Laser processing technology provides an effective means of controlling the colors of plasmonic metamaterials across large areas with micrometer resolution, allowing for the printing of images with structural colors that are visible to the naked eye. Despite the inhomogeneity in size and spatial distribution of metallic nano-objects inherent to the laser process, the colors generated are highly reproducible and can exhibit unique visual properties due to collective resonances that add to the localized surface plasmon resonances (LSPR). Here we investigate the effect of inhomogeneity in size and position on the surface lattice resonances that strongly contribute to the strong dichroism observed in laser-induced sself-organized metasurfaces. By exploiting the dichroic properties of these structures, we have successfully implemented two- and three-image multiplexing using direct laser printing techniques. These results demonstrate the potential of nanosecond laser processing for high-end anticounterfeiting applications. By combining our experimental findings with advanced computational approaches, we aim to advance the creation of even more complex and sophisticated images with enhanced optical properties.
Laser can be an effective tool to modify materials at the nanoscale in order to achieve desired optical properties. When dealing with metal-dielectric nanocomposite thin films, different mechanisms can be triggered by laser on large areas to control the statistical properties of these materials. Nanoparticles can be reshaped, resized and ordered according to self-organization mechanisms that set over micrometer wide areas. The dielectric crystal phase and film thickness can be changed upon laser-induced temperature rise. These mechanisms lead to changes in the optical properties of the films. Here, we investigate the structural changes that a Ag:TiO2 nanocomposite thin film undergoes under nanosecond laser scanning and their resulting optical properties. We especially focus on the color properties in different modes of observation such as reflection and diffraction. The colors originate from combination of absorption by the localized surface plasmon resonance of metallic nanoparticles, diffraction by the nanoparticles assemblies and interference between the incident, reflected and guided waves, the latter being excited by scattering on the nanoparticles. The morphological characterizations unveil the role of nanoparticle size, density and arrangement on the transition from a diffractive to a dichroic behavior. A full color image is also drawn to demonstrate the potential of the technique in industrial applications ranging from design, coloration to information storage and data security.
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