In an effort to make a futuristic tractor beam, researchers have turned to the distant past to create a particle-trapping laser.
It is not uncommon to hear about how ancient ideas have influenced the ideas and technology of the present, but a team from Tel Aviv University (TAU) in Israel is using millennia-old knowledge to create a true science-fiction staple: a laser tractor beam.
Familiar in series such as Star Trek, the tractor beam is a device capable of shining a laser on to an object and drawing it towards you.
Scientifically speaking, however, it is referred to as laser optical trapping that involves controlling the movement and position of particles of different sizes and shapes and can be used to contribute to further breakthroughs in biology, materials science and spectroscopy, for example.
The Archimedes screw
In a paper published to the journal Optica, the research team revealed how it was able to achieve a new breakthrough in laser optical trapping by harnessing 2,300-year-old water displacement technology to create a beam that can trap and move particles in specific directions.
The ancient technology in question is known as the Archimedes screw, believed to be one of the first effective water pumps with its design of a broad-threaded screw bent around an axis encased by a cylinder or a tube.
Back then, Archimedes demonstrated that the rotation of a mechanical screw displaces water along the axis of the screw, against the pull of gravity.
A major challenge in laser optical trapping is finding a way to move particles towards a light source because particles tend to move with the flow of light meaning they are pushed ‘downstream’, but, with the Archimedes screw solution, it is possible to create upstream movement.
Combination of light and dark
“We have devised an elegant tractor beam based on this simple idea,” said Dr Alon Bahabad of TAU’s School of Electrical Engineering.
“The movement of trapped particles in our case depends on the rotation of the beam. If you rotate it one way, the particles are pushed downstream. Rotate it the other way, and they are pulled upstream.”
Explaining the technology further, Bahabad and the team said it was achieved through the combination of different light beams to create an inference pattern called a standard wave, characterised by alternating bright and dark areas.
“When the particle is in a bright area of the beam, it gets hot and is pushed away by air molecules toward darker regions,” Bahabad said.
“When we rotate the beam, the dark areas move and carry the trapped particles with them. This is how a vending machine that has a screw for moving snacks operates.”