Interference of a vortex beam with a reference beam can specify the amount of orbital angular momentum carried by the beam. In this study, we demonstrate that the vortex beam produces spiral-shaped interference fringes when interfered with its converging and laterally displaced copy. The analysis will help determine the topological charge, especially its sign. Theoretical description, including intensity and phase profile, has been presented. It is expected that the demonstrated technique would find application in diverse areas, such as in the fields of optical communication and spiral interferometry. (C) 2019 Optical Society of America
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