Transmission through Highly Overdense Plasma Slabs with a Subpicosecond Relativistic Laser Pulse

Transmission of a subpicosecond relativistic laser pulse is observed through solid foils and preformed overcritical plasmas. Transmission rates near 10% for densities above $10\times n_c$ are measured. A moderately relativistic strong threshold in intensity is found in order to observe this effect. The experimental results as well as preliminary particle-in-cell simulations suggest that for thin solid foils the observed transmission is explicable by rapid heating and expansion to transmissive conditions during the pulse. Self-induced transparency and hole boring processes apply to thicker preformed plasmas. These results have important implications in fast ignition for inertial confinement fusion.