Frequency conversion, "superluminal" propagation, and compression of a powerful microwave pulse in propagating ionization front.

Frequency up-conversion (∼10%) and compression (almost twofold) of a powerful (≤250 MW) microwave pulse in the propagating ionization front produced by the pulse itself in a gas-filled waveguide, is investigated experimentally and analyzed theoretically. Pulse envelope reshaping and group velocity increase manifest themselves in a propagation of the pulse faster than in the empty waveguide. A simple one-dimensional mathematical model allows the adequate interpretation of the experimental results.

Momentum, angular momentum, and spin of waves in an isotropic collisionless plasma.

We examine the momentum and angular momentum (including spin) properties of linear waves, both longitudinal (Langmuir) and transverse (electromagnetic), in an isotropic nonrelativistic collisionless electron plasma. We focus on conserved quantities associated with the translational and rotational invariance of the wave fields with respect to the homogeneous medium; these are sometimes called pseudomomenta. There are two types of the momentum and angular momentum densities: (i) the kinetic ones associated with the energy flux density and the symmetrized (Belinfante) energy-momentum tensor and (ii) the canonical ones associated with the conserved Noether currents and canonical energy-momentum tensor.

Ionization-Induced Self-Channeling of an Ultrahigh-Power Subnanosecond Microwave Beam in a Neutral Gas.

Ionization-induced self-channeling of a ≤500  MW, 9.6 GHz, <1  ns microwave beam injected into air at ∼4.5×10^{3}  Pa or He at ∼10^{3}  Pa is experimentally demonstrated for the first time.

Anomalous time delays and quantum weak measurements in optical micro-resonators.

Quantum weak measurements, wavepacket shifts and optical vortices are universal wave phenomena, which originate from fine interference of multiple plane waves. These effects have attracted considerable attention in both classical and quantum wave systems. Here we report on a phenomenon that brings together all the above topics in a simple one-dimensional scalar wave system.

Bistability of anderson localized States in nonlinear random media.

We study wave transmission through one-dimensional random nonlinear structures and predict a novel effect resulting from an interplay of nonlinearity and disorder. We reveal that, while weak nonlinearity does not change the typical exponentially small transmission in the regime of the Anderson localization, it affects dramatically the disorder-induced localized states excited inside the medium leading to bistable and nonreciprocal resonant transmission. Our numerical modeling shows an excellent agreement with theoretical predictions based on the concept of a high-Q resonator associated with each localized state.

Coupling and level repulsion in the localized regime: from isolated to quasiextended modes.

We study the interaction of Anderson localized states in an open 1D random system by varying the internal structure of the sample. As the frequencies of two states come close, they are transformed into multiply peaked quasiextended modes. Level repulsion is observed experimentally and explained within a model of coupled resonators.

Electron-beam instability in left-handed media.

We predict that two electron beams can develop an instability when passing through a slab of left-handed media (LHM). This instability, which is inherent only for LHM, originates from the backward Cherenkov radiation and results in a self-modulation of the beams and radiation of electromagnetic waves. These waves leave the sample via the rear surface of the slab (the beam injection plane) and form two shifted bright circles centered at the beams.

Semiclassical dynamics of electron wave packet states with phase vortices.

We consider semiclassical higher-order wave packet solutions of the Schrödinger equation with phase vortices. The vortex line is aligned with the propagation direction, and the wave packet carries a well-defined orbital angular momentum (OAM) variant Planck's over 2pil (l is the vortex strength) along its main linear momentum. The probability current coils around the momentum in such OAM states of electrons.

Polarization, transverse shifts, and angular momentum conservation laws in partial reflection and refraction of an electromagnetic wave packet.

We present a solution to the problem of partial reflection and refraction of a polarized paraxial Gaussian beam at the interface between two transparent media. The Fedorov-Imbert transverse shifts of the centers of gravity of the reflected and refracted beams are calculated. Our results differ in the general case from those derived previously by other authors.

Localized modes in open one-dimensional dissipative random systems.

We consider, both theoretically and experimentally, the excitation and detection of the localized quasimodes (resonances) in an open dissipative 1D random system. We show that, even though the amplitude of transmission drops dramatically so that it cannot be observed in the presence of small losses, resonances are still clearly exhibited in reflection. Surprisingly, small losses essentially improve conditions for the detection of resonances in reflection as compared with the lossless case.

Conservation of angular momentum, transverse shift, and spin Hall effect in reflection and refraction of an electromagnetic wave packet.

We present a solution to the problem of reflection and refraction of a polarized Gaussian beam on the interface between two transparent media. The transverse shifts of the beams' centers of gravity are calculated. They always satisfy the total angular momentum conservation law for beams, but, in general, do not satisfy the conservation laws for individual photons as a consequence of the lack of the "which path" information in a two-channel wave scattering.

Total absorption of an electromagnetic wave by an overdense plasma.

We show both theoretically and experimentally that an electromagnetic wave can be totally absorbed by an overdense plasma when a subwavelength diffraction grating is placed in front of the plasma surface. The absorption is due to dissipation of surface plasma waves (plasmons polaritons) that have been resonantly excited by the evanescent component of the diffracted electromagnetic wave. The developed theoretical model allows one to determine the conditions for the total absorption.

Self-excitation of microwave oscillations in plasma-assisted slow-wave oscillators by an electron beam with a movable focus.

Plasma-assisted slow-wave oscillators (pasotrons) operate without external magnetic fields, which makes these devices quite compact and lightweight. Beam focusing in pasotrons is provided by ions, which appear in the device due to the impact ionization of a neutral gas by beam electrons. Typically, the ionization time is on the order of the rise time of the beam current.

Modified geometrical optics of a smoothly inhomogeneous isotropic medium: the anisotropy, Berry phase, and the optical Magnus effect.

We present a modification of the geometrical optics method, which allows one to properly separate the complex amplitude and the phase of the wave solution. Appling this modification to a smoothly inhomogeneous isotropic medium, we show that in the first geometrical optics approximation the medium is weakly anisotropic. The refractive index, being dependent on the direction of the wave vector, contains the correction, which is proportional to the Berry geometric phase.

Self-consistent nonstationary processes in phase-mixed electron beams focused by mobile ions.

This paper is devoted to the analysis of nonstationary self-consistent processes in electron beam propagation in the presence of mobile ions. This problem is of particular interest for the recently developed plasma-assisted slow-wave oscillators (pasotrons). In pasotrons beam focusing is provided by ions (in contrast to other high-power microwave sources where the beam is focused by a strong external magnetic field).

Cherenkov radiation of electromagnetic waves by electron beams in the absence of an external magnetic field.

In conventional sources of coherent Cherenkov electromagnetic radiation, the electrons move linearly, guided by external magnetic fields. In the absence of such fields, the electrons can move radially, being affected by the beam self-fields as well as by the radial component of the electric field of the wave. This radial motion can, first, improve the coupling of electrons to the field of a slow wave localized near the wall of a slow-wave structure, and second, cause an energy exchange between the electrons and the wave due to an additional transverse interaction.