Measuring the topological charge of orbital angular momentum radiation in single-shot by means of the wavefront intrinsic curvature

We show a method to measure the topological charge of orbital angular momentum radiation in single-shot by exploiting the intrinsic local curvature of the helicoidal wavefront. The method is based on oriented Hartmann cells in a suitable detection scheme. We show experimental results and propose a Shack-Hartmann configuration with sectored photodiodes to improve resolution and detection time. The method can be applied for telecommunication applications in the far field of the radiation beam and more in general to measure the topological charge from a small portion of the radiation wavefront.