Refluxed electrons direct laser acceleration in ultrahigh laser and relativistic critical density plasma interaction

Refluxed electrons direct laser acceleration is proposed so as to generate a high-charge energetic electron beam. When a laser pulse is incident on a relativistic critical density target, the rising edge of the pulse heats the target and the sheath fields on the both sides of the target reflux some electrons inside the expanding target. These electrons can be trapped and accelerated due to the self-transparency and the negative longitudinal electrostatic field in the expanding target. Some of the electrons can be accelerated to energies exceeding the ponderomotive limit 1/2a(0)(2)mc(2). Effective temperature significantly above the ponderomotive scaling is observed. Furthermore, due to the limited expanding length, the laser propagating instabilities are suppressed in the interaction. Thus, high collimated beams with tens of mu C charge can be generated. (C) 2015 AIP Publishing LLC.