A complex stimulated Raman scattering event against a background of
non-thermal ion acoustic waves in an inhomogeneous plasma is described. We obtain
analytic forms for the Raman gain due to a five-wave interaction consisting of
conventional three-wave Raman scattering followed by the decay of the Raman
Langmuir wave into a second Langmuir wave (or a second scattered light wave)
and an ion acoustic wave. Very modest levels of ion waves produce a significant
effect on Raman convective gain. A combination of plasma inhomogeneity and
suprathermal ion fluctuations may offer a means for the control of Raman gain.