Dynamic ESPI with subtraction–addition method for obtaining the phase

Dynamic electronic speckle pattern interferometry (DESPI) was developed for in situ observations. The quantitative evaluation of the deformation field was performed through 2-D subtraction–addition method (SAM) for phase analysis. This method does not require additional phase modulation, which makes it applicable to studying dynamic events. The method utilizes the ratio of the subtraction and addition correlation fringe patterns. The bias intensity that has to be removed from the addition images was determined by temporal averaging of a sequence of speckle patterns. To reduce the error, Gaussian filter was applied to the correlation fringe patterns. The deformation field was evaluated with accuracy of λ/10.