<title>Low coherence speckle interferometry (LCSI): when speckle interferometry goes sub-surface</title>

Abstract

In this paper the theoretical background 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 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.).

Near-infrared low-coherence speckle interferometry (NIR-LCSI) as a tool for the investigation of silicon in solar cell production

“…This has been introduced as Low Coherence Speckle Interferomtery (LCSI) [6]. The measurements start with a scan of the reference mirror.…”