The efficient transport of laser beams through over-dense plasmas is crucial for various applications such as fast ignition in inertial confinement fusion, relativistic electron generation, and the production of powerful electromagnetic emissions. Despite its importance, achieving stable beam transport in over-dense plasmas has posed significant challenges. In 1996, Harris proposed an electromagnetically induced transparency (EIT) mechanism, drawing parallels with concepts from atomic physics, to facilitate the transport of low-frequency (LF) lasers through over-dense plasmas with the assistance of a high-frequency pump laser. However, subsequent investigations have shown that real plasmas with boundaries preclude the occurrence of EIT. This study employs particle-in-cell simulations to demonstrate the occurrence of EIT within a strongly-relativistic regime, enabling the stable propagation of LF lasers through bounded plasmas with densities approaching tens of their critical values. Additionally, we develop a relativistic three-wave coupling model, elucidating the criteria and frequency passband required for EIT. Notably, our findings reveal a sufficiently wide passband within the strongly-relativistic regime, facilitating sustained operation of the EIT mechanism. Conversely, within the weakly-relativistic regime, the passband narrows significantly, almost collapsing to an isolated point. This shrinkage suggests the suppression of EIT in previous investigations in bounded plasmas.

electromagnetically induced transparency,laser-plasma interactions,fast ignition