Digital Holographic Speckle Pattern Interferometry (DHSPI)

Digital Holographic Speckle Pattern Interferometry (DHSPI) is a non-destructive and non-contact optical technique which investigates deformation, deterioration and fracture mechanisms in order to evaluate the structural condition of materials and systems as a result of ageing, mechanical alteration and materials’ failure. The technique is based on the principles of digital imaging and interferometry and thus it combines the ease of operation and high spatial resolution of digital cameras with the ultrahigh (in sub μm scale) displacement sensing. The technique enables sensing, detection and documentation of invisible defects, allowing their location, measurement and exact positioning within the structure of the object. Moreover monitoring structural changes as a result of environmental and climatic phenomena, conservation treatments, natural or provoked ageing, transportation or handling, are among the potentials of this technique. DHSPI is a custom-made system for high resolution interferometric imaging to capture microscopic alterations of sub-surface topography. Hidden defects are revealed as visible interference fringe patterns forming locally inhomogeneous intensity distribution shapes. The deformation data are extracted through the differential displacement of the surface under investigation and the deformation value is measured by multiples of half wavelength.