Modulated interference of reflected light from a liquid surface wave at tens Hertz frequencies

An analytic intensity expression of the reflected light from a liquid surface with acoustic wave at a few tens Hertz was derived. The expression displays a distinct modulated oscillation. Meanwhile high visibility and modulated interference fringes were obtained experimentally. Line scans across the reflection patterns indicate that the theory predication is well consistent with the experimental data. Moreover, a practical technique can be developed, based on this study, to determine the wavelength and amplitude of the SAW at these frequencies as well as the dynamic surface tension.