Demichel O, Petit M, Colas des Francs G, Bouhelier A, Hertz E, Billard F, de Fornel F, Cluzel B
Opt Express. 2014 Jun 16;22(12):15088-96. doi: 10.1364/OE.22.015088.
Plasmonic dark modes are pure near-field resonances since their dipole moments are vanishing in far field. These modes are particularly interesting to enhance nonlinear light-matter interaction at the nanometer scale because radiative losses are mitigated therefore increasing the intrinsic lifetime of the resonances. However, the excitation of dark modes by standard far field approaches is generally inefficient because the symmetry of the electromagnetic near-field distribution has a poor overlap with the excitation field. Here, we demonstrate the selective optical excitation of bright and dark plasmonic modes of single gold nanorods by spatial phase-shaping the excitation beam. Using two-photon luminescence measurements, we unambiguously identify the symmetry and the order of the emitting modes and analyze their angular distribution by Fourier-space imaging.
表面等离激元暗模是纯粹的近场共振，因为它们的偶极矩在远场中消失。这些模式对于增强纳米尺度下的非线性光与物质相互作用特别有趣，因为辐射损耗得以减轻，从而增加了共振的固有寿命。然而，用标准远场方法激发暗模通常效率低下，因为电磁近场分布的对称性与激发场的重叠性较差。在这里，我们通过对激发光束进行空间相位整形，展示了对单个金纳米棒的明亮和暗表面等离激元模式的选择性光学激发。利用双光子发光测量，我们明确地识别出发射模式的对称性和阶数，并通过傅里叶空间成像分析它们的角分布。
