Physics of correlated double ionization of atoms in intense laser fields: Quasistatic tunneling limit

We revisit the recollision picture of correlated multiphoton double ionization of atoms in strong laser fields and develop consistent semiclassical model in the tunneling limit. We illustrate the model by applying it to helium and obtain quantitative agreement with recent experiments [B. Walker, E. Mevel, Baorui Yang, P. Breger, J. P. Chambaret, A. Antonetti, L. F. DiMauro, and P. Agostini, Phys. Rev. A 48, R894 (1993); B. Walker, B. Sheehy, L. F. DiMauro, P. Agostini, K. J. Schafer, and K. C. Kulander, Phys. Rev. Lett. 73, 1227 (1994)]. Developing the model, we address several problems of general interest, such as the reduction of intense field-assisted electron-ion collision to the field-free one and the total-cross-sections that include all inelastic channels. We describe a set of important physical effects responsible for the surprisingly high yield of doubly charged ions of noble gas atoms. All effects originate from the key role of the Coulomb potential and its interplay with the laser field. In addition to the Coulomb focusing of the oscillating trajectories onto the parent ion, other effects include transient trapping of electrons after tunneling in the vicinity of the parent ion, the creation of high-velocity electrons at all phases of the laser field, and the dominant role of collisional excitation of the parent ion followed by laser-assisted ionization.