Orbital Angular Momentum of Structured Vortex Beams Induced by Intensity Singularity

A new category of optical orbital angular momentum (OAM) associated with intensity singularity independent of phase singularity is predicted, and a kind of structured vortex beams (VBs) with arbitrary transverse shapes is demonstrated. A universal inverse-designed caustic scheme is developed for generating such structured VBs which exhibit crucial intensity gradient and phase gradient. Additionally, they exhibit nonuniformly distributed phase gradients, capable of driving particles accelerately along a desired trajectory. Particle trapping experiments validate that such structured VBs without phase singularity drive the trapped particles to move along predefined trajectories. The idea not only provides an approach for generating and manipulating OAM from intensity singularity, enabling to spur further independent insights into the generation of OAM, but also paves the way for optically driving and accelerating particles along a desired trajectory.