Laser shock method

A device including a processing circuit configured for performing a method of focusing acoustic waves at an interface between two layers of a multilayer structure, the method comprising:

• emitting a laser beam in the direction of an external surface of the multilayer structure, the laser beam defining a spot at the external surface, the spot having a center and a periphery, the emission of the laser beam thereby producing a longitudinal wave propagating from the center of the spot and a transverse wave propagating from the periphery of the spot;
• determining a distance between said interface and the external surface;
• determining one or more propagation velocities VL of the longitudinal wave and one or more propagation velocities VT of the transverse wave to reach said interface from the layer(s) crossed by said longitudinal and transverse waves;
• and
• determining a radius r of the spot of the laser beam as a function of the propagation velocities and of said distance so that a travel time of the longitudinal wave to reach said interface and to be superimposed with the transverse wave is equal to three times a travel time of the transverse wave to reach said interface and to be superimposed with the longitudinal wave.