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Laser-generated ultrasonic waves were produced in the ablation regime at the surface of three steel samples, each having a different grain size. We show that the “noise” following the first longitudinal pulse behaves, with respect to frequency, as if it was the result of the scattering of the incident waves by the inhomogeneities in the material. We show that the grain size is related to the level of the relative “noise” spectrum, i.e. the “noise” spectrum compared to the first longitudinal pulse spectrum.

We have developed a 2 layer Laser-Ultrasonics model with interfacial conditions that describes the cohesion of materials. Different materials made with Schott’s BG18 and KG3 glass plates glued on aluminum plates were studied. Our model allows us to fit nicely the experimental results: the reflections coming from the interfacial medium are seen giving us information on the bonding of the two plates.

We present a numerical modelling of a laser ultrasonic process, which can be applied to the visualisation of near surface defects in composite materials. To this aim, the laser generation and propagation of ultrasound are described by a one-dimensional thermoelastic model and the detection of ultrasound is simulated by modelling the response of the Fabry-Perot receiver. Results have been compared to experimental data obtained on test samples with good agreement.

International audience; We present three all-optical methods that were used for the determination of the physical properties of a carbon-epoxy composite. The pulsed photothermal method, the photoacoustic method and the laser-ultrasonics method were used for the determination of, respectively, the thermal diffusivity, the optical penetration length, the thickness and the elastic coefficients of a carbon-epoxy composite covered with a 75 µm paint film at its surface.