It is shown that electrons with momenta exceeding the “free electron” limit of $m_{e}c{a}_0^2/2$ can be produced when a laser pulse and a longitudinal electric field interact with an electron via a non-wake-field mechanism. The mechanism consists of two stages: the reduction of the electron dephasing rate $\gamma -p_x/m_{e}c$ by an accelerating region of electric field and electron acceleration by the laser via the Lorentz force. This mechanism can, in principle, produce electrons that have longitudinal momenta that is a significant multiple of $m_{e}c{a}_0^2/2$. 2D particle-in-cell simulations of a relatively simple laser-plasma interaction indicate that the generation of superponderomotive electrons is strongly affected by this “antidephasing” mechanism.

• Received 1 March 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.065002