B. A. Zon

Dynamic polarizabilities of atoms in their low-excited states : He, Be, Mg and Ca

The quantum defect Green function formalism is applied to calculate the dynamic scalar and tensor polarizabilities of some atoms in their excited states (21S, 23S, 21P and 23P for He, 21P and 23P for Be, 33P for Mg and 43P for Ca). Experimental and calculated oscillator strength values were used to provide an account for low-excited states (reduce–adding correction of the Green function) while the high-excited and continuum states are accounted semi-analytically. The calculated polarizability values are in good (within several per cent) agreement with the available experimental data and the ab initio numerical data.

Depolarization of laser radiation in a nonlinear medium

A new phenomenon of statistical nonlinear optics is investigated theoretically and experimentally: The diminishing degree of linear polarization of incoherent and/or inhomogeneous laser radiation propagating in a nonlinear medium and with a square-law dependence on radiation intensity

The effect of space charge in ion mobility spectrometry

We present the study of expansion of an ion cloud in the process of its drift in the ion mobility spectrometer taking into account the influence of diffusion and electric field of the space charge of the ion cloud. Nonlinear integro-differential equation describing these effects was obtained and solved numerically in the one-dimensional case. We found a threshold value of the ion density, above which the nonlinear effects associated with the space-charge field become significant, which agrees well with the experimental data and the criterion of Spangler. These nonlinear effects lead to the fact that the spatial ion distribution ceases to be Gaussian, and with good accuracy are approximated by the distribution of Kohlrausch–Williams–Watts.

Oscillator strengths for Rydberg states in ArH calculated in QDT approximation

Abstract With the help of a simple semi-analytical procedure the oscillator strengths for Rydberg electronic transitions in the ArH molecule are calculated by accounting for the effects of non-spherical symmetry of the molecular core’s field due to its dipole moment. Such effects result in non-zero oscillator strength values for some transitions which are forbidden in the widely used atom-like model of molecular Rydberg states. For the allowed transitions we also report the difference between the atom-like calculations and the calculations which take into account the dipole moment of the molecular core.

Magnetic-field induced generation of A-like centers in Cz-Si crystals

Abstract The effect of the constant magnetic-field induced generation of oxygen–vacancy defects in Czochralski-grown silicon crystals was detected for the first time. The qualitative theory of the effect is given. It assumes that the effect arises from excitation of the Si–O bond of interstitial oxygen and is valid for both constant and pulsed magnetic fields. Experimental verification of the theory in the combined constant and pulsed fields strongly confirmed it.

Diabatic Rydberg states in polar molecules with a complex core

Based on a new solution of the Schrodinger equation for an electron in Coulomb + rotating dipole potential, diabatic (inverse Born-Oppenheimer) Rydberg states are treated in polar molecules. The obtained exact solution contains explicit dependence on the molecular core coupling scheme which is considered to be intermediate between Hunds (a), (c) and (b) cases. Analytical expressions are derived for the diabatic quantum defects of the Rydberg states in polar molecules with such a complex core.

The influence of a permanent dipole moment on the tunnelling ionization of a CO molecule

We show that the linear Stark effect due to a molecule permanent dipole moment does not influence the rate of molecule ionization by laser radiation in the multiphoton limit. However, it may influence the ionization rate in the tunnelling limit. A CO molecule is considered as an example. Its valence orbitals have σ symmetry. In this case, the tunnel effect rate is maximal if the permanent dipole moment (the molecule axis) is oriented along the direction of the laser-wave electric field, and the role of the linear Stark effect is the most noticeable. This situation differs from that when the valence orbitals have π symmetry which we have considered previously (Kornev and Zon 2014 Laser Phys. 24 115302). In that case, the tunnel effect rate is maximal if the molecule axis is oriented perpendicularly to the electric field direction and the role of the linear Stark effect is less significant. We consider the tunnel effect in both dc and ac fields, accounting for perturbation of vibrational motion by an external field. We show that the influence of the permanent dipole moment does not vanish even after averaging the tunnelling rate over the molecule orientations.

Pseudopotential calculations of photoionization of atoms in the x-ray photon energy range and FEL beam monitor development

A pseudopotential model for calculation of atomic processes under interaction with hard x-ray photons is applied to calculation of Krypton photoionization cross sections?by photons with energy in the 20?25?keV range. These cross sections, as well as the mean charge of the resulting ions calculated using the Monte Carlo simulation scheme, are in good agreement with the other theoretical calculations and with the experiment. The obtained results open the doors for new techniques in the design of gas-monitor detectors to control the intensity, coordinates and energy of x-ray free-electron laser (XFEL) beams in the hard x-ray photon energy range. First, Monte Carlo simulations of a scintillation detector application for gas-monitors have been performed.

Light intensity modulation in phototherapy

A hypothesis that blocking ATP synthesis is one of the main causes of the stimulating effect is considered based on analysis of the primary photostimulation mechanisms. The light radiation intensity modulation is substantiated and the estimates of such modulation parameters are made. An explanation is offered to the stimulation efficiency decrease phenomenon at the increase of the radiation dose during the therapy. The results of clinical research of the medical treatment in preventive dentistry are presented depending on the spectrum and parameters of the light flux modulation.

Keldysh theory in a few-cycle laser pulse, inelastic tunneling and Stark shift: comparison with ab initio calculation

Combining the Keldysh theory for a few cycle laser pulse with the theory of the inelastic tunneling (Kornev A S and Zon B A 2012 Phys. Rev. A 85 035402) agrees very well with the ab initio simulations performed by Rohringer and Santra (2009 Phys. Rev. A 79 053402) for the Ne atom. However, for the heavier Xe atom, agreement between analytical and numerical theories is not satisfactory. To eliminate this disagreement, we took into account the Stark shift of atomic level energies. As a result, the agreement between analytical and numerical theories significantly improved, but for Ne, it became worse. We discussed possible causes of these disagreements.