Light scattering from a nonequilibrium fluid undergoing a planar Poiseuille-Couette flow

We calculate the Rayleigh-Brillouin spectrum of a Newtonian fluid undergoing a planar Poiseuille-Couette flow using the fluctuating hydrodynamic approach of Landau and Lifshitz. Our results reduce to the corresponding results for pure Couette flow when the pressure gradient is made to vanish. The Brillouin spectrum is obtainable from that appropriate to Couette flow by a simple rescaling. There are very minute corrections which impart asymmetry to the Brillouin lines as well as the Rayleigh line, and these can be selectively picked up by suitable choice of the scattering geometry.