After confirming the physical origin of the multiple peaks of our array, we carried out an angle dispersion extinction measurement (see Methods) and plot it alongside data from FDTD simulations (Fig. ). From the data we can determine the different RA orders that give rise to the optical properties of the array (see calculation of Rayleigh anomalies in the Supplementary Information). The spectral shape is influenced by the higher (±1,±1) modes at shorter wavelengths and by the (±1,0) and (0,±1) modes at longer wavelengths. The latter lower order modes overlap with the LSPR deduced from the single-particle extinction peak at certain illumination angles. The coupling of the LSPR to the diffraction orders results in the narrowing of the resonance, while, as we show later below, maintaining its direct plasmonic sensing properties when exposed to H 2 gas.