Momentum-resolved study of the saturation intensity in multiple   ionization
  We present a momentum-resolved study of strong field multiple ionization of ionic targets. Using a deconvolution method we are able to reconstruct the electron momenta from the ion momentum distributions after multiple ionization up to four sequential ionization steps. This technique allows an accurate determination of the saturation intensity as well as of the electron release times during the laser pulse. The measured results are discussed in comparison to typically used models of over-the-barrier ionization and tunnel ionization. 
P. Wustelt, M. M\"oller, T. Rathje, A. M. Sayler, T. St\"ohlker, G. G.   Paulus
physics.atom-ph