Wide band spectroscopy of liquid surface ripplon by optical beating techniques

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Observation of waves propagating on liquid surfaces and interfaces provides us with interesting informations on various physical properties and their dynamics localized in the close vicinity of the surfaces.Previous studies on surface waves have been made onlyin the frequency range below several tens of kHz : both temporal and spatial resolution has been insufficient for the above purposes. The aim of this study, therefore, is to develop a new technique for measuring liquid surface and interface waves, which is useful over an extensive frequency range up to MHz region. We also intend to apply it for the dynamical study of liquid surfaces.In the investigation by this grant-in-aid, we obtained various important results which are summerized as follows.1) We established a new technique for wide band ripplon spectroscopy. The frequency of the measurement has been extended up to 6 MHz which is more than hundred times higher than the conventional.2) Frequency dependence of the surface tension has been measured for various pure simple liquids including water.3) Dynamic mechanical properties of the Langmuir films has been successfully measured by the ripplon spectroscopy technique.4) Gelation process of the polymer solution surface has been studied by observing the ripplon dispersion.