Radiation of an electron in an electric field. II

By the methods of quantum electrodynamics, the radiation of an electron moving in the field of a traveling electric wave is considered. It is shown that, in contrast to the classical case, the result given by quantum theory for the spectral-angular distribution of the radiant energy differs from the corresponding expression for an electron in a constant homogeneous electric field, even in the terms proportional to Planck's constant.Translated from Izvestiya Vysshikh Uchbenykh Zavedenii, Fizika, No. 6, pp. 92–98, June, 1976.In conclusion, the authors thank V. G. Bagrov, D. M. Gitman, and Sh. M. Shvartsmau for their interest in the work and for useful discussions.     

Influence of an electric field on the magnetoabsorption in a field of resonant laser radiation

The frequency dependence of the coefficient of interband magnetoabsorption of a weak electromagnetic wave propagating in a constant electric field and in a field of resonant laser radiation at a frequency equal to the cyclotron frequency (infrared magnetic resonance) is calculated. The specific features observed in interband absorption of the electromagnetic wave in a uniform electric field are considered for the case in which the frequency of laser radiation is equal to the confinement frequency in a parabolic quantum well (infrared quantum-well resonance).     

Equation of Motion of an Electric Charge

The appearance of the time derivative of the acceleration in the equation of motion (EOM) of an electric charge is studied. It is shown that when an electric charge is accelerated, a stress force exists in the curved electric field of the accelerated charge, and in the case of a constant linear acceleration, this force is proportional to the acceleration. This stress force acts as a reaction force which is responsible for the creation of the radiation (instead of the radiation reaction force that actually does not exist at low velocities). Thus the initial acceleration should be supplied as an initial condition for the solution of the EOM of an electric charge.     

Diffraction radiation of a fast particle induced by an external field

It is shown that when a fast heavy charged particle travels near the surface of a metal affected by a constant inhomogeneous electric field, there arises diffraction radiation appreciably depending on the external field.     

Recording of pulsed electromagnetic radiation in the radio-frequency range during the heating of periclase and technical glass

Schemes are given for recording the electromagnetic radiation emitted over a wide radio-frequency range (0.15–30 MHz) by dielectrics when heated with no voltage applied to the specimen and in a constant electric field. As examples, the paper describes the results of studies of pulsed electromagnetic radiation during the heating of specimens of periclase and technical glass, without any voltage being applied to the specimen and in a constant electric field, from liquid-nitrogen temperatures to 1000°C. An amplitude-frequency analysis is made of the radio pulses.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 124–131, April, 1977.     

Radiation From an Electric Charge

The conditions in which electromagnetic radiation is formed are discussed. It is found that the main condition for the emission of radiation by an electric charge is the existence of a relative acceleration between the charge and its electric field. Such a situation exists both for a charge accelerated in a free space, and for a charge supported at rest in a gravitational field. Hence, in such situations, the charges radiate. It is also shown that relating radiation to the relative acceleration between a charge and its electric field, solves several difficulties that existed in earlier approaches, like the energy balance paradox, and the relativistic nature of the observation of the emitted radiation.     

加脊TEM喇叭初步研究

针对恒阻抗TEM喇叭的上下面板电流分布不对称,采用小反射理论和阻抗渐变思想并通过设计脊结构对恒阻抗TEM喇叭进行了改进,研制了加脊TEM喇叭。仿真及实验研究结果表明:对于脉冲宽度约为1 ns的高斯脉冲,通过加脊在一定程度上改善了恒阻抗TEM喇叭上下面板电流分布的不对称性和E面辐射电场的不对称性;相对于相同口径的恒阻抗TEM喇叭,加脊TEM喇叭作为辐射天线和反射面脉冲天线馈源时系统的主轴远场辐射因子均有提高。     

Amplification of terahertz radiation in carbon nanotubes

We investigate theoretically the feasibility of amplification of terahertz radiation in aligned achiral carbon nanotubes, a zigzag (12,0) and an armchair (10,10) in comparison with a superlattice using a combination of a constant direct current (dc) and a high-frequency alternate current (ac) electric fields. The electric current density expression is derived using the semiclassical Boltzmann transport equation with a constant relaxation time. The electric field is applied along the nanotube axis. Analysis of the current density versus electric field characteristics reveals a negative differential conductivity behavior at high frequency, as well as photon assisted peaks. The photon assisted peaks are about an order of magnitude higher in the carbon nanotubes compared to the superlattice. These strong phenomena in carbon nanotubes can be used to obtain domainless amplification of terahertz radiation at room temperature.     

Dielectric constant and threshold electric field of charge-density-waves with strong impurity pinning

The dielectric constant ε and the threshold electric field E_T for the onset of charge-density-wave conduction are investigated within the phenomenological model proposed by Tua and Zawadowski for the strong pinning regime. The static dielectric constant ε (E) in a bias electric field E is found to be almost independent of E provided that E is not too close to E_T. For relatively small values of the pinning strength, the product ε E_T becomes independent of the parameters of the theory. Good agreement is found with the available experimental data on NbSe₃ for the case of strong pinning obtained by radiation damage.     

Linear Motion under Constant Force and Radiation Reaction

The classical relativistic equation of motion with radiation reaction is solved exactly when the motion is along the lines of force due to a constant electric field. For physically admissible solutions, there is no contribution due to the radiation reaction. The general motion without radiation reaction is not linear.     

Electric field of an isolated charged impurity in an ionic crystal

The character of the behavior of the electric field created by a charged impurity in an ionic crystal is studied on the basis of both cluster and analytical approaches. In the cluster approach about 30 000 ions surrounding the impurity are taken into account. These ions are described in a model of polarizable sites. A direct calculation shows that the asymptote of the electric field of a charged impurity at lattice points can differ strongly from the one given by the Coulomb equation written for a homogeneous polarizable medium. The behavior of the electric field at intermediate distances, where the asymptotic behavior cannot yet be used, is studied in detail. It is found that the electric field is increased significantly in comparison to the Coulomb field in the region near the defect. The size of this (strongly polarized) region increases as the dielectric constant increases. These data are in qualitative agreement with the results obtained by Vikhnin et al. and account for the results of recent experiments designed to investigate polarization in reduced virtual ferroelectrics. Fiz. Tverd. Tela (St. Petersburg) 40, 662–667 (April 1998)     

Particle creation by charged black holes

A simple derivation is given for the leading term (n=1) in the Schwinger formula for the pair creation by a constant electric field. The same approach is applied then to the charged particle production by a charged black hole. In this case, as distinct from that of a constant electric field, the probability of the charged particle production depends essentially on the particle energy. The production rate by black holes is found in the nonrelativistic and ultrarelativistic limits. The range of values for the mass and charge of a black hole is indicated where the discussed mechanism of radiation dominates the Hawking one.     

Polarization direction characters of local electric field around dielectric coated gold nanowire

The local electric field components in the dielectric wall with a long gold nanowire in its core are calculated based on quasi-static theory. The calculated results show that the complete polarized incident light does not only stimulate same directional complete polarized local electric field. The same directional polarized electric field only locates close to the poles of the core wire and is parallel or perpendicular to the polarized direction of the incident radiation. On the other hand, incident light also stimulates perpendicular directional polarization, which densely locates close to the poles of the core wire in the direction with an included angle π/4 or 3π/4 makes with polarization direction of incident light. Furthermore, local electric field components in the wall also depend on the dielectric constant of dielectric wall and surrounding medium. When dielectric constant of the wall is less than that of surrounding, the areas of perpendicular directional polarized local field in the wall reduce and shift greatly. At the same time, more parallel directional polarized local field focus in the poles of the wall along the incident polarization. PACS 78.67.Bf; 73.20.Mf; 36.40.Gk; 78.66.Bz; 73.20.Mf     

The break of L-S coupling and the double Stark resonance in the spectrum of 36P → 37P two-photon transition in Rydberg atoms of sodium

New results are presented of an experimental investigation of the spectrum of 36P → 37P two-photon microwave transition in Rydberg atoms of sodium in a constant electric field. Depending on the conditions of excitation of the initial 36P state (the constant electric field is switched on either before or after the exciting laser pulse) and polarization of laser radiation, a strong variation is observed of the amplitudes of individual two-photon transitions between the fine-structure Stark components of the 36P and 37P states. This effect is an analog of the Paschen-Back effect in a strong magnetic field and is due to the break of L-S coupling and to the variation of the wave functions of Rydberg electrons in an electric field. It is also found that the break of L-S coupling affects considerably the shape of double Stark resonance arising upon intersection of the virtual intermediate level of two-photon transition with the real intermediate 37S level.     

Linearly polarized terahertz radiation in uniaxially deformed Ge(Ga) upon the electric breakdown of an impurity

The polarization spectra of spontaneous terahertz radiation in uniaxially deformed germanium have been measured upon the electric breakdown of shallow acceptors. Lines with various degrees of polarization with respect to the compression axis have been observed in the radiation spectrum. These lines are associated with the optical transitions of holes between the excited and ground states of the acceptor, as well as with the transitions of holes from the valence band to the ground state of the impurity. At a pressure of about 3 ± 0.3 kbar in the [111] direction near the impurity breakdown, the linear polarization degree reaches ～80–90% in the main lines of terahertz radiation. As the electric field intensity increases, the depolarization of radiation is observed, which is caused by the heating of nonequilibrium holes by the electric field.     

Some problems in the classical theory of radiation

The article considers the problem of the complete radiation of the energy of a charged particle moving in constant and homogeneous electric and magnetic fields and in the field of a plane wave. Exact formulas are obtained for these cases. The problem is al so considered of the instantaneous radiation of an arbitrary moving charge. The problems are considered according to classical theory.     

Nuclear magnetic shielding of a hydrogen atom in an electric field

The nuclear magnetic screening constant of a hydrogen atom in a uniform electric field is calculated, neglecting any effect of electron spin. The screening is found to be reduced by the electric field for all directions of the applied magnetic field, the reduction being greatest if the two fields are perpendicular.     

Balance equations for electron transport in an arbitrary energy band driven by an intense terahertz field. Application to superlattice miniband transport

We suggest a balance-equation approach to hot-electron transport in a single arbitrary energy band subject to an intense radiation field of terahertz (THz) frequency, including all the multiphoton emission and absorption processes and taking account of realistic scatterings due to impurities and phonons. This approach, which allows one to calculate THz-driving, time-averaging transport based on a set of time-independent equations, provides a convenient method to study the effect of an intense THz electric field on carrier transport in a nonparabolic energy band. As an example, these fully three-dimensional, acceleration- and energy-balance equations are applied to the discussion of superlattice miniband transport at lattice temperature T=77 and 300 K driven by the THz radiation field of varying strengths. It is shown that the current through a dc biased miniband superlattice is greatly reduced by the irradiation of an intense THz electric field. Received: 23 January 1998 / Revised: 31 March 1998 / Accepted: 20 April 1998     

A heavy ion in a fluid in presence of an electromagnetic field seen as an ordinary Brownian motion

An alternative method of how to characterize, at equilibrium, the diffusion process of a Brownian charged particle (heavy ion) in a fluid in presence of an electromagnetic field is presented. The theory is formulated via a Langevin equation associated with the ion's velocity vector, which is transformed to another velocity-space in which the diffusion process is quite similar to that of the ordinary Brownian motion. The diffusion process is characterized, in absence and in presence of the electric field, through the mean square displacement in the transformed configuration-space and then returned to the original variables, by means of the corresponding transformation. Under the action of the electric field, the diffusion process is studied for a general time-dependent electric field. Explicit results are obtained for a constant and oscillating electric field.     

Creation of particles and the effective Lagrangian in the quasi-Euclidean model of the universe with an electro-magnetic field

A calculation of the number of scalar and spinor particles created in the quasi-Euclidean cosmological model with an electric field is carried out. The inverse effect of the created particles on the electric field is investigated. It is shown that for large times the creation of particles leads to a decrease of the electric field. The imaginary part of the effective action in quasi-Euclidean space with constant electric and magnetic fields is found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 12–16, May, 1982.