Stochastic heating and acceleration of electrons by high-intensity lasers in inhomogeneous plasmas

Electron acceleration by a sub-picosecond relativistic intense laser pulse propagating in inhomogeneous plasmas has been studied by particle-in-cell simulations. It is found that the effective temperature of electrons scales as (I·τL)1/2, where I is the laser intensity and τL is the laser pulse duration. The scaling coefficient is relevant to the plasma density scale length. The high-temperature electrons produced in the earlier stage are mainly due to the stochastic acceleration in the colliding laser fields, where the backward propagating fields are produced in part by the Raman backscattering in the underdense plasma region as well as by reflection from the overdense plasma region. The induced electrostatic fields in inhomogeneous plasma can accelerate electrons randomly, which contribute to the increase in the electron temperature at a later stage