Generation of Dispersive Acoustic Waves by the Phase Velocity Scanning of a Laser Beam

Laser ultrasonics is expected to provide a nondestructive evaluation (NDE) method of materials in circumstances where liquid or gel coupler can not be used[1-6]. However, the main limitation of this technique is its low sensitivity compared with the standard piezoelectric transducer method. One of this reason is the low amplitude of acoustic waves that can be generated without damage. If one uses high peak power laser to generate strong acoustic waves, ablation damage of the surface is resulted [2] as illustrated in Fig.1 (a). Even in the thermoelastic regime, photodissociation may be introduced in polymers by repeated laser irradiation [3]