Durham, NC—Researchers from Duke University have devised a technology that can bring true color to infrared imaging systems, like the one used to track Arnold Schwarzenegger through the jungle in the movie Predator.
Traditional infrared imaging systems may look colorful on screen, with warm objects appearing redder and whiter than their surroundings, but these images are not created from actual colors. They are based on the amount of thermal radiation—or infrared light—the camera captures. The ability to identify different wavelengths, or colors, of the infrared spectrum would capture much more information about the objects being imaged.
In a study published November 9, a team lead by Maiken H. Mikkelsen, the Nortel Networks Assistant Professor of Electrical & Computer Engineering and Physics at Duke University, demonstrated perfect absorbers for small bands of the electromagnetic spectrum, from visible light through the near infrared. The fabrication technique is easily scalable, can be applied to any surface geometry and costs much less than current light absorption technologies.
Once adopted, the technique would allow advanced thermal imaging systems to be produced faster and cheaper than today’s counterparts, as well as have higher sensitivity.
“By borrowing well-known techniques from chemistry and employing them in new ways, we were able to obtain significantly better resolution than with a million-dollar state-of-the-art electron beam lithography system,” said Mikkelsen.
“This doesn’t require top-down fabrication such as expensive lithography techniques and we don’t make this in a clean room,” added Gleb Akselrod, a postdoctoral researcher in Mikkelsen’s laboratory. “We build it from the bottom up, so the whole thing is inherently cheap and very scalable to large areas.”
The technology relies on a physics phenomenon called plasmonics. The researchers first coat a surface with a thin film of gold through a common process like evaporation. They then put down a few-nanometer-thin layer of polymer, followed by a coating of silver cubes, each one about 100 nanometers (billionths of a meter) in size. When light strikes the engineered surface, a specific color gets trapped on the surface of the
nanocubes in packets of energy called plasmons, and eventually dissipates into heat. By controlling the thickness of the polymer film and the size and number of silver nanocubes, the coating can be tuned to absorb different wavelengths of light from the visible spectrum to the near infrared.
Coating photodetectors to absorb only specific wavelengths of infrared light would allow novel and cheap cameras to be made that could see different infrared colors. duke.edu