Breather-like penetration of ultrashort linearly polarized laser into over-dense plasmas

The penetration of an ultrashort laser pulse into an overdense plasma in the relativistic transparency regime is reexamined. The interaction is governed by the Maxwell and relativistic hydrodynamic equations and investigated using a fully implicit energy-conserving numerical scheme. It is found that for a circularly polarized laser, the penetrated pulse has the expected soliton structure. However, for a linearly polarized laser, the penetrated light exhibits a breather structure, and energy exchange between it and the plasma is at twice the laser frequency.