Transparency of an overdense plasma layer.

The transition from opacity to transparency of overdense plasma layers for the propagation of high-intensity laser pulses of circular polarization is investigated theoretically and by simulation. We discuss in detail the regions where stationary solutions exist and therefore the plasma layer is opaque. We find that the opacity depends not only on the electron density and the laser intensity but also on the thickness of the plasma layer. We also discuss the overlap region where both transparency and opacity are possible and how it depends on the history. Ion acceleration is studied in both the opacity region and the transparency region.