Broadband plasmonic device concentrating the energy at the nanoscale: The crescent-shaped cylinder
Broadband plasmonic device concentrating the energy at the nanoscale: The crescent-shaped cylinder
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DOI：
10.1103/physrevb.82.125430
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发表时间：
2010-09
影响因子：
3.7
通讯作者：
A. Aubry;D. Lei;S. Maier;J. Pendry
中科院分区：
文献类型：
--
作者：
A. Aubry;D. Lei;S. Maier;J. Pendry
最近提出了一种新的策略来设计宽带等离子体纳米结构，使光具有显著的纳米聚焦。对薄板进行奇异保角变换，得到了一个具有月牙形截面的圆柱体。在本研究中，分析推导了相应的理论，并提供了不同的物理见解来分析该器件的宽带光收集和纳米聚焦特性。通过求解金属板问题，推导出了新月的光学响应。由于表面等离子体速度的降低，纳米结构表现出连续的吸收截面红移。并对纳米结构引起的场增强进行了解析推导。纳米聚焦性能是耗散损耗和表面等离子体速度之间的平衡结果。这意味着磁场增强对频率和新月形几何有很强的依赖性。数值模拟还研究了当结构尺寸与波长相当时辐射损耗的影响。辐射阻尼使吸收截面在物理截面的水平上饱和。磁场增强随器件尺寸的增大而减小。新月形结构被证明对辐射损失相当稳定，这为单分子检测等应用开辟了前景。
A new strategy has been proposed recently to design broadband plasmonic nanostructures capable of a significant nanofocusing of light. Applying a singular conformal transformation to a thin slab of metal, a cylinder with a crescent-shaped cross section is obtained. In this study, the corresponding theory is derived analytically and different physical insights are provided to analyze the broadband light harvesting and nanofocusing properties of this device. The optical response of the crescent is deduced by solving the metal-slab problem. The nanostructure is shown to exhibit a continuous absorption cross section which redshifts for thin crescents due to a decrease of the surface plasmon velocity. The field enhancement induced by the nanostructure is also derived analytically. The nanofocusing performance is shown to result from a balance between dissipation losses and surface-plasmons velocity. This implies a strong dependence of the field enhancement on the frequency and the crescent geometry. Numerical simulations have also been performed to investigate the effect of radiative losses when the structure dimension becomes comparable to the wavelength. Radiative damping makes the absorption cross section saturate at the level of the physical cross section. The field enhancement decreases with the size of the device. The crescent structure is shown to be quite robust to radiation losses, which opens perspectives for applications such as single-molecule detection.