows engineering the far-field SH emission and find that the interaction with quasi-odd-symmetry modes generates radiation patterns with a strong dipolar component

Nanowire Metal-Insulator-Metal Plasmonic Devices

In this paper we theoretically study the responsivity of Metal-Insulator-Metal nanostructures to light illumination over a broad wavelength band (1 - 25 microns) and we examine the role of a local field enhancement and electrostatic field on the responsivity

Quantum Electronics

Contains reports on three research projects.Joint Services Electronics Program (Contract DAAB07-75-C-1346