A team of researchers at the US Naval Research Laboratory (NRL) has demonstrated that a laser acoustic source they have developed is capable of long-distance acoustic propagation and shock generation.
The tests, performed at the Lake Glendora Test Facility of Naval Surface Warfare Center-Crane, expanded on earlier laboratory research on pulsed-laser propagation through the atmosphere.
Using a pulsed Nd:YAG (Neodymium-doped Yttrium Aluminium Garnet) 532-nanometre-wavelength laser housed in a floating platform, pulses were directed by steering mirrors down through a focusing lens and into the water surface.
Each laser pulse produced an acoustic pulse with a sound pressure level of approximately 190 decibels (dBs), which was detected and measured by boat-mounted hydrophones at distances up to 140 metres. Prior laboratory acoustic propagation distances were limited to about three metres.
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 could be used for remote acoustic generation.
A properly tailored laser pulse has the ability to travel many hundreds of metres through air, remaining relatively unchanged, then quickly compress upon entry into the water.
Atmospheric laser propagation is useful for applications where airborne lasers could produce underwater acoustic signals without any required hardware in the water, a highly useful and efficient tool for undersea communications from aircraft.
Additional potential applications benefiting from extended underwater acoustic propagation include rapid sonar search and detection of underwater mines and vessels, and navigation using remotely generated laser acoustic beacons.