MeV electrons generated using 100 GW level few-cycle IR laser pulses

Laser-based electron acceleration is an active research area which can provide a compact alternative to traditional sources. The utilization of longitudinal electric fields is a unique and promising approach which employs tightly focused ultrashort radially polarized laser pulses to produce ultrashort electron beams. Non-relativistic electrons beams produced through the ionization of a low-density gas and the subsequent longitudinal acceleration have been achieved some years ago, and simulations are clear that this process should result in ultrashort electron beams. Such electron beams are extremely useful due to their large scattering cross section compared to x-rays for dynamic imaging. In this work, we show our progress in increasing the electron energy to the relativistic regime via scaling of the incident laser pulse energy, extreme focusing, and the optimization of electron injection into the accelerating longitudinal fields by the natural ionization process. With laser pulse up to ∼100GW, we have generated electron energies greater than 1MeV in krypton gas. Numerical simulations highlight that the sub-cycle ionization dynamics determine the maximum electron energy.