Near-GeV electron beam from a laser wakefield accelerator in the bubble regime

The bubble regime of interaction of an ultra-short petawatt-class laser pulse with an underdense plasma is investigated with two-dimensional (2D) particle-in-cell (PIC) simulations. The primary interest is in generation of high-energy electron beams in GeV energy level with good quality (high charge, relatively small energy spread and short pulse length). A wide range of parameters in plasma density, laser pulse duration, and laser focal spot size were used in the simulations. It is shown that quality of the high-energy part of the electron beam substantially depends on the laser focal spot size. The simulation studies imply that an optimum condition exists for generation of quasi-monoenergetic electron beams near the GeV-level and the combination of a laser spot size and plasma density is a dominant factor.