Low-threshold plasmonic lasing based on high-Q dipole void mode in a metallic nanoshell.

We propose a novel type of plasmonic lasing nanostructure consisting of a metallic shell and a gain core. We demonstrate numerically that highly localized void modes of such metallodielectric core-shell nanoparticles have a very high quality factor. We found that the dipole void mode has a lasing threshold as low as 128 cm(-1) at 800 nm as a result of the unique mode distribution within the shell, due to a maximum field enhancement around the void center. The lasing condition for a symmetry-reduced silver nanocup is also investigated and the low plasmonic lasing threshold is sustained provided that the opening angle of the nanocup is smaller than 10°. Our proposal presents a new path toward plasmonic lasers with low gain threshold.