Active Plasmonic Lattice Resonance for Near-infrared Camoflage Applications

Abstract

Near-infrared (NIR) camouflage is the use of colored material or device mimicking the NIR spectra of environmental object, e.g. soils, leaves, and tress, for concealment. The molecular dyes and oxide nanoparticles are often used for this purpose but they remain passive, practically limiting their use when the object moves around. Here, this thesis introduces the concept of adaptive NIR nano-filters, electrically modulating the peak intensity and wavelength of the transmitted NIR lights in a reversibly tunable manner, ultimately used for NIR camouflage applications. Surface plasmonic lattice resonance (SLR) is utilized to selectively diffract photons in the NIR regime with a narrow spectral linewidth and trap them within the lattice. Crucially, the amount of these trapped lights can be tunable (i.e. contrast) when the gap between the lattice is filled with an active medium (here conductive polymer) that reversibly tunes refractive index surrounding environment. The SLR structures for the NIR resonance are optimized through numerical simulations and fabricated at the wafer-scale by formulating a regular array of plasmonic pyramidal nanostructures using nanosphere lithography. These structures are then encapsulated within a conductive polymer via the solution-based polymerization process. The fabricated SLR device exhibits the active contrast over 8% at 850 nm of wavelength, which is used to modulate the NIR contrast of the target object while observing through the commercial night vision goggle, facilitating the adaptive NIR camouflage applications.