CANADA: Tiny swirls of gold, so small they’re invisible to the human eye, could be a new weapon in the war against identity theft, researchers say.
Such “nano-spirals,” if they were printed onto objects like currency or identity cards, could make those objects almost impossible to counterfeit, they say.
Known as Archimedes spirals, they were created at Vanderbilt University by students and faculty, who then utilized ultrafast lasers to examine their optical properties, a study in the Journal of Nanophotonics reports.
“They are certainly smaller than any of the spirals we’ve found reported in the scientific literature,” says doctoral student Roderick Davidson II, who developed a method for studying the spiral’s optical behavior.
Shrunk down to sizes smaller than wavelengths of visible light, they glow blue only when exposed to infrared light.
The also have a unique response to polarized laser light, the researchers explain, giving off varying amounts of blue light as the polarization plane’s angle is rotated.
The unique characteristics of the spirals, when exposed to such varied wavelengths and types of light, give them customizable, unique “signatures” that would be extremely difficult to counterfeit, their developers say.
The spirals are so small than even a square array of 100 would still be invisible to the naked eye, the researchers note, while their “signature” responses are so strong they can be easily detected with the appropriate sensors.
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