Additive/subtractive decorrelated electronic speckle pattern interferometry

A hybrid additive-subtractive decorrelated electronic speckle pattern interferometry (ESPI) scheme using a continuous reference updating technique is presented. Unlike conventional ESPI techniques, this method uses speckle phase decorrelation between successively subtracted additive correlated speckle images, each of which contains information about the same two states of deformation of a test object undergoing vibrational stressing. It is shown that the susceptibility of this method to environmental noise caused by building vibrations or air currents is significantly lower than that of conventional subtractive ESPI methods, and fringe visibility and contrast are significantly improved over conventional additive ESPI techniques. The ability of this technique to work in a turbulent environment is demonstrated, and application to detection of defects in adhesively bonded structures, a problem of interest to the nondestructive evaluation (NDE) community, is shown.