Plasmon Dephasing and Near-Field Enhancement of Periodical Arrays of Au Nanogap Dimers

The manipulation of near-field enhancements in plasmonic nanostructures is essentially significant in boosting the performance of plasmon-enhanced near-fields in various applications. Far-field coupling induced in the periodically arrayed plasmonic nanostructures offers a promising platform for manipulating not only the near-field enhancements but also the dephasing dynamics in plasmonic nanostructures. In this study, we fabricated periodic arrays of Au nanoblock dimers with various pitch sizes and systematically investigated the far-field coupling effect on the plasmon dephasing time. Ultrafast time-resolved measurements revealed that the pitch size of the arrays crucially influences the plasmon dephasing of the Au nanoblock dimers. The observed pitch-size dependency of the dephasing time was qualitatively reproduced by electromagnetic simulations. We also simulated near-field distributions on the arrays and found that the far-field coupling enables us to manipulate the near-field enhancement without impairing the mode volume of the plasmonic nanostructures. Our study provides a deeper understanding of the plasmon dephasing of the periodically arrayed nanostructures and gives fruitful information for optimizing plasmonic near-field enhancements in various applications.