Electromagnetic Wave Propagation in an Inhomogeneous Highly Collisional Plasma

It is shown that in a highly collisional plasma, electromagnetic waves can propagate beyond the critical density nc. When the electromagnetic wave propagates obliquely to the plasma density gradient, there exists a critical angle of incidence, below which there is no reflection. When the incident angle is larger than the critical angle, there are two reflection points. One is at a density lower than 2nc, corresponding to the EM wave incident from low to high density regions. The other one is at a density higher than 2nc, corresponding to that from high to low density regions