Speckle interferometry for measurement of continuous deformations

An improved method for measurement of continuous displacement and deformations with digital speckle pattern interferometry is presented. The initial random phase of the speckle pattern is evaluated by having many phase-shifting steps before the deformation. By this way the accuracy of the initial phase estimation can be increased and the handling of the image noise is improved. This makes it also possible to use the phase stepped speckle patterns as references for comparison with the speckle patterns of the deformed object, thereby increasing the reliability and accuracy of the phase estimations of the deformed patterns. The technique can be used for measuring deformations such as transients and other dynamic events, heat expansion as well as other phenomena where it is difficult to accomplish phase shifting during deformation.