Ionization of a molecular hydrogen ion by a strong low-frequency electromagnetic field of laser radiation

Simple analytical expressions are obtained for the energy and angular distributions of outgoing electrons in ionization of a molecular hydrogen ion by a strong low-frequency electromagnetic field as well as for the ionization probabilities per unit time. The cases of linear and circular polarization of the laser radiation are studied. It is shown that in contrast to the case of the ionization of atoms oscillations appear in the energy spectra of the photoelectrons as a function of their kinetic energy. The well-known limits for the tunneling ionization probabilities for the hydrogen atom by a strong low-frequency alternating field are obtained in the case of large internuclear separations. Zh. é ksp. Teor. Fiz. 113, 583–592 (February 1998)     

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)     

Ionization and stabilization of atoms in a high-intensity,low-frequency laser field

The dynamics of a model silver atom in the strong radiation field of a Ti:sapphire laser is studied in the Keldysh parameter regions γ ⩾ 1 and γ ⩽ 1. It is found that in the entire range of Keldysh parameter variations, along with ionization, the efficient excitation of Rydberg states of the atom with principal quantum numbers n = 6−14 is observed. A Rydberg wavepacket appearing in this case proved stable with respect to ionization; i.e., the atomic system in strong low-frequency electromagnetic fields becomes stable with respect to ionization. The physical reasons behind the stabilization are discussed.     

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)     

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

Direct numerical simulations are performed to analyze stabilization of a two-electron model atom in a strong electromagnetic field. The system is found to be stabilized with respect to both single and double ionization. By comparing the present results with those concerning stability of one-electron atoms, it is shown that stabilization is due to the formation of a Kramers-Henneberger two-electron atom. Ionization and stabilization characteristics of excited singlet and triplet states of an atomic system are examined.     

Ionization of a hydrogen-like ion by a strong low-frequency linearly polarized laser field

The influence of the long-range Coulomb potential on the ionization rate of a hydrogen-like ion has been investigated within the framework of the quasi-classical method. In a rather strong field, the dependence of the ionization rate on the field intensity does not have a purely power-law character in the multiphoton region. The analytical equations obtained are in agreement with the experimental data on the cross section of multiphoton ionization and give an estimate of the threshold field values in the tunneling region.     

Ionization equilibrium of atoms in a strong magnetic field (the saha formula)

The effect of an external magnetic field on the ionization equilibrium of atoms in the nondegenerate nonrelativistic plasma is examined. When taken into account that the interaction of the magnetic moments of electrons with the magnetic field immediately changes their kinetic energy, which is incorrect, the degree of ionization of atoms will increase with increase in the magnetic field strength compared to the atomic concentration in the absence of a magnetic field at the same temperature. When taken into account that this energy changes in view of the Pauli principle and spontaneous minimization of the quantum system, the degree of ionization must decrease with increase in the external magnetic field strength, that is, a strong magnetic field suppresses ionization of atoms in the nonrelativistic plasma at a given temperature. Byelorussian State University; Brest State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 36–39, July, 1999.     

Ionization in a quantized electromagnetic field

An analytical expression for a matrix element of the transition from a bound state of an electron in an atom to continuum states is obtained by solving the problem of interaction of the electron with a quantized electromagnetic field. This expression is used to derive formulas for the photoelectron spectrum and the rate of ionization of the simplest model atomic system upon absorption of an arbitrary number of photons. The expressions derived are analyzed and compared with the corresponding relationships obtained via other approaches. It is demonstrated that there are differences as compared to the case of the classical field. In particular, the photoelectron spectrum exhibits dips due to the destructive interference of the transition amplitudes in the quantized electromagnetic field.     

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.     

Ionization of lithium in a strong laser field

In this work, we present ab initio computations of the interaction of helium and lithium with a strong laser field. By computing the two-and three-particle wave functions, we retain the full electron correlation and numerically integrate the time-dependent Schrödinger equation (TDSE) restricted to one dimension. The correlated nonsequential double ionization (NSDI) and the sequential double ionization (SDI) is studied. Our results show a clear transition from NSDI to SDI for increasing intensities. The correlated double ionization is found to be sensitive to the spin configuration of the ionized pair. Our model allows us to “measure” two different channels of double ionization (one with both spins aligned and one with spins antialigned).     

Quantum system in a strong electromagnetic field

We have used a projection operator technic to derive approximate analytical expressions for the quasi-energies and quasi-energy states of a multilevel system in a strong electromagnetic field.Translated from Izvestiya Vyssh'ikh Uchebnykh Zavednii, Fizika, No. 3, pp. 84–89, March, 1978.We thank R. Galimzyanov and E. Gandyl' for carrying out the machine calculation.     

Lorentz ionization of atoms in a strong magnetic field

Lorentz ionization emerges due to the motion of atoms or ions in a strong magnetic field. We use the semiclassical approximation to calculate the probability w _L of Lorentz ionization. We also find the stabilization factor S, which takes into account the reduction by the magnetic field of the probability of ionization decay of the bound s state. We estimate the probabilities w _L in magnetic-cumulation experiments and in astrophysics. We also qualitatively examine the dynamics of the magnetic cumulation process with allowance for the conductivity of the shell. Finally, we discuss a paradox related to the use of the quasistationary solution at the shell expansion stage. Zh. éksp. Teor. Fiz. 115, 1642–1663 (May 1999)     

Spontaneous emission of atoms in a strong laser field

The spontaneous emission of an atomic system in the field of a high-intensity femtosecond laser pulse is considered within the framework of a consistent quantum-mechanical approach based on an examination of the interaction of a quantum system with a set of quantized field modes in a vacuum state. Both even and odd harmonics of the driving field are shown to appear in the atomic emission spectrum, and the mechanisms of their generation are elucidated. A comparison with the semiclassical theory of laser harmonic generation is made. The semiclassical approach in describing the spontaneous emission in strong laser fields, especially under conditions of significant depletion of the ground (initial) state in a laser field, is shown to be limited.     

Influence of local relief on a low-frequency electromagnetic field

Leningrad State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 33, No. 1, pp. 17–21, January, 1990.