  Beams of light with helical wavefronts can be focused into ring-like optical
traps known as optical vortices. The orbital angular momentum carried by
photons in helical modes can be transferred to trapped mesoscopic objects and
thereby coupled to a surrounding fluid. We demonstrate that arrays of optical
vortices created with the holographic optical tweezer technique can assemble
colloidal spheres into dynamically reconfigurable microoptomechanical pumps
assembled by optical gradient forces and actuated by photon orbital angular
momentum.
