Engage the tractor beam, Scotty: Physicists move spheres with lasers

a laser suspends a tiny sphere of glass

Image: Dwight Look College of Engineering

A research team that includes physicists from Texas A&M University at Qatar has taken the “fiction” out of “science fiction.”

Laser physicist Wieslaw Krolikowski, a professor in the Science Program at Texas A&M at Qatar, and his research team in Qatar and at Australian National University (ANU) have moved small glass spheres with a laser beam — much like a tractor beam sci-fi fans have become accustomed to seeing on movie and television screens. The work is published in Nature Photonics.

The team covered small glass spheres, about 50 micrometers in diameter, with a thin gold coating to absorb light. A coated sphere was then placed in a special hollow-beam laser in which a circle of light surrounds a dark center. The sphere sat in the dark center of the beam. Interaction with the light edges of the beam causes the sphere to absorb energy from the laser beam through the special, thin gold layer coating the sphere, raising the temperature and changing the air pressure surrounding the sphere. This change in temperature pushes the sphere either toward or away from the laser.

“When we produced light to heat the backside of the sphere,” Krolikowski said, “the higher air pressure at the back of the sphere pushed it towards the light. The opposite occurred when we heated the front of the sphere.”

This tractor-beam effect had previously only been observed on the microscopic level using plastic beads that only moved a few nanometers, Krolikowski said. But the Texas A&M at Qatar—ANU research team has managed to move particles up to 20 centimeters.

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