Abstract: A method is provided for the non-destructive and contactless characterization of a multilayered structure having a substantially spherical shape and including at least two layers, separated by interfaces. The method includes using a laser for locally heating the structure in a thermoelastic state so that the structure is vibrated in a non-destructive manner, measuring the resonance frequencies of the vibration modes of the structure and deriving at least one characteristic concerning the integrity or the shape or the mechanical behavior of the structure from the resonance frequencies of the structure.

Abstract: A laser is capable of working at a wavelength L.sub.2 from an active material capable of generating radiating emissions at at least two wavelengths L.sub.1 and L.sub.2, through the presence of a semiconductor plate in the laser cavity. Notably, the laser can generate wavelengths ranging from 1.4 .mu.m to 2 .mu.m, a range in which the optical damage threshold of the eye is high, from an Nd.sup.3+ doped YAG having numerous radiating emission wavelengths ranging from 0.946 .mu.m to 1.8 .mu.m.