Laser-atom interaction at high intensities
Laser-atom interaction at high intensities





Up to one decade ago, the phenomena occurring in the context of the interaction of atoms and radiation were theoretically well described by perturbation theory. Within the past decade, however, laser sources with peak intensities of the order of 10 16 W/cm2 have become experimentally feasible. In this intensity regime, the external laser field is comparable to the binding energies of the electrons, and therefore it can no longer be treated as a perturbation [1]. The inadequacy of this theory has also been confirmed by several experimental observations concerning high-intensity optical phenomena, already for fields of the order of 10 13 W/cm2 [2]. Therefore, matter in strong laser fields poses now a great challenge to both theoretical and experimental physicists, such that this field of research constitutes one of the most active areas within atomic physics. Apart from the understanding of the main effects like high-harmonic generation and ionization in this intensity regime, one expects possible applications for instance to plasma physics (in particular fusion)[3], particle physics [4], and x-ray sources [5].

Moreover, for laser intensities of the order of 10 18W/cm2, for typical frequencies, the kinetic energy transferred to the atomic system by the field is of the order of the rest mass of the electron [6]. Thus, the laser-atom interaction needs a relativistic treatment [7](nowadays lasers with intensities up to 1021W/cm2 are experimentally feasible).

In this field of research, my work concerns basically four phenomena: High-harmonic generation, Stabilization, Above-threshold ionization and Nonsequential double ionization. In the four cases, only the response of a single atom is considered. Furthermore, for the first three phenomena we consider the atom to have only a single electron, assumption known as the Single Active Electron (SAE) approximation, in the nonrelativistic regime. For nonsequential double ionization, we address electron-electron correlation.


References
[1] See, e.g., M. Gavrila eds., ``Atoms in Intense Laser Fields'' (Advances in Atomic, Molecular and Optical Physics, Academic, London, 1992).
[2] P. Agostini, E. Mevel, P. Breger, A. Migus and L.F DiMauro,``Super Intense Laser-Atom Physics '', B. Piraux et al. eds., p. 155 (Plenum, New York, 1993).
[3] See, e.g., P. Gibbon and E. Förster, Plasma Phys. Control. Fusion 38, 769 (1996); A. Pukhov, J. Meyer-ter-Vehn, Phys. Rev. Lett. 76, 3975 (1996); ibid. 79, 2686 (1997).
[4]  H. Reiss, J. Math. Phys. 3, 59 (1962); N.B. Nahrozhnhy, Sov. Phys. JETP 20, 622 (1967); C. Symanowski, V. Véniard, R. Taïeb, A. Maquet and C.H. Keitel, Phys. Rev. 56, 3846 (1997); G. Pretzler, A. Saemann, A. Pukhov, D. Rudolph, T. Schätz, U. Schramm, P. Thirolf, D. Habs, J. Meyer-ter-Vehn, G.D. Tsakiris and K.J. Witte, Phys. Rev. E 58, 1165 (1998).
[5] See, e.g., A. Rundquist, C.G. Durfee III, Z. Chang, C. Herne, S. Backus, M.M. Murnane, H.C. Kapteyn, Science 280, 1412 (1998); X. F. Wang, R. Fedoseyevs, G.D. Tsakiris, Opt. Comm. 146, 363 (1998); I.P. Christov, M.M. Murnane and H.C. Kapteyn, Phys. Rev. A 57, R2285 (1998).
[6] See, e.g, Stuart et al, Opt. Lett 22, 242 (1997).
[7] L.S. Brown and T.W.B. Kibble, Phys.Rev. 133, 705 (1964); J.H. Eberly and A. Sleeper, Phys. Rev 176, 1570 (1968); A. Sarachik and E.S. Chappert, Phys. Rev. D 1, 2738 (1970); A. Bugacov, M. Pont and R. Shakeshaft, Phys. Rev. A 48, R4027 (1993); M. Protopapas, C.H. Keitel and P.L. Knight, J. Phys. B 29, L591 (1996); N. Kylstra et al., J. Phys. B 30, L449 (1997); U.W. Rathe, C.H. Keitel, M. Protopapas, and P.L. Knight, J. Phys. B 30, L531 (1997).