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Researchers use kirigami to spin terahertz rays

(Xinhua)    10:44, July 03, 2019

CHICAGO, July 2 (Xinhua) -- With a light-spinning device inspired by the Japanese art of paper cutting, researchers at the University of Michigan (UM) have detected microscopic twists in the internal structure of plant and animal tissue without harmful X-rays.

The approach is the first that can fully rotate terahertz radiation in real time, and could open new dimensions in medical imaging, encrypted communications and cosmology, according to a news release posted on UM's website on Monday.

With an eye to exploring how chirality may help distinguish tissues, the researchers gathered everyday biological materials to look for differences in the absorption of clockwise- or counter-clockwise-rotating radiation in the terahertz spectrum. They studied a maple leaf, a dandelion flower, pork fat and the wing case of an iridescent beetle,

While the leaf and fat showed no difference in absorption of clockwise or counter-clockwise radiation, the flower and wing case preferentially absorbed the one over the other, revealing microscopic twists in their structures.

The new device is deceptively simple, essentially a plastic ribbon, printed with a gold herringbone pattern and sliced with staggered rows of tiny cuts. The incisions are influenced by the Japanese art of kirigami, which uses arrangements of cuts to create 3D structures from paper.

When the ribbon is stretched, the cuts open up and the slices of ribbon twist. The gold lines then guide the radiation, twisting it in turn.

The researchers propose the same design could be scaled for other types of radiation as well, with larger patterns interacting with microwaves or radio waves, or shrinking the pattern down to manipulate infrared light.

As spinning terahertz light wasn't widely studied, one of the challenges for the researchers was figuring out how to see whether the kirigami device worked at all.

In addition to imaging living tissues, terahertz circular dichroism spectroscopy could also aid the development of new medicines based on large biological molecules such as proteins and antibodies.

"Our bodies have a lot of twisted structures that are close enough to the surface for terahertz photons to penetrate: vessels, ligaments, muscle fibers, molecules and even some helical bacteria," said Nicholas Kotov, a professor of engineering.

Terahertz radiation is the band of electromagnetic waves that runs from infrared radiation down to the range of the "millimeter scanners" that peer through your clothing at airports. It can travel about a quarter of an inch into the body, but unlike X-rays, it's non-ionizing, which means it doesn't free up potentially damaging electrical charges in the body.

The study has been published in the latest issue of the Nature Materials.

(For the latest China news, Please follow People's Daily on Twitter and Facebook)(Web editor: Kou Jie, Bianji)

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