Hu Junzheng, Ye Xiaofei, Huang Hui, Su Guangxu, Lv Zhekai, Qin Zhaofu, Hu Pan, Liu Fanxin, Wu Wei, Zhan Peng
National Laboratory of Solid State Microstructures, and School of Physics, Nanjing University, Nanjing 210093, China.
Department of Applied Physics, Zhejiang University of Technology, Hangzhou 310023, China.
Nanophotonics. 2024 Sep 16;14(11):1907-1915. doi: 10.1515/nanoph-2024-0293. eCollection 2025 Jun.
Second-harmonic generation (SHG) facilitated by plasmonic nanostructures has drawn considerable attention, owing to its efficient frequency up-conversion at the nanoscale and potential applications in on-chip integration and nanophotonic devices. Herein, we present a nanodimer array fabricated by nanoimprinting, composed of nanofinger-pair symmetrically leaning at an off-angle with a well-defined sub-nanometric gap. Commonly, geometric symmetry would suppress the far-field SHG due to the near-field cancelling of symmetric surface SH polarization. However, we find that the light-induced surface SH polarization distribution along the wave-vector of incidence could be influenced by the off-angle, which is consistent to the requirement of SH polarization symmetry-breaking in symmetric metallic nanocavity. A dramatic enhancement of far-field SHG is achieved by tuning the off-angle of nanofinger-pair, even approaching up to over 4 orders of magnitude for an optimal value. The demonstration of SHG enhancement on our well-defined plasmonic nanodimer provides a new way of on-chip integration to activate high-efficient SH radiation, which might be potential for applications in novel nonlinear optical nanodevices with remarkable efficiency and sensitivity.
由于等离子体纳米结构促进的二次谐波产生（SHG）在纳米尺度上具有高效的频率上转换以及在片上集成和纳米光子器件中的潜在应用，因此受到了广泛关注。在此，我们展示了一种通过纳米压印制造的纳米二聚体阵列，它由纳米指对组成，纳米指对以非零角度对称倾斜且具有明确的亚纳米级间隙。通常，由于对称表面SH极化的近场抵消，几何对称性会抑制远场SHG。然而，我们发现沿入射波矢的光诱导表面SH极化分布会受到非零角度的影响，这与对称金属纳米腔中SH极化对称性破缺的要求一致。通过调整纳米指对的非零角度，实现了远场SHG的显著增强，对于最佳值甚至接近超过4个数量级。在我们定义明确的等离子体纳米二聚体上实现SHG增强的演示为激活高效SH辐射提供了一种新的片上集成方式，这对于具有卓越效率和灵敏度的新型非线性光学纳米器件的应用可能具有潜力。
