Brillouin Spectrum of Xenon Near Its Critical Point

We have accurately measured the Brillouin spectrum of pure xenon along the critical isochore using two high-resolution spherical Fabry-Perot interferometers in tandem. The spectrum, which contained an extra diffusive mode, is analyzed in terms of a hydrodynamic model employing a relaxing bulk viscosity. We obtain the temperature dependence of the relaxation time, the bulk viscosity, the specific heat ratio $\frac{C_p}{C_v}$ at finite $k$ and $\omega$, the correlation range, and the $k=0\mathrm{}$, $\omega =0\mathrm{}$ values for the compressibility and $C_p-C_v$.