Zero group velocity (ZGV) Lamb modes have already shown their potential in nondestructive testing applications as they are sensitive to the sample structural characteristics. In this paper, we first consider an aluminum sample to validate a method based on the beam shaping of the generation laser. This method is proven to enhance ZGV Lamb modes in aluminum, and then advantageously applied to a composite material plate. Finally, based on the proposed method, scanning the sample over healthy and flawed zones demonstrates the ability to detect subsurface flaws.

A fast slot detection and characterization method using all-optical ultrasound generation and detection is presented in this paper. It is based on the relative properties of the Rayleigh wave transmitted by a slot and the Rayleigh wave mode-converted from the head wave. Considering finite element analysis, it appears that only one A-scan is necessary to both detect the slot position and evaluate its depth. Good agreement has been found with experiments carried out on an aluminium sample with a laser line source and an interferometric optical probe.

Laser-ultrasound-based non-destructive testing (NDT) applications usually use circular or linear thermoelastic sources. This paper studies two more complex sources and presents their specific advantages. The first thermoelastic source is a regular line array, whereas the second one is a chirped line array. The surface acoustic waves generated on an aluminum sample by these two thermoelastic sources are detected by an interferometric optical probe, the measurements showing a good agreement with theoretical expectations. Finally, the potentialities of these two sources in NDT applications are described.

Two complementary techniques, picosecond ultrasonics (PU) and Brillouin light scattering (BLS), have been performed to measure the mechanical properties of layers involved in an optical stack. One of the advantages of these two techniques is their ability to analyze samples whose thickness varies from a few tens of nanometers (the anti-reflective coating) to several millimeters (the polymer substrate). Since all the layers constituting the optical stack have proved to be isotropic, they are completely elastically characterized thanks to the two techniques. Moreover, as the two independent elastic coefficients are measured by PU and BLS, c 33 and c 44 , respectively, the complete stiffness matrix and, hence, the Poisson's ratio and the Young's modulus can be deduced.