Optimal plasmonic multipole resonances of a sphere in lossy media
Optimal plasmonic multipole resonances of a sphere in lossy media
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有损介质中球体的最佳等离子体多极共振
DOI：
10.1103/physrevb.99.054301
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发表时间：
2018
影响因子：
3.7
通讯作者：
S. Tretyakov
中科院分区：
文献类型：
--
作者：
S. Nordebo;G. Kristensson;M. Mirmoosa;S. Tretyakov
给出了嵌入在有耗周围介质中的旋转不变介质球的等离子体多极子吸收和散射的基本上界。一个专门的米氏理论是为此目的而开发的，当与相应的广义光学定理相结合时，得到一个优化问题，这是明确解决的直接分析。特别是，吸收截面是一个凹的二次型在相关的米氏（散射）参数和凸散射截面可以最大化通过使用一个拉格朗日乘子约束的吸收是非负的。对于均匀球，Weierstrass准备定理被用来建立的存在性和唯一性的等离子体奇异性和明确的渐近表达式给出的偶极子和四极。研究表明，对于色散介质中均匀介质小球的多极吸收和散射，最佳无源材料分别近似地表示为相应极点位置的复共轭和真实的部分。数值例子来说明的理论，包括与等离子体偶极子和四极共振的金，银，铝纳米球的基础上，这些金属的一些特定的Brendel-Bormann（BB）介电模型的比较。基于这些BB模型，有趣的是注意到金属球可以在特定频率下以特定尺寸调谐到最佳吸收。
Fundamental upper bounds are given for the plasmonic multipole absorption and scattering of a rotationally invariant dielectric sphere embedded in a lossy surrounding medium. A specialized Mie theory is developed for this purpose and when combined with the corresponding generalized optical theorem, an optimization problem is obtained which is explicitly solved by straightforward analysis. In particular, the absorption cross section is a concave quadratic form in the related Mie (scattering) parameters and the convex scattering cross section can be maximized by using a Lagrange multiplier constraining the absorption to be non-negative. For the homogeneous sphere, the Weierstrass preparation theorem is used to establish the existence and the uniqueness of the plasmonic singularities and explicit asymptotic expressions are given for the dipole and the quadrupole. It is shown that the optimal passive material for multipole absorption and scattering of a small homogeneous dielectric sphere embedded in a dispersive medium is given approximately as the complex conjugate and the real part of the corresponding pole positions, respectively. Numerical examples are given to illustrate the theory, including a comparison with the plasmonic dipole and quadrupole resonances obtained in gold, silver, and aluminum nanospheres based on some specific Brendel-Bormann (BB) dielectric models for these metals. Based on these BB models, it is interesting to note that the metal spheres can be tuned to optimal absorption at a particular size at a particular frequency.
金纳米粒子悬浮液中射频吸收的物理限制
影响因子：
--
作者：
Nordebo S
通讯作者：
Nordebo S