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Precision phase measurement in digital speckle shearing interferometry

The measurement of phase in Digital Shearing Speckle Interferometry (DSSI) is a challenging problem because of the inherently noisy nature of shearing speckle interferograms. Accurate phase measurement depends on having a high-precision imaging system, a finely-controlled phase-shifting technique and good algorithms. In this paper, two selected algorithms used for carrying out phase measurement in ESPI (Electronic Speckle Pattern Interferometry) are applied to phase measurement in DSSI. The components and requirements of the high-precision imaging system developed to improve the recording quality of shearing interferograms are discussed. A new precisely-controlled phase shifting method developed to reduce systematic measurement error is also described. Experimental results are presented to illustrate the method.