Depolarized light scattered from a fluid near its Bénard instability

Bilinear response theory is extended and applied to a fluid of non-spherical molecules in a gravitational field and with time independent different temperatures on its upper and lower boundaries. The spectral line-shape of the depolarized component in a light-scattering experiment is worked out. It is found that there are two dips in the central peak and that one of these dips becomes infinitely sharp as the external constraints approach their critical values. It is hoped that this kind of experiment will provide relevant information about the dynamics of fluctuations near hydrodynamical instabilities.