Underwater three-dimensional imaging with an amplitude-modulated laser radar at a 405 nm wavelength

We report the results of underwater imaging with an amplitude-modulated single-mode laser beam and miniaturized piezoactuator-based scanning system. The basic elements of the device are a diode laser source at 405 nm with digital amplitude modulation and a microscanning system realized with a small-aperture aspheric lens mounted on a pair of piezoelectric translators driven by sawtooth waveforms. The system has been designed to be a low-weight and rugged imaging device suitable to operate at medium range (~10 m) in clear seawater as also demonstrated by computer simulation of layout performance. In the controlled laboratory conditions a submillimeter range accuracy has been obtained at a laser amplitude modulation frequency of 36.7 MHz.