On October 19th 2014, scientist at the Australian National University announced that they had created a reversible tractor beam. Dr. Vladlen Shevdov and Dr. Cyril Hnatovsky say that they have created a long range optical tractor beam that uses a hollow laser.
The tractor beam is capable of moving particles that are one fifth of a millimeter in size, a distance of 20 centimeter, which is 100 times further than any previous experiment. The ANU tractor beam uses the energy of the laser to heat up particles and the air around them. The team at ANU used gold coated hollow glass particles in their demonstration.
The ANU tractor beam works by trapping the particles in the dark center of the laser. Energy from the beam hits the particles and travels across their surfaces where it is absorbed, creating hot spots. When air particles collide with the hot spots, they shoot away from the surfaces of the gold particles, causing them to recoil in the opposite direction.
The gold particles where then manipulated by changing the polarization of the laser beam. The polarization was changed by altering the shape of the laser from a doughnut shape to a star shape (axial), or a ring shape (azimuthal). Moving smoothly from one polarization to another causes the particle to stop or reverse its direction.
The ANU team say that because lasers can retain the quality of their beams over long distances, their tractor beam could possibly work over meters.
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