Wang Qifa, Li Chenyang, Hou Liping, Zhang Hanmou, Gan Xuetao, Liu Kaihui, Premaratne Malin, Xiao Fajun, Zhao Jianlin
Key Laboratory of Light Field Manipulation and Information Acquisition, Ministry of Industry and Information Technology, and Shaanxi Key Laboratory of Optical Information Technology, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710129, China.
State Key Laboratory for Mesoscopic Physics, Collaborative Innovation Centre of Quantum Matter, School of Physics, Peking University, Beijing 100871, China.
Nanophotonics. 2022 Jan 4;11(3):487-494. doi: 10.1515/nanoph-2021-0506. eCollection 2022 Jan.
Plasmonic radial breathing mode (RBM), featured with radially oscillating charge density, arises from the surface plasmon waves confined in the flat nanoparticles. The zero net dipole moment endows the RBM with an extremely low radiation yet a remarkable intense local field. On the other hand, owing to the dark mode nature, the RBMs routinely escape from the optical measurements, severely preventing their applications in optoelectronics and nanophotonics. Here, we experimentally demonstrate the existence of RBM in a hexagonal Au nanoplate-on-mirror nanocavity using a far-field linear-polarized light source. The polarization-resolved scattering measurements cooperated with the full-wave simulations elucidate that the RBM originates from the standing plasmon waves residing in the Au nanoplate. Further numerical analysis shows the RBM possesses the remarkable capability of local field enhancement over the other dark modes in the same nanocavity. Moreover, the RBM is sensitive to the gap and nanoplate size of the nanocavity, providing a straightforward way to tailor the wavelength of RBM from the visible to near-infrared region. Our approach provides a facile optical path to access to the plasmonic RBMs and may open up a new route to explore the intriguing applications of RBM, including surface-enhanced Raman scattering, enhanced nonlinear effects, nanolasers, biological and chemical sensing.
等离子体径向呼吸模式（RBM）的特征是电荷密度呈径向振荡，它源于限制在扁平纳米颗粒中的表面等离子体波。零净偶极矩赋予RBM极低的辐射，但具有显著的强局部场。另一方面，由于暗模式的性质，RBM通常无法通过光学测量检测到，这严重阻碍了它们在光电子学和纳米光子学中的应用。在此，我们使用远场线性偏振光源，通过实验证明了在六边形镜上金纳米板纳米腔中存在RBM。偏振分辨散射测量与全波模拟相结合，阐明了RBM源自存在于金纳米板中的驻等离子体波。进一步的数值分析表明，RBM在同一纳米腔中比其他暗模式具有显著的局部场增强能力。此外，RBM对纳米腔的间隙和纳米板尺寸敏感，为将RBM的波长从可见光区域调整到近红外区域提供了一种直接的方法。我们的方法为获取等离子体RBM提供了一条简便的光路，并可能开辟一条探索RBM有趣应用的新途径，包括表面增强拉曼散射、增强非线性效应、纳米激光器、生物和化学传感。
