Recollision revisited: How far can we push the classical picture?

The double ionization probability of nobel gases in strong laser fields at intermediate intensities exceeds the probability that can be expected on grounds of an independent electron picture by \emph{several orders of magnitude}. Electron-electron correlation is the well-known origin for this dramatic effect. We have revisited this so called nonsequential double ionization in the simplest 2-electron system, the Helium atom, and, using very high resolution coincidence techniques, we observe a surprising structure in the correlated electron momentum distribution. The structure can be interpreted as a signature of the microscopic dynamics in the recollision process, taking the analogy to the classical (e,2e) processes one step further. This interpretation is supported by inspecting the solution of the 2-body 3-dimensional time-dependent Schr\"{o}dinger equation.