What is real is not always as it appears. ΒιΆΉΣ³»­΄«Γ½ researchers have found a way to hide information on materials and only make it visible to a person using the right tech.

β€œWe found we can create a surface where we preferentially control absorption of light,” says Debashis Chanda, an associate professor of physics, optics and nanoscience who has developed the technique.

The findings were published recently in the Nature journal Light: Science & Applications.

The trick is to put the information on a surface that is riddled with nanoscale patterns, which can fool the naked eye by reflecting only a solid color rather than the intended information. To get the intended information, a person must look through an infrared lens or camera tuned to the correct infrared band.

The information can also be changed so that the secret messages invisible to the human eye can appear and reappear.

And not only can information be hidden this way, the information can also be changed so that the secret messages invisible to the human eye can appear and reappear. These further developments were published recently as a cover article in the journal ACS Photonics.

The applications for this technology could include anticounterfeiting security, infrared tagging or infrared camouflages where, for instance, the presence of a designer label could be confirmed with a look through an infrared camera. It also has military applications, such as confirming which assets are friendly and which are enemy by tags on their surfaces that are only visible in a specific infrared band or by dynamically changing the information for infrared camouflage.

Two men stand side by side, the one on the left wears a lab coat and blue gloves and holds a small computer chip toward the camera
Associate Professor Debashis Chanda and Postdoctoral Fellow Sayan Chandra’s findings were published recently in the Nature journal Light: Science & Applications.

In the Light: Science & Applications study, the researchers demonstrated that they can hide images within the infrared spectrum while the same area appears as a solid color in the visible spectrum.

To do so, they created a three-level, layered, β€œplasmonic” system that sandwiches a polymer layer imprinted with nanoscale holes, between a gold mirror at the bottom and a gold layer at the top with holes that match the polymer layer.

Images can be imprinted on top of the β€œplasmonic sandwich,” and aspects of the holes, such as size and depth, help dictate which infrared band the image can be seen in. Without looking through an infrared camera tuned to the right band, the top of the device looks like a solid color, such as a yellow square, thanks to the unique properties that can be achieved with materials at the nanoscale.

Varying the pattern characteristics allows the researchers to control the electron plasma resonance, or the electric energy, created when light hits the device.

β€œSo by controlling this electron plasma resonance we can actually control which color of light or which band of light is absorbed and reflected,” Chanda says.

“We can actually control which color of light or which band of light is absorbed and reflected.” β€” Debashis Chanda, ΒιΆΉΣ³»­΄«Γ½ associate professor

In the ACS Photonics study, the researchers went a step further and developed a way to erase and display the image in selected infrared bands.

They did this by adding a layer of phase change material vanadium dioxide within the β€œplasmonic sandwich” that dynamically changes the light reflection from the surface from 100 to 0 percent and back as the phase change is triggered.

β€œIt provides an additional element of dynamic tunability where the coded information is concealed or revealed to infrared cameras,” Chanda says.

Co-authors of the Light: Science & Applications study were Daniel Franklin ’18PhD, now a postdoctoral fellow at Northwestern University; Sushrut Modak ’14MS ’18PhD, who recently graduated from ΒιΆΉΣ³»­΄«Γ½β€™s physics doctoral program; Abraham VΓ‘zquez-Guardado ’16MS ’18PhD, a postdoctoral fellow in ΒιΆΉΣ³»­΄«Γ½β€™s Nano-Optics Group; and Alireza Safaei ’18MS, a physics PhD. student.

Co-authors of the ACS Photonics study were Sayan Chandra, a postdoctoral fellow in ΒιΆΉΣ³»­΄«Γ½β€™s Nano-Optics Group; Daniel Franklin; Jared Cozart, an undergraduate honors student majoring in photonics; and Alireza Safaei ’18, a PhD physics student.

The research was funded by the National Science Foundation and Northrop Grumman Mission Systems’ University Research Program.

Chanda received his PhD in photonics from the University of Toronto and worked as a postdoctoral fellow at the University of Illinois at Urbana-Champaign. He joined ΒιΆΉΣ³»­΄«Γ½ in 2012.