Laser modified processes: bremsstrahlung and inelastic photon–atom scattering Olimpia Budriga, Mihai Dondera, Viorica Florescu * Department of Physics, University of Bucharest, P.O. Box MG-11, 76900 Bucharest-Magurele, Romania Available online 28 March 2007 Abstract We consider the influence of a low-frequency monochromatic external electromagnetic field (the laser) on two basic atomic processes: electron Coulomb bremsstrahlung and inelastic photon scattering on an electron bound in the ground state of a hydrogenic atom. We briefly describe the approximations adopted and illustrate in figures how the laser parameters modify the shape of the differential cross- sections and extend the energy domain for emitted electrons, due to simultaneous absorption or emission of a large number (hundreds) of laser photons. Ó 2007 Elsevier B.V. All rights reserved. PACS: 34.50.Rk; 32.80.Rb Keywords: Laser; Bremsstrahlung; Inelastic photon–atom scattering 1. Introduction Atomic physics with intense electromagnetic sources includes not only induced processes but also modified pro- cesses. These are basic atomic processes possible in the absence of the external field, which could be strongly affected by its presence. The most studied process from this category is electron–atom scattering [1]. In this paper we use the term laser for the external elec- tromagnetic field in the presence of which we consider the modification of two basic atomic processes: spontaneous bremsstrahlung and inelastic scattering of photons. In bremsstrahlung, in the absence as well in the presence of the laser, the electron emits one photon in a free–free transition. The electron states are modified (dressed) by the laser. In photon scattering a photon of angular fre- quency x 1 from a weak intensity source is scattered by an electron and comes out with a different frequency x 2 . If the electron was bound it will become free. The presence of the laser modifies the values of the specific cross-sections of the processes and also the possible range of final photon and electron energy. In the usual description, which is based on a classical treatment of the laser field, the theoretical results have a structure which corresponds to the simple physical inter- pretation of an exchange of laser photons between the laser and the atomic system. In Section 2 we present briefly the formalism and the approximations implied by a nonrelativistic description of the two processes. Section 3 refers to the case of brems- strahlung, for which more details can be found in two of our recent publications [2,3]. In Section 4 we present results from recent nonrelativistic calculations of laser assisted inelastic photon scattering on ground state atomic hydrogen. 2. The theoretical framework In both processes, bremsstrahlung and photon scatter- ing, one photon is emitted spontaneously, due to the electron interaction with the atomic field in the first case and to the 0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.03.046 * Corresponding author. Tel.: + 40 457 4419; fax: + 40 457 4521. E-mail address: flor@barutu.fizica.unibuc.ro (V. Florescu). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 261 (2007) 180–183 NIM B Beam Interactions with Materials & Atoms