Physicists have built a tractor beam that can both repel and attract objects.
The newly developed device employs a hollow laser beam that is bright around the edges and has a dark center, the Australia National University reported. The innovation is the first long-distance optical tractor beam, and has the ability to move objects one fifth of a millimeter in diameter a distance of up to 20 centimeters, which is up to 100 times farther than past experiments.
"Demonstration of a large scale laser beam like this is a kind of holy grail for laser physicists," said Professor Wieslaw Krolikowski, from the Research School of Physics and Engineering.
The device could be used for applications such as controlling atmospheric pollution or retrieving tiny, but deadly, particles.
"Because lasers retain their beam quality for such long distances, this could work over [meters]. Our lab just was not big enough to show it," said co-author Vladlen Shvedov, who worked on the ANU project.
Similar devices created in the past have used photon momentum to create movement; this new tractor beam relies on the energy of the laser heating up the particles and air around it. Particles are trapped in the dark center of the laser, and energy from the laser hits these particles and travels across their surface. The energy is then absorbed, creating hotspots on the surface. When air particles collide with these hotspots they heat up and shoot away, causing the subject to recoil in the opposite direction.
"We have devised a technique that can create unusual states of [polarization] in the doughnut shaped laser beam, such as star-shaped (axial) or ring [polarized] (azimuthal)," said Cyril Hnatovsky, who also worked on the laser's development. "We can move smoothly from one [polarization] to another and thereby stop the particle or reverse its direction at will."
The findings were published in a recent edition of the journal Nature Photonics.
