Spin-Controlled Second Harmonic Generations on Plasmonic Metasurfaces

等离激元超构表面上自旋控制的二次谐波产生

唐宇涛

11752005

博士

哲学博士

李贵新

2020-08-24

2020-08-31

香港浸会大学

香港

Plasmonic metasurfaces provide a novel platform for designing and implementing optical functional devices with distinguished advantages of their compactness and ultrathin footprint over traditional optical elements. The constituent metallic structures, or so-called “meta-atoms” or “meta-molecule” can interact with light at a subwavelength scale and introduce local modulations over multiple degrees of freedom like amplitude, phase, polarization, etc. The specific functions of the devices are then realized by assembling those meta-atoms together to form a planar interface with predesigned distributions. In this thesis we mainly studied nonlinear plasmonic metasurfaces made of gold meta-atoms for second harmonic generations (SHG). These metasurfaces work in the near infrared regime, and exhibit spin-controlled nonlinear responses due to the nonlinear geometric Pancharatnam-Berry phase-based designs.Firstly, a quasicrystal metasurface was demonstrated to modulate the far-field second harmonic radiations based on both the local symmetry of the meta-atoms and the global symmetry of the lattice those meta-atoms adhere to. Our designs of the nonlinear optical quasicrystal metasurfaces are based on the well-known Penrose tiling and the newly found bronze-mean hexagonal quasiperiodic tiling. The optical diffraction behaviors are studied in both linear and nonlinear regimes to reveal the effects of local and global symmetries on the far-field radiations.Secondly, a polarization manipulation metasurface was designed to encode a grayscale image into the polarization profiles of the generated second harmonic waves. We use single meta-atoms to manipulate the polarization directions of the second harmonic waves into predefined directions. With homogenous intensity profiles, the vectorial second harmonic beam can encode and decode information securely.At last, we utilized the state-of-the-art nano-kirigami technology to design and fabricate a three-dimensional plasmonic metasurface, which exhibits giant nonlinear circular dichroism in second harmonic generations. The second harmonic generations from the metasurface is much stronger when pumping by right circularly polarized fundamental waves than left circularly polarized ones. Broadband near-unity nonlinear circular dichroism was observed and numerical models were developed to explain the phenomenon. We believe that our works presented in this thesis enriched the study of plasmonic metasurfaces in the nonlinear optical regimes, and may be used to design novel nonlinear light sources, encryption applications, chiroptical devices, etc.

基于等离激元超构表面设计和实现的新型光学功能器件相较于传统光学元件具有结构紧凑、体积轻便等突出优点。组成它们的金属结构，即所谓的“超构原子”或“超构分子”，能在亚波长尺度下与光相互作用，从而引入对光场的振幅、相位、偏振等多个自由度的局域调控。通过将这些超构原子按预先设计的分布组装在一个平面上则可以进一步实现特定的光学功能。本论文主要研究由金超构原子构成的非线性等离激元超构表面上的二次谐波产生过程。这些超构表面工作在近红外波段，并因基于Pancharatnam-Berry几何相位的设计而具有自旋控制的非线性响应。首先，我们研究了准晶超构表面，并证实超构原子的局域对称性和他们依附的晶格具有的全局对称性均对倍频信号的远场辐射有调制作用。该非线性光学超构表面的设计是基于著名的彭罗斯拼接和新近提出的“黄铜分割比”六角准周期拼接。我们通过研究线性和非线性的光学衍射行为揭示了局域和全局对称性对远场辐射的影响。其次，我们设计了一种偏振调控超构表面，可将灰度图像编码进倍频光束的偏振分布上。我们利用单个超构原子将倍频光波的偏振调控至预定义的方向上。由于产生的倍频光波有均匀的强度分布，该矢量倍频光束可以用于安全性加密和解密信息。最后，我们利用前沿的纳米剪纸技术设计和制备了具有三维等离激元超构表面，其在二次谐波频域具有很强的非线性圆二向色性。该超构表面在右旋基频光泵浦下产生的倍频信号远大于左旋基频光泵浦下产生的信号。我们实验上观测到了宽带的、接近于一的非线性圆二向色性并且建立了数值模型来解释该现象。我们相信本论文的工作丰富了等离激元超构表面在非线性光学范畴内的应用，可用于设计新型非线性光源、信息加密、手性光学器件等。

second harmonic generations plasmonic metasurfaces nonlinear optics

英语

联合培养

南方科技大学

Tang YT. Spin-Controlled Second Harmonic Generations on Plasmonic Metasurfaces[D]. 香港. 香港浸会大学,2020.