Opening stop-gaps in plasmonic crystals by tuning the radiative coupling of surface plasmons to diffracted orders

TL;DR

This paper demonstrates how tuning the radiative coupling in plasmonic nanorod arrays can open and control stop-gaps in surface lattice resonances, with experimental and simulation results showing predictable relationships between structural parameters and gap properties.

Contribution

It introduces a method to tune plasmonic stop-gaps by adjusting nanorod size, combining experiments and simulations to reveal how structural changes affect gap characteristics.

Findings

Stop-gap central frequency decreases quadratically with nanorod width.

Stop-gap width increases linearly with nanorod width.

Standing wave momentum width increases quadratically with nanorod width.

Abstract

By tuning the radiative coupling of localized surface plasmons to diffracted orders, we demonstrate how stop-gaps in plasmonic crystals of nanorods may be opened and tuned. The stop-gap arises from the mutual coupling of surface lattice resonances (SLRs), which are collective resonances associated with counter-propagating surface polaritons. We present experimental results for three different nanorod arrays, where we show how the dispersion of SLRs can be controlled by modifying the size of the rods. Combining experiments with numerical simulations, we show how the properties of the stop-gap can be tailored by tuning a single structural factor. We find that the central frequency of the stop-gap falls quadratically, the frequency width of the stop-gap rises linearly, and the in-plane momentum width of the standing waves rises quadratically, as the width of the nanorods increases. These relationships hold for a broad range of nanorod widths, including duty cycles of the array between 20% to 80%. We discuss the physics in terms of a coupled oscillator analog, which relates the tunability of the stop-gaps to the coupling strength of plasmonic modes.