Propagation of ultraintense laser pulses through overdense plasma layers

Due to relativistic effects, a large amplitude electromagnetic wave can propagate in a classically overdense plasma with ω2 p ≳ω2≳ω2 p /γ, where ω p is the plasma frequency, ω the laser frequency, and γ the relativistic factor of an electron in the laser field. Particle‐in‐cell simulations are used to study the interaction of an ultrahigh intensity laser pulse in normal incidence on a one‐dimensional preformed plasma layer. Both electrons and ions dynamics are included. The width of the layer is 10 to 30 μm and the plasma is characterized by (ω p /ω)2=1.5. During the penetration of the electromagnetic wave a large longitudinal electric field is generated. It results in a strong longitudinal heating of electrons which reach relativistic temperatures. This heating further lowers the effective plasma frequency ω p /γ so the layer becomes almost transparent after the plasma crossing by the wave front. Velocity of the wave front, reflection and transmission rates are studied as functions of the incident energy flux, the plasma thickness, and the pulse duration.