Abstract:
Laser-based methods for generation and detection of ultrasonic signals have proven useful in the laboratory and for niche applications in industrial and field measurements. Their further utility continues to be limited by the cost of producing systems with high-detection sensitivity. Overall, laser ultrasonic detection sensitivity can be enhanced in part by insuring that, for a given material and surface condition, the laser source couples optimally and is converted efficiently to elastic energy. Variables to be considered for optimization of elastic wave amplitudes include the laser wavelength, pulse shape, pulse duration, and spatial distribution of the incident laser light. In a laboratory setting in particular, the laser ultrasonic practitioner is able to select propagation angles and modes which contain the greatest amount of ultrasonic energy. Several of these source parameters have been considered carefully for both isotropic and anisotropic materials and may be optimized for maximum ultrasonic energy generated by a pulsed laser source. [Work supported, in part, by the U.S. Air Force Wright Laboratories.]