Reconstruction of refractive indices distribution in 3D using a single pattern of multiple-beam interference fringes for online investigation of necking phenomenon

A proposed model for reconstructing the refractive indices distribution in three dimensions is introduced. The reconstruction process requires a single multiple-beam interference pattern which facilitates online investigation of structural changes. In order to increase the accuracy of the measured refractive indices, fringe analysis was applied on the basis of the inverse interferogram principle proposed in this article. Verification of the modified technique was made using reconstructed noise-free interference patterns. The modified technique is helpful in studying the necking phenomenon observed during creep extension of polypropylene fibres. Refractive index distribution in 3D across the fibre was determined and the birefringence profile was calculated. Microinterferograms are given for illustration.