Group equations for moments of the relativistic electron distribution function in a cold gas of neutral atomic particles in an external electric field

A set of multigroup equations is derived for the first three moments of the distribution function for high-energy electrons in a gas of immobile atomic particles. The equations are intended for numerical simulation of processes in a dense weakly ionized plasma with the participation of high-energy electrons, including runaway electrons.     

Radiation trapping in a cold atomic gas

We experimentally study radiation trapping of near-resonant light in a cloud of laser-cooled rubidium atoms. Unlike in most previous studies, dealing with hot vapors, collisional broadening is here negligible and Doppler broadening due to the residual atomic velocity is narrower than the homogeneous broadening. This is an interesting new regime, at the boundary between coherent and incoherent radiation transport. We analyze in detail our low-temperature data (quasi-elastic regime) and then provide some experimental evidence for Doppler-based frequency redistribution. The data are compared with an analytical model valid for coherent transport and a Monte Carlo simulation including the Doppler effect. PACS 42.25.Dd; 32.80.Pj     

Scattering of atomic particles at relativistic energies

This article is concerned with excitation, ionization and electron capture collisions between charged particles and atomic systems involving a single active electron, at impact energies which are so great that Lorentz transformations between the frames of reference of the incident and target particles must be carried out as well as relativistic dynamics employed. For excitations and ionization it is sufficiently accurate to use the relativistic generalization of the first Born approximation, but for electron capture it is necessary to carry through the analysis using a relativistic generalization of the second Born approximation. Also relativistic wave functions are employed to describe the active atomic electron.     

Coupled tensorial form for atomic relativistic two-particle operator given in second quantization representation

General formulas of the two-electron operator representing either atomic or effective interactions are given in a coupled tensorial form in relativistic approximation. The alternatives of using uncoupled, coupled and antisymmetric two-electron wave functions in constructing coupled tensorial form of the operator are studied. The second quantization technique is used. The considered operator acts in the space of states of open-subshell atoms.     

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.     

Cavity optomechanics with cold atomic gas

We present a tutorial review on the topics related to current development in cavity optomechanics, with special emphasis on cavity optomechanical effects with ultracold gases, Bose-Einstein condensates, and spinor Bose-Einstein condensates. Topics including the quantum model and nonlinearity of the cavity optomechanics, the principles of optomechanical cooling, radiation-pressure-induced nonlinear states, the chaotic dynamics in a condensate-mirror-hybrid optomechanical setup, and the spin-mixing dynamics controlled by optical cavities are covered.     

Radiation of relativistic electrons in a magnetic undulator

Expressions are obtained for the spectral-angular characteristics of the radiation in two limiting cases: 1 and 1 ( is the angle of deflection of the electron in the field, and is the energy of the electron in units of mc²). It is shown that in the latter case the maximum of the radiation occurs at higher harmonics.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 88–91, October, 1973.In conclusion the authors thank Professor A. A. Sokolov for useful discussions.     

Radiation of relativistic electrons in a variable undulator

A study is made of the polarization, spectral, and angular characteristics of the radiation of an electron in an arbitrary system of constant undulators with different strengths, distributions, periods, and number of periods of the magnetic field. It is shown that such a system enables one to obtain any form of the radiation spectrum in a wide range of wavelengths.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 48–51, June, 1977.     

Excitation of atomic nuclei and atoms by relativistic charge particles bound in a one-dimensional potential

The process of exciting atoms and atomic nuclei by relativistic electrons and positrons bound in a one-dimensional potential is investigated theoretically. It is shown that a pole corresponding to the emergence of a virtual photon on a bulk surface occurs in the matrix interaction element under definite kinematic relationships. It is obtained that the probability of the excitation process depends on the lifetime of the level being excited, the virtual photon, and the charged particle in a definite energetic state. An estimate of the magnitude of the excitation section of low-lying nuclear states yields a value exceeding by several, orders the section obtained for charged particles in the absence of a binding potential.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 7–11, May, 1987.     

Interference effects in X-ray radiation from relativistic electrons moving at a small angle to an atomic plane

X-ray radiation of relativistic electrons interacting with a set of parallel atomic planes is considered. The anomalous behavior of the radiation due to the interplay of parametric and coherent bremsstrahlung emission mechanisms, which simultaneously occur under specific conditions, is studied.     

适用于中等耦合等离子体的碰撞算子

完全电离等离子体中，当试探粒子分布函数f_α是关于试探粒子速度v_α的偶函数时，导出了一个新的动力学方程的碰撞算子.该碰撞算子同时包括了大角散射(库仑近碰撞)和小角散射(库仑远碰撞)的二体碰撞的贡献,因此，该碰撞算子同时适用于弱耦合(库仑对数lnΛ≥10)和中等耦合(库仑对数2≤lnΛ≤10)等离子体.而且经过修改的碰撞算子和Rosenbluth势有直接的联系，当试探粒子和场粒子满足条件m_αm_β(如电子-离子碰撞或Lor 关键词： 中等耦合等离子体 小角散射 大角散射 碰撞算子     

Two-dimensional vector solitons in a cold atomic gas via electromagnetically induced transparency

We investigate the formation and propagation of vector vortex solitons (VSs) and unipolar solitons (USs) in a cold coherent atomic gas with a Bessel lattice (BL). The system considered is a gas with a tripod level configuration. Owing to the big enhancement of Kerr nonlinearity contributed by the electromagnetically induced transparency (EIT), a weak vector vortex soliton can be effectively formed with ultraslow propagation velocity. We also demonstrate that the characteristics of two-dimensional VSs and USs can be controlled and manipulated by adjusting the parameters of BL. Results obtained may be useful for designing all-optical switches at low light levels.     

Coherent effect in the radiation of relativistic electrons in the field of bent atomic crystallographic planes

The effect of the intense monochromatic radiation arising when relativistic electrons intersect periodically bent atomic crystallographic planes in a crystal is predicted. This effect is independent of the channeling of the particles in the crystal and is possible for relativistic positrons and electrons.     

Visible-laser acceleration of relativistic electrons in a semi-infinite vacuum

We demonstrate a new particle acceleration mechanism using 800 nm laser radiation to accelerate relativistic electrons in a semi-infinite vacuum. The experimental demonstration is the first of its kind and is a proof of principle for the concept of laser-driven particle acceleration in a structure loaded vacuum. We observed up to 30 keV energy modulation over a distance of 1000 lambda, corresponding to a 40 MeV/m peak gradient. The energy modulation was observed to scale linearly with the laser electric field and showed the expected laser-polarization dependence. Furthermore, as expected, laser acceleration occurred only in the presence of a boundary that limited the laser-electron interaction to a finite distance.     

A relativistic gas of interacting particles in the phase volume approximation

The equation of state of a non-ideal gas is calculated in the framework of the S-matrix formulation of statistical mechanics given by Dashem, Ma and Bernstein, the interaction of the particles being determined by the amplitude which is constant in the total and in the transversely cut phase volume. It is shown that there is a limiting temperature in such a system.     

Emission of relativistic electrons in a periodic magnetic field

The polarization properties and the angular and spectral-angular distribution of the emission of electrons moving in a periodic magnetic field are investigated. The emission power is expressed in the near-axial approximation in terms of the Fourier component of the vector potential of the external magnetic field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 16–20, July, 1981.     

Moment-generated radiative-transfer functions for relativistic Maxwellian electrons

Coupling the relativistic expressions for various momentum moments of Maxwellian electron distributions to an invariant representation of Compton photon scattering permits fast and accurate approximations of the effective transfer kernels appearing in the photon transport equation. The method is detailed, earlier approaches are discussed, and numerical results and comparisons are presented.