Measurement of the frequency and spectral width of the Langmuir wave spectrum driven by stimulated Raman scattering

Thomson scattering was used to measure the spectrum of Langmuir waves, in b oth frequency and wave number, driven below quarter-critical density by a l aser beam. These measurements were capable of detecting and identifying wav es driven by stimulated Raman scattering (SRS) and also of detecting waves driven by other effects such as the bump-on-tail instability postulated by the enhanced Thomson scattering model of Raman emission. The observed Langm uir waves were consistent with SRS and not with other possible sources. The width in k-space of the measured Thomson scattering signals also has impli cations for the saturation amplitude of the Langmuir waves. (C) 1999 Americ an Institute of Physics. [S1070-664X(99)00111-1].