Making and identifying optical superpositions of high orbital angular momenta

We report the experimental preparation of optical superpositions of high orbital angular momenta (OAM). Our method is based on the use of a spatial light modulator to modify the standard Laguerre-Gaussian beams to bear excessive phase helices. We demonstrate the surprising performance of a traditional Mach-Zehnder interferometer with one inserted Dove prism to identify these superposed twisted lights, where the high OAM numbers as well as their possible superpositions can be inferred directly from the interfered bright multiring lattices. The possibility of the present scheme working at the photon-count level is also shown using an electron multiplier CCD camera. Our results hold promise in high-dimensional quantum-information applications when high quanta are beneficial.