High‑Q Plasmonic Nanocavities Enabled by Integration of Au Nanogap Dimers with a Distributed Bragg Reflector

The light confinement capability of optical cavities plays an important role in amplifying the light–matter interactions. To realize high-performance optical cavities, not only a small mode volume but also a high quality (Q) factor is indispensable. Plasmonic nanocavities can squeeze light into deep subwavelength spaces, resulting in ultrasmall mode volumes. However, the Q factors of plasmonic nanocavities are seriously impaired by the intrinsic Ohmic losses, and thus the improvement of the Q factors of plasmonic nanocavities is highly challenging. In this study, we integrate Au nanogap dimers with a distributed Bragg reflector (DBR) to realize the high-Q plasmonic nanocavities. Near-field spectral characterizations reveal that the sharp resonance peak appears near the photonic stopband of the DBR, resulting in a Q factor of ∼75. Ultrafast time-resolved measurements also unveil that the plasmon dephasing time of the Au dimer on the DBR is extended compared to that on a glass substrate. The electromagnetic simulations can qualitatively reproduce the experimental observations and reveal that the high-Q plasmonic nanocavities are achievable due to the synergistic interaction of the Au dimers with the slow light induced at the photonic band edge of the DBR. The integrated system demonstrated in this study exhibits stronger near-field enhancement compared to conventional plasmonic nanocavities on a glass substrate, providing a promising platform for boosting the performance of plasmonic nanocavities in various applications.