Ultrasonic velocity and attenuation determination by laser-ultrasonics

Materials are often characterized by measuring the velocity and attenuation of ultrasonic waves. Laser-ultrasonics, which uses lasers for generation and detection of ultrasound, has several advantages compared to the classical piezoelectric techniques, but the use of lasers is often associated with ill-defined source and receiver characteristics making diffraction effects hard to evaluate. We have identified two regimes which, in practice, allow the measurement of velocity and attenuation: the point source/point receiver and the large uniform source/large uniform receiver regimes. These approaches are discussed and illustrated with several examples of application. Limitations caused by misalignment between the generating and detecting laser spots are also analyzed.