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Using a plasmonic nanostructure, researchers at the University of Central Florida (UCF) have devised a way to hide information on the surface of a material, so that it is only visible through an IR lens or camera that is tuned to the correct IR band.
In a Light: Science & Applications study, the researchers demonstrated a method for hiding images within the IR spectrum, so that while visible in the IR, the same area appears as a solid color in the visible spectrum. To do so, they created a dielectric layer patterned with regularly spaced nanosize holes, sandwiched between a reflective metallic mirror and a thin upper gold layer with holes corresponding to the middle layer’s discs. They encoded images onto the surface of the plasmonic sandwich using spun coat films of thermoplastic. They showed that by changing the diameters and depths of the holes, they could change how different wavelengths of light react with the materials.
The team was able to tune the device’s parameters in a way that made the surface appear as a uniform block of color unless viewed through an IR camera over a specific band. Varying the pattern characteristics allowed the researchers to control the electron plasma resonance, or the electric energy, created when light hits the device.
