Universal scaling of the electron distribution function in one-dimensional simulations of relativistic laser-plasma interactions

A formula based on simulations is given for the distribution function of energetic electrons which stream in the forward direction when a relativistically intense laser pulse irradiates a short-scale-length dense plasma at normal incidence. If the energy absorption fraction is known, the entire function can be characterized in terms of the laser intensity I. A number of important characteristics can then be obtained, including the fast-electron energy, current density, and angle of ejection. An objective means for calculating the fast-electron energy is proposed which gives a value of ∼0.6 of the vacuum oscillatory energy. This reduction in energy is shown to be consistent with the energy required to draw a return current. These results could be used to provide the characteristics of the electron source in theory and simulation of intense laser-solid interactions.