电子在激光驻波场中运动产生的太赫兹及X射线辐射研究

采用单电子模型和经典辐射理论分别对低能和高能电子在线偏振激光驻波场中的运动和辐射过程进行了研究. 结果表明: 垂直于激光电场方向入射的低速电子在激光驻波场中随着光强的增大, 逐渐从一维近周期运动演变为二维折叠运动, 并产生强的微米量级波长的太赫兹辐射; 高能电子垂直或者平行于激光电场方向入射到激光驻波场中, 都会产生波长在几个纳米的高频辐射; 低能电子与激光驻波场作用中, 激光强度影响着电子的运动形式、辐射频率以及辐射强度; 高能电子入射时, 激光强度影响了电子高频辐射的强度, 电子初始能量影响着辐射的频率; 电子能量越高, 产生的辐射频率越大. 研究表明可以由激光加速电子的方式得到不同能量的电子束, 并利用电子束在激光驻波场的辐射使之成为太赫兹和X射线波段的小型辐射源. 研究结果可以为实验研究和利用激光驻波场中的电子辐射提供依据.     

Invariance of electromagnetic radiation spectra in undulators based on plane magnets

Radiation of relativistic particles in a plane magnetic field (for example, in an undulator) is studied. The magnetic system is assumed to be plane and composed of permanent magnets. It is shown that there is a class of special continuous rotations of the magnetization vector for magnetic substances providing changes in the magnetic field of the system without changing the spectrum of spontaneous radiation of relativistic particles. This property of electromagnetic radiation can be used in developing new models for undulators.     

Magnetically Controlled Tunneling of a TE Wave through the Ferrite—ε-Negative Layer Structure

We have considered the tunneling of a normally incident electromagnetic wave through a bilayer structure that consists of a ferrite layer and an adjoining layer with a negative permittivity. The ferrite layer is transversely magnetized by an external magnetic field that corresponds to the range of negative values of the effective permeability. It has been shown that the transmission of the structure can be controlled in wide limits by varying the external magnetic field. In particular, nearly perfect tunneling (viz., nonreflective transmission of incident radiation) can be realized.     

On the Energy-loss in the CERENKOV Radiation

The object of this paper is to find the electromagnetic field and the rate of increase of the field energy due to a pair of charged particles soon after their creation. It is shown that in case of the CERENKOV radiation, there is a constant rate of increase of the field energy. The power spectrum is similar to that obtained in the usual formulation, where the particles are assumed to be moving with uniform velocity since infinite past.     

Transition radiation from relativistic charged particles interacting with atomic strings in a crystal

The problem of transition radiation generated by relativistic particles incident on atomic strings in a crystal at a small angle is considered. Conditions are obtained under which the problem of transition radiation reduces to that of radiation generated by a collision with a filament-like target. It is shown that the angular distribution of transition radiation is symmetric with respect to the atomic-string axis.     

Compression of terahertz radiation in resonant systems with a quantum superlattice

It is shown theoretically that ultrashort terahertz electromagnetic pulses can be generated in resonant systems containing a quantum semiconductor superlattice. This effect is due to the compression of radiation incident on a cavity as a result of ultrafast self-modulation of the cavity Q factor upon cyclic switching of the superlattice from the screening to the transparent state in a pump field.     

Surface plasmon-polaritons wave fields in the vicinity of a metallic nanohole

It is shown that metal surface with a nanohole can support surface plasmon-polaritons (SPP), whose wave fields are described by Hankel functions. These plasmons can be excited by an electromagnetic wave incident at the metal surface. The optical transmission through subwavelength holes in metal films can essentially be enhanced by interaction of the incident light with surface plasmons. Dependence of excitation of the wave field of SPP on the incidence angle and on the wavelength of incident light is considered.     

Conditions for generation of X-ray cherenkov radiation during motion of charges in realistic media

The influence of the spatial distribution of electrons, atoms, and nuclei in condensed media on a medium’s susceptibility and on the conditions for the formation of short-wavelength Cherenkov radiation are considered. It is shown that taking into account the inhomogeneous (atomic and electronic) structure of material media in which fast charged particles travel leads to a change in the effective susceptibility and permittivity in the X-ray range, as compared with cases of model homogeneous media with the same average concentration of electrons. The influence of the distribution functions of electrons and nuclei in a target on the conditions for Cherenkov radiation generation and its parameters and on the threshold energy of fast charged particles required to generate such radiation is studied. It is shown that the function of the spatial distribution of electrons and nuclei in a target affects the conditions for generating laser radiation in the X- and λ-ray ranges (on the problem of X- and λ-ray lasers). The obtained results show that using the Fresnel approximation in the X-ray range is insufficiently justified and can lead to significant errors.     

微纳粒子光学散射分析

为实现利用光学方式对微纳尺度粒子性质的研究,探讨了亚微米线及亚微米球对光电磁波的散射效应.微纳米尺度粒子的光学散射,散射粒子尺寸与入射光波长尺寸可满足米氏(Mie)散射条件.利用Matlab数值模拟的方式,将分析结果以模拟图的形式清晰地展现出来.满足尺寸条件的层状粒子以及任意多个散射粒子存在时对电磁波的散射都可采用Mie散射分析方法,并且针对多粒子散射,分析了散射体位于不同位置时对散射造成的影响.通过分析光学散射光场相关的微分散射截面及近场散射电磁场分布,可得出散射光场随散射角度的变化趋势,以及散射光场受各类因素的影响,包括入射光偏振态、散射粒子尺寸、散射粒子结构及粒子构成层数、散射粒子数量等的影响,也包括一些隐含因素对散射光场的影响,如散射粒子与周围介质的相对折射率.本文的科学意义体现在:与入射光波长尺寸可比的亚微米尺度的粒子,可用作传感器,对于其位移的探测可通过光学方式来实现,而由于粒子本身特性对散射光的影响具有一定的参考价值,从而使通过光学方式对机械位移的读出具有更高准确度.研究结果对于光学方式探测亚微米线机械振动具有指导意义.     

Coherent backscattering of light by a layer of discrete random medium

We consider the problem of backscattering of light by a layer of discrete random medium illuminated by an obliquely incident plane electromagnetic wave. The multiply scattered reflected radiation is assumed to consist of incoherent and coherent parts, the coherent part being caused by the interference of multiply scattered waves. Formulas describing the characteristics of the reflected radiation are derived assuming that the scattering particles are spherical. The formula for the incoherent contribution reproduces the standard vector radiative transfer equation. The interference contribution is expressed in terms of a system of Fredholm integral equations with kernels containing Bessel functions. The special case of the backscattering direction is considered in detail. It is shown that the angular width of the backscattering interference peak depends on the polar angle of the incident wave and on the azimuth angle of the reflection direction.     

Statistics and light squeezing in the dissipative two-atom Jaynes-Cummings model

The statistical and fluctuational properties of an electromagnetic field in a nonideal cavity are studied with the help of the collective two-atom Jaynes-Cummings model taking into account losses of photons and spontaneous radiation of atoms into bath modes. For the coherent state of the field and excited initial state of atoms, the general analytical expressions for the second-order field correlation function, the second-order squeezing parameters, and the squared field amplitude are obtained by solving the master equation for the density matrix. The statistics and the degree of squeezing of the cavity field mode are studied as functions of the initial field intensity and of the coefficients of the energy dissipation of the system. It is shown that, for the two-atom dissipative model, compared to the single-atom model, the type of field statistics can be changed and the maximal degree of short-term squeezing can be increased.     

Light absorption by island metal films in the infrared range

This study reports on theoretical investigations of the electric and magnetic absorption of small metallic particles as functions of their shape, with the wavelength of incident e/m radiation assumed to be much greater than the size of the particles. A general expression for the absorption cross-section is derived for the cases when both the bulk and surface electron scattering are dominant. In the IR-region the absorption cross-section is shown to be extremely sensitive to the shape of particles; for particles of a constant volume, yet different in shape, it can change by several orders of magnitude. It is also shown that under dominant surface scattering the optical conductivity of an asymmetric particle is described by a tensor whose principal values are calculated for the ellipsoidal shape. The expression obtained for the electric and magnetic absorption renders ground to infer that the ratio of the contributions due to these absorption mechanisms greatly depends on the shape of particles and polarization of light.     

Kinetic theory of radiation in non-equilibrium relativistic plasmas

Many-particle QED is applied to kinetic theory of radiative processes in many-component plasmas with relativistic electrons and non-relativistic heavy particles. Within the framework of non-equilibrium Green’s function technique, transport and mass-shell equations for fluctuations of the electromagnetic field are obtained. We show that the transverse field correlation functions can be decomposed into sharply peaked (non-Lorentzian) parts that describe resonant (propagating) photons and off-shell parts corresponding to virtual photons in plasmas. Analogous decompositions are found for the longitudinal field correlation functions and the correlation functions of relativistic electrons. As a novel result a kinetic equation for the resonant photons with a finite spectral width is derived. The off-shell parts of the particle and field correlation functions are shown to be essential to calculate the local radiating power in relativistic plasmas and recover the results of vacuum QED. The influence of plasma effects and collisional broadening of the relativistic quasiparticle spectral function on radiative processes is discussed.     

Motions of particles in an oscillating plasma

An alternative consideration of oscillations and waves in plasma is suggested based on equations for small deflections of particles from their equilibrium trajectories instead of equations for perturbations of distribution functions and fields, so that average values are calculated with equilibrium distribution functions. Instead of the Maxwell equations for an electromagnetic field their solutions in the Lienard-Wiechert form are used. All the known results of the linear kinetic theory of plasma oscillations are shown to be derivable in this way, and small correlations for dispersion relations of the first order in the plasma parameter due to the Debye screening have been obtained. A simplified consideration of a rarefield plasma in a strong magnetic field is given showing a non-cyclotron character of the motion of the particles. Such a combination of statistical and dynamical approaches may be useful in many problems of plasma physics.     

随机电磁涡旋光束的深聚焦特性

基于德拜矢量积分理论,研究了随机电磁涡旋光束经过大数值孔径透镜之后的聚焦特性及透镜的数值孔径、入射光束的偏振度、拓扑荷以及横向相干长度对焦平面附近聚焦光束的光强分布和相干度的影响.结果表明:适当地选择相关参量,可在焦平面上得到椭圆形光斑的光强分布以及平顶光强分布.随机电磁涡旋光束在焦平面上同一点处两个相互垂直分量之间的相干度,不同两点处两个相同分量之间的相干度以及不同两点处两个相互垂直分量之间的相干度研究表明,入射光束的拓扑荷和横向相干长度对聚焦光束的相干性有着十分明显的影响.     

Intensity distribution of electromagnetic radiation in one-dimensional superstructures

Distribution function of density of particles in one-dimensional sample with weak disorder has been found using Berezinsky diagram technique. For open systems, when a particle having reached the end of the sample can leave it, logarithmically normal distribution for density of particles has been obtained. It has been shown that the function obtaineddescribes radiation intensity distribution in weakly disordered superlattice.     

Induced radiation by charged particles moving in a plane electromagnetic wave

It is shown that when a charged particle moving in the field of a plane electromagnetic wave is subjected to another electromagnetic wave, incident at some angle with respect to the first, induced radiation and absorption occur. Under certain conditions the induced radiation predominates over the absorption.Translated from Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 50–53, September, 1969.The authors thank professor I. M. Ternov for useful discussions.     

Coherent polarization driven by external electromagnetic fields

The coherent interaction of the electromagnetic radiation with an ensemble of polarizable, identical particles with two energy levels is investigated in the presence of external electromagnetic fields. The coupled non-linear equations of motion are solved in the stationary regime and in the limit of small coupling constants. It is shown that an external electromagnetic field may induce a macroscopic occupation of both the energy levels of the particles and the corresponding photon states, governed by a long-range order of the quantum phases of the internal motion (polarization) of the particles. A lasing effect is thereby obtained, controlled by the external field. Its main characteristics are estimated for typical atomic matter and atomic nuclei. For atomic matter the effect may be considerable (for usual external fields), while for atomic nuclei the effect is extremely small (practically insignificant), due to the great disparity in the coupling constants. In the absence of the external field, the solution, which is non-analytic in the coupling constant, corresponds to a second-order phase transition (super-radiance), which was previously investigated.