Measuring the topological charge of an optical vortex by using a tilted convex lens

We demonstrate, analytically and experimentally, a simple, but effective method to determine the topological charge of an optical vortex by using a spherical bi-convex lens, a ubiquitous optical element found in any optics laboratory. Just by tilting the lens and recording the intensity distribution of a propagating vortex at a predicted position past the lens, we have been able to measure both the sign and the magnitude of the topological charge m up to m = +/- 14. Our experimental results are in excellent agreement with analytical predictions. (C) 2013 Elsevier B.V. All rights reserved.