A Laser-Accelerator Injector Based on Laser Ionization and Ponderomotive Acceleration of Electrons

A new laser-accelerator injector based on the high-energy electrons ejected from a laser focus following the ionization of high-charge states of gases has been investigated. This method can generate electron pulses with MeV energies and pulse widths substantially less than the laser pulse width using terawatt lasers. Experiments at intensities of $3\ifmmode\times\else\texttimes\fi{}{10}^{18}\mathrm{W}/\mathrm{cm}{}^{2}$ show that two highly directional electron beams with energies up to 340 keV are produced in the laser polarization direction. These highly directional beams are inconsistent with simulation results using Ammosov-Delone-Krainov (ADK) tunneling theory to model the ionization process. It is shown that this is likely due to the release of electrons with larger canonical momentum than predicted by ADK theory.