Washington, DC--A research team at the U.S. Naval Research Laboratory (NRL) led by physicist Ted Jones performed the first successful long-distance acoustic-propagation and shock-generation demonstration of their novel underwater photo-ionization laser acoustic source. These tests, performed at the Lake Glendora Test Facility of Naval Surface Warfare Center-Crane (Crane, IN), expanded on their earlier laboratory research on pulsed-laser propagation through the atmosphere.
Using a pulsed Nd:YAG 532-nm-wavelength laser housed in a floating platform, pulses were directed by steering mirrors down through a focusing lens and at the water surface. Each laser pulse produced an acoustic pulse with a sound-pressure level of approximately 190 dB, which was detected and measured by boat-mounted hydrophones at distances up to 140 m away. Prior laboratory acoustic-propagation distances were limited to about 3 m.
"The goal of this laser acoustic-source development is to enable efficient remote acoustic generation from compact airborne and ship-borne lasers, without the need for any source hardware in the water," said Jones. "This new acoustic source has the potential to expand and improve both Naval and commercial underwater acoustic applications."
The driving laser pulse has the ability to travel through both air and water, so that a compact laser on either an underwater or airborne platform can be used for remote acoustic generation. A properly tailored laser pulse has the ability to travel many hundreds of meters through air, remaining relatively unchanged, then quickly compress upon entry into the water. Atmospheric laser propagation is useful for applications in which airborne lasers produce underwater acoustic signals without any required hardware in the water, a highly useful and efficient tool for undersea communications from aircraft.
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