Time-Dependent Defect Detection by Combination of Holographic Tools

The most widely known application of holographic and speckle interferometry (termed HINDT, ESPI, or DSHI) is in the sensing of invisible structural flaws, which are represented visually as discontinuous interference patterns. This property raised laser metrology techniques as the candidates best suited for nondestructive detection of subsurface defects in qualitative assessment of artworks [1–6]. Nonetheless, in the case of multilayered structures, an underlying imperfection may not always generate directly the expected visible discontinuity in the interference pattern since its influence may not reach the top of the illuminated surface which witnesses its presence, size, and magnitude. Hence effectiveness of the sensing method depends on the investigation procedure and experimental tactics are developed to warranty results standardisation [7, 8]. In this context, the authors have performed inspection of known construction samples with excitation and relaxation time variants [9]. It confirmed that the routine procedure of inspection for artworks should foresee the need for in-time observation of defect kinetics; if a misleading assessment due to mismatch between surface deformation effect and the time of image capture is to be avoided. Herein, part of the ongoing study on defect detection dependencies [8,9] is presented and strong evidence is provided for the time-dependent capturing of the spatial evolution of deformation based on a combination of interferometric measurement techniques.