A technique is developed to detect underwater acoustic signals by utilizing the resultant surface perturbations. It
uses light wave in air and uses acoustic wave under water. Because two best channels are combined together, it is
an ideal method for remotely detecting underwater acoustic signals. The underwater acoustic signal can cause the
perturbations at water-air interface. These perturbations result in an amplitude modulation effect on a laser beam
reflected by the water surface. The modulated underwater laser signal can be detected by using a direct light
intensity detecting method. Based on the theory of modulation of the intensity of laser, a detection system was
developed in the laboratory. By analyzing the massive experimental data, the technique of laser detection of
underwater acoustic signals is validated.