Evanescent wave interference and the total transparency of a warm high-density plasma slab

It is shown that an overcritical density plasma slab can be totally transparent to a \textit{p}-polarized obliquely incident electromagnetic wave. High transparency is achieved due to the interference of the evanescent waves in the subcritical region. The transmission coefficient has the resonant character due to the excitation of a plasma surface mode (plasmon-polariton). It is crucial that two evanescent waves have certain phase shift to provide non-zero energy flux through non-transparent region. The required phase shift is obtained at the exact resonance and corresponds to the absolute transparency. In a warm plasma case, the excitation of the propagating longitudinal (electrostatic) modes becomes possible. We demonstrate that these longitudinal excitations facilitate the total transparency of an opaque plasma slab creating additional resonances in the transmission property of the system.