Lighting Up Multipolar Surface Plasmon Polaritons by Collective Resonances in Arrays of Nanoantennas

We demonstrate the coupling of multipolar surface plasmons with photonic modes in periodic arrays of metallic nanoantennas. This coupling leads to sharp resonances known as lattice surface modes. In spite of the weak interaction of multipolar surface plasmons with light, lattice surface modes provide an efficient radiative decay channel for emitters in the proximity of the array. We observe a tenfold emission enhancement of dyes coupled to lattice resonances. Lattice surface modes light up multipolar plasmonic resonances, opening new possibilities for fluorescence spectroscopies.

Figure 1

(a) Schematic representation of a single nanoantenna. (b) SEM image of an array of nanoantennas. (c) Extinction cross section of a single gold nanoantenna; and (d) extinction, defined as one minus the transmittance $T$, of an array of antennas. Light is incident at $\alpha =\theta =0°$ (red dashed curve) and $\alpha =0°$, $\theta =20°$ (blue solid curve).

Figure 2

(a) Calculation and (b) measurements of the optical extinction by an array of gold nanoantennas for angles of incidence $\alpha =\theta =0°$ (red dashed curve) and $\alpha =0°$, $\theta =20°$ (blue solid curve). The arrows in (b) indicate the Rayleigh anomalies.

Figure 3

(a) Extinction of an array of nanoantennas. The incident light is polarized parallel to the long axis of the antennas. The solid black curve represents the (0, $\pm 1$) Rayleigh anomaly. (b) Modulus of the electric field and electric field vectors (arrows) in the ($x\mathrm{\text{−}}y$) plane of the array, both calculated on the plane intersecting the nanoantennas at their middle height, $\lambda =895\mathrm{nm}$ and $\theta =20°$. The wavelength and angle are indicated by the small red solid circle in (a). (c) Modulus of the electric field in a single gold nanoantenna at the frequency of the $3\lambda /2$ resonance.

Figure 4

(a) Fluorescence normalized by the emission in an unpatterned substrate. Black squares are measurements of the fluorescence emitted at $\alpha =\theta =0°$, while the red circles are measurements at $\alpha =0°$, $\theta =20°$. (b) Extinction through the same array as in (a) measured at the angle of incidence $\alpha =\theta =0°$ (black squares) and $\alpha =0°$, $\theta =20°$ (red circles).