Abstract: One possibility for communicating from an airplane above water surface to submarine in sea involves the use of laser- generated underwater sound. Because the air-submarine communication should be in the sea-environment i.e. very large volume of water, higher photoacoustic coefficient is the first important factor to be considered. Solid state laser Nd:YAG as one kind of high-power laser is possible for this application, since it has such advantages: (1) high power to do optical breakdown in water, (2) compact for airborne; (3) 1.06 $mu IR beam being absorbed strongly by water but still penetrating into water a bit in depth, it will be good for making a sound source under water-surface. In this paper, we introduce the way to generate strong optical breakdown acoustic signal in a limited large volume of water in lab. The optical breakdown mechanism of strong Nd:YAG laser pulse (6 - 8 ns; max 600 mj/p) with water generates acoustic signals in water having pulse widths about 25 $mu@s and a frequency spectrum peak about 58 kHz. And, its sound source level of 196 dB for low frequencies less than 58 kHz is to be detected at a distance deep in water. Also, special new requirements are mentioned for solid state laser's designer.!5
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