Denys M. Natarov

Periodicity-induced effects in the scattering and absorption of light by infinite and finite gratings of circular silver nanowires

We study numerically the effect of periodicity on the plasmon-assisted scattering and absorption of visible light by infinite and finite gratings of circular silver nanowires. The infinite grating is a convenient object of analysis because of the possibility to reduce the scattering problem to one period. We use the well-established method of partial separation of variables however make an important improvement by casting the resulting matrix equation to the Fredholm second-kind type, which guarantees convergence. If the silver wires have sub-wavelength radii, then two types of resonances co-exist and may lead to enhanced reflection and absorption: the plasmon-type and the grating-type. Each type is caused by different complex poles of the field function. The low-Q plasmon poles cluster near the wavelength where dielectric function equals -1. The grating-type poles make multiplets located in close proximity of Rayleigh wavelengths, tending to them if the wires get thinner. They have high Q-factors and, if excited, display intensive near-field patterns. A similar interplay between the two types of resonances takes place for finite gratings of silver wires, the sharpness of the grating-type peak getting greater for longer gratings. By tuning carefully the grating period, one can bring together two resonances and enhance the resonant scattering of light per wire by several times.

Periodicity-Enhanced Plasmon Resonances in the Scattering of Light by Sparse Finite Gratings of Circular Silver Nanowires

We consider the H -polarized plane wave scattering by a finite linear grating of circular silver wires using the angular field expansions in local coordinates and addition theorems for cylindrical functions. The study is focused on the influence of the plasmon and the grating resonances on each other. It demonstrates that the scattering per one silver cylinder can be dramatically enhanced if the grating period is tuned to the plasmon-resonance wavelength value.

Seeing the order in a mess: optical signature of periodicity in a cloud of plasmonic nanowires

We consider the two-dimensional (2-D) problem of the H-polarized plane wave scattering by a linear chain of silver nanowires in a cloud of similar pseudo-randomly located wires, in the visible range. Numerical solution uses the field expansions in local coordinates and addition theorems for cylindrical functions and has a guaranteed convergence. The total scattering cross-sections and near- and far-zone field patterns are presented. The observed resonance effects are studied and compared with their counterparts in the scattering by the same linear chain of wires in free space.

Plasmon and grid resonances in the electromagnetic scattering by finite grids of silver nanowires

The problem of the H-polarized wave scattering by finite chains of circular nanowires is considered. A two-dimensional diffraction problem with rigorous boundary conditions is solved by partial separations of variables method using local polar coordinates of each scatterer. The obtained results demonstrate convergence of the algorithm and good agreement with data known for the conducting and dielectric cylinders. Plasmonic and grid resonances are found and calculated for grids from a big number of silver nanowires. This opens a way to the accurate numerical simulation of various finite configurations of wires met in todays nano and microsize photonic devices.

Wave scattering and emission by a plasmonic strip placed into a circular quantum wire

Presented are preliminary results related to two electromagnetic-wave problems: of the plane-wave scattering by a silver strip placed into a circular dielectric shell and of the wave emission by the same strip inserted into a quantum wire (QW), in the optical range. Auxiliary analysis is focused on the wavelength dependence of the total scattering cross-section of such resonant scatterer. Then we assume that the shell is a QW under pumping and analyze the localized surface plasmon (LSP) modes and also the shell modes as QW polariton modes perturbed by the strip, of such a two-dimensional (2-D) nanolaser.

Plasmon-assisted scattering of light by a circular silver nanowire with concentric dielectric coating

We study the scattering and absorption of an H-polarized plane electromagnetic wave by a silver nanowire, in the visible range of wavelengths. The wire is assumed to have circular cross-section and coated with a concentric circular dielectric layer. The analytical solution of the wave-scattering problem is obtained in classical manner, using the separation of variables and the transfer-matrix method in polar coordinates. In computations, we use the accurate data of Johnson and Christy for the complex refractive index of silver. If the coating thickness and its dielectric permittivity become larger, the computed spectra of the total scattering cross-section (TSCS) and the absorption cross-section (ACS) display, at first, a shift of broad surface-plasmon resonances to the red side and then their hybridization with the modes of the coating. This data can be useful for the design of nanowire-based sensors where the analyzed substance makes a finite-thickness layer on the wire.

Basic ideas and advantages of the method of analytical regularization in wave optics: Overview

By the method of analytical regularization (MAR) we understand a family of techniques casting the electromagnetic boundary-value problems to the Fredholm second-kind infinite- matrix equations, with or without intermediate stage of the Fredholm second kind integral equation (IE). This approach possesses many merits however is rarely used in computational optics and photonics. In the optical, infrared and THz ranges, perfect electrical conductor (PEC) condition cannot be used to approximate even noble-metal scatterers. Therefore for thick material bodies the most universal and reliable computational instrument of MAR is Muller boundary IE. Still thinner-than- wavelength material screens can be characterized with effective (i.e. resistive, dielectric, and impedance) boundary conditions, which allow adapting the MAR solutions previously developed in the scattering by PEC zero-thickness screens. In any case MAR enables numerically exact analysis of both the scattering and the absorption of optical, infrared and THz waves by various scatterers made of graphene, dielectrics and metals.

Grating resonances in the scattering of light by periodically structured dielectric nanowires

We present the results of numerical simulation of the scattering of the H-polarized electromagnetic wave by a finite grating made of dielectric nanowires, in the visible range of light. Numerical solution uses the field expansions in local coordinates of each wire and addition theorems for cylindrical functions and has a guaranteed convergence. Numerical results are presented for the analysis of the far-field and near-field characteristics of the studied scatterers. This work is focused on the detection of the grating-type resonances in the far-field characteristics and specific near-field patterns in these resonances.

Essentials and merits of the method of analytical regularization in computational optics and photonics

Although still underestimated in computational optics and photonics, the conversion of electromagnetic field problems to the Fredholm second kind integral equations (IEs), also called analytical regularization, and finally Fredholm second-kind infinite-matrix equations has many remarkable merits. We discuss them at the background of specific features of material properties of metals and dielectrics in the optical range.

Electromagnetic analysis of a silver nanotube laser with two active regions

Considered is the two-dimensional (2-D) source-free problem of the H-polarized electromagnetic field in the presence of a silver circular nanotube coated with a concentric layer of active material and with a core of similar active material. We assume that the natural-mode frequency is real-valued and look for it together with the threshold value of material gain in the active regions. As a method, we use the separation of variables and examine numerically the characteristic equations for different azimuthal indices. We demonstrate that the considered nanotube laser can emit light on a number of modes of different nature including the hybrid surface plasmon (SP) modes, like nanowire laser considered in our previous works.