The plasma as a phase conjugate reflector

Plasma is a nonlinear medium and two waves propagating in it interact electromagnetically with each other. If the plasma is pumped by two strong counterstreaming waves of equal frequency, and a third wave enters, the nonlinear interaction generates a fourth wave, phase conjugate to the third wave. This interaction becomes very significant if the frequency and wave vector differences between the third wave and one of the pump waves resonate with the frequency and wave vector of the ion acoustic mode of the plasma. This resonance can be predicted from a fluidlike description of the plasma, but it is shown that the Vlasov description can provide more details of behavior near the resonance. Possible applications of the emergent technology range from improved focusing of radiation in hyperthermia therapy of cancer to the formation of a microwave laser between a phase conjugate plasma reflector and a mirror, for improved radar imaging. Another application is cordless, self‐guiding, power transmission.