Optical nanoantennas coherently scatter incident optical radiation, creating a localized electromagnetic near-field imprinted with subwavelength phase distribution, rapidly changing in space. The nanostructuring of phase by a nanoantenna makes the scattered field locally interfere with the incident far-field, whose phase lacks nanostructuring and depends only on wave propagation in time and space. Depending on the resonance conditions and material properties, the interference strongly modifies the resultant near-field intensity of the nanoantenna. Here, we present direct imaging of the local near-field interference effect in the near-field of a resonant dipole nanoantenna, supported by numerical calculations. We use single fluorescent emitters as local detectors to map the field distribution of nanoantennas with nanometer precision in the presence of an incident field. Taking advantage of the dipole orientation of the molecule we probe the vectorial character of the near-field interference map. Exploiting the local interference we demonstrate position control of the localized field, i.e., the plasmonic hotspots in the near-field of a nanoantenna. The results shown in this paper are important for applications where the enhancement and precise hotspot position at the nanoantenna are crucial, such as in high-resolution fluorescence imaging. Moreover, the interference effect can be exploited to shape the nanoantenna near-field to produce a tailored optical response such as polarization-controlled nanoscale hotspot switching, as we show here.

中文翻译：

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利用近场干扰对纳米热点进行远场控制

光学纳米天线相干地散射入射的光辐射，从而形成一个局部电磁近场，该近场印有亚波长相位分布，并在空间中快速变化。纳米天线对相位的纳米构造使散射场局部干扰入射的远场，而远场的相位缺乏纳米构造，仅取决于波在时间和空间上的传播。根据共振条件和材料特性，干扰会强烈改变纳米天线的合成近场强度。在这里，我们通过数值计算支持对共振偶极子纳米天线近场中局部近场干扰效应的直接成像。我们使用单个荧光发射器作为局部检测器，以在存在入射场的情况下以纳米精度绘制纳米天线的场分布。利用分子的偶极取向，我们研究了近场干扰图的矢量特性。利用局部干扰，我们展示了局部场的位置控制，即纳米天线近场中的等离子激元热点。本文显示的结果对于在纳米天线上增强和精确热点位置至关重要的应用非常重要，例如在高分辨率荧光成像中。此外，如此处所示，可以利用干扰效应来对纳米天线近场进行整形，以产生定制的光学响应，例如偏振控制的纳米级热点切换。