Low-frequency spectrum of light multiply scattered by a critical mixture

In this paper we present both the first realistic calculation of the spectrum of multiply scattered light near a critical point, and the first experimental determination of the corresponding spectrum. We assume the double scattering to be the dominant phenomenon, and we use the Ornstein-Zernike cross section and the Kawasaki dynamical structure factor. Experimental data, obtained in a critical mixture of nitrobenzene and n-hexane, are seen to be in good agreement with the calculated spectra. Both are clearly not Lorentzian.