Lu Fanfan, Zhang Wending, Sun Lixun, Mei Ting, Yuan Xiaocong
Opt Express. 2022 Jun 6;30(12):21377-21385. doi: 10.1364/OE.460394.
Tip-enhanced Raman spectroscopy (TERS) is a promising label-free super-resolving imaging technique, and the electric field gradient of nanofocusing plays a role in TERS performance. In this paper, we theoretically investigated the enhancement and manipulation of the electric field gradient in a bottom-illumination TERS configuration through a tightly focused perfect radially polarized beam (PRPB). Improvement and manipulation in electric field enhancement and field gradient of the gap-plasmon mode between a plasmonic tip and a virtual surface plasmons (SPs) probe are achieved by adjusting the ring radius of the incident PRPB. Our results demonstrate that the method of optimizing the ring radius of PRPB is to make the illumination angle of incident light as close to the surface plasmon resonance (SPR) excitation angle as possible. Under the excitation of optimal parameters, more than 10 folds improvement of field enhancement and 3 times of field gradient of the gap-plasmon mode is realized compared with that of the conventional focused RPB. By this feat, our results indicate that such a method can further enhance the gradient Raman mode in TERS. We envision that the proposed method, to achieve the dynamic manipulation and enhancement of the nanofocusing field and field gradient, can be more broadly used to control light-matter interactions and extend the reach of tip-enhanced spectroscopy.
针尖增强拉曼光谱（TERS）是一种很有前景的无标记超分辨成像技术，纳米聚焦的电场梯度对TERS性能有影响。在本文中，我们从理论上研究了通过紧聚焦的完美径向偏振光束（PRPB）在底部照明TERS配置中增强和操纵电场梯度的方法。通过调整入射PRPB的环形半径，可以实现对等离子体针尖与虚拟表面等离子体（SPs）探针之间的间隙等离子体模式的电场增强和场梯度的改善与操纵。我们的结果表明，优化PRPB环形半径的方法是使入射光的照明角度尽可能接近表面等离子体共振（SPR）激发角。在最佳参数激发下，与传统聚焦的RPB相比，间隙等离子体模式的场增强提高了10倍以上，场梯度提高了3倍。通过这一成果，我们的结果表明这种方法可以进一步增强TERS中的梯度拉曼模式。我们设想，所提出的实现纳米聚焦场和场梯度动态操纵与增强的方法，可以更广泛地用于控制光与物质的相互作用，并扩展针尖增强光谱的应用范围。
