The production of electron-positron pairs from vacuum by counterpropagating laser beams of linear polarization is calculated. In contrast to the usual approximate approach, the spatial dependence and magnetic component of the laser field are taken into account. We show that the latter strongly affects the creation process at high laser frequency: the production probability is reduced, the kinematics is fundamentally modified, the resonant Rabi-oscillation pattern is distorted and the resonance positions are shifted, multiplied and split. PACS numbers: 42.50.Hz;42.55.Vc;12.20.Ds In the presence of very strong electromagnetic fields the quantum electrodynamic vacuum becomes unstable and decays into electron-positron (e + e − ) pairs [1]. This phenomenon has been realized experimentally, e.g., in relativistic heavy-ion collisions [2]. Shortly after the invention of the laser almost 50 years ago, theoreticians began to study e + e − pair production by intense laser light [3]. Because of the remarkable progress in laser technology during recent years, the interest in the process has been revived since an experimental investigation of pair creation by pure laser light is coming into reach. The only observation of laser-induced pair production until now was accomplished ten years ago at SLAC (Stanford, California), where a 46 GeV electron beam was brought into collision with an intense optical laser pulse [4]. In this experiment, a γ-photon produced via Compton scattering or the electron Coulomb field assisted the laser beam in the pair production.The most simple field configuration for realization of purely laser-induced pair production consists of two counterpropagating laser pulses of equal frequency and intensity (see [5,6,7,8] and references therein). The resulting standing wave is inhomogeneous both in time and in space which represents a formidable task for the nonperturbative quantum field theory, see e.g. [9]. All theoretical investigations so far have approximated the standing laser wave by a spatially homogeneous electric field oscillating in time. This dipole approximation is expected to be well-justified in optical laser fields, where the wavelength is much larger than the typical length scale of the process: λ ≫ l ∼ 2m/(|e|E) in natural units ( = c = 1) which are employed throughout. In terms of the relativistic parameter ξ = |e|E/(mω), this relation corresponds to ξ ≫ 1. Here E and ω are the laser field and its frequency, e and m the electron charge and mass, respectively. Meanwhile the experimental realization of laser-induced pair production is also extensively discussed in connection with upcoming x-ray freeelectron laser (XFEL) facilities [7,8]. In this case, however, the laser frequency is high, ξ 1 and the magnetic field component is not negligible. The latter, in general, can have an important influence on the pair creation process. This is most evidently demonstrated by the fact that a single plane laser wave cannot extract pairs from the vacuum, whereas a purely electric field can. In this Le...

No abstract

No abstract

By numerically solving the relativistic equations of motion of a single electron in laser fields modeled by those of a Gaussian beam, we demonstrate electron capture by, reflection from, and transmission through the beam. In modeling the fields, terms of order up to 5 , where is the diffraction angle, are retained. All cases of capture are accompanied by energy gain that may reach a few GeV, from fields of present-day intensities. Reflection and transmission, on the other hand, result sometimes in no gain or even in a loss of energy. It is shown that a laboratory static magnetic field may be used to eject a captured electron, a process that sometimes results in even more energy gain. For example, a 2.5 T uniform magnetic field suffices to eject a 3.633 MeV electron injected at 6 to the axis of a linearly polarized beam of a 10 PW power output and aimed at a point near the focus. Such an electron gains 1128 MeV from the laser field alone. However, it emerges with a 1230 MeV net energy gain under the additional action of the small magnetic field.

No abstract