Electromagnetic fields at near-field exhibit distinctive properties with respect to their free-space counterparts. In particular, an optical transverse spin appearing in a confined electromagnetic field provides the foundation for many intriguing physical effects and applications. We present a transverse spin coupling configuration where plasmonic nanoparticles are employed to couple the transverse spin in a focused beam to that of a surface plasmon polariton. The plasmonic resonance of nanoparticles on a metal film plays a significant role in transverse spin coupling. We demonstrate in experiments that Ag and Au nanoparticles yield distinct imaging patterns when scanned over a focused field, because of their different plasmonic responses to the transverse and longitudinal electric fields. Such resonance-dependent spin-coupling enables the identification of nanoparticles using a focused field, as well as electric field mapping of a specific field component of a focused beam using a plasmonic nanoparticle. These interesting findings regarding the transverse spin coupling with a plasmonic nanoparticle may find valuable applications in near-field and nano-optics.

中文翻译：

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通过等离激元纳米粒子的光学横向自旋耦合，用于粒子识别和场映射

相对于自由空间，近场的电磁场表现出独特的特性。特别地，出现在受限电磁场中的光学横向自旋为许多有趣的物理效果和应用奠定了基础。我们提出了一种横向自旋耦合构型，其中采用等离激元纳米粒子将横向自旋耦合在聚焦束中与表面等离激元极化。纳米粒子在金属膜上的等离子体共振在横向自旋耦合中起重要作用。我们在实验中证明，在聚焦场上扫描时，Ag和Au纳米颗粒会产生不同的成像模式，这是因为它们对横向和纵向电场的等离激元响应不同。这种依赖于共振的自旋耦合使得能够使用聚焦场来识别纳米颗粒，以及使用等离激元纳米颗粒来对聚焦束的特定场分量进行电场映射。这些与等离激元纳米粒子的横向自旋耦合的有趣发现可能会在近场和纳米光学中找到有价值的应用。