A laser interferometry technique is developed to detect water surface capillary waves caused by an impinging acoustic pressure field. The frequency and amplitude of the water surface capillary waves can be estimated from the local signal data at some special points of the phase modulated interference signal, which is called the turning points. Demodulation principles are proposed to explain this method. Experiments are conducted under conditions of different intensity and different frequency driving acoustic signals. The results show the local signal data analysis can effectively estimate the amplitude and frequency of water surface capillary waves.

To determine the amplitude of weak sinusoidal water surface acoustic wave (WSAW), a method based on the spectrum analysis of the phase-modulated interference signal is developed. Calculated from the amplitude spectrum of the detection signal, a characteristic ratio indicates that the phase-modulation depth of a WSAW is suggested by determining the amplitude of a WSAW according to their functional relationship. Experimental investigations for a 4 kHz WSAW evaluate the measurement’s precision with an amplitude measurement standard deviation of 0.12 nm. The measurement accuracy also is demonstrated by the experimental investigations. The theory of this method is briefly described, and the experimental setup is presented.