Mobius Strips Conjured from Beam Polarization
ROCHESTER, N.Y. — A light beam can be structured so that its polarization twists around like a Mobius strip.
The finding, by a team of researchers from the U.S., Canada, and Europe, confirms a theoretical prediction that it is possible for light’s electromagnetic field to assume this peculiar shape. Depending on the structure of the laser beam, the observed Mobius strips had either 3/2 or 5/2 twists.
Gradually shifting light polarization within the cross section of a laser beam creates a Mobius strip. Courtesy of the University of Rochester.
“This is one of the very few known examples of a Mobius structure appearing in nature,” said Dr. Robert W. Boyd, a professor of optics at the universities of Rochester and Ottawa. These strips demonstrate the rich structure that a light beam can possess at very small, subwavelength distance scales, he said.
Light controlled in this fashion “may be important for complex light-beam engineering and optical micro- and nano-fabrication,” the researchers wrote in a study published in Science (doi: 10.1126/science.1260635).
The researchers achieved the Mobius-strip effect by tightly focusing a laser beam after it had passed through a liquid crystal lens, called a q-plate, that modifies polarization in a space-variant manner.
A nanoparticle was used to detect how the light was polarized. By scanning a nanoparticle over the cross-section of the beam — essentially using it as an interferometer — the researchers could observe how the light was scattered and therefore how it was polarized.
For more information, visit www.rochester.edu.
- With respect to light radiation, the restriction of the vibrations of the magnetic or electric field vector to a single plane. In a beam of electromagnetic radiation, the polarization direction is the direction of the electric field vector (with no distinction between positive and negative as the field oscillates back and forth). The polarization vector is always in the plane at right angles to the beam direction. Near some given stationary point in space the polarization direction in the beam...
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