An attosecond time-resolved study of strong-field atomic photoionization

The time evolution of atomic photoionization by an intense few-cycle laser pulse is theoretically investigated. A possible modification of the recent attosecond tunnelling experiment in Uiberacker et al ( 2007 Nature 446 627) is proposed, which consists of measuring the yield of the doubly charged Li ions produced by the combined action of a strong few-cycle infrared pulse and an ultrashort ( attosecond) extreme ultraviolet (XUV) pulse. We predict the results of such an experiment, based on the numerical solution of the time-dependent Schrodinger equation, which describes the atomic electron in a strong laser field. The influence of the XUV pulse is treated in the sudden approximation. It is shown that the dependence of the double ionization cross section on the time delay between the two pulses reflects the time evolution of the strong-field ionization. We demonstrate that even more detailed information can be gained from the forward-backward asymmetry of the photoelectron emission.