The growth of ion waves at a wave number of $2k_{\mathrm{pump}}$ has been studied in a C${\mathrm{O}}_2$-laser-plasma interaction, by use of Thomson scattering. Time- and wave-number-resolved spectra have been obtained. Harmonic generation has been observed in the ion-wave spectrum. Saturation of the reflectivity is also observed. These results are consistent with nonlinearities in the ion wave affecting both the damping and the interaction length.

• Received 17 March 1982

DOI:https://doi.org/10.1103/PhysRevLett.48.1483