F. Ehlotzky

Fundamental processes of quantum electrodynamics in laser fields of relativistic power

In this review we summarize our progress in the investigation of fundamental processes of quantum electrodynamics in laser fields of relativistic power in view of the more recent experimental progress in the generation of laser field intensities, yielding ponderomotive energy shifts Up of the order of magnitude mc2 and beyond. In particular, the generation of electron–positron pairs during the collision of laser pulses with ions or protons appears to become feasible.

Atomic phenomena in bichromatic laser fields

Abstract We present a review of work that has been done during the last 10 years on atomic scattering and reaction processes in bichromatic laser fields. Of particular interest will be the case where the field is composed of two components of commensurate frequencies, usually consisting of a fundamental component ω and one of its low harmonics 2 ω or 3 ω . These two components are in general out of phase by an angle ϕ . The above processes are then investigated as a function of the relative phase ϕ . This procedure was termed the coherent phase control (CPC) of the atomic process considered. The idea was originally born in molecular physics as a possible means to manipulate molecular reactions.

Electron–atom collisions in a laser field

Abstract The present work is a report on recent progress made in our understanding of electron–atom collisions in a laser field. To some extent it is a continuation of a previous review covering a somewhat larger subject (Can. J. Phys. 63 (1985) 907). We shall discuss the present status of investigations in this field from the theoretical as well as experimental point of view but most of the report will be devoted to an analysis of the various approximation schemes used at present in this field to describe the different aspects of laser-assisted electron–atom interactions. As the table of contents shows, most of the work done so far is treating the atom as a spectator, described by a potential and only very little has been achieved over the years to include the atomic structure into consideration since the inclusion of these structure effects poses considerable computational problems. Since, for example, multiphoton ionization and its inverse process laser-assisted recombination may be considered as one half of a scattering process, it is quite natural that some of the theoretical techniques described here are also of interest for the treatment of other multiphoton processes not considered here since there are several other recent reviews available on these topics.

Positronium decay in intense high frequency laser fields

Abstract The 2γ- and γ-decay probabilities of para- and ortho-positronium in an intense high frequency laser field are estimated and a rapid decrease of these probabilities with increasing field intensity is predicted.

Scattering phenomena in strong radiation fields. II

Several seemingly different scattering and absorption phenomena in the presence of a strong coherent electromagnetic background field are considered from a unifying point of view to elucidate the essential similarities and also the differences of these processes with regard to the induced nonlinear radiation effects. The consequences are discussed with respect to the possible physical implications and conditions of experimental verification.

Numerical calculations of the Delbrück scattering amplitude

SummaryFormulae for the imaginary part of the Delbrück scattering amplitude, derived by Kessler some years ago, and a simple fixed-angle dispersion relation, are used to calculate numerically the real and imaginary parts for energies between 1 and 20 MeV and scattering angles from 0 to 120‡ with an accuracy of at best 5 to 10%. Comparison is also made with some of the experimental data available and conclusions are drawn for future work.RiassuntoSi usano le formule per la parte immaginaria dell’ampiezza dello scattering di Delbrück, dedotte da Kessler qualche anno fa, ed una semplice relazione di dispersione ad angolo fisso, per calcolare numericamente le parti reale ed immaginaria per energie comprese fra 1 e 20 MeV ed angoli di scattering fra 0‡ e 120‡ con una esattezza dal 5 al 10% al massimo. Si fanno confronti con alcuni dei dati sperimentali disponibili e si traggono conclusioni per i futuri lavori.

S-matrix theory of above-threshold ionization in a bichromatic laser field

We apply the strong-field S-matrix theory to the above-threshold ionization (ATI) in a bichromatic linearly polarized laser field having frequencies and , and the relative phase between the laser field components. The presented theory includes both the Coulomb and rescattering effects. We compute and discuss the electron energy spectra for different angles between the momentum of the ionized electron and the polarization vector of the laser field. We found that the plateau for and for the backward emission of electrons extends up to , where is the ponderomotive energy of the first laser field component (assuming equal intensities of both components). There are no such high-energy electrons for , in contrast to the symmetry , valid in the monochromatic case. In the bichromatic case the ionization rates possess the more general symmetry property . Therefore, for we predict the emission of the high-energy electrons in the forward direction . In a bichromatic field the sidelobe structures are strongly influenced by quantum mechanical interference effects. We also explore the -dependence of the ionization rates for different relative phases , and for those energies which correspond to the classical cutoff law.

Modifications of the photoelectric cross section induced by an intense and coherent electromagnetic background field of very low frequency

Abstract We investigate the remarkable modifications and enhancements of the differential and total cross sections of the photoelectric effect, which are induced by an intense and coherent radiation field of very low frequency, into which the atom has been placed while absorbing an X-ray quantum.

COULOMB CORRECTIONS IN ABOVE-THRESHOLD IONIZATION IN A BICHROMATIC LASER FIELD

We calculate the total ionization rate as a function of the kinetic energy of electrons ionized by a bichromatic laser field in an above-threshold ionization process. An improved Keldysh-Faisal-Reiss model, which includes the Coulomb effects of the residual ions on the ionized electron, is used. We compare the results obtained using the length and the velocity gauge. In the case of the bichromatic laser field the phase-dependent effects are observed and a comparison with recent experiments is presented. A classical analysis of the rescattering cut-off laws in a bichromatic laser field is also given.

Electron-positron pair creation by powerful laser-ion interaction

Presently available high-power laser pulses of ponderomotive energy Up ≫ 2mc2 should permit the fundamental processes of quantum electrodynamics in such fields, in particular, the formation of electron-positron pairs in impacts of laser pulses with highly charged ions, to be observed. We evaluate the highly nonlinear production rates of this process and investigate the most favorable conditions of pair production, in particular, either along the direction of linear polarization or in the propagation direction of the laser pulse. For femtosecond radiation pulses, it is possible to represent the laser beam by a monochromatic and linearly polarized electromagnetic plane wave. This approximation considerably simplifies the calculations required.