Mechanism of heating of pre-formed plasma electrons in relativistic laser-matter interaction

摘要

The role of the longitudinal ambipolar electric field, present inside a pre-formed plasma, in electron heating and beam generation is investigated by analyzing single electron motion in the presence of one electromagnetic plane wave and V shaped potential well (constant electric field) in a one dimensional slab approximation. It is shown that for the electron confined in an infinite potential well, its motion becomes stochastic when the ratio of normalized laser electric field a 0, to normalized longitudinal electric field E _z, exceeds unity, i.e., a 0 / E _z ≤ 1. For a more realistic potential well of finite depth, present inside the pre-formed plasma, the condition for stochastic heating of electrons gets modified to 1 ≥a 0 / E _z ≥ L, where L is the normalized length of the potential well. The energy of electron beam leaving such a potential well and entering the solid scales ～ a _0 ~2 / E _z, which can exceed the laser ponderomotive energy (～ a 0) in the stochastic regime.