Electromagnetically induced transparency in plasma

The coupled propagation of two electromagnetic waves in plasma is studied t o establish the conditions for induced transparency. Induced transparency r efers to the situation where both waves propagate unattenuated, although th e frequency of one (or both) of them is below the plasma frequency so, that it could not propagate in the absence of the other. The effect is due to t he interaction of the waves through their beat, which modulates both the el ectron mass and, by exciting longitudinal plasma oscillations, their number density, and thus the plasma frequency. Starting from a relativistic fluid description, a dispersion relation for plane waves of weakly relativistic intensities is derived, which takes into account the polarization of the wa ves and the nonlinearities with respect to both their amplitudes. This serv es as a basis for the exploration of the conditions for induced transparenc y and the modes of propagation.