EXPERIMENTAL EVALUATION OF ENHANCED GENERATION OF ULTRASONIC-WAVES USING AN ARRAY OF LASER SOURCES

An array of ten pulsed Nd:YAG lasers was constructed in order to study the effects of generating ultrasound with an array of laser sources. The laser system permitted the spatial and temporal control of the fir ing of the individual lasers in the array necessary for the production of both narrow-band ultrasonic signals and phased array single pulses . The increase in sensitivity of a laser ultrasonic system associated with the generation of narrow-band and phased array acoustic waves is discussed theoretically and verified experimentally for surface and bu lk wave generation. The ultrasonic signals were generated in aluminium samples of various thicknesses and with source laser power densities consistent with generation in the thermoelastic regime, thus causing n o damage to the surface of the specimens. The signals were detected us ing a path stabilized Michelson interferometer. In the narrow-band cas e, the waveforms were digitally filtered in order to take advantage of the reduced spectral range of the generated acoustic energy. A signif icant increase in the sensitivity of the laser ultrasonic system, cons istent with theoretical predictions, was observed in both the narrow-b and and phased array cases.