Optimization of strong coupling between dipole and quadrupole modes through variations in plasmonic nanodimers

It is highly desirable to form compact and easily controllable optical systems based on simple units to achieve the manipulation of strong coupling to huge intensity accompanied by wide spectral splitting and fast energy transfer, which is particularly important for promoting the further development of miniaturized plasmonic photodevices. Here, we realize the optimization of strong coupling between dipole and quadrupole modes in variable plasmonic nanodimers based on the improvement of effective spatial overlap of electric field distribution and high excitation efficiency of quadrupole mode, as well as expansion of coupling region and enhancement of radiation field, caused by the change of the unit structure and arrangement. Specifically, we demonstrate the Rabi splitting and anticrossing behavior in the plasmon nanodimers as well as time-domain oscillations of energy exchange, ultimately obtaining the maximum Rabi splitting of 365 meV and the interaction potential of 198 meV, and the shortest energy exchange period of 11.5 fs. The results demonstrate that the orthogonal-configured nanodimers exhibit a stronger mode coupling compared to the parallel configuration with the same units, due to a greater effective spatial overlap of the electric field distribution between the units and higher excitation efficiency of the quadrupole mode. Furthermore, within the same configuration, dipole units with larger surface areas and dipole moments exhibit stronger coupling with quadrupole units due to the extended coupling range and enhanced radiative field. It is also found that the hybridization mode lifetimes in the orthogonal configuration are shorter than those in parallel configurations with identical units, and within the same configurations, the hybridization mode lifetimes decrease as the lifetime of the dipole unit becomes shorter, accompanied by an increase in coupling strength. © 2024 Elsevier B.V.