Xia Juan, Tang Jianwei, Bao Fanglin, Sun Yongcheng, Fang Maodong, Cao Guanjun, Evans Julian, He Sailing
Centre for Optical and Electromagnetic Research, State Key Laboratory of Modern Optical Instrumentation, National Engineering Research Center for Optical Instrumentation, JORCEP, College of Optical Science and Engineering, Zhejiang University, 310058 Hangzhou, China.
School of Physics, Huazhong University of Science and Technology, 430074 Wuhan, China.
Light Sci Appl. 2020 Sep 21;9:166. doi: 10.1038/s41377-020-00398-1. eCollection 2020.
Optical nanoantennas can convert propagating light to local fields. The local-field responses can be engineered to exhibit nontrivial features in spatial, spectral and temporal domains, where local-field interferences play a key role. Here, we design nearly fully controllable local-field interferences in the nanogap of a nanoantenna, and experimentally demonstrate that in the nanogap, the spectral dispersion of the local-field response can exhibit tuneable Fano lineshapes with nearly vanishing Fano dips. A single quantum dot is precisely positioned in the nanogap to probe the spectral dispersions of the local-field responses. By controlling the excitation polarization, the asymmetry parameter of the probed Fano lineshapes can be tuned from negative to positive values, and correspondingly, the Fano dips can be tuned across a broad spectral range. Notably, at the Fano dips, the local-field intensity is strongly suppressed by up to ~50-fold, implying that the hot spot in the nanogap can be turned into a cold spot. The results may inspire diverse designs of local-field responses with novel spatial distributions, spectral dispersions and temporal dynamics, and expand the available toolbox for nanoscopy, spectroscopy, nano-optical quantum control and nanolithography.
光学纳米天线可以将传播的光转换为局域场。局域场响应可以被设计成在空间、光谱和时间域中展现出非平凡的特性，其中局域场干涉起着关键作用。在此，我们在纳米天线的纳米间隙中设计了几乎完全可控的局域场干涉，并通过实验证明，在纳米间隙中，局域场响应的光谱色散可以呈现出可调谐的法诺线形，且法诺凹陷几乎消失。单个量子点被精确地放置在纳米间隙中，以探测局域场响应的光谱色散。通过控制激发偏振，所探测的法诺线形的不对称参数可以从负值调谐到正值，相应地，法诺凹陷可以在很宽的光谱范围内进行调谐。值得注意的是，在法诺凹陷处，局域场强度被强烈抑制达约50倍，这意味着纳米间隙中的热点可以变成冷点。这些结果可能会激发具有新颖空间分布、光谱色散和时间动态的局域场响应的多样化设计，并扩展用于纳米显微镜、光谱学、纳米光学量子控制和纳米光刻的可用工具箱。
