Brillouin scattering from isotropic metals

Abstract

Brillouin scattering from isotropic metals is investigated experimentally and theoretically. The observation of highly asymmetric Brillouin spectra from liquid mercury and liquid gallium is reported. A comparison is made between theory and experiment; the theory includes the damping of the acoustic phonons. It is found that the present state of the theory only qualitatively describes the Brillouin scattering of light from highly opaque materials. The velocities of sound of mercury and gallium deduced from the measurements are found to be 38% larger than the corresponding values determined by ultrasonic techniques. The observed intensity is at least an order of magnitude larger than the theory predicts, and the line shape, especially in the case of liquid gallium, differs appreciably from the theoretical line shape. The major origin of the discrepancy between theory and experiment is believed to be the simple model employed for the description of the dynamics of the density fluctuations near the surface. The spectra observed may therefore contribute to further understanding of the surface physics of liquid metals.