Yu.G. Rapoport

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.

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.

Modulation instability of terahertz electromagnetic pulses in SrTiO 3 paraelectric

It is investigated the modulation instability of terahertz electromagnetic waves in paraelectric crystals SrTiO3 at the temperatures 77 K. The cubic nonlinearity and the frequency dispersion correspond to the existence of bright envelope solitons and the modulation instability of long input pulses. The threshold of modulation instability can be reduced by reflection at the boundaries of the crystal. There is a possibility to generate the sequences of short terahertz pulses due to the modulation instability.

Nonlinear reshaping of terahertz pulses with graphene metamaterials

We study the propagation of electromagnetic waves through a slab of graphene metamaterial composed of the layers of graphene separated by dielectric slabs. Starting from the kinetic expression for two-dimensional electric current in graphene, we derive a novel equation describing the nonlinear propagation of terahertz electromagnetic pulses through the layered graphene-dielectric structure in the presence of losses and non-linearities. We demonstrate strong nonlinearity-induced reshaping of transmitted and reflected terahertz pulses through the interaction with the thin multilayer graphene metamaterial structure.

Modeling AGW and PEMW in inhomogeneous atmosphere and ionosphere

The paper discusses some recently solved problems of wave dynamics in the ionosphere as well as the methods developed for analysis and solving of them: (1) a possibility of waveguiding AGW in upper atmosphere; (2) resonant atmospheric gravity waves (AGW) in inhomogeneous atmospheric waveguide; (3) planetary electromagnetic waves (PEMW) in the system “Lithosphere-Atmosphere Ionosphere-Magnetosphere (LAIM)” and means for waves detection and data processing. The paper also discusses the prospects of further studies and emphasizes the role of PEMW as indicators of ionospheric processes.

Formation of Structures Under Parametric Coupling of Two-Dimensioanal Nonlinear Pulses of Magnetostatic Waves in Magnetic Films

A possibility of formation of the nonlinear structures under the parametric interaction of nonlinear pulses of the backward volume magnetostatic waves (BVMSWs) in the ferrite film (FF) is shown

Spatial and spatiotemporal self-focusing of spin waves in garnet films observed by space- and time-resolved Brillouin light scattering

A new advanced space- and time-resolved Brillouin light scattering technique is used to study diffraction of two-dimensional beams and pulses of dipolar spin waves excited by strip-line antennas in tangentially magnetized garnet films. The technique is an effective tool for investigations of two-dimensional spin wave propagation with high spatial and temporal resolution. Nonlinear effects such as stationary and nonstationary self-focusing are investigated in detail. It is shown that nonlinear diffraction of a stationary backward volume magnetostatic wave (BVMSW) beam, having a finite transverse aperture, leads to self-focusing of the beam at one spatial point. Diffraction of a finite-duration (nonstationary) BVMSW pulse leads to space–time self-focusing and formation of a strongly localized two-dimensional wave packet (spin wave bullet).

Modulation instability of terahertz pulses in the structures with n-InSb layers

The nonlinear interaction of transversely limited terahertz waves with layered structures that include n-InSb layers and dielectric ones is investigated theoretically. The nonlinearity possesses the focusing character both in longitudinal and transverse directions. The modulation instability of long terahertz pulses is investigated that leads to the generation of sequences of short pulses of picosecond durations at the output.

New method for modeling nonlinear hyperbolic concentrators

Tunable, nonlinear, and active metamaterials can be created on the base of layered media, when alternating thin layers possess permittivities of different signs. Nonlinear concentrators based on these hyperbolic metamaterials are investigated. The new method for modeling nonlinear field and energy concentrators is reported, which includes the combination of a new version of complex geometrical optics (CGO) and full-wave nonlinear electromagnetic solution used in different regions of a concentrator and matching of these solutions. The new strongly nonlinear phenomena, namely nonlinear focusing and creation of hotspots, taking place when input amplitude of concentrated beams exceeds some threshold value, is found in these field concentrators and searched. The use of active dielectric layers to compensate losses is proposed. Possible applications in optics, signal processing, and energy harvesting are discussed.