Experimental Observations of Nonlinear Saturation of the Two-Plasmon Decay Instability

Direct measurements by time-resolved Thomson scattering of the saturation of the two-plasmon decay instability driven by a C${\mathrm{O}}_2$ laser in an underdense plasma are presented. A time-correlated growth in ion fluctuations is also seen, enabling the saturation mechanism to be identified with the ion motions driven by the ponderomotive force associated with the large-amplitude electrostatic waves.