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Detection of Optical Vortices
An Optical vortex, fundamentally being a phase structure, the OAM content or the vortex order, cannot be detected from the intensity profiles alone. Furthermore, as vortex beams of orders, l, have roughly identical intensity profiles, they cannot be solely characterized from their intensity distributions. As a result, a wide range of interferometric techniques are employed.


 * The simplest of the techniques is to interfere a vortex beam with an inclined plane wave, which results in a fork-like interferogram. By making a count of the number of forks in the pattern and their relative orientations, the vortex order and its corresponding sign can be precisely estimated.


 * A vortex beam can be deformed into its characteristic lobe structure while passing through a tilted lens. This happens as a result of a self-interference between different phase points in a vortex. A vortex beam of order, l, will be split into n = l+1 number of lobes, roughly around the depth of focus of a tilted convex lens. Furthermore, the orientation of lobes (right and left diagonal), determine the positive and negative OAM orders.


 * Furthermore, a vortex beam when interfered with a vortex of opposite sign, generates a lobe structure. However, this technique offers no detection mechanism to characterize the signs. This technique can be employed by placing a Dove prism in one of the paths of a Mach–Zehnder interferometer, pumped with a vortex profile.