Inelastic processes and interference effects during the interaction of positronium with ultrashort electromagnetic pulse
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Inelastic Processes and Interference Effects during the Interaction of Positronium with Ultrashort Electromagnetic Pulses M. K. Eseev* and V. I. Matveev** Lomonosov Northern (Arctic) Federal University, Arkhangelsk, 163002 Russia *email: [email protected] **email: [email protected] Received May 23, 2013
Abstract—The excitation, breakup, and reradiation during the interaction of a positronium atom with ultrashort electromagnetic pulses are considered. The probabilities of inelastic processes and reradiation spectra have been obtained. The interference between the amplitudes of the photon emission by the electron and positron is shown to contribute noticeably to the reradiation spectra. The developed approach is appli cable for describing the interaction of positronium with ultrashort pulses of attosecond or shorter duration. DOI: 10.1134/S1063776113130037
1. INTRODUCTION The positronium atom, which is the bound state of an electron and a positron, is a unique object of inves tigation in quantum electrodynamics [1, 2]. This exotic atom composed of a lepton and an antilepton allows new information about the nature of the elec troweak interaction, the processes involving antiparti cles, and the annihilation of antimatter to be obtained. Among the exotic atoms, positronium was the first to be produced experimentally [3], and its studies con tinue in a number of laboratories worldwide [4–6]. The laser excitation of positronium atoms to Rydberg states, in which the atoms can exist for a fairly long time, arouses particular interest [7]. Considerable progress in the generation and use of ultrashort elec tromagnetic pulses [8, 9] stimulates the studies of the behavior of positronium in the fields of ultrashort pulses. The probability of positronium ionization by femtosecond laser pulses was calculated by the meth ods of direct numerical integration of the timedepen dent Schrödinger equation in [10–12]. The Keldysh model for the Volkov wave functions with Coulomb corrections was compared in [13] with the numerical solution of the timedependent Schrödinger equation when inelastic processes in a positronium atom in a femtosecond laser field were calculated. In addition to using the Keldysh model, Borbely et al. [14] numeri cally solved the classical equations of motion for parti cles by the Monte Carlo method to describe the positronium ionization. The pulse duration in this case was ~100 as. Apart from the excitation and ion ization, the electromagnetic field scattering from positronium is being actively investigated. The absorp tion and emission of photons in a positronium atom including the polarization was considered in terms of quantum electrodynamics, for example, in [15]. Since
the positronium atom is free from the relativistic drift of the electron relative to the positron in the field of an intense electromagnetic wave, it is of interest from the viewpoint of high harmonic generation capabilities [16]. The cross section for Compton scattering of Xray photons from positronium
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