Electron Injection in Laser Plasma Accelerators by High-Order Field Ionization.

Electron injection and trapping in a laser wakefield accelerator by high-order field ionization is studied theoretically and by particle-in-cell simulations. To obtain low energy spread beams we use a short region of gas mixture (H+N) near the start of the stage to trap electrons, while the remainder of the stage uses pure H and is injection-free. Effects of gas mix parameters, such as concentration and length, on the final electron injection number and beam quality are studied. Laser polarization and shape effects on injection number and final electron emittance are also shown. [ABSTRACT FROM AUTHOR]