Self-induced transparency and self-induced opacity in laser-plasma interactions

The interaction of a strong electromagnetic wave with a layer of overdense plasma is considered under conditions that allow for self-induced transparency (SIT). In a certain range of the amplitude of the incoming wave, the corresponding nonlinear one-dimensional (1D) set of equations is shown to admit two competing steady-state solutions that satisfy the same boundary conditions. One of those solutions describes just the well-known SIT regime of propagation, the other one corresponds to the full reflection of the incident wave. Their coexistence indicates the possibility of hysteresis-like effects in ultraintense laser interactions with overdense plasmas. 1D Particle-In-Cell simulations confirm analytical results and suggest the dominance of the opaque solution over the entire parameter window where it is possible. Fast longitudinal heating of plasma electrons occurs then in a natural way as a result of the breakup of the opaque solution above some threshold in laser intensity.