GeV Electrons Acceleration in Focused Laser Fields after Above-threshold Ionization

Electrons produced as a result of above-threshold ionization of high-Z atoms can be accelerated by currently producible laser pulses up to GeV energies, as shown recently in Hu and Starace, Phys. Rev. Lett. 88 (2002) Article No. 245003. To describe electron acceleration by general focused laser fields, we employ an analytical model based on a Hamiltonian, fully relativistic, ponderomotive approach. Analytical expressions are derived and the applicability conditions of the ponderomotive formulation are studied both analytically and numerically. The theoretical predictions are supported by the numerical simulations.