Evolution of an intense elliptically polarized electromagnetic wave in underdense plasmas

An elliptically polarized electromagnetic wave in an underdense plasma acquires a longitudinal component of the electric field which oscillates as even harmonics of the fundamental frequency. The phase shift between transverse field components and the wave amplitudes exhibit nonlinear oscillations.     

Resonant interaction between intense electromagnetic waves during ionization of an atom

Resonant interaction through the continuum between two intense electromagnetic waves of different frequencies during ionization of an atom is considered. A general solution of the problem is found by using a procedure based on the application of the Laplace transform to the equations for the time-dependent amplitudes of the probability. When one of the EM waves is considerably weaker than the other, the dynamics of the absorption of light by an atom are investigated, and a final value for the ionization probability in the illumination region is found.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 63–70, January, 1978.     

Basis of polarization-dressed states of an atom in an elliptically polarized resonant field

A basis of polarization-dressed states is proposed for atomic energy levels degenerate in the total angular momentum projections in the case of interaction with elliptically polarized light. It is shown that instead of selection rules for the magnetic quantum number, the interaction in this basis can be presented as the sum of direct transitions between corresponding pairs of polarization-dressed states of the upper and lower levels. The explicit form of the basis is derived for ten possible combinations of dipole transitions between energy levels with angular momenta J = 0, 1/2, 1, 3/2, and 2. The problem of Rabi oscillations in such a system is considered as an application.     

Response of an atom interacting with an arbitrarily polarized electromagnetic field

We develop the theory of interaction of the electromagnetic field and a single atom being in an arbitrary state and having an arbitrary direction of the angular momentum of the atomic electron with respect to the direction of the field polarization vector. It is shown that the atom response current has a tensor structure and depends on both the direction of the angular momentum of the atom, and the polarization vector of the external field. The tensor character of the response is determined by the externally induced anisotropic distribution of the probability density of spatial localization of the atomic electron. It is shown that the induced-anisotropy effects clarify the harmonic generation mechanism at play during the non-resonance interaction of laser radiation with atomic media. The developed theory is applied to the analysis of the problem about the generation of terahertz waves in a two-color laser field. It is shown that the change in the mutual orientation of wave polarization vectors leads to a significant increase in the efficiency of conversion of high-frequency fields to low-frequency ones. It is shown for the first time that the generation of terahertz waves is possible in the preionization regime, when the generation mechanism is related to atomic nonlinearity.     

Interaction of a three-level atom with an elliptically polarized wave

The interaction of elliptically polarized radiation with a resonant medium consisting of atoms with an excited state split into a doublet was studied theoretically. Interference terms associated with the coherent interaction of the field with the excited sublevels of the doublet were found to appear in the refractive index. The dispersion dependence of the refractive index was studied. It was shown that the decay constants for the multipole moments of the current of a dipole-forbidden atomic transition can be determined by the choice of the wave polarization.     

Above-threshold ionization by an elliptically polarized field: interplay between electronic quantum trajectories

Measurements of energy-resolved angular distributions of electrons generated in above-threshold ionization of rare gases in a field with elliptical polarization are presented, with emphasis on the high-energy part of the spectra. The data show a second plateau at a specific angle with respect to the large component of the laser field. The results are compared to a calculation based on a strong-field rescattering approximation. This is interpreted in terms of the superposition of quantum trajectories. The second plateau is associated with the interference of electrons that do and that do not rescatter.     

Multiphoton ionization of the hydrogen atom by a circularly polarized electromagnetic field

This paper examines the multiphoton ionization of the ground state of the hydrogen atom in the field of a circularly polarized intense electromagnetic wave. To describe the states of photoelectrons, quasiclassical wave functions are introduced that partially allow for the effect of an intense electromagnetic wave and that of the Coulomb potential. Expressions are derived for the angular and energy distributions of photoelectrons with energies much lower than the ionization potential of an unperturbed atom. It is found that, due to allowance for the Coulomb potential in the wave function of the final electron states, the transition probability near the ionization threshold tends to a finite value. In addition, the well-known selection rules for multiphoton transitions in a circularly polarized electromagnetic field are derived in a natural way. Finally, the results are compared with those obtained in the Keldysh-Faisal-Reiss approximation. Zh. éksp. Teor. Fiz. 116, 807–820 (September 1999)     

A new approach to the resonant interaction between atoms and strong electromagnetic field

The interaction of a two-level system with an intense electromagnetic field, is analysed by an approach which is capable of taking into account the character of interatomic collisions. This approach demonstrates why the Rabi shift cannot be observed in the Doppler limit, and clarifies the assumptions underlying the work of other authors.     

Self-consistent equations for the interaction of an atom with an electromagnetic field of arbitrary intensity

A system of equations is suggested for the interaction of an atom with an electromagnetic field of arbitrary intensity. The distinctive feature of the equations is that, in the absence of the field, the electron density in the atom is determined by the Schrödinger equation and, in the presence of the field, by the equation resembling the classical equation for an electron in the Lorentz force field.     

Radioelectric effect in a superlattice under the action of an elliptically polarized electromagnetic wave

The density of the current associated with the drag of charge carriers in a superlattice by an elliptically polarized electromagnetic wave is calculated. Two cases of the mutual orientation of the Umov-Poynting vector and the superlattice axis, i.e., their parallel and perpendicular orientations, are analyzed. It is shown that, for the parallel orientation, the radioelectric effect can change sign. The influence of the longitudinal dc electric field on the radioelectric effect is investigated under the conditions where a circularly polarized electromagnetic wave propagates along the superlattice axis. The current density is studied as a function of the electric field strength and the electromagnetic wave intensity. It is demonstrated that the direction of the electric current is changed at specific values of the dc field strength and the wave intensity.     

Emission of an atom during its interaction with an ultrashort pulse of electromagnetic field

The electronic transitions and emission of an atom during its interaction with a spatially inhomogeneous ultrashort pulse of electromagnetic field are considered. The probabilities of excitation and ionization, as well as the spectra and cross sections of reemission of such a pulse by the atom, are obtained. As an example, the one-and two-electron inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-and helium-like atoms are considered.     

Atom in an elliptically polarized resonance field: Exact stationary solution

An analytical method is developed for finding the exact stationary solution for the density matrix of atoms in a monochromatic resonance field of arbitrary ellipticity and intensity. A solution for the transitions F _g=F → F _e=F+1 (F _g and F _e are the angular momenta of the ground and excited states) is obtained in an analytical invariant form. The properties of this solution are investigated. Pis'ma Zh. éksp. Teor. Fiz. 64, No. 1, 8–12 (10 July 1996)     

Electron scattering in the presence of an intense electromagnetic field

The general theory of electron scattering in the presence of an external electromagnetic field, provided by an intense laser beam, accompanied by absorption ofn photons, each with energy ?ω is discussed. The calculation leads to many summations over intermediate states. A general method for exactly evaluating several sums is described in detail. Numerical results show that the cross-section varies with intensity in a power law fashion.     

Quantum processes in an intense electromagnetic field. II

An approach is suggested to the treatment of processes in an external electromagnetic field that generates real pairs. The interaction with the field is allowed for exactly by means of the solutions of the Dirac equation. Processes of arbitrary order in the electron-photon interaction are considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 86–92, October, 1976.In conclusion the author wishes to thank V. G. Bagrov and Sh. M. Shvartsman for useful discussions and critical comments.     

Quantum processes in an intense electromagnetic field. I

The Furry approach for arbitrary external electromagnetic fields that do not generate real pairs is considered. Problems of the existence of a stable vacuum in the field are discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 81–86, October, 1976.The author is grateful to F. A. Berezin for refinement of the theorems used in this work and to A. A. Grib, S. G. Mamaev, and V. M. Mostepanenko for valuable critical comments.     

β-Decay of an unpolarized neutron in an intense electromagnetic field

This study will consider the effect of a circularly polarized electromagnetic field on- decay of a neutron for values of the parameter ea/m 1 and ea/m 1, where e and m are the charge and mass of the electron; anda is the amplitude of the field potential. Within the framework of the V=A variant of the weak interaction theory, in the first-order perturbation theory, it is shown that with increase in field intensity the probability of neutron decay increases. The energy distributions of the electrons generated are calculated for ea/m = 0.5 and ea/m=1, and the results obtained are evaluated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 115–120, April, 1974.The author thanks S. V. Izmailov and R. Yu. Volkovyskii for their evaluation of the study.     

Kinetics of atoms in the field produced by elliptically polarized waves

The kinetics of atoms with degenerate energy levels in the field produced by elliptically polarized waves is considered in the semiclassical approximation. Analytic expressions for the force acting on an atom and for the diffusion coefficient in the momentum space are derived for the optical transition J _g =1/2→J _e = 1/2 in the slow atom approximation. These expressions are valid for an arbitrary one-dimensional configuration of the light field and for an arbitrary intensity. The peculiarities of the atomic kinetics are investigated in detail; these peculiarities are associated with ellipticity of light waves and are absent in particular configurations formed by circularly or linearly polarized waves, which were considered earlier.     

Excitation of an atom by a nonmonochromatic electromagnetic field

The time evolution of the process of excitation of an atom in the field of a laser wave is considered. It is shown that there exist three stages of relaxation. The first stage carries the most complete information about the mechanism of the interaction of the field with material inside the laser source.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 23–27, June, 1981.