Observation of Solid-Density Laminar Plasma Transparency to Intense 30 Femtosecond Laser Pulses

Near total transmission of 30 fs laser pulses through $0.1\mu \mathrm{m}$ plastic foil targets has been observed for the first time at an intensity of $3\times {10}^{18}\mathrm{W}/{\mathrm{cm}}^2$ in absence of precursor plasma. This level of transmittivity is far above the level predicted by current theoretical models or numerical simulations. The transmittivity was found to drop by 40 times at an intensity of $4\times {10}^{17}\mathrm{W}/{\mathrm{cm}}^2$ and was within the experimental background level at $5\times {10}^{16}\mathrm{W}/{\mathrm{cm}}^2$. Our measurements strongly suggest a new mechanism of propagation of electromagnetic waves through overdense plasmas.