Abstract
Electronic Speckle Pattern Interferometry (ESPI) is used for optical non destructive testing based on interferometrical deformation measurement of the surface of an object. Low Coherence Interferometry (LCI), in particular Optical Coherence Tomography (OCT), are well established techniques for structural imaging based on depth-resolved interferometrical measurements. OCT is mainly used in medical applications, like structural imaging of the human eye. Low Coherence Speckle Interferometry (LCSI) combines the depth-resolved measurement from OCT and the high-accuracy out-of-plane deformation measurement from ESPI. Depth-resolved deformation measurement enables, for example, the characterisation of the behaviour of interfaces in semi-transparent and transparent multi-layered materials or structures while changing the ambient conditions. In this presentation the theoretical background and basic principles of LCSI are described. Furthermore the main parts of our research work over the last 6 years are briefly introduced:development of an dual wavelength, open-path LCSI setup introduction of a new method for the detection of zero path length difference for temporal phase shifting optimisation of the optical parameters of LCSI to increase the probing depth (beam ratio, position of the coherence function and imaging parameters) fundamental understanding of the measurement effect and quantification of the measurements using an one-dimensional transmission line modelFinally, LCSI is introduced as a tool 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, surface topography or other surface phenomena (e.g. corrosion, inter-metallic particles, etc.).