title: Experimental demonstration of multiple pulse nonlinear optoacoustic signal generation and control.
abstract: Generating underwater acoustic signals from a remote, aerial location by use of a high-energy pulsed infrared laser has been demonstrated. The laser beam is directed from the air and focused onto the water surface, where the optical energy was converted into a propagating acoustic wave. Sound pressure levels of 185 dB re microPa (decibel re microPa) were consistently recorded under freshwater laboratory conditions at laser-pulse repetition rates of up to 1000 pulses/s. The nonlinear optoacoustic transmission concept is outlined, and the experimental results from investigation of the time-domain and frequency-domain characteristics of the generated underwater sound are provided. A high repetition rate, high-energy per pulse laser was used in this test under freshwater laboratory conditions. A means of deterministically controlling the spectrum of the underwater acoustic signal was investigated and demonstrated by varying the laser-pulse repetition rate.
authors.affiliation: Naval Undersea Warfare Center, Newport, Rhode Island 02841, USA. blackmonfa@npt.nuwc.navy.mil
authors.forename: Fletcher
authors.initials: F
authors.lastname: Blackmon
authors.forename: Lynn
authors.initials: L
authors.lastname: Antonelli