Phase conjugation via Brillouin enhanced four-wave mixing in a plasma

Detailed studies of phase conjugation via Brillouin enhanced four-wave mixing (BEFWM) of high power microwaves in a large, well diagnosed unmagnetized hydrogen plasma have been performed. Both the transient and steady state behaviour are shown to agree well with the predictions of two-fluid plasma theory for low power, low density operation. Strong suppression of the BEFWM interaction is observed at an electron density ne=nc/4, indicative of the two plasmon decay instability. High power, high density operation is seen to deviate strongly from simple theoretical predictions; evidence of the onset of ponderomotive whole-beam self-focusing is given. (author) 4 refs., 5 figs