Tel Aviv University scientists have developed a new laser based on a 2,300-year-old water displacement technique; the laser can trap particles and move them in specific directions.
"Instead of traveling in a straight line like regular laser beams, our beam consists of two helical strands, akin to the shape of DNA, and we can use this beam to move very small particles," said Dr. Alon Bahabad of the Physical Optics Laboratory at TAU's School of Electrical Engineering. "The rotation of the beam determines the direction in which the particles, whose size ranges between tens of nanometers to about 10 microns, are conveyed."
Water pumps were first invented by Archimedes in 3rd-century Greece. His water pump was made with a broad-thread screw that was bent around an axis and encased by a cylinder or tube. In this water pump, the mechanical screw pushes water along the screw’s axis, pushing it against gravity.
The team created a tractor beam based on Archimedes’ idea. The particles that the laser beam is trapping are completely dependent on the way that the laser beam is moving. If the laser is moving to the left, the particles move to the left and vice versa.
"A major challenge in laser optical trapping is how to move particles toward a light source. This is a problem because particles tend to move with the flow of light, or are pushed 'downstream,' so to speak. Our objective was to generate an upstream movement of trapped particles to create a 'tractor beam.' We've done just this by referring to an ancient idea," said Alon Bahabad.
In order to do this, the team combined light beams in order to create an interference pattern-standing wave. These laser types typically have light and dark areas. The particles trapped in the laser are trapped by air movement near the particles and heat near the laser beam.
"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 explained. "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."
The paper on this technology was published in Optica.