Medical News
Physics
27 June 2019
A laser beam can be twisted to move like a vortexJILA (USA) Rebecca Jacobson, Servicio de Produccion e Innovacion Digital – Universidad de Salamanca (Spain)
By Leah CraneThere’s a new kind of twisted light. A rotating “vortex beam” whose twist changes across the length of the beam has been created in the lab for the first time.
Researchers discovered in 1992 that a beam of light could have orbital angular momentum, meaning that the beam twists as it propagates forward, with each photon circling around the centre of the beam.
Now, Kevin Dorney at the University of Colorado Boulder and his colleagues have found that it’s possible to make light that not only twists, but has a different degree of twist along the length of the beam.
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They did this by shining two infrared laser pulses, each with a slightly different orbital angular momentum and a delay between them, through argon gas. The two pulses overlap so that the second hits the gas before the first finishes passing through.
As the beams hit the gas, their energy is absorbed and then quickly re-emitted by the argon atoms. “It’s sort of like currency exchange but with light, and the argon is like the bank teller” says Dorney. The argon takes in the two infrared light beams and re-emits their light in a single pulse with a much shorter wavelength in the ultraviolet (UV) range.
The result is a UV pulse with a gradually changing twist, a property the researchers call self-torque. A photon at the front of the beam orbits around the beam’s centre slower than a photon at the back.
“This light can be used to manipulate or study very very fast dynamics on very very small scales, which happens to be where we’re heading naturally with technology,” says Dorney. Light can be used not just for imaging, but also for trapping and moving tiny objects, so these twisted beams may help us understand and manipulate the materials we’ll need for the next generation of faster, smaller devices, he says.
Journal reference: Science, DOI: 10.1126/science.aaw9486
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