The coupling of a large amplitude plasmon, generated by the beat-wave process, to ion acoustic waves may lead to modulational or decay instabilities, which are investigated here. A general dispersion relation obtainable from Zakharov equations predicts large growth rates (∼ωpi) for short wavelength modulations. To avoid these, extremely short pulse lengths are required in the beat-wave experiments. Due to the very long wavelength of the beat-plasmon, the decay instability is not likely below the ke V-temperatures.
Pesme, D., Karttunen, S., Salomaa, R., Laval, G., & Silvestre, N. (1988). Modulational instability in the beat wave generation. Laser and Particle Beams, 6(2), 199-210. https://doi.org/10.1017/S0263034600003943