Driving optical micromachines with orbital angular momentum

The symmetry of an object such as an optically driven microrotor and the driving light beam is a key element in the generation of optical torque. The optical torque occurs when electromagnetic angular momentum is transferred from the driving beam to the microrotor by scattering. We discuss the effect of such symmetries on the generation of optical torque, and some consequent general principles for the design of optically driven micromachines. We describe the experimental test of a design based on these principles, including the quantitative evaluation of its performance through measurement of the orbital angular momentum (OAM) transfer. We describe the computational modeling of such rotors, and investigate the dependence of the performance on the geometry of the microrotor.