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For the purpose of visually comparing two similar objects (the master and the test), comparative speckle pattern interferometry is presented. The comparison result is displayed as an interference pattern that illustrates the displacement difference. Using the stored master and test objects in the photorefractive material (LiNbO3 crystal), different phase-stepping algorithms are implemented. A new formula for the addition of the difference and sum phases of deformations and the error in the calculated phase is obtained using three, four, and five-phase step algorithms. The difference correlation fringes that coexist with the sum correlation fringes can be obtained and analyzed using the unwrapped phase maps in order to extract only the difference fringe map that corresponds to the difference correlation fringes and measure the difference in displacement accurately and with high performance. The results show that when it comes to the unwrapped phase map of the difference in displacement of the two stressed objects, the five-phase stepping method produces more accurate results than the three- and four-phase stepping algorithms.
Moustafa et al. (Sat,) studied this question.