Researchers from The Australian National University (ANU) has invented an optical tractor beam that can move objects at a distance of about 20 cm, or approximately 100 times further than what have been exhibited in previous experiments.
The invention, which was described in the journal Nature Photonics on Oct. 19, can repel and attract particles with diameter of at least 0.2mm using a hollow laser beam, a laser with bright edges around and a dark center.
The device is considered to be the first long-distance optical tractor beam researchers described to be a Holy Grail for laser physicists.
Unlike earlier experiments on tractor beams that relied on photon momentum to move particles, the ANU experiment used the energy of the laser to heat up gold-coated hollow glass particles and the air surrounding them.
For their experiment, the researchers trapped the particles in the dark center of the beam. The laser's energy then travels across surface of the particles, where it gets absorbed and creates hotspots. The collision of the air particles with these hotspots then heats them up and shoots them away from the surface, causing the particle to recoil in the other direction.
"Here, we demonstrate the stable transfer of gold-coated hollow glass spheres against the power flow of a single inhomogeneously polarized laser beam over tens of centimetres," study researcher Wieslaw Krolikowski, from ANU's Research School of Physics and Engineering, and colleagues wrote. "Additionally, by varying the polarization state of the beam we can stop the spheres or reverse the direction of their motion at will."
The concept of tractor beams, which uses a beam of light to move and manipulate objects, have long been a staple in science fiction movies such as George Lucas' Star Wars.
The tractor beam created by the researchers may not have the same power and capabilities that were envisioned for such devices in these fictional movies but the team's invention appears to have a number of potential real world uses.
The technique used in the experiment, for instance, could be used in controlling air pollution, or to retrieve dangerous and tiny particles for sampling. The effects exhibited in the experiment can also be possibly scaled up.
"Because lasers retain their beam quality for such long distances, this could work over metres," said study co-author Vladlen Shvedov, also from Anu. "Our lab just was not big enough to show it."
