Attosecond electron thermalization by laser-driven electron recollision   in atoms
  Nonsequential multiple ionization of atoms in intense laser fields is initiated by a recollision between an electron, freed by tunneling, and its parent ion. Following recollision, the initial electron shares its energy with several bound electrons. We use a classical model based on rapid electron thermalization to interpret recent experiments. For neon, good agreement with the available data is obtained with an upper bound of 460 attoseconds for the thermalization time. 
X. Liu, C. Figueira de Morisson Faria, W Becker and P.B. Corkum