Low-threshold surface plasmon amplification from a gain-assisted core-shell nanoparticle with broken symmetry

摘要

We report that the gain threshold of a core-shell nanoparticle-based spaser can be reduced significantly by offsetting the gain-doped dielectric core within the metallic shell. By investigating the optical cross sections of the reduced symmetry core-shell nanoparticle with different levels of gain, we determined the gain threshold of the asymmetric nanoparticle-based spaser fueled by different plasmon modes. The calculation results indicate that when multipolar plasmon oscillations excited in asymmetric core-shell nanostructures are used as lasing modes, the gain threshold of an asymmetric spaser particle can drop by 30% as compared to the case of a perfect or symmetric particle. The underlying physics of low-threshold surface plasmon amplification is explained by investigating the Q factor and the optical field confinement and enhancement associated with the lasing mode.