Remote Intense Laser Acoustic Source
NAVAL RESEARCH LAB WASHINGTON DC
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NRL is developing a novel underwater acoustic source, in which a tailored intense broadband laser pulse propagates many meters underwater and generates an acoustic pulse at a predetermined remote location. Such a new acoustic source could enable or improve several critical Navy and commercial applications, including acoustic imaging, undersea communications, and navigation. As part of this work we are exploring intense laser propagation physics through both air and water. Air propagation of the laser pulse will be useful for applications where airborne lasers generate underwater acoustic signals. Controlled underwater compression of these optical pulses is achieved using a combination of group velocity dispersion GVD, which provides longitudinal compression, and nonlinear self-focusing NSF, which provides transverse compression. The resulting high-intensity laser pulse then causes photoionization, intense localized heating, and shock generation. Recent experiments included the first demonstration of underwater acoustic generation using an intense broadband laser pulse. Intense acoustic source levels were measured, and are in the range of useful levels for some Navy applications. Optical GVD was precisely measured, and characterization of this acoustic source, including power spectrum and radiation pattern, is under way.