The forced Brillouin and Rayleigh scattering techniques under the probe reflected transient grating configuration were used to probe various dynamics at gas-liquid interfaces in the time domain over the wave-number range of 0.2ϫ10 6 ϳ2.0ϫ10 6 m Ϫ1 . From the forced Brillouin scattering signal, the temporal behaviors of the capillary wave ͑CW͒ were investigated. The observed wave does not consist of one sine or cosine wave but shows dual features. This feature was explained in terms of two mechanisms of the capillary wave creation by the photothermal effect; the thermal expansion and the temperature dependence of the surface tension. Besides the oscillatory behavior for nonviscous liquids, a heavily damped capillary wave was observed in a range of wave number above 1.6ϫ10 6 m Ϫ1 from a viscous liquid ͑1-hexanol͒ surface, which has never been detected before. The observed signals were compared with the phenomenologically expressed wave forms and the theoretically calculated wave forms based on the hydrodynamic equations. For CW on the organic liquid surface, the hydrodynamic equation predicts the observed temporal profile well, whereas the agreement is less satisfactory for CW on water surface. Using the theoretical equations, the surface motion as well as liquid motion beneath the surface under the forced light scattering condition is presented. The temporal profile of the forced Rayleigh scattering signal provides information on the thermal diffusivity and molecular movement at the surface. The thermal diffusivity at the surface region is found to be very close to that in the bulk phase, whereas the molecular motion at the surface is revealed to be faster than that in the bulk phase. The faster movement at the surface may be explained by the transverse motion of the surface by CW.

The capillary wave at air/liquid interfaces is detected by the forced Brillouin and Rayleigh light scattering in the time domain. The forced Brillouin scattering signal from the air/water surface shows clear oscillation. The wave is not pure sine or cosine wave but it shows dual features. A strongly overdamped signal is observed from the air/hexanol surface in 1.4–2.0×106 m−1, while the signal shows a trace of oscillation in a lower wave number region. The oscillation also indicates the existence of two waves. The mechanism to create the capillary wave by the photothermal effect is discussed.

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