The tractor beams seen in shows like “Star Trek” have become staple of the sci-fi genre, and now it looks like some clever physicists are getting closer than ever to making them a reality. It may not be the starship halting tractor beam we’ve seen in the movies, but the team was able to use an optical beam to pull a 1.5 micrometer silica sphere suspended in water, proving that a tractor beam could actually exist.
First discovered by Friedrich Bessel over a hundred years ago, we’ve known for quite some time that Bessel beams could potentially act as a kind of tractor beam. However, up until this point no one has been able to prove it. So, in order to do so, physicists David Ruffner and David Grier set out to harness a particular property of the Bessel beam.
Apparently, these lasers have the ability to reconstruct themselves on the opposite side of an object, which, in theory, allows them to sort of grab on to an object and drag it back up the stream of light. Presto, a real-life tractor beam.
To create the “optical conveyor,” Ruffner and Grier adjusted the periodic intensity of the Bessel beam’s axis in a way that allowed it to trap the micrometer silica sphere. By changing the beam’s relative phase the object was moved both upstream and downstream along the beam of light… Sounds like a tractor beam to me!
If you want all of the details on Grier and Ruffner’s work you can read their paper, published in Physical Review Letters, right here.