低阈值表面等离子体激元从增益辅助核-壳纳米粒子对称性的破坏。
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IOP PUBLISHING JOURNAL OF OPTICS
J. Opt. 15 (2013) 105001 (8pp) doi:10.1088/2040-8978/15/10/105001
Low-threshold surface plasmon
amplification from a gain-assisted
core–shell nanoparticle with broken
symmetry
Pei Ding
1
, Jinna He
2
, Junqiao Wang
2
, Chunzhen Fan
2
, Genwang Cai
2
and Erjun Liang
2
1
Department of Mathematics and Physics, Zhengzhou Institute of Aeronautical Industry Management,
Zhengzhou 450015, People’s Republic of China
2
School of Physical Science and Engineering and Key Laboratory of Materials Physics of Ministry of
Education of China, Zhengzhou University, Zhengzhou 450052, People’s Republic of China
E-mail: dingpei@zzia.edu.cn
Received 10 May 2013, accepted for publication 19 July 2013
Published 9 August 2013
Online at stacks.iop.org/JOpt/15/105001
Abstract
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.
Keywords: spaser, gain threshold, core–shell nanoparticle, symmetry breaking
(Some figures may appear in colour only in the online journal)
1. Introduction
Coherent light sources free from diffraction limitations have
recently attracted significant attention due to their potential
applications in biosensing, data storage, photolithography
and optical communications [1–3]. Based on the strong
interaction between nanosized emitters and localized surface
plasmons (SPs), Bergman and Stockman first proposed
that a coherent light field can be generated directly at
the nano-scale through surface plasmon amplification by
stimulated emission of radiation, named a spaser or plasmon
laser [4]. With the idea of the spaser, many theoretical
schemes and experimental studies have been carried out
on the amplification of localized SPs or propagating SPs.
Plasmon lasers using propagating SPs are usually constructed
through waveguide configurations, by replacing the dielectric
layers in waveguides with gain materials and forming a
Fabry–Perot cavity to generate feedback [5, 6]. Plasmon
lasers based on localized SPs are constructed by combining
metal nanoparticles or nanostructure arrays with dielectric
media incorporating gain [7–9]. The particle itself serves as a
resonator (or a resonant cavity) and the adjacent gain medium
delivers energy to the plasmon mode. Since the particle is
considerably smaller than the wavelength, further reduction
in both the physical laser size and the mode size is possible.
As shown by Noginov and co-workers, a spaser particle with a
12040-8978/13/105001+08$33.00
c
2013 IOP Publishing Ltd Printed in the UK & the USA
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