Alexei Ermolaev

Relativistic effects in the time evolution of a one-dimensional model atom in an intense laser field

Using a B-spline expansion in momentum space, we have solved the time-dependent Dirac equation numerically for a model, one-dimensional atom which is subjected to an ultra-intense, high-frequency laser field. We find that for a peak electric field strength of 175 atomic units (au) and for angular frequencies of 1 and 2 au, relativistic effects start to become apparent. Even under these extreme conditions the wavefunction remains localized in a superposition of field-free bound states and very-low-energy continuum states. Comparing our results with the numerical solution of the time-dependent Schrodinger equation, we find that the Dirac wavefunction is slightly more stable against ionization. We also find that the energy distribution of the ionized electrons is strongly concentrated near threshold and that a cut-off in the high-energy spectrum occurs at the energy corresponding to the maximum momentum of a classical electron in the laser field.

Theoretical studies of antihydrogen formation in collisions between positronium atoms and antiprotons

The current state of the theoretical methods that are used in calculations of cross sections for the production of antihydrogen in collisions between antiprotons and positronium atoms is reviewed. A broad outline of available methods together with the results of recent computations are presented. The main emphasis is made on the general close-coupling approach that allows any reaction channel to be taken as the initial state of the collision system. In this way, and on account of charge-conjugation invariance, the formation of antihydrogen in collisions between antiprotons and positronium atoms becomes linked to positron-hydrogen scattering and the same computational methods can be applied to either reaction. The review gives references to recent papers on the subject.

Atomic states in the relativistic high-frequency approximation of Kristic - Mittleman

The three-dimensional atomic potentials in the presence of a superintense laser field have been discussed within the relativistic high-frequency approximation of Kristic and Mittleman. Using a one-dimensional model, similar to that employed by Kylstra, Ermolaev and Joachain in ab initio calculations on the time-dependent Dirac equation, the electron mass shift due to dressing by a superstrong laser field is investigated. In the full domain of the laser parameters, frequency and the peak field strength , the one-dimensional bound states exhibit remarkable features. The numerical calculations show the existence of a very wide intermediate range of field strengths where, in the zeroth-order of the high-frequency approximation, the binding is stabilized by the field.

Close-coupled calculations of collisions at intermediate and high energies and applications to JET plasmas

The close-coupling method based on semiclassical impact parameter theory has been applied to collisions in the range of proton impact energies from 30 keV through to 10 MeV. The cross sections for hydrogen production, target excitation and ionization have been computed using two-centre AO expansions with up to 55 atomic states and pseudostates. The results can be used as reference data for further close-coupling studies of the system as well as for assessing the validity range and accuracy of various perturbational models at both intermediate and high energies. Applications to current plasma research at JET where accurate data are required for diagnostic purposes, are discussed.

A semi-relativistic eikonal distorted wave model for collisions of fast highly charged ions with light atomic targets

We propose a semi-relativistic symmetric eikonal distorted wave method for treating collisions of fast projectiles with light atomic targets. The projectile interaction with target electrons is described by the Li?nard?Wiechert potential, within the impact parameter approach. Our model allows one to estimate two-centre effects in fast heavy-particle collisions. It is found that in the dipole approximation the first-order eikonal cross sections differ from the corresponding Born cross sections by a simple factor that accounts for the forward?backward asymmetry of the ejected electron with respect to the direction of the projectile motion. As an illustration of our method we have carried out calculations for single ionization in collisions of fast U92+ ions (1?GeV?u?1) with helium targets.

Sums of products of Coulomb wave function over degenerate states

The sums of products of Coulomb wave function over degenerate states are expressed in terms of quadratic forms that depend on the wave function of only one state with zero orbital angular momentum l = m = 0. These sums are encountered in many fields in the physics of atoms and molecules, for example, in investigations of the perturbation of degenerate atomic energy levels of a small potential well, a delta-function potential. The sums were found in an investigation of the limit of the Coulomb Green’s function G(r, r′, E), where the energy parameter E approaches an atomic energy level: E → En, En = −Z2/2n2. The Green’s function found by L. Hostler and R. Pratt in 1963 was used. The result obtained is a consequence of the degeneracy of the Coulomb energy levels, which in turn is due to the four-dimensional symmetry of the Coulomb problem.

Single ionization of the 1 1Se and 2 1Po states of He by 1-GeV/u U92+ ions

We report calculations of the cross sections for single ionization of the ground 1 1 S and excited 2 1 P helium states by relativistic impact of a bare uranium ion of charge Z p = 92 with energy 1 GeV/u. The heavy particle collision is treated within the semirelativistic first Born approximation. The nonrelativistic initial and final two-electron correlated atomic states are obtained by numerical procedures from variational principles. The continuum final states are considered below the n=2 threshold of the He + ion The differential ionization cross section dσ/dE is obtained for electron energies E≤37 eV. This energy range includes a wide nonresonant region as well as the resonance structures due to the autoionizing helium states (2s 2 ) 1 S, (2s2p) 1 P and (2p 2 ) 1 D.

Single ionization of the [Formula Presented] and [Formula Presented] states of He by 1-GeV/u [Formula Presented] ions

We report calculations of the cross sections for single ionization of the ground 1 1 S and excited 2 1 P helium states by relativistic impact of a bare uranium ion of charge Z p = 92 with energy 1 GeV/u. The heavy particle collision is treated within the semirelativistic first Born approximation. The nonrelativistic initial and final two-electron correlated atomic states are obtained by numerical procedures from variational principles. The continuum final states are considered below the n=2 threshold of the He + ion The differential ionization cross section dσ/dE is obtained for electron energies E≤37 eV. This energy range includes a wide nonresonant region as well as the resonance structures due to the autoionizing helium states (2s 2 ) 1 S, (2s2p) 1 P and (2p 2 ) 1 D.

Single ionization of the 1 {sup 1}S{sup e} and 2 {sup 1}P{sup o} states of He by 1-GeV/u U{sup 92+} ions

We report calculations of the cross sections for single ionization of the ground 1 1 S and excited 2 1 P helium states by relativistic impact of a bare uranium ion of charge Z p = 92 with energy 1 GeV/u. The heavy particle collision is treated within the semirelativistic first Born approximation. The nonrelativistic initial and final two-electron correlated atomic states are obtained by numerical procedures from variational principles. The continuum final states are considered below the n=2 threshold of the He + ion The differential ionization cross section dσ/dE is obtained for electron energies E≤37 eV. This energy range includes a wide nonresonant region as well as the resonance structures due to the autoionizing helium states (2s 2 ) 1 S, (2s2p) 1 P and (2p 2 ) 1 D.

Relativistic theory of atom-laser interactions at very high laser intensities

The high-frequency approximation of Kristić and Mittleman is considered in detail as a basis for the relativistic theory of atom-laser interactions. The properties of the 3D potentials are discussed. Within a one-dimensional model similar to that employed by Kylstra, Ermolaev, and Joachain in ab initio calculations on the time-dependent Dirac equation, the electron mass-shift due to dressing by a superstrong laser field is investigated. In the full domain of the laser parameters, the frequency ω and the peak field strength ℰ0, the 1D bound states exhibit remarkable features. The numerical calculations show the existence of a very wide intermediate range of the field strengths where, in the zeroth order of the high-frequency approximation, the binding is stabilized by the field.