Transfer of angular momentum to matter from acoustical vortices in free space

Phys Rev Lett. 2008 Jan 18;100(2):024302. doi: 10.1103/PhysRevLett.100.024302. Epub 2008 Jan 16.

Abstract

An experimental demonstration of the mechanical transfer of orbital angular momentum to matter from acoustical vortices in free field is presented. Vortices with topological charges l=+/-1 and l=+/-2 were generated and a torsion pendulum was used to study the angular momentum transfer to hanging disks of several sizes. This allowed us to make a comparative study of the effective acoustical torque in terms of topological charge of the vortex, the disk radius, and its position along the main propagation axis. A theoretical discussion of the generated sound fields is also provided.