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A noncontact laser-ultrasonic technique is described that allows determination of materials anisotropic properties. Plane waves are synthesized by scanning the surface with a laser line source at judiciously chosen intervals. The identification of the stiffness-tensor components is based on the inversion of the phase velocities of these transmitted plane waves. The procedure developed is presented and applied to both simulated and experimental signals. The influence of the spatial extent of the laser source in the identification of the stiffness-tensor components is also discussed; the effect of the spot size is analyzed in the ablation regime for which the acoustic source is localized at the surface, whereas the influence of the optical penetration depth is quantified in the thermoelastic regime.

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PACS 68.60. Bs, 78.47.+p We present experimental and calculation results demonstrating the generation of longitudinal and shear acoustic waves in picosecond laser ultrasonics in an isotropic aluminium plate of 0.54 µm thickness. The waves are detected by an interferometric set-up.