Dynamics of Second-Harmonic Generation in a Plasmonic Silver Nanorod

Second-harmonic generation in plasmonic nanostructures is known to enable the observation of modes with vanishing dipolar moments, i.e., having small radiation losses and thus long lifetimes. With the aid of a full wave numerical method, we study the far-field temporal dynamics of the linear and nonlinear responses of a silver nanorod driven by femtosecond pulses. The results show that the plasmons lifetime is observable in the decaying field oscillations surviving after the exciting pulse, for both processes, and fits with the damped harmonic oscillator model. In addition, using a detailed mode analysis, we find that the multipolar characteristic of the nonlinear radiation is strongly influenced by both the pulse central frequency and width. Implications for the accurate measurement of plasmon lifetime with the help of nonlinear optics are discussed, especially the need to carefully disentangle the linear and nonlinear plasmon dynamics.