Search

The nature of plasma waves which are resonantly excited when two laser beams beat in a rippled-density plasma is explored both theoretically and experimentally. A theoretical model is presented which, for commonly encountered experimental parameters, predicts rapid saturation of the high—phase-velocity beat wave at an amplitude below that expected for relativistic detuning. Results of experimental studies of this process are presented.

Clayton et al. Respond: The authors of the Comment are quite correct when they point out that the ruby-laser scattering system used in our study can only respond to beat-excited density fluctuations with ky = k2, where the CO2 (ruby) beam propagates in the z (y) direction.

The relativistic plasma wave excited when the frequency difference between two copropagating CO2 laser beams equals the plasma frequency is detected for the first time. The plasma-wave frequency, wave number, spatial extent, and saturation time are directly measured by use of 7-mrad, collective, ruby Thomson scattering and the forward-scattered ir spectrum. The wave amplitude ñ/n0 is inferred to be (1-3)% which gives a longitudinal electric field of 0.3 to 1 GV/m at a laser intensity of 1.7×1013 W/cm2, in reasonable agreement with theory.