Optical interferometry diagnostics in laser-induced spallation on film–substrate systems

Two novel optical interferometry diagnostics methods, wave pattern identification and correlation detection, were developed for measuring the adhesion strength between a film or coatings and substrate. The method of wave pattern identification was constructed on the analysis of the physical procedure of the film spallation. According to the intensive reflective apex we could judge the film spallation intuitively, and also determine the spall moment, spall depth and spall strength directly. Furthermore, to accurately determine the initial critical spall strength and distinguish the damage degrees of the interface, through studying the alternation of propagation routes at the present of interface delamination, we advanced the correlation detection method to calculate the time delay τ for characterizing the progressive damage, such as interface delamination, film spallation and film expulsion. Based on this theory, new criteria for diagnosis of the film spallation were established, which could determine the degree of damage and the dimensions of damage quantitatively, such as the minimum width of delamination radius and the film thickness.