Visualization of Internal Plasmonic Wave Photosensitized by Quantum Dots.

Visualizing and characterizing surface plasmon polaritons (SPPs) that propagate along a metal-dielectric interface is essential for controlling advanced plasmonic devices that incorporate photofunctional nanomaterials. Herein, we report the development of an imaging method that employs an ultrathin layer of photofunctional quantum dots (QDs) as an SPP sensitizer. Microscopic images of upconversion fluorescence from the QD layer deposited on the plasmonic structure display fringe patterns that represent the spatiotemporal evolution of photoexcited propagating SPPs. This allows SPPs to be visualized under ambient conditions, not only for pristine plasmonic metals but also for buried interfaces overcoated with dielectric films. Furthermore, the wave properties (e.g., dispersion and velocity) of the SPPs can be accurately evaluated from the fringe patterns and the time-resolved imaging. This SPP imaging method can be widely used for designing and controlling plasmonic/photonic devices, as well as for gaining a fundamental understanding of plasmon-matter interactions.