Abstract
Peculiar enhanced backscattering of light as well as selective vapor sensing were recently observed in a layered plasmonic nanocomposite which consisted of gold nanospheres randomly distributed in a sol-gel glass thin film on top of a soda-lime glass substrate, including a buried leaky waveguide. In order to understand the underlying physical mechanisms, we performed three-dimensional transfer-matrix numerical simulations and calculated the reflectance in both backward and specular directions as functions of the incidence angle. First, assuming a layered periodic particle arrangement, we confirmed that backscattering took place at grazing incidence if the spatial period in the layers was chosen within an optimal range, in agreement with theoretical predictions. Then, using a pseudo-random particle arrangement to describe the actual nanocomposite, we revealed that strong backscattering could nevertheless persist for specific particle distributions, in spite of their randomness. This behavior was tentatively explained by putting backscattering in relation with the particle interdistance statistics. Finally, we showed that backscattered reflectance was much more sensitive than specular reflectance to the adsorption of water vapor either on the surface or inside the likely porous structure of the glass host.
Highlights
Plasmonic nanostructures with enhanced and controllable optical properties are key elements in nanophotonics and biosensing [1,2]
Simplest schemes are based on adsorbateinduced local refractive index changes at the metallic surface
We theoretically study the coupling and enhanced backscattering of light in layered plasmonic nanocomposites, such as the thermally poled sample used in the experiments described above
Summary
Plasmonic nanostructures with enhanced and controllable optical properties are key elements in nanophotonics and biosensing [1,2]. Metal-glass nanocomposites, in which metallic nanoparticles are embedded in a glass matrix [9], are clearly an attractive low-cost alternative solution. In such layered plasmonic nanocomposites, one must take into account the facts that plasmonic particles do not lie at the surface and are randomly distributed within a layer. In order to enable in-coupling of light into the nanocomposite layer from the incident medium (here the glass substrate), a leaky optical waveguide was intentionally created in the substrate by thermal poling. We theoretically study the coupling and enhanced backscattering of light in layered plasmonic nanocomposites, such as the thermally poled sample used in the experiments described above. We evaluate the sensitivity of backscattering to the presence of adsorbed water either on the surface or inside the likely porous structure of the glass host
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