Generalized Newton's rings with vortex beams.

The Newton's rings are interference patterns with concentric rings, and Newton's rings experiment is one of the most famous classic optics experiments. Here, we show that if we use a vortex beam, we can obtain generalized Newton's rings. Unlike traditional Newton's rings, the generalized ones are no longer concentric rings but spiral arms, and fork-shaped dislocations appear in spiral arms. More interesting, we reveal that both the number of spiral arms and the number of fork-shaped dislocations are equal to the value of topological charge of incident vortex beams. Our theoretical results are demonstrated experimentally. This novel interference pattern can be used for measuring the topological charge of vortex beams.