Figure 1. Surface plasmons in the time- and frequency domains.

(a) A fast electron traverses a gold particle, exciting localized surface plasmons. (b) In the time domain, the various harmonic plasmon modes in this 210 nm long gold nanorod are represented as damped harmonic oscillations. These were calculated from the plasmon energy and peak width measured with EELS (using equation (5)), and were normalized according to their amplitude. (c) The experimental frequency-domain EELS spectrum of the whole particle is plotted here, showing four distinct harmonic plasmon modes. (d) Each plasmon mode has a well-defined spatial distribution of anti-nodes plotted here as a function of distance along the gold rod, corresponding to the aligned TEM image.