Anatoliy V. Goncharenko

Lichtenecker's equation : applicability and limitations

Lichteneckers equation for the effective dielectric function is considered with the help of spectral representation. The spectral density function of resonances is determined and its behavior is analyzed. This analysis is carried out at different values of a parameter specifying the composite topology. It is shown that Lichteneckers equation describes a specific composite topology only. It is not reduced to the Bruggeman topology but may be represented as a spheroid system.

Effective dielectric response of a shape-distributed particle system

To calculate the effective dielectric response of a dilute composite, a generalization of the Maxwell Garnett theory for small nonspherical particles distributed in shape is proposed. Various types of distribution function are analysed and the applicability of the simplest (steplike) distribution is discussed. It is shown that the use of the steplike distribution is more valid for particles having a higher imaginary part of the permittivity in the actual region. Besides, an alternative approach to the problem based on the spectral representation is also considered. As an illustration, the effective dielectric response of a system of semiconductor (SiC) and metal (Al) ellipsoidal particles is calculated.

Electric field enhancement by a nanometer-scaled conical metal tip in the context of scattering-type near-field optical microscopy

We present a numerical study of the electric field enhancement in the immediate vicinity of the apex of a conical silver tip and show that an optimal cone angle exists, allowing one to maximize the electric field. This angle depends on the tip length, the wavelength, as well as on the distance from the apex to the observation point. So both the angle and length of the tip can be considered as parameters to adjust the peak enhancement resonant position for a laser source wavelength. At the same time, reducing the cone angle does not ensure a concurrent increase in the electric field enhancement. A simple qualitative interpretation is proposed to explain this phenomenon based on competition of two mechanisms affecting the electric field near the tip apex. The results obtained show that the point-like dipole approximation is invalid for description of the field enhancement of a finite-size metal tip in the case of scattering-type near-field optical microscopy. One more conclusion is that the model of a sharp...

Effect of weak nonsphericity on linear and nonlinear optical properties of small particle composites

A small particle composite in which the inclusions are slightly nonspherical and distributed in shape is considered. Within the framework of the mean-field approximation, the functions of linear and nonlinear optical responses are calculated in terms of a nonsphericity parameter specifying the width of the distribution function in shape. To estimate the effect of weak nonsphericity on the functions, their second derivatives with respect to the nonsphericity parameter are computed. The derivatives are shown to be complexly structured surfaces in the coordinates (Re(ei/em), Im(ei/em)), where ei and em are the inclusion and matrix permittivity, respectively. Based on the results obtained, applicability area of the classical Maxwell Garnett theory is discussed. The main conclusion is that weak nonsphericity is significant only in the close vicinity of a dipole resonance of a single ball made of inclusion material. At the same time, the role of nonsphericity increases with decreasing the imaginary part of inclusion permittivity.

Effective absorption cross section of an assembly of small ellipsoidal particles

For an assembly of small noninteracting ellipsoidal particles the effect of the shape distribution function on light absorption is considered. Possible determinations of the function parameters from experimental absorption spectra are analyzed. Some features of the problem are discussed that are characteristic of assemblies of dielectric and metal particles.

Strategy for designing epsilon-near-zero nanostructured metamaterials over a frequency range

In terms of the effective medium theory, we propose a general solution to such a fundamental problem as designing nanostructured materials with the very low permittivity (epsilon-near-zero metamaterials) over a frequency range. We show, in particular, that this can be accomplished for a columnar metal-dielectric composite consisting of parallel cylinders with varied thickness that resembles a forest of identical stems. The applicability of our method and some limitations are also discussed. Whilst the corresponding production procedure does not appear to be very simple, it nevertheless is realizable.

Effective scattering cross section of an assembly of small ellipsoidal particles

A model of light scattering from an assembly of small shape-distributed ellipsoidal particles is considered. The three principal assumptions used are the neglect of multiple scattering, the dipole polarizability, and the equiprobable distribution for the ellipsoid depolarization factors. These assumptions enabled us to find analytically the effective cross section for light scattering. {That for light absorption was found in a similar way by Goncharenko [J. Opt. Soc. Am. B13, 2392 (1996)]}. The solution obtained is analyzed for some special cases, in particular for low and no absorption.

Broadband epsilon-near-zero composites made of metal nanospheroids

We use a homogenization technique to estimate the efficiency of the real part of the effective permittivity nulling for suspensions of randomly oriented metal spheroids in terms of bandwidth and dielectric losses. The design of broadband epsilon-near-zero metamaterials have been demonstrated through the solution of an inverse problem. Manyfold solution branches for extracted geometrical parameters have been predicted, their origin has been explained, and the behavior of losses has been briefly considered. Realizability of metamaterials with the extracted parameters has been discussed in terms of aspect ratio and size of spheroids, and their promise for high broadband absorption has been demonstrated.

Effects of dimension on optical transmittance of semicontinuous gold films

The thickness dependence of dielectric response of semicontinuous gold films evaporated onto glass substrates under various temperatures has been studied. A wide range of mass thicknesses (and filling factors) was considered, up to those corresponding to continuous films. The work includes a brief introduction, description of sample preparation and transmittance measurements, as well as determination of the dielectric response function using simple phenomenological model, namely, the generalized Bruggeman approximation. The approximation considers systems dimension as a varied noninteger quantity near the percolation threshold where the correlation length is large. The results obtained show that our model is valid in the actual range and dielectric properties of films are related to their morphological peculiarities. So, we refine and supplement some of our results reported in an earlier work (Proc. SPIE 3133 (1997) 300).

Nanostructured metamaterials with broadband optical properties

We propose and develop a technique for designing a special class of nonmagnetic metamaterials possessing desired dielectric and optical properties over a broad frequency band. The technique involves the design of nanostructured metallodielectric materials (photonic crystals) with a special layered geometry where the metal content in each layer has to be determined using a fitting procedure. For illustration, we demonstrate the performance of our technique for tailoring metamaterials having epsilon-near-zero and on-demand refractive index (real or imaginary part) over a frequency band. One-, two-, as well as three-dimensional geometries have been considered. In the one-dimensional and two-dimensional cases, the results of semi-analytical calculations are validated by ab initio FDTD simulations.