Propagation of an arbitrary vortex pair through an astigmatic optical system and determination of its topological charge.

We embed a pair of vortices with different topological charges in a Gaussian beam and study its evolution through an astigmatic optical system, a tilted lens. The propagation dynamics are explained by a closed-form analytical expression. Furthermore, we show that a careful examination of the intensity distribution at a predicted position past the lens can determine the charge present in the beam. To the best of our knowledge, our method is the first noninterferometric technique to measure the charge of an arbitrary vortex pair. Our theoretical results are well supported by experimental observations.