Electromagnetically Induced Transparency in Strongly Relativistic Regime

Stable transport of laser beams in highly over-dense plasmas is ofsignificance in fast ignition of inertial confinement fusion, relativisticelectrons generation, and powerful electromagnetic emission, but hard torealize. Early in 1996, Harris proposed an electromagnetically inducedtransparency (EIT) mechanism, analogous to the concept in atom physics, totransport a low-frequency (LF) laser in over-dense plasmas aided by ahigh-frequency pump laser. However, subsequent investigations show that EITcannot occur in real plasmas with boundaries. Here, our particle-in-cellsimulations show that EIT can occur in strongly-relativistic regime and resultsin stable propagation of a LF laser in bounded plasmas with tens of itscritical density. A relativistic three-wave coupling model is developed, andthe criteria and frequency passband for EIT occurrence are presented. Thepassband is sufficiently wide in strongly-relativistic regime, allowing EIT towork sustainably. Nevertheless, it is narrowed to nearly an isolated point inweakly-relativistic regime, which can explain the quenching of EIT in boundedplasmas found in previous investigations.