not change the state of measurand itself. Laser ultrasonics is a contactless ultrasonic inspection technique based on excitation and ultrasound measurement using two lasers. A laser pulse is directed onto the sample under test and the interaction with the surface generates an ultrasonic pulse that propagates through the material. The reading of the vibrations produced by the ultrasounds can be subsequently measured by the self-mixing vibrometer: the high performance of the instrument makes it suitable for an accurate measurement of the ultrasonic wave and therefore for a modeling of the characteristics of the sample. When the laser beam hits the surface of the material, its behavior may vary according to the power of the laser used. In the case of high power, there is a real "ablation" or "vaporization" of the material at the point of incidence between the laser and the surface: this causes the disappearance of a small portion of material and a small recall force, due to compression longitudinal, which would be the origin of the ultrasonic wave. This longitudinal wave tends to propagate in the normal direction to the surface of the material, regardless of the angle of incidence of the laser: this would allow to accurately estimate the thickness of the material, knowing the speed of propagation of the wave, without worrying about the angle of incidence. The use of a high power laser, with consequent vaporization of the material, is the optimal way to obtain an ultrasonic response from the object. However, to fall within the scope of non-destructive measurements, it is preferred to avoid this phenomenon by using low power lasers. In this case, the generation of ultrasound takes place thanks to the local overheating of the point of incidence of the laser: the cause of wave generation is now the thermal expansion of the material. In this way there is both the generation of waves longitudinal, similarly to the previous case, and the generation of transverse waves, whose angle with the normal direction to the surface depends on the material. After a few moments the thermal energy dissipates, leaving the surface intact: in this way the measurement is repeatable an infinite number of times (assuming the use of a material sufficiently resistant to thermal stresses) and non-destructive, as required in almost all areas of application of this technology. The movement of the object causes a shift in the phase of the signal,