arXiv subjects

V. N. Ostrovsky

Publications and source records attributed to V. N. Ostrovsky.

10 recordsLinked to original sources

arXiv2006

Exact results for state-to-state transition probabilities in the multistate Landau-Zener model by non-stationary perturbation theory

Multistate generalizations of Landau-Zener model are studied by summing entire series of perturbation theory. A new technique for analysis of the series is developed. Analytical expressions for probabilities of survival at the diabatic potential curves with extreme slope are proved. Degenerate situations are considered when there are several potential curves with extreme slope. New expressions for some state-to-state transition probabilities are derived in degenerate cases.

cond-mat.other↗

arXiv2000

Atomic antenna mechanism in HHG and ATI

This paper reviews recent development of the atomic antenna, a theoretical framework which describes a number of laser-induced multiphoton phenomena in atoms, in particular in High Harmonic Generation and in Above Threshold Ionization. The paper presents a progress report made at the conference "Atoms, molecules and quantum dots in laser fields: fundamental processes", PISA, Italy, June 12-16, 2000

physics.atom-ph↗

arXiv2000

Comment on "Degenerate Wannier Theory for Multiple Ionization"

Recent Letter of T.Pattard and J.M.Rost (Phys.Rev.Lett 80, 5081 (1998)) suggests that there exist logarithmic corrections to the near threshold cross section for the processes of break up of a particle into several charged fragments. This comment shows that it is incorrect, the logarithmic terms never exist. The cross section for all processes behaves as some power of the above-threshold energy, similarly to the known Wannier problem.

physics.atom-ph↗

arXiv2000

Effective ATI Channels in High Harmonic Generation

Harmonic generation by an atom in a laser field is described by the three-step mechanism as proceeding via above-threshold ionization (ATI) followed by the electron propagation in the laser-dressed continuum and the subsequent laser assisted recombination (LAR). An amplitude of harmonic production is given by the coherent sum of contributions from different intermediate ATI channels labeled by the number m of absorbed laser photons. The range of m-values that gives substantial contribution is explored and found to be rather broad for high harmonic generation. The coherence effects are of crucial importance being responsible for the characteristic pattern of harmonic intensities with a plateau domain followed by a cutoff region. Due to multiphoton nature of the process, an efficient summation of m-contributions can be carried out in the framework of the saddle point method. The saddle points correspond to some complex-valued labels m=m_c associated with the intermediate effective ATI channels in the three-step harmonic generation process. The advantage of this approach stems from the fact that summation over large number of conventional ATI m-channels is replaced by summation over small number of effective m_c-channels. The equation governing m_c has a transparent physical meaning: the electron ejected from the atom on the first (ATI) stage should return to the core to make LAR possible. The calculated rates are in good agreement with the results obtained by other approaches.

physics.atom-ph↗

arXiv1999

Multiphoton radiative recombination of electron assisted by laser field

In the presence of an intensive laser field the radiative recombination of the continuum electron into an atomic bound state generally is accompanied by absorption or emission of several laser quanta. The spectrum of emitted photons represents an equidistant pattern with the spacing equal to the laser frequency. The distribution of intensities in this spectrum is studied employing the Keldysh-type approximation, i.e. neglecting interaction of the impact electron with the atomic core in the initial continuum state. Within the adiabatic approximation the scale of emitted photon frequencies is subdivided into classically allowed and classically forbidden domains. The highest intensities correspond to emission frequencies close to the edges of classically allowed domain. The total cross section of electron recombination summed over all emitted photon channels exhibits negligible dependence on the laser field intensity.

physics.atom-ph↗

arXiv1999

Quantum theory of a high harmonic generation as a three-step process

Fully quantum treatment explicitly presents the high harmonic generation as a three-step process: (i) above threshold ionization (ATI) is followed by (ii) electron propagation in a laser-dressed continuum. Subsequently (iii) stimulated (or laser assisted) recombination brings the electron back into the initial state with emission of a high-energy photon. Contributions of all ATI channels add up coherently. All three stages of the process are described by simple, mostly analytical expressions that allow a detailed physical interpretation. A very good quantitative agreement with the previous calculations on the harmonic generation by H-minus ion is demonstrated, thus supplementing the conceptual significance of the theory with its practical efficiency. The virtue of the present scheme is further supported by a good accord between the calculations in length and velocity gauges for the high-energy photon.

physics.atom-ph↗

arXiv1999

Quantum Theory of High Harmonic Generation via Above Threshold Ionization and Stimulated Recombination

Fully quantum treatment explicitly presents the high harmonic generation as a three-stage process: above threshold ionization (ATI) is followed by the continuum electron propagation in a laser field and subsequent stimulated recombination back into the initial state. The contributions of all ATI channels add up coherently. All three stages of the process are described by simple, mostly analytical expressions. A very good quantitative agreement with the previous calculations on the harmonic generation by H$^-$ ion is demonstrated, thus supplementing the conceptual significance of the theory with its practical efficiency.

physics.atom-ph↗

arXiv1998

Adiabatic Theory of Electron Detachment from Negative Ions in Two-Color Laser Field

Negative ion detachment in bichromatic laser field is considered within the adiabatic theory. The latter represents a recent modification of the famous Keldysh model for multiphoton ionization which makes it quantitatively reliable. We calculate angular differential detachment rates, partial rates for particular ATD (Above Threshold Detachment) channels and total detachment rates for the Hydrogen ion in a bichromatic field with 1:3 frequency ratio and various phase differences. Reliability of the present, extremely simple approach is testified by comparison with much more elaborate earlier calculations.

physics.atom-ph↗

arXiv1998

Threshold Laws for the Break-up of Atomic Particles into Several Charged Fragments

The processes with three or more charged particles in the final state exhibit particular threshold behavior, as inferred by the famous Wannier law for (2e + ion) system. We formulate a general solution which determines the threshold behavior of the cross section for multiple fragmentation. Applications to several systems of particular importance with three, four and five leptons (electrons and positrons) in the field of charged core; and two pairs of identical particles with opposite charges are presented. New threshold exponents for these systems are predicted, while some previously suggested threshold laws are revised.

physics.atom-ph↗

arXiv1997

Electron detachment from negative ions in bichromatic laser field

Negative ion detachment in two-colour laser field is considered within the recent modification of Keldysh model which makes it quantitatively reliable. The general approach is illustrated by calculation of angular differential detachment rates, partial rates for particular ATD (Above Threshold Detachment) channels and total detachment rates for H$^-$ ion in bichromatic field with 1:2 frequency ratio. Both perturbative and strong field regimes are examined. Polar asymmetry and phase effects are quantitatively characterized with some new features revealed. Phase effects are found to result in a huge anisotropy factor $\sim 10^3$ in the electron angular distribution in the perturbative regime.

physics.atom-ph↗