Spatial phase measurement techniques in modified grating interferometry

Abstract

High sensitivity grating interferometry has become an important method in experimental mechanics to measure, with submicron sensitivity, the in-plane displacements of nearly flat objects under load. This study looks to extend the use of this interferometric setup through specific modifications to the interferometric setup, focusing specifically on developing the system's ability to register simultaneously both the in-plane and out-of-plane displacements so that dynamic events may be examined with great precision and speed. First presented is the author's approach for mapping in- and out-of-plane displacements through modifications to a conventional grating interferometer. Then, the author extends the method to the analysis of dynamic events, proposing a few workable solutions for registering two interferograms at the same time. Included in this discussion are suggestions for acquiring the orthogonal in-plane displacements u and v and the out-of-plane displacement w simultaneously. The second part of the work details the analysis of different phase measurement techniques, focusing on the error sources inherent in each approach. New, error-reducing algorithms are presented and the influence of the intensity sample weighting (window function) on phase errors is described. A spatial, phase measurement technique advanced by the author, the M-point technique, is chosen as the best choice for achieving fast analysis and high accuracy in displacement testing in the modified grating interferometric setup.