Laser wakefield accelerator driven by the super-Gaussian laser beam in the focus

The injection process is one of the most crucial attributes that determine the final properties of the electron bunch in laser wakefield accelerators. Here, a new injection method is proposed and studied via particle-in-cell simulations for the typical parameters of the bubble regime. The injection is triggered by the laser beam that reaches the super-Gaussian profile in the focus. Such a beam undergoes rapid variations in its intensity distribution during the diffraction process. If this diffraction occurs in underdense plasma, consequent changes in the bubble structure activate a localized transverse injection process. The generated electron bunch is characterized by the short duration (∼2 fs) and low transverse emittance (≤1 mm mrad) while maintaining relatively high charge (∼0.2 nC). (paper)