Mobius Strips Conjured from Beam Polarization

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.