Covert Infrared Image Encoding – Hiding In Plasmonic Sight

Because of their nano-scale surface architecture, plasmonic materials can uniquely control the electromagnetic spectrum. A multilayer cavity-coupled nanostructured system was used to control a variety of light wavelengths using plasmonics. The system maintained continuously tunable absorption throughout the mid-wave and long-wave infrared (MWIR and LWIR) spectral regimes.

Franklin et al. used infrared and visible cameras to observe images and data encoded onto material surfaces. Using a multispectral engineering setup, the researchers demonstrated cavity-induced plasmonics for applications in camouflage and anti-counterfeit technologies. Images were visible in the infrared domain but hidden in the visible domain due to consistent pixel-to-pixel absorption and diffraction.

The resonant surfaces of the system were imaged with cameras designed for their respective operating bands. Grayscale images and data were encoded into the surfaces by mapping the diameter of the system’s holes to their corresponding pixels. Scientists could encode infrared images on the surface within a desired spectral range by varying parameters. These images were not visible to others. In the study led by the research group, devices were primarily defined and simulated to operate in the MWIR and LWIR atmospheric transparency windows.

The researchers used FDTD to calculate the device’s diffraction efficiency as a function of hole diameter. The results show that by varying the diameter of the hole/disk, they can be tuned for different wavelengths.

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