Technologies that use underwater acoustics -- for sonar, communications, or navigation -- often require a piece of hardware in the water to create sound remotely. Physicist Ted Jones and his team at the U.S. Naval Research Laboratory in Washington, DC, are working on ways to use flashes of laser light instead.
These lasers travel through air and water to generate an underwater explosion of sound at a remote location without the need for extra hardware. They will present their latest experimental data testing laser acoustics in a bubbly salt water tank and comparing two types of lasers.
The conversion of light into sound is possible because certain kinds of light pulses will self-compress, superheating a small volume of water. This optical compression happens because the intense laser light changes the properties of water so that it acts like a focusing lens and because slightly different colors of the laser travel at different speeds in water. The resulting explosion of steam it creates can generate a 210 decibel pulse of sound.
Currently, Jones is tailoring two different kinds of visible and infrared lasers to produce these pulses, which could eventually be used to encode information. The NRL group has created broadband laser pulses that can travel up to 20 meters through water to create acoustic pulses at precise distances. The laser light can also travel hundreds of meters through clear air, so one potential application is airplane-to-submarine communication. Acoustic reflections from the pings they produce could also be monitored to gather information about underwater environments, from detecting mines to mapping the bottom of the ocean floor.
The talk "Intense underwater laser acoustic source for Navy applications" by Ted Jones will be presented at the 157th Acoustical Society of America Meeting to be held May 18-22 in Portland, Ore.