Brillouin scattering from fluids subject to large thermal gradients

The implications on the Brillouin lines of our recently developed theory of the density fluctuations in a fluid exposed to a strong stationary heat flux are discussed. This theory takes into account, for the first time, the combined effects of sound-absorbing and -reflecting walls as well as the spatial inhomogeneities induced by the temperature gradient. The theory is slightly generalized to be applicable to arbitrary bending of sound, in particular when sound rays are totally bent inside the fluid. No restrictions are made concerning the thermal equations of state. This allows a critical reexamination of earlier theories and experiments, the resolution of an existing ambiguity, and the proposal of new experiments.