表面等离激元纳米聚焦研究进展

Research progress of plasmonic nanofocusing

表面等离激元是束缚于金属纳米结构表面的电磁模式,具有突破光学衍射极限和局域场增强等特点.当表面等离激元沿一维锥形纳米结构表面传播时,由于纳米聚焦效应,使得等离激元能量汇聚于锥形结构的纳米尖端,从而在该位置产生巨大的局域场增强.这一现象为电磁场能量在纳米尺度的定向输送提供了十分有效的路径,在分子光谱增强及传感领域得到广泛的应用.本文对近年来表面等离激元纳米聚焦在纳米光子学领域的研究进展进行了综述,并展望了这一领域未来的发展方向.

Surface plasmons(SPs) are the surface waves of collective oscillations of free electrons at metal-dielectric interface, which have the ability to overcome the diffraction limit and to enhance the giant near-field. Tapered metallic nanostructures that support surface plasmons’ propagation are highly attractive to nanophotonic applications because of their waveguiding and field-focusing properties. This distinct morphologic feature enables the functionality known as nanofocusing. As a result, the plasmons can be guided in these nanostructures and finally focused on the sharp apex to greatly enhance the local field. This attractive effect can be widely used for effective remote-excitation detection/sensing. In this paper, we review various types of plasmonic nanofocusing structures operating in the visible and infrared region. We focus on their fundamentals,fabrications, and applications. Firstly, we discuss the mechanisms of the plasmonic nanofocusing. Then, the characteristics of various tapered metallic nanostructures of SPs are reviewed, including on-chip waveguides,metal tips and bottom-up fabricated nanowires. For applications, some prototypes of plasmonic nanofocusing for bio/chemo sensing are demonstrated. Finally, a summary and outlook of plasmonic waveguides are given.