Relativistic Self-Induced Transparency Effect During Ultraintense Laser   Interaction with Overdense Plasmas: Why It Occurs and Its Use for Ultrashort   Electron Bunch Generation
  A novel explanation of the relativistic self-induced transparency effect during superintense laser interaction with an overdense plasma is proposed. We studied it analytically and verified with direct modeling by both PIC and kinetic equation simulations. Based on this treatment, a method of ultrashort high-energy electron bunch generation with durations on a few femtosecond time scale is also proposed and studied via numerical simulation 
V. I. Eremin, A. V. Korzhimanov and A. V. Kim