Reduced linewidth multipolar plasmon resonances in metal nanorods and related applications

Using dark-field scattering spectroscopy, we study the multipolar plasmon resonances in single crystallized silver nanorods. The lineshapes and homogenous linewidths of the surface plasmon resonances (SPRs) of different orders are analyzed and compared. The high-order resonances are found to sustain asymmetric Fano lineshapes and their linewidths are narrower than the dipolar resonance. A quantitative comparison using the finite element method reveals more than a three times reduction in the linewidth for the third order resonance, as compared with the dipolar one. These narrow linewidths result from the smaller radiative damping of the multipolar SPRs. Benefiting from the reduced damping, multipolar SPRs in nanorods are better candidates for many plasmonic applications, including increased-sensitivity single particle SPR sensors and reduced-threshold nanolasers.