Nonlinear Optical Properties of Stimulated Brillouin scattering to submerged objects detecting are analyzed. With the characteristics of threshold, SBS only occurs when the incident laser is focused in the focusing regime. When there is an object present in front of the focus leading to lower incident intensity then SBS don't occur. The backward SBS signal depends on the location of the submerged object. With the object come near to focusing regime, the backward Stokes signal rise up from zero to a Maximum, and then grow to saturation. The delay time of echo signal to pump signal can give the location of submerged object. Relationships of reflected energy dependent on location of object in SBS cell is analyzed both theretically and experimentally.

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