Enhanced dephasing time and sensing performance of double Fano resonance in split-ring-disk nanostructure

Abstract Dephasing time is one of the key parameters used to characterize the evolution of localized surface plasmons and is essential for practical applications such as plasmon-based sensing. In this paper, we combine quasi-normal mode analysis with finite-difference time-domain simulations to study the dephasing time of plasmonic double-Fano resonances in a split-ring-disk nanostructure. The results show that, with the emergence of double-Fano resonances, the dephasing times of the two modes are 8.8 fs at 795 nm and 6.7 fs at 648 nm, respectively—both significantly longer than that of the single-Fano resonance (4 fs at 910 nm). An investigation into the geometric dependence of dephasing time and near-field enhancement in the ring-disk and split-ring-disk systems reveals that, in this coupled mode system, weaker field strength corresponds to a longer dephasing time due to reduced radiation damping. Further analysis of sensing performance indicates that the double-Fano structure outperforms the single-Fano structure. This study provides a solid foundation for applications in sensing, photocatalysis, and other related fields.