Classical double ionization of atoms in strong fields
  Recent high resolution measurements of the momenta of two electrons emitted from Argon atoms in a strong laser field show a strong preference for the outgoing electrons to have similar momenta and to be ejected in the same direction along the field. We discuss the final stages of this process in a classical model in the spirit of Wanniers approach to double ionization after electron impact. Starting from an intermediate state of high but negative energy the field opens up a channel through which both electrons can escape. Near the threshold for this process Coulomb repulsion favors an escape with the electron momenta and positions symmetric with respect to the electric field axis. Classical trajectory simulations within this symmetry subspace account for most features of the observed momentum distribution. 
Bruno Eckhardt and Krzysztof Sacha