Department of Electrical Engineering, The State University of New York at Buffalo, Buffalo, NY, 14260, USA.
State Key Laboratory for Mesoscopic Physics, Collaborative Innovation Center of Quantum Matter, School of Physics, Peking University, Beijing, 100871, China.
Sci Rep. 2017 Jun 28;7(1):4346. doi: 10.1038/s41598-017-04688-4.
Broadband light trapping and field localization is highly desired in enhanced light-matter interaction, especially in harmonic generations. However, due to the limited resonant bandwidth, most periodic plasmonic nanostructures cannot cover both fundamental excitation wavelength and harmonic generation wavelength simultaneously. Therefore, most previously reported plasmonic nonlinear optical processes are low in conversion efficiency. Here, we report a strong enhancement of second harmonic generation based on a three-layered super absorbing metasurface structure consisting of a dielectric spacer layer sandwiched by an array of random metallic nanoantennas and a metal ground plate. Intriguingly, the strong light trapping band (e.g. >80%) was realized throughout the entire visible to near-infrared spectral regime (i.e., from 435 nm to 1100 nm), enabling plasmonically enhanced surface harmonic generation and frequency mixing across a broad range of excitation wavelengths, which cannot be achieved with narrow band periodic plasmonic structures. By introducing hybrid random antenna arrays with small metallic nanoparticles and ultra-thin nonlinear optical films (e.g. TiO) into the nanogaps, the nonlinear optical process can be further enhanced. This broadband light-trapping metastructure shows its potential as a building block for emerging nonlinear optical meta-atoms.
宽带光捕获和场局域化在增强光物质相互作用中是非常需要的，特别是在谐波产生中。然而，由于有限的共振带宽，大多数周期性等离子体纳米结构不能同时覆盖基本激发波长和谐波产生波长。因此，大多数先前报道的等离子体非线性光学过程的转换效率都很低。在这里，我们报告了一种基于由随机金属纳米天线阵列和金属接地板夹在介电间隔层组成的三层超吸收超表面结构的强二次谐波增强。有趣的是，强光捕获带（例如，>80%）实现了整个可见光到近红外光谱范围（即，从 435nm 到 1100nm），能够在宽激发波长范围内实现等离子体增强的表面谐波产生和频率混合，这是窄带周期性等离子体结构无法实现的。通过在纳米间隙中引入具有小金属纳米粒子和超薄非线性光学薄膜（例如 TiO）的混合随机天线阵列，可以进一步增强非线性光学过程。这种宽带光捕获超结构显示了其作为新兴非线性光学元原子的构建块的潜力。
