High-resolution Rayleigh-Brillouin spectroscopy in the critical mixture nitroethane-isooctane

We report new measurements of the Rayleigh-Brillouin spectrum of a critical binary mixture and review the existing data in this field. We used a double-pass Fabry-Pérot interferometer and a weakly scattering system (nitroethane-isooctane) so that the Brillouin lines were not affected by the wings of the Rayleigh line, even in the immediate vicinity of the critical point. No anomaly was detected in the shift or width or intensity of the Brillouin lines. From the ratio of the intensities of the Rayleigh and Brillouin lines we deduced the ratio of specific heats ${\gamma }_0$, the correlation length ${\xi }_0$, and the susceptibility amplitude ${\left(\frac{\partial c}{\partial \mu }\right)}_{\mathrm{pT}}^0$, without any hypothesis about light-scattering amplitudes. These values lead to an amplitude ratio $R_{\xi }^{+}{R}_c^{-\frac{1}{3}}$ in full agreement with the theoretical values.