Scissor-cross ionization injection in laser wakefield accelerators

We propose to use a frequency-doubled pulse colliding with the driving pulse at an acute angle to trigger ionization injection in a laser wakefield accelerator. This scheme effectively reduces the duration of the injection; thus, high injection quality is obtained. Three-dimensional particle-in-cell simulations show that electron beams with energy of similar to 500 MeV, a charge of similar to 40 pC, energy spread of similar to 1% and normalized emittance of a few millimeter milliradian can be produced by similar to 100 TW laser pulses. By adjusting the angle between the two pulses, the intensity of the trigger pulse and the gas doping ratio, the charge and energy spread of the electron beam can be controlled.