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An active three-layer silica-silver-silica nanoshell-based plasmon laser with a super low threshold is proposed. Using the finite element method, the optical cross-sections of the core-shell nanoparticle with different gain levels were calculated and the gain thresholds of the nanoparticle-based plasmon lasers fueled by different plasmon modes were determined. The calculation results indicated that when quadrupole plasmon oscillations excited in nanoshell structures were used as the lasing mode, the gain threshold of the plasmonic laser dropped by 87 % compared with that of a conventional plasmon laser with a dipole mode. By optimizing the structural parameters of the layered nanoshell, an extremely low threshold (~0.0133) over a wider resonant range of wavelength tunings was obtained. The underlying physics of low-threshold surface plasmon amplification was explained by investigating the Q factor, the mode volume, the Purcell factor, and the optical field confinement and enhancement associated with the lasing mode. [ABSTRACT FROM AUTHOR]