Binary and Recoil Collisions in Strong Field Double Ionization of Helium

Abstract

We have investigated the correlated momentum distribution of both electrons from nonsequential double ionization of helium in a 800 nm, $4.5\times {10}^{14}\mathrm{W}/{\mathrm{cm}}^2$ laser field. Using very high resolution coincidence techniques, we find a so-far unobserved fingerlike structure in the correlated electron momentum distribution. The structure can be interpreted as a signature of the microscopic dynamics in the recollision process. We identify features corresponding to the binary and recoil lobe in field-free ($e,2e$) collisions. This interpretation is supported by analyzing ab initio solutions of a fully correlated three-dimensional helium model.