New mechanisms for generating super-ponderomotive electrons in   laser-irradiated targets
  It is shown that static longitudinal and transverse electric fields can significantly alter electron acceleration by a long laser beam in a sub-critical plasma, enabling generation of super-ponderomotive electrons. The role of the plasma fields in this regime is not to directly transfer substantial energy to the electron, but rather to reduce the axial dephasing rate between the electron and the laser beam. The reduced dephasing in both cases leads to a subsequent enhancement of the axial momentum and total electron energy. These mechanisms can be relevant to experiments with solid-density targets where a sub-critical plasma layer occurs as a result of a considerable prepulse. 
A. V. Arefiev, A. P. L. Robinson, V. N. Khudik, B. N. Breizman, and M.   Schollmeier
physics.plasm-ph