[en] Stimulated Brillouin scattering spectra observed from homogeneous and extended target plasma being irradiated with CO₂ laser pulses reveal the presence of ion trapping, the onset of which coincides with a pronounced deviation from the steep stimulated Brillouin scattering increase with laser power. The evaluation of spectra permits the direct measurement of the amplitude of the backscattering ion-acoustic wave and it also provides information on the deformation of the ion velocity distribution under the influence of this wave