Excitation of excitons in semi-infinite solids with a nonrelativistic electron beam

The instability of an infinite thin electron beam propagating in vacuum over the surface of an isotropic nongyrotropic crystal is investigated. The possibilities of exciting additional longitudinal waves and polarization waves are analyzed. The dispersion laws of exciton-beam coupled waves are obtained. It is demonstrated that the interaction of the beam with the additional bulk longitudinal wave and the surface polarization wave leads to the appearance of the absolute instability.     

分层半空间表面非线性瑞利波的激发*

针对非线性瑞利波在均匀分层半空间结构中的激发和传播规律进行研究。根据摄动理论和模态分解将分层半空间结构中瑞利波的二次谐波声场表示为二倍频瑞利波模式的线性组合,经由互易关系得到各模式的展开系数表达式。对不同分层半空间结构中瑞利波二次谐波的激发和传播特性进行讨论,结果表明相速度匹配的瑞利波模式其二次谐波分量随传播距离线性增长,非匹配模式的二次谐波分量则沿传播方向周期震荡传播。此外,文中定义非线性参数表征瑞利波模式产生的非线性程度,这有利于选择出具有明显非线性效应的匹配点,为后续检测工作提供理论依据,具有指导意义。     

Excitation of waves in magnetoactive plasma by a strongly “spread” inhomogeneous electron beam

The stability of beam-plasma systems is studied assuming that the distribution of beam-electrons in the velocity space corresponds to the first period of the quasilinear relaxation. The necessary condition is derived for the usual quasilinear equations to be applicable within the whole period of quasilinear relaxation.The authors wishes to thank Dr. R. Klíma for his interest in this paper.     

Kinetic theory of surface waves in a semibounded plasma flow

A study is made of the spectrum of surface waves in a semibounded plasma flow. The frequency spectra and damping rates of the waves propagating along the flow are analyzed both in the high-frequency range (in which the spatial dispersion is weak and the wave damping is governed primarily by electron collisions) and the low-frequency range (in which the spatial-dispersion effects dominate), with focus on the effect of the flow velocity on the propagation of ion-acoustic waves. Special attention is paid to the penetration of a static field into a plasma flowing at a supersonic velocity.     

Excitation of wake-field waves in plasma by a microtron beam

The experimental study of excitation of wake-field waves in plasma by a sequence of electron bunches of a microtron beam has been carried out. Results of measurement of the spectrum of electrons after their passage through plasma confirm the effect of adding of waves from a sequence of about 100 bunches which leads to the increase in the amplitude from 1 V/cm up to 100 V/cm.     

Excitation of surface plasma waves over metallic surfaces by lasersand electron beams

A laser incident on a metal film (deposited on a glass substrate) from the glass side at a specific angle of incidence, excites a surface plasma wave (SPW) at the metal-free space interface. The ratio of the SPW field to the laser field increases with the laser spot size b attaining a value much greater than one at b>exp(2wα/c) where a is the film thickness and ω is the laser frequency. The SPW (ω, k_z,) can also he excited by a relativistic electron beam, propagating parallel to the interface in the free space region, via Cerenkov interaction when beam energy ϵb=(|ϵ|-1)mc² where ϵ is the effective metal permittivity, and mc² is the electron rest mass energy. When the surface has a ripple of wave number k₀, the SPW (ω, k_zz) can be excited at lower beam energy via sideband coupling, ω=(k_zz +k₀)v_b where v_bzˆ is the beam velocity. In both cases, however, the positioning of the beam in the close proximity of the interface is required. The scheme is useful for the generation of wavelengths longer than 1 μm     

Surface Josephson plasma waves in layered superconductors

We predict the existence of surface waves in layered superconductors in the THz frequency range, below the Josephson plasma frequency omega J. This wave propagates along the vacuum-superconductor interface and dampens in both transverse directions out of the surface (i.e., towards the superconductor and towards the vacuum). This is the first prediction of propagating surface waves in any superconductor. These predicted surface Josephson plasma waves are important for different phenomena, including the complete suppression of the specular reflection from a sample (Wood's anomalies) and a huge enhancement of the wave absorption (which can be used as a THz detector).     

Excitation of surface and volume electromagnetic waves in left-handed media by an electron bunch

We study theoretically the Vavilov-Čerenkov radiation from a nonrelativistic electron bunch moving in free space over a left-handed medium. It is shown that in the frequency range in which the refractive index of the medium is negative, Vavilov-Čerenkov radiation leads to simultaneous excitation of volume and surface electromagnetic waves in the same frequency range. The wave vector of the surface wave in the plane of an interface of two media is greater in magnitude than the corresponding quantity for the volume wave. The energy fluxes of volume and surface waves in the left-handed medium are studied. The radiation pattern of the bunch is found. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 5, pp. 406–417, May 2007.     

Excitation of surface plasmons by electrons in a parabolic beam

A theory is presented for the excitation of surface plasmons by an electron beam following a non-touching path above a metal surface in Born approximation. The metal is assumed to possess only surface plasmon excitations. Configurations involving deflection of the electron beam in a parallel plate condensor, and by scattering from a field emission tip are envisaged. The relation between experimental conditions and the validity of the semiclassical approximation is discussed. The region of space above the surface in which scattering occurs is calculated, but the feasability of the experiment depends on electron optical factors which are outlined.     

Scattering of light waves by electron electrostatic waves in laser produced plasmas

The propagation of light waves in an underdense plasma is studied using one-dimensional Vlasov-Maxwell numerical simulation.It is found that the light waves can be scattered by electron plasma waves as well as other heavily and weakly damping electron wave modes,corresponding to stimulated Raman and Brilluoin-like scatterings.The stimulated electron acoustic wave scattering is also observed as a high scattering level.High frequency plasma wave scattering is also observed.These electron electrostatic wave modes are due to a non-thermal electron distribution produced by the wave-particle interactions.The collision effects on stimulated electron acoustic wave and the laser intensity effects on the scattering spectra are also investigated.     

Nonlinear electrostatic surface waves in a semi-infinite plasma

The nonlinear equations which govern the filamentation of a large-amplitude high-frequency electrostatic surface wave are studied considering solutions in the form of stationary traveling waves. It is shown that solitary surface waves exist at certain amplitude and phase conditions.     

Spin waves of a layered ferromagnetic electron gas

Using a first-order Green's function technique, the spin wave spectrum of a layered ferromagnetic electron system is determined in the long-wave length limit. It is shown that the spin wave stiffness is a highly anisotropic quantity. A discussion of the Stoner-Overhauser-Wohlfarth condition shows that both electron tunneling processes and a more sophisticated expression of the Coulomb interaction matrix element than the usual Hubbard form are important for the existence of ferromagnetic ordering.