Observation of the nonlinear saturation of Langmuir waves driven by ponderomotive force in a large scale plasma

We report the observation of nonlinear saturation of Langmuir waves produced by a probe laser beam interacting with a high intensity pumping laser beam. Amplification of the probe beam is observed and interpreted as scattering of pump energy by a Langmuir wave that is produced by the beating of the two beams. It is found that, as the probe beam amplitude is increased, the scattering and Langmuir wave amplitude do not increase proportionally, demonstrating that the wave is nonlinearly saturated consistent with saturation by secondary-ion-wave instabilities.