Optical Extinction in a Single Layer of Nanorods

Abstract : We demonstrate that almost 100% of incident photons can interact with a monolayer of scatterers in a symmetrical environment. Nearly perfect optical extinction through free-standing transparent nanorod arrays has been measured. The sharp spectral opacity window, in the form of a characteristic Fano resonance, arises from the coherent multiple scattering in the array. In addition, we show that nanorods made of absorbing material exhibit a 25-fold absorption enhancement per unit volume compared to unstructured thin film. These results open new perspectives for light management in high-Q, low volume dielectric nanostructures, with potential applications in optical systems, spectroscopy, and optomechanics. Enhancing light-matter interactions at the nanometer scale is a key for many applications in the area of pho-tonics, biophysics and material sciences [1,2]. Metallic particles are the archetype of nano-objects that can lead to strong interaction with light due to plasmonic resonances , with the drawback of intrinsic metal absorption [3]. Conversely, the weak scattering cross section of tiny dielectric nanoparticles originates from their nonresonant nature, making them inefficient for optical manipulation at the nanoscale. However, the extinction cross section can be increased by coherent multiple scattering in assemblies of nanoparticles, offering another degree of freedom to manipulate their optical response. It has been shown theoretically that it can lead to extremely sharp geometric resonances [4–9]. From the experimental point of view, arrays of resonant, metallic nanoparticles demonstrated the potential of the effect [10,11], making the localized surface plasmon resonance much narrower [12,13]. Arrays of non-resonant, dielectric nanorods should offer new possibilities for even higher quality-factor geometric resonances [14,15]. Indeed, sharp reflection resonances [7,8] and absorption enhancement [9] have been predicted for dielec-tric, sub-wavelength cylinder arrays. It has to be emphasized that the scattering properties of nanoparticles are substantially modified, or even suppressed , in the proximity of a surface [6,7,16–19]. Here, we study a free-standing array of nanorods, with a filling fraction around 0.15. In contrast with the periodic nano-structures studied extensively in the past ten years (nano-hole arrays in metal films [20,21], metal nanoparticle arrays [10–13], high-index-contrast gratings [22], guided-mode resonant structures [23,24]), resonant effects cannot be attributed to localized resonances neither to interactions between nanostructures mediated by electromagnetic
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Petru Ghenuche, Grégory Vincent, Marine Laroche, Nathalie Bardou, Riad Haıdar, et al.. Optical Extinction in a Single Layer of Nanorods. Physical Review Letters, American Physical Society, 2012, 109 (14), pp.143903. ⟨10.1103/PhysRevLett.109.143903⟩. ⟨hal-01334727⟩

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