Laser speckle decorrelation technique for in-plane deformation measurement

Abstract

Application of laser speckle to the measurement of surface displacement/ deformation has been described herein. When a laser illuminated diffuse surface undergoes displacement, the speckle pattern appears in the scattered field and its image shows displacement accompanied by change in structure. They can be quantitatively described in terms of the cross-correlation function of the intensity distributions at an observation plane before and after the surface movement. The peak of the autocorrelation is always located at zero. Peak position of the cross-correlation, which generally deviates from zero, corresponds to the speckle displacement, whereas the decrease in peak height is associated with change in structure, so-called decorrelation.