Last year, we looked at three potential “tractor beam” technologies being evaluated by NASA to deliver planetary or atmospheric particles to a robotic rover or orbiting spacecraft. At the time, the third of these, which involved the use of a Bessel beam, only existed on paper. Researchers at Singapore’s Agency for Science, Technology and Research (A*STAR) have now proven the theory behind the concept, demonstrating how a tractor beam can be realized in the real world – albeit on a very small scale.

Haifeng Wang at the A*STAR Data Storage Institute and colleagues studied the properties of Bessel beams, which, unlike normal laser beams, don’t diffract or spread out as they propagate. While light will usually be scattered backwards when a laser beam hits a small particle in its path, pushing the particle forward, the A*STAR team showed theoretically that light from a Bessel beam scatters off particles that are sufficiently small in a forward direction. This means that the particle is pulled back towards the observer.

The team says the amount of tractor beam force depends on various factors, including the electrical and magnetic properties of the particles. While, like a different tractor beam technology developed by researchers at the Australian National University (ANU), the forces exerted on the particles are very small, Wang says his team’s tractor beams do have real world applications.

While true Bessel beams are impossible to create, as they would require an infinite amount of energy, reasonably good approximations can be made and are used in many optical applications.

“These beams are not very likely to pull a human or a car, as this would require a huge laser intensity that may damage the object,” says Wang. “However, they could manipulate biological cells because the force needed for these doesn’t have to be large.”

He adds that the technology could also be used to gauge the tensile strength of cells, which can reveal whether a cell has been infected. “For instance, the malaria-infected blood cell is more rigid, and this technology would be an easy-to-use tool to measure this,” says Wang.

The team’s research appears in the journal Physical Review Letters.