Efficient Third Harmonic Generation and Nonlinear Subwavelength Imaging at a Higher-Order Anapole Mode in a Single Germanium Nanodisk
Efficient Third Harmonic Generation and Nonlinear Subwavelength Imaging at a Higher-Order Anapole Mode in a Single Germanium Nanodisk
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DOI：
10.1021/acsnano.6b07568
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发表时间：
2017-01-01
期刊：
影响因子：
17.1
通讯作者：
Maier, Stefan A.
中科院分区：
文献类型：
--
作者：
Grinblat, Gustavo;Li, Yi;Maier, Stefan A.
受益于大的固有非线性，低吸收，和高场增强能力，所有的电介质纳米天线被认为是在亚波长体积的有效的非线性过程中必不可少的。特别是，当介电纳米天线支持非辐射的anapole模式，其特征在于在消光截面的最小值和材料内的最大电能，三次谐波产生（THG）过程可以大大增强。在这项工作中，我们证明了在200 nm厚的锗纳米盘中的高阶anapole模式在光频率下在纳米尺度上提供最高的THG效率。通过加倍的直径的磁盘支持的基本的阿那普尔模式，我们发现出现了一个阿那普尔模式的高阶，与一个山谷中的消光截面显着窄于基本的阿那普尔。在这种条件下，我们观察到电介质盘中的电场限制效应得到了极大的改善，从而在550 nm的三次谐波波长下使THG转换效率高达0.001%。此外，通过映射整个纳米盘的THG发射，我们能够揭示的近场强度分布，这与数值模拟显示出良好的协议。我们的研究结果显着扩大了当代知识的介电纳米系统中的本地化模式，揭示了高效的频率上转换纳米器件的阐述的关键要素。
Benefiting from large intrinsic nonlinearities, low absorption, and high field enhancement abilities, all dielectric nanoantennas are considered essential for efficient nonlinear processes at subwavelength volumes. In particular, when the dielectric nanoantenna supports the nonradiating anapole mode, characterized by a minimum in the extinction cross section and a maximum electric energy within the material, third harmonic generation (THG) processes can be greatly enhanced. In this work, we demonstrate that a higher-order anapole mode in a 200 nm thick germanium nanodisk delivers the highest THG efficiency on the nanoscale at optical frequencies. By doubling the diameter of a disk supporting the fundamental anapole mode, we discover the emergence of an anapole mode of higher order, with a valley in the extinction cross section significantly narrower than that of the fundamental anapole. Under this condition, we observe a highly improved electric field confinement effect within the dielectric disk, leading to THG conversion efficiencies as large as 0.001% at a third harmonic wavelength of 550 nm. In addition, by mapping the THG emission across the nanodisk, we are able to unveil the anapole near-field intensity distributions, which show excellent agreement with numerical simulations. Our findings remarkably expand contemporary knowledge on localized modes in dielectric nanosystems, revealing crucial elements for the elaboration of highly efficient frequency upconversion nanodevices.