Observation of coupled plasmon-polariton modes in Au nanoparticle chain waveguides of different lengths: Estimation of waveguide loss

Near-field interactions between closely spaced Au nanoparticles were characterized by studying the spectral position of the extinction bands corresponding to longitudinal $\mathrm{(L)}$ and transverse $\mathrm{(T)}$ plasmon-polariton modes of Au nanoparticle chains. Far-field spectroscopy and finite-difference time-domain simulations on arrays of 50 nm diameter Au spheres with an interparticle spacing of 75 nm both show a splitting $\mathrm{\Delta E}$ between the $L$ and $T$ modes that increases with chain length and saturates at a length of seven particles at $\text{ΔE=65\hspace{0.17em}}\mathrm{meV}.$ We show that the measured splitting will result in a propagation loss of 3 dB/15 nm for energy transport. Calculations indicate that this loss can be reduced by at least one order of magnitude by modifying the shape of the constituent particles.