Frequency Shifting of Low-Frequency Electromagnetic Waves Using Magnetoplasmas.

The effect of creating time-varying magnetoplasma on an incident wave, with an emphasis in the low frequency region is investigated. The time-varying magnetoplasmas can be approximated as either suddenly created or slowly varying. Both the cases are analyzed. The exact analysis is carried out and analytical solutions are obtained by taking ion motion into account when the magnetoplasma medium is created suddenly for longitudinal propagation i.e., when the static magnetic field is in the direction of propagation as well as transverse propagation i.e., when the electric field of the incident wave is perpendicular to both the direction of propagation as well as static magnetic field. The main effect of creating a magnetoplasma medium is the creation of new waves whose frequencies are different from the incident wave frequency. For longitudinal propagation there are four new waves created when the incident wave is circularly polarized. First and the third waves are backward propagating waves and the second and the fourth waves are forward propagating waves when the incident wave is right circularly polarized (R incidence). The situation reverses when the incident wave is left circularly polarized (L incidence). Alfven and hydromagnetic approximations can be made in the low frequency region. The frequency shifts, power content, energy distribution which are strongly controlled by the strength of the static magnetic field are discussed in the low frequency region. Optimum parameters for an experiment illustrating the generation of the new waves are given. For the case of transverse propagation there are six new extraordinary waves created due to medium switching when the incident wave is linearly polarized. Hydromagnetic approximations can be made in the low frequency region. The frequency shifts, power content and energy distribution are discussed in the low frequency region especially in the first two waves, which look like wiggler fields in the radio frequency region. The case of creating slowly varying magnetoplasma medium is analyzed, by switching a slowly varying magnetic field on a right circularly polarized incident wave, traveling in an isotropic plasma medium, for longitudinal propagation. The analysis involves formulating the Riccati equation describing the complex instantaneous frequencies of the newly created waves and solving the same by a perturbation method similar to WKB type solution. An exponentially varying magnetic field is considered for the sake of illustration of the slowly varying magnetic field. The frequency shifts, time -varying electric fields, magnetic fields and power flux of the newly created waves are computed for the profile under consideration. The condition of validity of the proposed solution is derived. Parameters and typical values for an experiment that will illustrate the generation of the new waves are given.