Synergistic Laser Wakefield/Direct Laser Acceleration in the Plasma   Bubble Regime
  The concept of a hybrid laser wakefield/direct laser plasma accelerator is proposed. Relativistic electrons undergoing resonant betatron oscillations inside the plasma bubble created by a laser pulse are accelerated by gaining energy directly from the laser pulse and from its plasma wake. The resulting bifurcated phase space of self-injected plasma electrons contains a population that experiences wakefield acceleration beyond the standard one-dimensional limit because of the multi-dimensional nature of its motion that reduces the phase slippage between the electrons and the wake. 
Xi Zhang, Vladimir N. Khudik, and Gennady Shvets
physics.plasm-ph