Analysis of dephasing time of plasmonic hybridization modes using a quasi-normal mode method

Measuring and regulating the localized surface plasmon (LSP) dephasing time (lifetime) of bonding and antibonding modes in nanosystems is the basis for the application of LSP devices. Here, we investigate the modulation of the dephasing time of hybridization modes generated by the coupling between dipole and quadrupole LSP modes in an asymmetric nanorod dimer by combining finite-difference time-domain numerical simulations with the quasi-normal mode (QNM) method. We surprisingly find that the dephasing time of the antibonding mode can be as long as 10.55 fs, which is 30% longer than that of the quadrupole mode supported by an isolated long rod (7.94 fs). Moreover, it is found that the dephasing times of the antibonding and bonding modes can be selectively modulated by changing the gap size or rod length in the dimer. A 6 THz difference between peak frequencies obtained from directly reading the near-field spectra and from the QNM fitting of near-field spectra is observed due to mode interactions existing with a gap size of 60 nm. This work demonstrates that QNM is a superior method in analyzing complex spectra, and it advances our understanding of the dynamical evolution of plasmonic hybrid modes.