Energy considerations for a superlens based on metal/dielectric multilayers

We investigate the resolution and absorption losses of a Ag/GaP multilayer superlens. For a fixed source to image distance the resolution is independent of the position of the lens but the losses depend strongly on the lens placement. The absorption losses associated with the evanescent waves can be significantly larger than losses associated with the propagating waves especially when the superlens is close to the source. The interpretation of transmittance values greater than unity for evanescent waves is clarified with respect to the associated absorption losses.Comment: to be published in Optics Expres

Influence of the losses on the super-resolution performances of an impedance matched negative index material

We discuss by a Poynting vector analysis how the losses of a negative index material (NIM) affect the resolution performances of a Veselago-Pendry lens and we analyze those performances in the framework of the Abbe criterion. Both the limit of high losses and low losses are explored. We find that the impedance matched NIM is able to resolve 30% better than the limit imposed by the Abbe criterion even when the imaginary part of the refractive index (the material losses) exceeds the absolute value of the real part of the refractive index. The NIM is described by a lossy Drude model with equal permittivity and permeability. By increasing the damping parameter of the Drude model we also explore the regime where both permittivity and permeability are positive and point out the conditions under which the metamaterial is still able to super-resolve

A Dynamical Model of Harmonic Generation in Centrosymmetric Semiconductors

We study second and third harmonic generation in centrosymmetric semiconductors at visible and UV wavelengths in bulk and cavity environments. Second harmonic generation is due to a combination of symmetry breaking, the magnetic portion of the Lorentz force, and quadrupolar contributions that impart peculiar features to the angular dependence of the generated signals, in analogy to what occurs in metals. The material is assumed to have a non-zero, third order nonlinearity that gives rise to most of the third harmonic signal. Using the parameters of bulk Silicon we predict that cavity environments can significantly modify second harmonic generation (390nm) with dramatic improvements for third harmonic generation (266nm). This occurs despite the fact that the harmonics may be tuned to a wavelength range where the dielectric function of the material is negative: a phase locking mechanism binds the pump to the generated signals and inhibits their absorption. These results point the way to novel uses and flexibility of materials like Silicon as nonlinear media in the visible and UV ranges

Analysis of second harmonic generation in photonic-crystal-assisted waveguides

We study second harmonic generation in a planar dielectric waveguide having a low-index, polymer core layer, bounded by two multilayer stacks. This geometry allows exceptionally strong confinement of the light at the fundamental wavelength inside the core region with virtually zero net propagation losses for distances that exceed several centimeters, provided material and scattering losses are neglected. A phase-matched configuration of the waveguide is reported in which the pump signal is the lowest-order mode of the waveguide, and the generated second harmonic signal corresponds to the third propagation mode of the waveguide. Using a polymer waveguide core, having chi(2)=100 pm/V, we predict a conversion efficiency of approximately 90% after a propagation distance of 2 mm, using peak pump intensities inside the core of the waveguide of 1.35 GW/cm^2. If the waveguide core contains polymer layers with different glass transition temperatures, the layers can be poled independently to maximize the overlap integral, and similar pump depletions may be achieved over a distance of approximately 500 microns.Comment: 20 pages, 7 figures, 330k

Transmission function properties for multi-layered structures: Application to super-resolution

We discuss the properties of the transmission function in the k-space for a generic multi-layered structure. In particular we analytically demonstrate that a transmission greater than one in the evanescent spectrum (amplification of the evanescent modes) can be directly linked to the guided modes supported by the structure. Moreover we show that the slope of the phase of the transmission function in the propagating spectrum is inversely proportional to the ability of the structure to compensate the diffraction of the propagating modes. We apply these findings to discuss several examples where super-resolution is achieved thanks to the simultaneous availability of the amplification of the evanescent modes and the diffraction compensation of the propagating modes

Newspaper commentaries on terrorism in China and Australia: A contrastive genre study

This thesis is a contrastive genre study which explores newspaper commentaries on terrorism in Chinese and Australian newspapers. The study examines the textual patterning of the Australian and Chinese commentaries, interpersonal and intertextual features of the texts as well as considers possible contextual factors which might contribute to the formation of the newspaper commentaries in the two different languages and cultures. For the framework of its analysis, the study draws on systemic functional linguistics, English for Specific Purposes and new rhetoric genre studies, critical discourse analysis, and discussions of the role of the mass media in the two different cultures. The study reveals that Chinese writers often use explanatory rather than argumentative expositions in their newspaper commentaries. They seem to distance themselves from outside sources and seldom indicate endorsement of these sources. Australian writers, on the other hand, predominantly use argumentative expositions to argue their points of view. They integrate and manipulate outside sources in various ways to establish and provide support for the views they express. It is argued that these textual and intertextual practices are closely related to contextual factors, especially the roles of the media and opinion discourse in contemporary China and Australia. The study, by providing both a textual and contextual view of the genre under investigation in the two languages and cultures, aims to establish a framework for contrastive rhetoric research which moves beyond the text into the context of production and interpretation of the texts as a way of exploring reasons for the linguistic and rhetorical choices made in the two sets of texts

Second and Third Harmonic Generation in Metal-Based Nanostructures

We present a new theoretical approach to the study of second and third harmonic generation from metallic nanostructures and nanocavities filled with a nonlinear material, in the ultrashort pulse regime. We model the metal as a two-component medium, using the hydrodynamic model to describe free electrons, and Lorentz oscillators to account for core electron contributions to both the linear dielectric constant and to harmonic generation. The active nonlinear medium that may fill a metallic nanocavity, or be positioned between metallic layers in a stack, is also modeled using Lorentz oscillators and surface phenomena due to symmetry breaking are taken into account. We study the effects of incident TE- and TM-polarized fields and show that a simple re-examination of the basic equations reveals additional exploitable dynamical features of nonlinear frequency conversion in plasmonic nanostructures.Comment: 33 pages, including 11 figures and 74 references; corrected affiliations and some typo

Optical Vortices during a Super-Resolution Process in a Metamaterial

We show that a super-resolution process with 100% visibility is characterized by the formation of a point of phase singularity in free space outside the lens in the form of a saddle with topological charge equal to -1. The saddle point is connected to two vortices at the end boundary of the lens, and the two vortices are in turn connected to another saddle point inside the lens. The structure saddle-vortices-saddle is topologically stable. The formation of the saddle point in free space explains also the negative flux of energy present in a certain region of space outside the lens. The circulation strength of the power flow can be controlled by varying the position of the object plane with respect to the lens