Ripplon spectroscopic study on non-uniform liquid surface induced by temperature gradient

Using ripplon spectroscopy, we observed the dynamic structure factor of liquid-surface displacement in a non-uniform state with a temperature gradient. The sensitivity of this light-scattering experiment has been considerably improved by employing lock-in detection of the optical beating signal, which is generated by the mixing of the scattered and reference light. We may also suppress the Marangoni flow due to the temperature gradient by expanding an insoluble monomolecular layer on the surface and to establish a mechanically stable water surface, even under a temperature gradient. The observed asymmetry of the ripplon spectrum, which is the dynamic structure factor of the surface displacement, is in quite good agreement with our formula describing the asymmetry of the structure factor.