Collective resonances in plasmonic crystals: Size matters

Abstract

Periodic arrays of metallic nanoparticles may sustain Surface Lattice Resonances (SLRs), which are collective resonances associated with the diffractive coupling of Localized Surface Plasmon Resonances (LSPRs). By investigating a series of arrays with varying number of particles, we traced the evolution of SLRs to its origins. Polarization resolved extinction spectra of arrays formed by a few nanoparticles were measured, and found to be in very good agreement with calculations based on a coupled dipole model. Finite size effects on the optical properties of the arrays are observed, and our results provide insight into the characteristic length scales for collective plasmonic effects: for arrays smaller than 5 x 5 particles, the Q-factors of SLRs are lower than those of LSPRs; for arrays larger than 20 x 20 particles, the Q-factors of SLRs saturate at a much larger value than those of LSPRs; in between, the Q-factors of SLRs are an increasing function of the number of particles in the array.Comment: 4 figure

Plasmonic surface lattice resonances on arrays of different lattice symmetry

“…3(a), two peaks dominate the extinction spectrum, one at ∼650 nm, the other at ∼755 nm, we attribute these peaks to SLRs. The dip at ∼520 nm is due to the 1,1 diffracted order and the small peak at ∼720 nm is usually attributed to divergence of the illumination beam [16]. From the calculations, see Fig.…”

“…Investigations have explored, for example, the effect of disorder on the SLRs [15]. More recent work has involved looking at the effect that the number of particles that comprise an array has on the SLR [16], while Zhou and Odom explored out-of-plane resonances [17]. SLRs associated with metal nanoparticle arrays are also interesting due to the way their modes interact with emissive species such as fluorescent molecules, both with regard to light emission [18], and with regard to strong coupling between lattice resonances and quantum emitters [19,20].…”

“…Particles thus experience driving fields due to the incident light and due to light scattered by all of the other particles in the array. We may write the modified susceptibility α * as [13,16,29] …”

Spectrally selective chiral silicon metasurfaces based on infrared Fano resonances

“…That is because only several neighbouring unit cells (two to three on each side horizontally, one on each side vertically according to Supplementary Note 1) effectively interact with each given unit cell. This short-range collective interaction contrasts with longrange coherence required for achieving narrow spectral width in photonic structures that rely on diffractive effects 44,45 . The unique capability to combine these small area high-Q metasurfaces with thermal infrared radiation sources is absolutely crucial for the future sensing applications described below.…”

“…A notable exception is the special class of diffraction-coupled plasmonic arrays 25,[43][44][45] , which rely on the geometric resonance that arises when the wavelength of light is commensurate with the array's periodicity 44 . Such plasmonic arrays can possess a very high Q-factor, but suffer from the same limitations as GRM-based photonic crystals, affecting a number of important applications that involve ultrasmall (several wavelengths in size) samples.…”