Real-life tractor beam developed at NYU
We experimentally demonstrate a class of tractor beams created by coherently superposing coaxial Bessel beams. These optical conveyors have periodic intensity variations along their axes that act as highly effective optical traps for micrometer-scale objects. Varying the Bessel beams' relative phase shifts the traps axially thereby selectively transports trapped objects either downstream or upstream along the length of the beam. The same methods used to project a single optical conveyor can project arrays of independent optical conveyors, allowing bi-directional transport in three dimensions.
A tractor beam is a traveling wave that can transport illuminated material along its length back to its source. By this definition, an optical tweezer  is not a tractor beam because of its inherently limited range. Nor is an optical conveyor belt [2, 3], which is created from a standing wave rather than a traveling wave. A one-sided variant of the optical conveyor belt created from coaxial Bessel beams has been demonstrated, but relies on auxiliary forces to achieve retrograde motion . Here, we demonstrate one-sided optical conveyors that act as tractor beams without requiring outside assistance. The same technique we use to project a single optical conveyor also can project arrays of optical conveyors each with independently controlled transport properties.