A rigorous analytical solution for the description of wave dynamics originated at the interface between a homogeneous half-space and a half-space metamaterial made by arrayed plasmonic nanospheres is presented. The solution is cast in terms of an exact analytical representation obtained via a discretized Wiener-Hopf (WH) technique assuming that each metallic nanosphere is described by the single dipole approximation. The solution analytically provides and describes the wave species in the metamaterial half-space, their modal wavenumbers and launching coefficients at the interface. It explicitly satisfies the generalized Ewald-Oseen extinction principle for periodic structures, and it also provides a simple analytical solution for the reflection coefficient from the half-space. The paper presents a new WH formulation for this class of problems for the first time, and describes the analytical solution, which is also tested against a purely numerical technique. While only the case of orthogonal plane wave incidence and isotropic inclusions is considered here, the method can be easily generalized to the oblique incidence and anisotropic constituent (tensorial polarizability) cases. © 2011 Optical Society of America.

This study aims at describing the field propagation in terms of pulsed rays, that are particularly advantageous when dealing with short-pulse excitations. In the framework of the Geometrical Theory of Diffraction we augment Geometrical Optics and uniform singly diffracted field solutions available in the time domain (TD), by TD doubly diffracted (DD) rays, that are expressed in simple closed forms. Impulsive double diffraction at a pair of coplanar edges is here formulated directly in the TD, as a double superposition of impulsive spherical waves. Nonuniform and uniform wavefront approximations for TD-DD fields are determined in closed form, defining two novel TD transition functions. The scalar case with either hard or soft boundary conditions is analyzed first, and then used to build an electromagnetic dyadic DD coefficient for a pair of coplanar edges with perfectly conducting faces. Particular attention is given to the definition of TD transition regions, i.e., the elliptical regions where the TD-DD field does not exhibit a ray optical behavior. The compensation mechanism by which the TD-DD fields repair the discontinuity introduced by singly diffracted fields at their shadow boundaries is also analyzed in detail. Our result for the TD-DD field excited by an impulsive spherical wave is valid only for early times, at and close to (behind) the DD ray wavefront. The TD-DD field response to a more general pulsed excitation is obtained via convolution, and if the exciting signal has no low-frequency components the range of validity of the resulting pulsed response is enlarged to later observation times behind the wavefront. © 2005 IEEE.

Spherical nanoclusters (NCs) with a central dielectric core surrounded by several satellite plasmonic nanospheres have been recently investigated as aggregates supporting electric and magnetic collective resonances. Notably, the collective magnetic resonance has been exploited to provide magnetic properties in optics, i.e., materials with macroscopic relative permeability different from unity. The NCs discussed in this paper can be realized using state-of-the-art nanochemistry self-assembly techniques. Accordingly, perfectly regular disposition of the nanoplasmonic satellites is not possible and this paper constitutes the first comprehensive analysis of the effect of such irregularities onto the electric and magnetic collective resonances. In particular we will show that the peak of the scattering cross section associated to the magnetic resonance is very sensitive to certain irregularities and significantly less to others. It is shown here that "artificial magnetic" properties of NCs are preserved for certain degrees of irregularities of the nanosatellites positions, however they are strongly affected by irregularities in the plasmonic nanosatellites sizes and by the presence of "defects" caused by the absence of satellites in the process of self-assembly around the dielectric core. The "artificial electric" resonance is instead less affected by irregularities mainly because of its wider frequency bandwidth.

A Fabry-Perot cavity (FPC) between a ground plane and a partially reflective surface (PRS) is used here to design array antennas with large distance between the radiating elements. This configuration provides some advantages: i) a reduction of the number of array elements to achieve high directivity; ii) large space between contiguous elements that may host a bulky feeding network as required for dual polarization or active antennas; iii) small coupling and easy feeding network designs because of the smaller number of elements with larger inter-element distance. We show that when designing the FPC antenna a frequency shift of the gain maximum may occur, especially in this sparse array configuration. We also show the existence of preferred distances between elements that controls both the directivity and the side lobe level, and how the presence of the FPC and the relaxed requirement of the interelement distance result in a lower interelement coupling. The presented dual polarized antenna comprises two interleaved 2 × 2 arrays placed in a 2-layer FPC, and exhibits a 19 dBi gain and 30 dB of isolation between the two ports over an operating bandwidth of approximately 5.7%, i.e., typical for patch antennas. © 2006 IEEE.

We report an investigation on the optical properties of three-dimensional nanoclusters (NCs) made by spherical constellations of metallic nanospheres arranged around a central dielectric sphere, which can be realized and assembled by current state-of-the-art nanochemistry techniques. This type of NCs supports collective plasmon modes among which the most relevant are those associated with the induced electric and magnetic resonances. Combining a single dipole approximation for each nanoparticle and the multipole spherical-wave expansion of the scattered field, we achieve an effective characterization of the optical response of individual NCs in terms of their scattering, absorption, and extinction efficiencies. By this approximate model we analyze a few sample NCs identifying the electric and magnetic resonance frequencies and their dependence on the size and number of the constituent nanoparticles. Furthermore, we discuss the effective electric and magnetic polarizabilities of the NCs, and their isotropic properties. A homogenization method based on an extension of the Maxwell Garnett model to account for interaction effects due to higher order multipoles in dense packed arrays is applied to a distribution of NCs showing the possibility of obtaining metamaterials with very large, small, and negative values of permittivity and permeability, and even negative index. (C)2011 Optical Society of America

Numerically efficient results for short pulse propagation in a complex environment is presented in terms of multiple diffraction. As such, the time domain (TD) diffraction propagators are based on discretization of a generic short-pulse in terms of narrow rectangles, and on closed form representations of diffracted fields when the excitation is a narrow rectangular pulse.

The selective excitation of localized surface wave modes remains a challenge in the design of both leaky-wave and bound-wave devices. In this Letter, we show how the truncation of a metasurface can play an important role in breaking the spatial inversion symmetry in the excitation of surface waves supported by the structure. This is done by combining a large anisotropy in the dispersion relation and the presence of an edge that also serves as a coupling mechanism between the plane wave excitation and the induced surface waves. By resorting to the exact solution to the scattering problem based on a discrete Wiener-Hopf technique, we show that by inverting the component of the impinging wavevector parallel to the truncation, two distinct surface waves are excited.

The optical response of irregular spherical nanoclusters (NCs) are studied by Monte Carlo simulations. Deviations from nominal arrangements are considered by introducing either randomly variable sizes of the constituent particles or random displacements of particle locations around the NC core. The impact of disorder on NC resonances is examined by decomposing the scattered fields in terms of contributions of electromagnetic multipoles, such as electric and magnetic dipoles, quadrupoles, and higher order moments. © 2012 IEEE.

We investigate the optical properties of metamaterials formed by collections of three-dimensional clusters of plasmonic nanoparticles. This type of nanoclusters (NCs) consist of spherical constellations of metallic nanospheres arranged around a central dielectric sphere and support collective plasmon modes among which the most relevant are those associated with the induced electric and magnetic dipole resonances. We discuss the effective electric and magnetic polarizabilities of NCs, emphasizing their isotropic properties, and we show that dense packed arrays of NCs can be used to realize metamaterials with negative effective permittivity and permeability, and even negative effective refractive index at visible frequencies. © 2011 IEEE.