Radiation of an electron in the quantum field of a nonmonochromatic electromagnetic wave

This study considers the radiation of an electron upon its interaction with one photon and a vacuum of all remaining photons of a quantum plane nonmonochromatic electromagnetic wave. Consideration of the vacuum of an infinite number of photons leads to a change in the spectrum and differential probability of radiation. In the case of a low-intensity plane wave the corresponding finite corrections are calculated, reflecting the role of the vacuum in the process under consideration.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 120–127, July, 1978.The authors thank V. G. Bagrov and D. M. Gitman for their valuable advice on the questions considered in this study.     

Ionization and stabilization of an atom in a quantum electromagnetic field

The dynamics of a model atomic system interacting with a quantum electromagnetic field has been investigated. The effect of statistics and average number of photons in a quantum state of the field on the ionization and stabilization of the atomic subsystem has been studied. The formation of a state with the maximum entanglement between the atomic and field subsystems in the case of interaction with a single-photon field has been demonstrated.     

Polynomial pseudosupersymmetry underlying a two-level atom in an external electromagnetic field

We study chains of transformations introduced in B.F. Samsonov and V.V. Shamshutdinova: J. Phys. A: Math. Gen. 38 (2005) 4715, in order to obtain electric fields with a time-dependent frequency for which the equation of motion of a two-level atom in the presence of these fields can be solved exactly. We show that a polynomial pseudosupersymmetry may be associated to such chains. Presented at the 3rd International Workshop “Pseudo-Hermitian Hamiltonians in Quantum Physics”, Istanbul, Turkey, June 20–22, 2005.     

Force acting on an atom and a classical oscillator in an electromagnetic field

The expression for the force exerted by the field on an atom and averaged over the field period is derived in quantum-mechanical perturbation theory, in which a quasi-monochromatic electromagnetic field plays the role of a perturbation. An approximate solution is obtained to the classical (Newton) equation of motion in the same field for a harmonic isotropic oscillator. In both problems, the expressions for the force acting on a particle are completely identical if they are written in terms of the polarizability (of the atom and the oscillator). These results conform with the data obtained in macroscopic electrodynamics for rarefied media.     

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.     

Excitation and ionization of sodium clusters by a strong electromagnetic field

This paper reports on a study of the excitation and ionization of small sodium clusters by femtosecond light pulses with a maximum intensity of 5×10¹²–1×10¹⁴ W/cm² and photon energy from 1 to 3 eV made in terms of the density functional theory and jellium model through direct numerical solution of the Kohn-Sham time-dependent equation. The dependence of the degree of ionization on the intensity, duration, and frequency of the light pulses, as well as on the cluster size, is studied. The efficiency of the processes is shown to be determined primarily by the field intensity rather than by the total pulse energy.     

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)     

Excitation of an atom in a nonstationary cavity

The effect of excitation of an atom in an initially photon-free nonstationary cavity is predicted. Two excitation mechanisms are considered, both different from the trivial absorption of photons created due to the nonstationary Casimir effect. The first one is based on the fact that the photon states appear simultaneously with atomic excitation if the characteristic time of cavity nonstationarity is of the same order as the atomic transition time. The second one is associated with the “shake-up” effect caused by the modulation of the atomic ground-state Lamb shift upon a fast change in the cavity parameters. The presence of an atom in the nonstationary cavity affects the photon creation process. In particular, it changes the average number of generated photons and removes the constraint (inherent in the nonstationary Casimir effect) that only an even number of photons can be created. In addition, a new mechanism of photon generation associated with the shake-up effect appears.     

Ionization of a two-electron atom in a strong electromagnetic field

A one-dimensional model of a helium atom in an intense field of a femtosecond electromagnetic pulse has been constructed using the Hartree technique. “Exact” calculations have been compared to the approximations of “frozen” and “passive” electrons. A nonmonotonic dependence of the single-electron ionization probability on the radiation intensity has been detected. Minima in the ionization probability are due to multiphoton resonances between different atomic states due to the dynamic Stark effect. We suggest that the ionization suppression is due to the interference stabilization in this case. Zh. éksp. Teor. Fiz. 112, 470–482 (August 1997)     

Excited hydrogenic atom in a strong low-frequency electromagnetic field

The multiphoton ionization of a bound electron state which is twofold degenerate with respect to its orbital angular momentum is considered in a quasiclassical approximation. It is shown that the ionization probability increases strongly in an intense electromagnetic field, in which nonresonant mixing of the levels forming the degenerate state is significant, in comparison to the case described by the Keldysh formula. It is also shown that such degeneracy leads to a sharp increase in the intensity of the radiation scattered by the bound electron, and the high-frequency cutoff of the emission spectrum is shifted to higher frequencies. Zh. Tekh. Fiz. 69, 15–20 (August 1999)     

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.     

Helium atom in the monochromatic electromagnetic field

We apply a non-perturbative procedure for the calculation of the total photoionization cross-section of two-electron atomic systems. The procedure is based on the Floquet-Fourier representation of the time-dependent Schr?dinger equation. With the use of the Hylleraas-type basis functions, the total photoionization cross-sections obtained are within the accuracy of a fraction of a percent, which, we believe, is the most accurate estimate for the cross-sections available. The total photoionization cross-sections for neutral helium deviate notably from the benchmark experimental data [J.A.R. Samson et al., J. Phys. B 27, 887 (1994)].     

Excitation of natural oscillations in bounded media by a stream of electrons or the energy of an electromagnetic field

The problem is solved concerning the excitation of natural electromagnetic oscillations in a semiconductor or a dielectric layer by the action of charged particles or quanta of an electromagnetic field. The increments of buildup in the case of quasiresonance interaction of the surface and body plasmons are determined. The excitation of a dielectric waveguide by an electron beam is investigated. The possibility is shown for generating excitons in a dielectric layer by an external electromagnetic wave.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 21, No. 12, pp. 1840–1845, December, 1978.