Laser Interferometry 

LI Laser Interferometry is an established technique for measuring small changes in displacement based on the very small, stable and accurately defined wavelength of light. There are several NDT LI techniques: shearography, electronic speckle pattern interferometry (ESPI) and holographic interferometry. Holographic interferometry is mainly a laboratory-based technique, but the other two have found use in the inspection of composite materials for the detection of surface and sub-surface damage. LI works by comparing two images obtained with the laser for two states of deformation. The two images are compared and produce a fringe pattern, which allows the displacement due to damage to be identified. LI techniques can be applied to a surface with an area of a few square millimetres, as well as being used for large-area inspections.

For more information on LI see:
A M Amaro et al, ‘Damage detection on laminated composite materials using several NDT techniques’, Insight, Vol 54, No 1, January 2012

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