Ultrashort pulse laser used to generate sound under water

The generation of the photoacoustic effect using laser beam with very high intensity is an attractive method. According to the energy deposited by the laser, three mechanisms are involved in the laser generation of sound: (1) thermoacoustics, (2) evaporation and (3) optical breakdown. In this paper, the ultrashort pulse laser has been used to generate sound under water. An effect of induced lens has been observed. There are two focusing points in water. One of them is the convex lens used for the focusing laser beam to produce focusing point. The other is the laser energy induced lens which produces induced focus point. The time process occurs when the index of water is changed; a different variety of index is induced by laser beam. This phenomenon can be used to estimate the response time of the changes of index in water.