N. A. Zharova

Adiabatic frequency up-conversion of a powerful electromagnetic pulse producing gas ionization

The theory of strong frequency upconversion of the powerful ionizing electromagnetic radiation in gases is presented based on the modified nonlinear geometrical optics approximation. The permanent spectrum upshift versus propagation path, exceeding considerably the initial frequency, is demonstrated without strong wave dissipation for the cases of impact and field-induced ionization in the high-intensity field range. Reflectionless propagation into the supercritical plasma and broad-band tuning of the laser radiation are emphasized as highly promising physical applications of the phenomenon described. >

Subwavelength imaging with opaque nonlinear left-handed lenses

We introduce the concept of subwavelength imaging with an opaque nonlinear left-handed lens by generating the second-harmonic field. We consider a slab of composite left-handed metamaterial with quadratic nonlinear response and show that such a flat lens can form, under certain conditions, an image of the second-harmonic field of the source being opaque at the fundamental frequency.We consider a slab of a composite left-handed metamaterial with quadratic nonlinear response and discuss the properties of opaque nonlinear left-handed lens. We find the conditions when this left-handed flat lens can create, with a subwavelength resolution, an image of the second-harmonic field of the source being opaque for the fundamental frequency.

Nonlinear transmission and spatiotemporal solitons in metamaterials with negative refraction

We study one- and two-dimensional transmission of electromagnetic waves through a finite slab of a dielectric material with negative refraction. In the case when the dielectric slab possesses an intensitydependent nonlinear response, we observe the nonlinearity-induced wave transmission through an opaque slab accompanied by the generation of spatiotemporal solitons. We solve this problem numerically, by employing the finite-difference time-domain simulations, for the parameters of microstructured materials with the negative refractive index in the microwave region, but our results can be useful for a design of nonlinear metamaterials with the left-handed properties in other frequency range.

Nonlinear Magnetoinductive Waves and Domain Walls in Composite Metamaterials

We describe novel physics of nonlinear magnetoinductive waves in left-handed composite metamaterials. We derive the coupled equations for describing the propagation of magnetoinductive waves, and show that in the nonlinear regime the magnetic response of a metamaterial may become bistable. We analyze modulational instability of different nonlinear states, and also demonstrate that nonlinear metamaterials may support the propagation of domain walls (kinks) connecting the regions with the positive and negative magnetization.

Defect modes and transmission properties of left-handed bandgap structures

We analyze transmission of electromagnetic waves through a one-dimensional periodic layered structure consisting of slabs of a left-handed metamaterial and air. We derive the effective parameters of the metamaterial from a microscopic structure of wires and split-ring resonators possessing the left-handed characteristics in the microwave frequency range, and then study, by means of the transfer-matrix approach and the finite-difference time-domain numerical simulations, the transmission properties of this layered structure in a band gap associated with the zero averaged refractive index. By introducing defects, the transmission of such a structure can be made tunable, and we study the similarities and differences of the defects modes excited in two types of the band gaps.

Birefringent left-handed metamaterials and perfect lenses for vectorial fields

In this paper, possibilities of wave focussing by a birefringent left-handed lens are discussed. It is shown that such lenses can focus either TE or TM polarized waves or both of them, with a varying distance between TE and TM images, and this property allows expanding the applicability limits of the perfect lenses.

Inside-out electromagnetic cloaking

We introduce a novel concept of an inside-out (or inverse) cloak for electromagnetic waves based on the coordinate transformation of Maxwells equations. This concept can be employed for creating absorbing non-reflecting media as matching layers in numerical simulations. In contrast to the commonly used perfectly matched layers, such absorbing boundaries are characterized by physically meaningful parameters, and the concept can be used in various numerical simulation schemes.

Multipactor in a coaxial transmission line. II. Particle-in-cell simulations

The effects of nonuniform radiofrequency fields are analyzed for a cylindrical coaxial transmission line using a particle-in-cell code. The behavior predicted by the analytical analysis is confirmed by this study. In addition, by including an initial velocity spread and different maximum secondary electron yields, a more elaborate analysis is performed. It is found that in the case of high secondary emission, an increase in the spread of initial velocities results in an overlapping of the multipactor zones for both double and single sided multipactor. In the other case, when the secondary emission is low, a large enough initial velocity spread can lead to total suppression of the electron avalanche for the higher order modes. Comparison with available experimental data shows good agreement.

Simulations of multipactor in circular waveguides

Detailed numerical simulations have been done to investigate the properties of multipactor breakdown in circular waveguides operating in the propagating fundamental TE11 mode. Main attention has been given to a comparison between the two fundamental cases corresponding to linear and circular polarizations, respectively, of the propagating electromagnetic wave. It is found that circular polarization is considerably more susceptible to multipactor than linear polarization. The reason for this difference is clarified by a comprehensive study of the electron motion in the waveguide.

Multiphase regimes of single-surface multipactor

Single-surface multipactor is studied within a plane-parallel model for the case when the rf electric field is normal to the surface of emission and the electron return to this surface is caused by the action of a dc electric field. The corresponding resonance zones are found for finite initial velocity of the secondary electrons. The new multiphase regimes of multipactor are found by numerical simulations of a successive series of electron trajectories. The existence of these regimes is shown to result in a considerable broadening of the multipactor zones. This conclusion is also confirmed by particle-in-cell simulations.