Nonlinear propagation of low-frequency electromagnetic disturbances in plasmas

Electromagnetic (EM) waves/disturbances are typically the best means to understand and analyse an ionized medium like plasma. However, the propagation of EM waves with a frequency lower than the plasma frequency is prohibited by the freely moving charges of the plasma. In dense plasmas, though the plasma frequency can be typically quite high, EM sources at such higher frequency are not easily available. It is, therefore, of interest to seek possibilities wherein a low frequency (lower than the plasma frequency) EM disturbance propagates inside a plasma. This is possible in the context of magnetized plasmas. However, in order to have a magnetized plasma response in high-density plasmas, one requires an extremely strong external magnetic field. In this manuscript, it is demonstrated that the nonlinearity of the plasma medium can aid the propagation of a slow (effective frequency lower than the plasma frequency) EM wave inside an overdense plasma. A possible mechanism of guiding, collimating, and trapping of the EM pulse or electron current pulses by appropriate tailoring of the local plasma density profile is also shown. Certain interesting applications of the propagation of such slow EM pulse through the inhomogeneous plasma is also discussed.