ar X iv : 0 81 2 . 30 54 v 1 [ nl in . C D ] 1 6 D ec 2 00 8 Strong field double ionization : The phase space perspective

One of the most striking surprises of recent years in intense laser-matter interactions has come from multiple ionization by intense short laser pulses: Correlated (nonsequential) double ionization rates were found to be several orders of magnitude higher than the uncorrelated sequential mechanism allows. This discrepancy has made the characteristic “knee” shape in the double ionization yield versus intensity plot into one of the most dramatic manifestations of electron-electron correlation in nature. The precise mechanism that makes correlation so effective is far from settled. Different scenarios have been proposed to explain the mechanism behind ionization [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18] and have been confronted with experiments [19, 20], the recollision scenario [2, 3], in which the ionized electron is hurled back at the ion core by the laser, being in best accord with experiments. In Fig. 1, a typical double ionization probability as a function of the intensity of the laser field is plotted. Similar knees have been observed in experimental data [1, 4, 20, 21, 22, 23, 24, 25, 26] and successfully reproduced by quantal computations on atoms and molecules [5, 27, 28, 29]. In a recent series of articles [8, 9, 12, 13, 29, 30, 31] characteristic features of double ionization were reproduced using classical trajectories and this success was ascribed to the paramount role of correlation [12]. Indeed, entirely classical interactions turn out to be adequate to generate the strong two-electron correlation needed for double ionization.