Light Scattering from First and Second Sound near theλTransition in Liquid He

Abstract

We have observed the second-sound contribution to the Brillouin spectrum of liquid ${\mathrm{He}}^4$ near the $\lambda$ transition at saturated vapor pressure and at 25.1 atm. Its spectral shape is compared with theoretical predictions. We have determined the intensity ratio of second- and first-sound scattering between ${10}^{-5\mathrm{}}{}_{}{}^{\circ }{}_{}{}^{}\mathrm{K}<T_{\lambda }-T<\mathrm{}{10}^{-1\mathrm{}}{}_{}{}^{\circ }{}_{}{}^{}\mathrm{K}$, and we present data on the dispersion and damping of high-frequency first and second sound.