Suppressing loss mechanisms in plasmonic structures is critical for the demonstration of high-quality-factor resonances with narrow linewidths. An extensively explored approach for loss reduction in these structures is the implementation of lattice plasmons (LPs) in which the primary loss mechanisms (i.e., Ohmic and radiation losses) can be simultaneously reduced. LPs take advantage of in-plane dipolar coupling of the scattered light from plasmonic arrays to provide narrow resonance linewidths at wavelengths approaching inter-particle distances. Here, we report numerical design and experimental demonstration of ultra-sharp (FWHM ≈ 6 nm) and tunable LP resonance modes in an array of gold (Au) nanopatches separated from a backside metallic film via a thin alumina (Al2O3) spacer layer. We show that oblique excitation of the array induces out-of-plane electric dipoles, which enable diffractive coupling of the incident light to the array, thus, exciting the LP mode. Furthermore, the excitation angle can be controlled to precisely tune important attributes of the LP lineshape including the resonance linewidth and the spectral position. Using spectroscopic ellipsometry measurements and finite-difference time-domain modeling, we show that the LP modes are only achievable through TM-polarized excitations, as a TE-polarized light lacks an out-of-plane electric-field component. The structure reported here holds a great promise for applications seeking strong light-matter interactions.
Mohammad Taghinejad, Hossein Taghinejad, and Ali Adibi, "Ultra-sharp and tunable lattice plasmons in film-coupled metallic nanostructures (Conference Presentation)," Proc. SPIE 10541, Photonic and Phononic Properties of Engineered Nanostructures VIII, 105410T (Presented at SPIE OPTO: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2300968.5751516190001.
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