Multiphoton stimulated bremsstrahlung for broad (in the momentum representation) electron wave packets in an ultrashort
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Multiphoton Stimulated Bremsstrahlung for Broad (in the Momentum Representation) Electron Wave Packets in an Ultrashort Laser Pulse Field I. A. Burenkov and O. V. Tikhonova Skobeltsyn Research Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia email: [email protected] Received October 27, 2009
Abstract—We consider features of absorption and emission of external laser field quanta by a broad (in the momentum representation) electron wave packet during its scattering from a potential center. Various scat tering modes for the electron wave packet in a highintensity laser field are analyzed using perturbation theory of potential energy. It is found that the absorption of laser field energy by an electron is substantially more effective as compared to the case of a plane wave. The important role of a number of interference effects asso ciated with the large width of the initial electron momentum distribution is demonstrated. DOI: 10.1134/S1063776110060038
1. INTRODUCTION Stimulated absorption and emission of laser field quanta by a free electron during scattering from a potential center is an important problem in the physics of interaction of ultrastrong laser fields with atomic– molecular systems. This phenomenon, which is known as stimulated bremsstrahlung (SB), was con sidered for the first time in [1] and subsequently ana lyzed in detail in [2] for the initial state of an electron chosen in the form of a plane wave. Later, analogous results were obtained by the Green function method in the lowfrequency limit [3]. A further generalization of the Bunkin–Fedorov approach was carried out by many authors [4–12]. Considerable attention was paid to analysis of multiple scattering events as well as col lective effects in scattering of electrons from atoms and ions in laser fields. In the rapid development of experimental facilities at present, laser radiation acting on a substance may be characterized by a superatomic intensity and ultrashort pulse duration on the order of a few optical periods. Interaction with such ultrashort laser pulses is responsible for specific features and new properties of familiar processes and phenomena. In particular, the interaction of an ultrashort pulse with nanostructures and clusters may lead to intense heating of the plasma formed during ionization. Electrons with energies of up to 5 keV were detected in experiments with IR laser radiation [13–16] as well as under the action of UV radiation [17, 18]. In the case of lowfrequency (IR) action, such a high degree of heating may be due to resonant absorption of laser radiation at the natural frequency of the collective selfconsistent potential produced in a cluster during ionization [19⎯21].
However, in the case of UV radiation, the plasma fre quency in an ionized cluster is too small and, hence, resonant absorption is impossible; the mechanism of heating and the factors responsible for the production of highenergy electrons are not completely clear [22]. One of the possible mechanisms e
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