Scattering of Electromagnetic Waves by a Semi-Infinite Carbon Nanotube

Scattering of electromagnetic cylindrical waves by an isolated, semi-infinite, open-ended, single-shell, zigzag carbon nanotube (CN) is considered in the optical regime. The CN is modeled as a smooth homogeneous cylindrical surface with impedance boundary conditions known from quantum-mechanical transport theory. An exact solution of the diffraction problem is obtained by the Wiener-Hopf technique. The differences between the scattering responses of metallic and semiconducting CNs are discussed.     

Radial cracking with closure

Progressive radial cracking of a clamped plate subjected to crack-face closure is studied. The material behavior is assumed to be elastic-brittle. The cracks are assumed to be relatively long in the sense that the three-dimensional contact problem can be described via a statically equivalent two-dimensional idealization. The number of cracks is supposed large enough to permit a quasi-continuum approach rather than one involving the discussion of discrete sectors. The formulation incorporates the action of both bending and stretching as well as closure effects of the radial crack face contact. Fracture mechanics is used to explore the load-carrying capacity and the importance of the role of the crack-surface-interaction. For a given crack radius, the closure contact width is assumed to be constant. Under this condition, a closed-form solution is obtained for the case of a finite clamped plate subjected to a concentrated force. Crack growth stability considerations predict that the system of radial cracks will initiate and grow unstably over a significant portion of the plate radius. The closure stress distribution is determined exactly in the case of narrow contact widths and approximately otherwise.     

Third-order optical nonlinearity in single-wall carbon nanotubes

The third-order optical nonlinearity in carbon nanotubes (CNT) exposed to an intensive external electromagnetic field has been investigated. The analysis is based on the quantum kinetic equations for the density matrix of π-electrons in CNT. In the regime of weak driving field, the kinetic equations have been solved by the perturbation method and the third-order nonlinear polarizability of different achiral CNTs has been calculated. The theory elaborated has been used for the evaluation of nonlinear susceptibility of CNT-based composites. Comparison with available experimental data has been presented. In the case of high intensive driving field a nonperturbative numerical simulation of the process has been carried out in the time domain. The axial current density in CNT has been calculated. Excitation of π-plasmons in CNTs has been analyzed.     

Electromagnetic response of 3D arrays of quantum dots

A phenomenological theory of electromagnetic response properties of regular ensembles of quantum dots has been elaborated on the basis of the effective medium approach. We show that the QD composite comprising QDs with a given axis of symmetry is effectively a uniaxial dielectric continuum and the phenomenon of birefringence is inherent in it. It has been shown that arrays of resonantly amplifying QDs exhibit, threefold splitting of the gain band. This fine structure of the gain band originates from both the diffraction of the electromagnetic field by single anisotropically shaped QD and the electromagnetic interaction of QDs in array. The analytical results are compared with that obtained via direct numerical simulation by a minimal autonomic block (MAB) method for a tetragonal array of disk-like and pyramidal QDs. The numerics quantitatively confirm our prediction.     

Irregular-waveguide elements coupling high-Q resonators with single-mode waveguides

A new type of element coupling a high-Q resonator with single-mode rectangular waveguides is proposed. The element is an irregular tapered section. A technique of electrodynamic calculation of such a coupling element is described. The element is experimentally investigated in the case of two-mirror open resonators. The high efficiency exhibited by the coupling element over a wide frequency band is confirmed by theoretical calculations and demonstrated experimentally.     

Towards Cholesteric Absorbers for Microwave Frequencies

Metal-backed cholesteric absorbers for microwave frequencies are presented, and their circular-polarization-sensitive absorption properties are numerically illustrated.