The displacement of a water-air interface and its relaxation as a function of acoustic energy density and surface tension were analyzed both experimentally and numerically. Experimental systems were devised to observe the time evolution of the surface. A theoretical model to predict the response of the interface to acoustic excitation was also developed. It was found that the Langevin pressure due to a focused acoustic beam will cause the interface to rise to a height that is a function of the

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... nergy density of the beam. The rise time, which is the time it takes for the wafer surface to rise to its maximum height, was found to be independent of the incident energy, but was found to be a function of the surface tension. The time of mound formation measurements in clean water at low-energy acoustic excitations were found to be within 20% of the simulation results. These results imply that surface rise time measurements may present a novel way of measuring surface tension of water-surfactant combinations accurately and rapidly by a simple noncontacting technique.