V. Grimalsky

Penetration of an electrostatic field from the lithosphere into the ionosphere and its effect on the D-region before earthquakes

Abstract The penetration of an electrostatic field, from a source located in the lithosphere into the ionosphere is investigated. The electrostatic problem is solved numerically for a medium with an inhomogeneous anisotropic conductivity coupled to an “effective upper boundary condition”. The results show that the electric field in the ionosphere D-layer can effectively change the parameters of the lower ionosphere. The kinetics in the D-region are considered along with calculations of the atmospheric conductivity at an altitude of 60 km . It is concluded that (i) the atmospheric conductivity at 60 km can change by 30–70% as a result of electrostatic perturbations, created before the onset of earthquakes, and (ii) the penetration of an electrostatic field from the lithosphere into the ionosphere above 60 km is much better at night-time than during the day.

Collision properties of quasi-one-dimensional spin wave solitons and two-dimensional spin wave bullets.

Collision properties of quasi-one-dimensional spin wave envelope solitons propagating in narrow ferrite film waveguides and of two-dimensional self-focused spin wave packets (spin wave bullets) propagating in wide ferrite film samples are studied both experimentally and numerically. The experiments, performed by means of a space- and time-resolved Brillouin light scattering technique, have shown that quasi-one-dimensional spin wave envelope solitons retain their shapes after collisions, while two-dimensional spin wave bullets are destroyed in collisions. The experiments have also shown that the introduction of a fixed phase shift between the colliding envelope solitons leads to a qualitative change in their interaction at the collision point. Numerical modeling of head-on collisions of nonlinear spin wave packets based on two different approaches provides a good qualitative description of the observed collision phenomena.

Metamaterials for space physics and the new method for modeling isotropic and hyperbolic nonlinear concentrators

Tunable, nonlinear and active metamaterials are discussed, as a basis of optical instrumentation and signal processing such as filters, birefringent devices, lenses etc. The new method for modeling nonlinear field and energy concentrators is reported, which includes the combination of the new version of complex geometrical optics (CGO) and full-wave nonlinear electromagnetic solution (FWNES) used in different regions of a concentrator and matching of these solutions. Nonlinear concentrators based on both isotropic and hyperbolic metamaterials are discussed. The new strongly nonlinear phenomena- nonlinear focusing switching, taking place when input amplitude of concentrated rays/beams exceeds some threshold value, is found in both types of the field concentrators and searched.

Mode beating of spin wave beams in ferrimagnetic Lu/sub 2.04/Bi/sub 0.96/Fe/sub 5/O/sub 12/ films

We report on measurements of the two-dimensional intensity distribution of linear and non-linear spin wave excitations in a LuBiFeO film. The spin wave intensity was detected using a high-resolution Brillouin light scattering spectroscopy setup. The observed snake-like structure of the spin wave intensity distribution is understood as a mode beating between modes with different lateral spin wave amplitude distributions. The theoretical treatment of the linear regime is performed analytically, whereas the propagation of non-linear spin waves is simulated by a numerical solution of a non-linear Schrodinger equation with suitable boundary conditions.

Nonlinear Transformational Optics and Electromagnetic and Acoustic Fields Concentrators

A nonlinear electromagnetic field (energy) concentrator is considered and the new method of nonlinear transformational optics is developed. This method includes two connected techniques: the complex geometrical optics (CGO) and the full‐wave nonlinear solution. A possibility of the strong “nonlinear superfocusing” of a field in a small volume is predicted theoretically and a tendency to formation of “hot spot(s)” is shown. The proposed method of nonlinear energy concentration may be perspective for solar cells, subwavelength imaging, high harmonic generation etc.

Nonstationary effects of the space charge in semiconductor structures

A study of nonstationary effects of space charge in semiconductor structures, such as nonlinear wave interactions in active media operating in the microwave and millimeter wave range, is presented in this paper. Also, an exhaustive analysis of different models describing the propagation of space charge waves is carried out. Furthermore, we have concluded that the most appropriate nonlocal model to describe the space charge wave propagation in thin films possessing negative differential conductivity is the detailed balance model.

Dispersion Relation for Two-Valley QuasiHydrodynamic Models in SCWs Propagation in n-GaAs Thin Films

The space charge wave propagation in thin n-GaAs films has been considered within a framework of different quasi-hydrodynamic balance models. A comparative study of the dependencies k(omega) of a complex longitudinal wave number on frequency, which are obtained from different balance equation models are presented and discussed. It has been demonstrated that the model where the balance equations are written for different valleys directly seems to be the most correct. The balance models based on averaging over the valleys may lead to incorrect results in the case of long distances of propagation of space charge waves. When the thermal conductivity term is taken into account and the length of the system is short, the averaged balance models can get satisfactory results

2D Electron Dynamics in Single Layer “Graphene Metamaterial”

The method is developed for modeling ballistic transport of 2D electron beams propagating in graphene subjected to spatial modulation. The spatial modulation is provided by means of application of periodical bias magnetic and/or electric field(s). Effects of spin‐orbital interaction and magnetization are accounted for. Some resonance effects and 2D effects of electron wave propagation in quasiperiodical magnetic barrier structures are demonstrated, accounting for spin‐orbit and exchange interactions. “Metamaterial” approaches to electron transport control such as using “slowing down” of electron waves, evanescent waves, and phase velocities of different signs are developed on the basis of the proposed method.

Influence of nonlocality on amplification of space charge waves in n-GaN films

Amplification of space charge waves (SCW) due to the negative differential conductivity (NDC) in n-GaN films of submicron thicknesses is investigated theoretically. An influence of nonlocal dependence of average electron velocity on the electron energy is considered. The simplest nonlocal model is used where the total electron concentration is taken into account. The relaxation momentum and energy frequencies have been calculated. An influence of nonlocality on NDC results in the decrease of absolute value of its real part and appearance of the imaginary part. The simulations of spatial increments of amplification of SCW demonstrate that nonlocality is essential at frequencies f ≥ 100 GHz, and amplification is possible up till the frequencies f ≤ 400…500 GHz.

Nonlinear spatiotemporal focusing of terahertz pulses in the structures with graphene layers

The nonlinear interaction of transversely bounded terahertz pulses with layered structures that include graphene layers is investigated theoretically. The nonlinearity possesses the focusing character both in longitudinal and transverse directions. There exist the optimum input amplitudes and transverse widths of the input pulse to get the maximum pulse compression.