  We study theoretically the exchange of angular momentum between
electromagnetic and electrostatic waves in a plasma, due to the stimulated
Raman and Brillouin backscattering processes. Angular momentum states for
plasmon and phonon fields are introduced for the first time. We demonstrate
that these states can be excited by nonlinear wave mixing, associated with the
scattering processes. This could be relevant for plasma diagnostics, both in
laboratory and in space. Nonlinearly coupled paraxial equations and instability
growth rates are derived.
