Laser-induced acoustic detection of buried objects

We have investigated the use of acoustic energy produced by a pulsed CO2 laser to detect objects underwater or buried in sand. The CO2 laser produced 150 mJ pulses of duration 100 ns. The resulting acoustic pulses were detected with an audio microphone with a response to 15 kHz or a PZT transducer with a resonant frequency at 28 kHz. With the laser incident on the surface of a water-filled tank, acoustic echoes were observed from the tank walls and from objects in the tank. For objects buried in sand, changes in the acoustic lineshape related to the presence of subsurface objects were observed. Analysis of the data to extract clear signatures of the mine are in progress.