  Trapping and manipulation of particles using laser beams has become an
important tool in diverse fields of research. In recent years, particular
interest is given to the problem of conveying optically trapped particles over
extended distances either down or upstream the direction of the photons
momentum flow. Here, we propose and demonstrate experimentally an optical
analogue of the famous Archimedes' screw where the rotation of a
helical-intensity beam is transferred to the axial motion of optically-trapped
micro-meter scale airborne carbon based particles. With this optical screw,
particles were easily conveyed with controlled velocity and direction, upstream
or downstream the optical flow, over a distance of half a centimeter. Our
results offer a very simple optical conveyor that could be adapted to a wide
range of optical trapping scenarios.
