We investigate collective effects in plasmonic oligomers of different symmetries using second-harmonic generation (SHG) microscopy with cylindrical vector beams (CVBs). The oligomers consist of gold nanorods that have a longitudinal plasmon resonance close to the fundamental wavelength that is used for SHG excitation and whose long axes are arranged locally such that they follow the distribution of the transverse component of the electric field of radially or azimuthally polarized CVBs in the focal plane. We observe that SHG from such rotationally symmetric oligomers is strongly modified by the interplay between the polarization properties of the CVB and interparticle coupling. We find that the oligomers with radially oriented nanorods exhibit small coupling effects. In contrast, we find that the oligomers with azimuthally oriented nanorods exhibit large coupling effects that lead to silencing of SHG from the whole structure. Our experimental results are in very good agreement with numerical calculations based on the boundary element method. The work describes a new route for studying coupling effects in complex arrangements of nano-objects and thereby for tailoring the efficiency of nonlinear optical effects in such structures.

中文翻译：

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等离子体低聚物产生的第二次谐波产生的集体效应。

我们使用圆柱矢量束（CVBs）使用二次谐波（SHG）显微镜研究不同对称性的等离激元低聚物的集体效应。低聚物由金纳米棒组成，这些金纳米棒的纵向等离振子共振接近用于SHG激发的基本波长，并且其长轴在局部排列，以使其遵循径向或方位极化CVB电场的横向分量的分布。在焦平面上。我们观察到，来自这种旋转对称低聚物的SHG被CVB的极化特性和粒子间耦合之间的相互作用强烈地修饰。我们发现具有径向取向的纳米棒的低聚物表现出小的偶联效应。相比之下，我们发现，具有方位角取向的纳米棒的低聚物表现出较大的偶联效应，导致整个结构中的SHG沉默。我们的实验结果与基于边界元法的数值计算非常吻合。这项工作描述了一条新的途径，用于研究纳米物体复杂排列中的耦合效应，从而调整此类结构中非线性光学效应的效率。