Low Coherence Speckle Interferometry (LCSI) when speckle interferometry goes sub-surface

In this paper the theoretical back-ground and basic principles of Low Coherence Speckle Interferometry (LCSI) are described. Furthermore the main parts of our research work are briefly introduced (1) the development of a dual wavelength. open-path LCSI setup (2) the introduction of a new method for the detection of zero path length difference for temporal phase shifting (3) the optimisation of the optical parameters of LCSI to increase the probing depth (beam ratio, position of the coherence layer and imaging parameters) (4) the fundamental understanding of the measurement effect and quantification of the measurements using a one-dimensional transmission line model. Finally, LCSI is introduced as a too] for characterisation of adhesion. In this work fundamental studies on interfacial instabilities in adhesive bonded aluminium joints are carried out. The basic hypothesis is that low adhesion is due to the existence of microscopic delaminations at the interface between the substrate and the adhesive. These delaminations can be caused by imperfect pre-treatment, surf, ace topography or other surface phenomena (e.g. corrosion. inter-metallic particles, etc.).