Ripplon spectroscopic study on multilayered liquid surface

Ripplon spectroscopy was used to observe the propagation modes of surface waves on a layered structure. We experimentally prepared a water surface covered with an oil layer of µm-order thickness, on which two surface modes, bending and squeezing, were theoretically predicted to stand independently. Thermally excited capillary waves, called ripplons, propagating on the layered surface were observed with an optical beating light-scattering system developed by us and two modes were clearly observed as the doublet peaks of the Stokes and anti-Stokes components, respectively. The dispersion and the damping constant of ripplons of the two modes as well as their intensity ratio agreed well with the theoretical calculations. The dispersion of the mechanically excited surface waves, which is attributed to the bending mode, was also measured to examine the mode assignment in the light-scattering experiment.