Relativistic electron acceleration in focused laser fields after above-threshold ionization

The acceleration of electrons produced in focused laser fields as a result of above-threshold ionizations up to ultrarelativistic energies was discussed. A model was also developed that was based on a fully ponderomotive treatment. The applicability conditions of the ponderomotive formulation were studied numerically and the analytical expressions for electron energy gain were derived. As compared to laser oscillations the above-threshold ionization represented an abrupt process. But then also the resulting energy gain of electrons was adequately predicted by the ponderomotive approach when proper initial conditions were introduced for the particle drift following the ionization event.