Nonthermal acceleration of charged particles due to an incoherent wakefield induced by a large-amplitude light pulse

We discuss the acceleration of charged particles in an incoherent wakefield induced by large-amplitude light waves, which are considered to be excited in the upstream region of relativistic perpendicular shock waves. In order to model such shock environments in a laboratory plasma, we substitute an intensive laser pulse for the large-amplitude waves. Performing particle-in-cell simulations, we calculate the energy distribution functions of electrons in various laser and plasma conditions. When the laser intensity is relativistic and the spatial scale of the laser is larger than the electron inertial scale, the electrons are nonthermally accelerated by incoherent wakefields. The distribution functions are universally represented by power-law spectra with an index similar to 2 independent of the laser intensity and the plasma density.