First observation of ion acoustic waves produced by the Langmuir decay instability

Thomson scattering measurements are presented which demonstrate conclusivel y the occurrence of the Langmuir decay instability (LDI) in a laser-produce d plasma experiment. Both products of the instability, the ion acoustic wav e and the electron plasma wave, were simultaneously observed and identified with their spectral characteristics. The secondary decay of the LDI-genera ted electron plasma wave, into another Langmuir wave and an ion acoustic wa ve, has been observed for the first time. The connection with growth and sa turation of the stimulated Raman instability is discussed.