Electronic correlations in double ionization of atoms in pump probe experiments

The (correlated) dynamics of few-body systems in strong laser fields is in focus of active research since the last two decades. One example is the famous non-sequential double ionization of Helium. With nowadays experimentally available tools it is possible to investigate these processes on the sub-femtosecond timescale. Typically, a short extreme ultraviolet (XUV) pump pulse is combined with a longer infrared (IR) probe pulse. We present theoretical results based on the time-dependent Schr\"odinger equation for such a pump-probe experiment involving two active electrons [1]. A dramatic change of the double ionization yield with variation of the pump-probe delay is reported. We identify the governing role of electron-electron correlations, through a complex interplay of (1) inner-atomic electron shake up and (2) rescattering with subsequent impact ionization. Our results allow for a direct control of the double ionization yield, and the relative strength of double and single ionization. \\[4pt] [1] S. Bauch, K. Balzer and M. Bonitz, Europhys. Lett. 91 53001 (2010)