基于矢量光场的等离激元模式调控 
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Owing to the remarkable field confinement ability, surface plasmons have become an ideal platform for investigating light-matter interactions at the sub-wavelength scale. The intriguing properties make surface plasmons the fundamental block for future optoelectronic applications, including biomedical detection, photocatalysis, nanolaser, and data storage. Notably, the aforementioned fundamental and application research calls for surface plasmons with large tunability. Conventionally, the properties of surface plasmons can be tailored by changing the size, shape, environmental refractive index, and gap of the structure. However, these methods are usually static and lack of flexibility.
Recently, the advance of light field manipulation has expanded the dimension of light utilization and provided rich and flexible strategies for regulating light-matter interactions. For example, through the amplitude, phase, and polarization modulation of the light field, a variety of super-resolution imaging techniques have been developed. Precise control of molecular rotation, dissociation, and ionization can be achieved by employing the time domain regulation of the light field. By controlling the coherence and polarization state of the light field, the conversion efficiency of nonlinear optical processes can be improved. Correspondingly, these methods for controlling the light-matter interactions have also been successively applied to surface plasmons, which open up a new way for exploring novel phenomena and developing related applications.
The eigen-response theory is first introduced to describe the polarization matching method to selectively excite plasmonic modes. We show the typical work on the tuning of dipole moment orientation [Fig. 2(b)] and the excitation of plasmonic dark modes (Fig. 3) with the aid of vector beams. The plasmonic mode controlling enables the generation of a strong local field to precisely manipulate the light-matter interactions at the single molecular level [Fig. 4(a)] and enhance the efficiency of surface-enhanced Raman spectroscopy [Fig. 4(b)]. Additionally, the nanosize particles with ultrasmall hot spots are trapped [Figs. 4(c) and 4(d)], and the optical upconversion frequency of a plasmonic octamer is tuned [Fig. 4(e)].
Subsequently, the mechanism for controlling plasmonic mode coupling is explained in the frameworks of plasmon hybrid theory (Fig. 5) and coupled harmonic oscillator model (Fig. 6). Specifically, we present the work on controlling the bonding and antibonding modes of the plasmonic dimer with vector beams [Fig. 7(a)]. In 2010, Volpe et al. demonstrated a method to deterministically control the local field of the plasmonic nanostructure. They employed the optical inversion algorithm to superpose the Hermit-Gaussian beams with different amplitudes and phases to construct the vector excitation and successfully produce the target local field distribution as shown in Fig. 7(b). Meanwhile, we emphasize the excitation progress of single and multiple Fano resonances in highly symmetric plasmonic nanoclusters using the vector beams [Figs. 7(c) and 7(d)]. In addition, we show the applications of controlling plasmonic mode coupling in the optical binding force reversion [Fig. 8(a)], enhanced second harmonic generation [Fig. 8(b)], and the detection of structural defect and beam misalignment [Fig. 8(c)].
Finally, the method to control the far-field scattering of plasmonic structures with vector beams is interpreted by combing Mie theory and Kerker condition. As an example, we show that the unidirectional scattering of a core-shell plasmonic nanosphere can be achieved by adjusting the phase differences and amplitude between electric and magnetic dipoles (Fig. 9). Interestingly, the tightly focused radially polarized beams can excite a spinning dipole moment in an Au nanosphere [Fig. 10(a)]. The polarization distribution at the focal plane allows for tuning the emission from a homogeneous to a unidirectional pattern by simply moving the particle relative to the beam axis [Fig. 10(b)], which is found to have an application in the directional coupling to a planar two-dimensional dielectric waveguide [Fig. 10(c)]. Additionally, Zang et al. demonstrate a method to realize the asymmetric excitation of surface plasmon polaritons (SPPs) by illuminating a pair of slot antennas with the Hermite-Gaussian beam [Fig. 10(e)]. They summarized the asymmetric intensity ratio of the SPP pattern as a displacement function of slot antennas [Fig. 10(f)], delayering a displacement sensor with angstrom precision.
We briefly introduce the basic theory and physical mechanism of the interactions between vector beams and plasmonic modes and review the recent progress of plasmon mode excitation, coupling, and far-field radiation regulated by the vector beams. Furthermore, their applications in enhanced spectroscopy, nanometric optical trapping, and nano-displacement sensing are introduced. It is worth noting that the research on light field manipulation is still in a rapid development track, and some new types of light fields have been emerging, such as the superchiral optical needle, photonic skyrmions with topological features, and optical M?bius strips. These advances provide great opportunities for people to control plasmonic modes with extra freedom. Meanwhile, ultra-compact plasmonic structures represented by plasmonic nanocavities have emerged as a promising route to squeeze light into the true nanoscale level. It is foreseeable that if the merits of these two aspects are combined, one will have more abundant strategies to manipulate the optical properties of surface plasmons, ranging from the mode volume and optical chirality to the local optical density of the state. In this sense, it would open up a new avenue for studying basic physical phenomena such as strong coupling at room temperature, optical nonlinearity, and polarization-dependent optomechanics. Then, it will undoubtedly expand the applications of surface plasmons in information, energy, biology, and many other fields.
1 引言
随着通信数据量的激增和设备便携性要求的增长，光电子器件的高集成度、超小型化与低功耗已成为其发展的必然趋势。等离激元可以突破衍射极限，将光波的能量限域在亚波长尺度内，是微纳尺度下光子操纵与集成的优良载体，因此成为构建未来光电子器件的理想选择［1-3］。近年来，等离激元的研究拓展了人们对光与物质相互作用的认识，也极大促进了太阳能电池［4］、生物医学检测［5］、光催化［6］、新型光源［7］、信息存储［8］、处理及显示［9］等应用领域的发展，成为纳米光子学最为活跃的研究方向之一。
等离激元的相关应用离不开对其共振模式性质的探究。通过探索强局域等离激元模式的高效产生方法，进而选择模式的类型与相位差，能操控模式叠加来裁剪近场分布，并能借助模式间的干涉，调节结构远场的分布。以此，可实现灵活可控的近场和远场，从而为多种功能化应用提供亚波长平台。例如，激发等离激元的高阶模式可生成强局域电磁场，为稳定捕获亚波长颗粒甚至单分子操控提供了有效的途径［10］。调谐等离激元亮模式和暗模式的耦合，能够产生Fano共振现象，通过其非对称、尖锐的光谱线型可实现高灵敏度的生物化学传感［11］。借助等离激元模式的耦合，还可以有效地调控远场辐射［12］或片上光传输的特性［13］，实现局域能量与远场能量的高效转化，以此可提升纳米光源的方向性［14］。等离激元灵活的可调性，也为上述模式操控提供了可能。典型地，形貌、尺寸、间隙等几何构型的变化会带来等离激元边界条件的改变，进而实现模式响应的显著调谐［15］。除了静态调控外，利用相变［16］、液晶［17］等材料带来的环境折射率的改变也可以实现等离激元模式的动态控制。更引人注目的是，光场调控技术的飞速发展，大大提升了光场利用的自由度，为调控光与物质的相互作用提供了丰富、灵活的手段［18］。例如，通过对光场振幅、相位、偏振等的调制，已发展出多种超分辨成像技术［19］；通过对光场的时域调控，可实现分子转动、解离、电离等过程的精密控制［20］；通过对光场的相干性和偏振态的调控，可提高非线性光学过程的转换效率［21-22］。相应地，这些调控方法也被陆续应用于等离激元的研究中，为拓展和开发等离激元的相关应用开辟了全新的途径。本文将讨论矢量光场对等离激元模式激发、耦合和辐射过程的调控，并介绍相关的基本原理、现象与应用。
2 等离激元模式的激发
2.1 紧聚焦矢量光场与等离激元结构的作用
相较于传统的标量光场，矢量光场可通过紧聚焦及焦场调控的方法，生成亚波长尺度的高度局域且任意设计的光场偏振分布。这为提高光场与亚波长等离激元结构的耦合效率，特别是激发高阶的等离激元模式提供了便利。以柱矢量光场为例，通过高数值孔径（NA>0.7）物镜的聚焦后，焦场的电矢量分布可由理查德-沃尔夫矢量衍射理论计算获得。如入射光场为径向矢量光，则焦场的径向分量Eρ和纵向分量Ez［23］分别为
式中：A为常数；α为物镜的最大会聚角；l0为入射光场的振幅；Jn（kρsin θ）为n阶第一类贝塞尔函数。若入射光场为角向矢量光，则焦场只有角向分量Eϕ［23］可表示为
基于上述光场聚焦的矢量衍射理论，可数值计算得到径向和角向矢量光束在紧聚焦条件下（NA=0.9）焦场的电场强度、偏振和相位分布，如
式中：
式中，
图 1. 紧聚焦条件（n=1，NA=0.9，β0=1）下，矢量光束焦场的电场强度、偏振和相位分布。（a）~（d）径向偏振矢量光束；（e）~（h）角向偏振矢量光束。（a）、（e）总电场强度（|E |2=|E x|2+|E y|2+|E z|2）在xy平面的分布；（b）、（f）总电场强度在xz平面的分布；（c）、（g）横向电场强度（|E⊥ |2=|E x|2+|E y|2）；（d）、（h）纵向电场强度（|E z|2）。图中黑色箭头代表偏振态，插图表示相位分布
Fig. 1. Electric field intensity, polarization, and phase distributions of tightly focused cylindrical vector beams (n=1,NA=0.9,β0=1). (a)-(d) Radially polarized vector beam; (e)-(h) azimuthally polarized vector beam. (a), (e) Distribution of total electric field intensity (|E |2=|E x|2+|E y|2+|E z|2) in xy plane; (b), (f) distribution of total electric field intensity in xz plane; (c), (g) transverse electric field intensity (|E⊥ |2=|E x|2+|E y|2); (d), (h) longitudinal electric field intensity (|E z|2). The dark arrows represent polarization states and insets are for phase distributions
2.2 矢量光场对等离激元模式激发的调控
电偶模式是等离激元结构中最常见的一类模式。它具有强的远场辐射能力和较宽的共振峰，也被称为“亮模式”，可方便地通过光学的方式来激发［31］。例如，具有面内偶极矩的电偶模式可以由常用的线偏光来激发。然而，纵向的电偶模式因在衬底法线方向上的辐射能力较弱，则很难由聚焦的线偏光激发，为其观测和应用带来了困难［32］。紧聚焦的径向矢量光场在焦点处有很强的电场纵向分量，借助焦场与电偶极矩的匹配，则能高效激发纵向等离激元电偶模式。如
图 2. 矢量光场对等离激元偶极模式的激发与调控。（a）紧聚焦径向偏振矢量光对金纳米球中纵向偶级模式的激发［33］；（b）径向矢量光焦场的电矢量分布（上图），及其激发的任意方向的电偶极矩（下图）［35］；（c）角向偏振矢量光束激发的磁偶模式［36］
Fig. 2. Excitation and manipulation of plasmonic dipole modes with vector beam. (a) Longitudinal electrical dipole in an Au nanosphere excited by tightly focused radially polarized vector beam[33]; (b) electric vector distribution of radial vector focal field (upper panel) and electric dipole distance in any direction excited by it (below panel) [35]; (c) magnetic dipole mode excited by azimuthally polarized vector beam[36]
除亮模式外，等离激元结构还支持一类偶极矩为零的模式，即暗模式［37］。该类模式具有较小的辐射损耗、较窄的共振峰和更为显著的局域场增强效应。这些性质使暗模式在增强光与物质的相互作用方面，表现出无与伦比的优势。目前，暗模式已广泛用于表面增强拉曼散射［38］、增强非线性光学效应［39］、生物传感［40］，以及纳米激光［41］等研究中。然而，暗模式由于极小的净偶极距，很难直接被常规的标量光场激发，需借助聚焦的高速电子［42］（如电子能量损失能谱法和阴极发光技术）或倏逝场来实现观测［43］。这些较为复杂的激发方式对暗模式的实际应用带来了困难。相比之下，矢量光场可以与普通光学显微镜兼容，利用其焦场丰富的偏振态分布，可以方便灵活地激发、观测等离激元暗模式。以电四模式为例，它可以看成两个反相电偶模式的集合，故总的净偶极矩为零，是最常见的一类暗模式。
图 3. 矢量光场对等离激元暗模式的激发。（a）紧聚焦径向偏振矢量光在金纳米棒中激发的电四模式［44］。其中，左图为相对于纳米棒的激发光配置，右图为纳米棒在不同y轴位移下的散射光谱；（b）矢量光在金纳米盘七聚体中选择性激发的径向和角向暗模式［45］；（c）径向偏振矢量光在金膜-介质层-六聚体中激发的环偶极子［46］。其中，左图为等离激元结构的示意图和激发矢量光的磁场分布，右图为环偶极子的散射光谱
Fig. 3. Excitation of plasmonic dark modes with vector beam. (a) Electric quadrupole mode of Au nanorod generated by a tightly focused radially polarized vector beam[44]. Left and right panels are for excitation configuration relative to nanorod and scattering spectra of nanorod at different y displacements, respectively; (b) selectively exciting azimuthal and radial plasmonic dark modes by vector beam in Au nanodisk heptamers [45]; (c) toroidal dipole mode excited in gold film-dielectric layer-hexamer using radially polarized vector beam[46]. Left and right panels are schematics of plasmonic structure as well as magnetic field distributions of vector beam and scattering spectrum of toroidal dipole mode, respectively
以矢量光场为激发光，为观测、表征等离激元模式提供了便利，也推进了等离激元的相关应用，如增强光谱、纳米粒子捕获、增强非线性光学效应等。2006年，Anger等［47］采用紧聚焦的径向矢量光束作照明光，选择性激发了金纳米球的等离激元模式并使之与荧光分子垂直偶极子相互作用，结果如
图 4. 等离激元模式的高效光激发与应用。（a）紧聚焦的径向偏振矢量激发光对等离激元电偶模式-荧光分子相互作用的控制［47］；（b）角向等离激元暗模式的激发及在表面增强拉曼光谱中的应用［48］；（c）银纳米光阑中的径向呼吸模式及其对5 nm介质纳米球的光学捕获［49］；（d）径向矢量光激发的等离激元纳米腔模式对2 nm量子点的光学捕获［50］；（e）基于矢量光场的模式匹配实现八聚体纳米盘二次谐波频率的调谐［51］
Fig. 4. Efficient excitation and applications of plasmonic modes. (a) Manipulation of interaction between plasmonic dipole mode and fluorescence molecule using tightly focused radially polarized vector beam[47]; (b) excitation of azimuthal plasmonic dark mode and its applications in surface enhanced Raman spectroscopy[48]; (c) radial breathing mode in silver nanoaperture and its optical trapping of 5 nm dieletric nanosphere[49]; (d) optical trapping of 2 nm quantum dot[50] using plasmonic cavity mode excited by radial plasmonic breathing mode; (e) tuning frequency of second harmonic generation from octamer nanodisk using mode matching technique based on vector beam[51]
3 等离激元模式耦合的调控
3.1 等离激元模式的耦合模型
根据Huckel 分子轨道杂化概念，Prodan等［52］提出了表面等离激元杂化理论，可直观地描述模式间的强耦合行为。根据等离激元杂化理论，自由电子可以看作均匀分布在正电荷背景上不可压缩的无旋流。若该电子流发生形变，便会在金属表面引起表面电荷密度分布，而表面等离激元可以认为是电子流的自激振荡。通过计算整个系统的拉格朗日量，可确定电子流微小形变的动力学方程，进而得到系统的等离激元共振模式。以金属球壳为例，它可以看作金属纳米球形腔和纳米球的组合［52］，如
图 5. 金属球壳等离激元结构的模式杂化示意图［52］
Fig. 5. Schematic illustration of plasmon hybridization in metallic nanoshell[52]
假设金属球壳的内、外半径分别为a和b，且金属壳层厚度有限。类似于分子轨道的杂化现象，金属球形腔和金属球颗粒各自的等离激元模式会相互耦合，形成金属球壳的等离激元共振模式［52］。根据该杂化理论，可得金属球壳的两个l阶等离激元模式的频率［53］为
式中，x=a/b为金属球壳内外半径之比。可以看出，金属球壳内外表面的等离激元相互作用，产生了新的杂化等离激元共振模式
另一种处理模式耦合问题的方法是耦合谐振子模型［54］，如
图 6. 描述等离激元模式耦合的耦合谐振子模型
Fig. 6. Coupled harmonic oscillator model describing plasmonic mode coupling
这样，等离激元结构的散射光谱可表示为
以此，通过
3.2 矢量光场对等离激元模式耦合的调控
借助矢量激发场空间依赖的偏振分布，通过极矩匹配的方法可以确定性地选取参与耦合的等离激元模式的相位或类型，从而实现模式耦合的控制。例如，Deng等［55］分别利用角向和径向矢量光束在相邻金纳米球中激励了反相的电偶模式，由此生成了“肩并肩”和“首尾”耦合的两种暗模式，并利用等离激元杂化模型给予解释，如
图 7. 矢量光场对等离激元模式耦合的控制。（a）角向和径向矢量光在金纳米球二聚体中激发的反相成键和反键的暗模式［55］；（b）厄米-高斯光束对五聚体纳米片近场分布的精确管理［56］，其中，从左到右各列对应目标近场分布、矢量光激发的近场及叠加矢量激发场的各级厄米-高斯光束的振幅与相位；（c）矢量光场在金纳米球二聚体中激发的Fano共振［57］；（d）角向矢量光在开口环多聚体结构中激发的双重Fano共振［58］
Fig. 7. Controlling plasmonic mode coupling with vector beam. (a) Out-of-phase bonding and antibonding dark mode of Au nanosphere dimer excited by azimuthal and radial vector beams[55]; (b) deterministically tuning local field distribution in plasmonic nanocluster using Hermite-Gaussian beams[56], in which left to right panels correspond to target local field, vector beam excited local field as well as amplitudes and phases of Hermit-Gaussian beams for constructing vector excitation; (c) Fano resonance of Au nanosphere dimer under excitation of vector beam[57]; (d) double Fano resonances in a split ring oligomer structure excited by azimuthally polarized vector beam[58]
矢量光场激发的等离激元模式耦合展现了出众的近场和光谱线型的调控能力，为其在光力控制、二次谐波增强、等离激元结构形貌和缺陷检测中的应用奠定了基础。如
图 8. 等离激元模式耦合调控的应用［62］。（a）径向矢量光调控的金纳米盘二聚体间光学结合力的反转；（b）等离子三聚体中基于等离激元模式耦合调控的二次谐波增强；（c）角向矢量光激发的等离激元Fano共振在结构缺陷（左图）和光束对准监测（右图）方面的应用
Fig. 8. Applications of vector beam controlled plasmonic mode coupling[62]. (a) Reversible optical binding force in a plasmonic heterodimer by controling mode coupling under illumination of radially polarized vector beam; (b) enhanced second harmonic generation in a plasmonic trimer based on control of plasmonic mode coupling; (c) applications of structural defect (left panel) and beam misalignment (right panel) using plasmonic Fano resonance excited by azimuthally polarized vctor beam
4 等离激元模式远场辐射分布的调控
4.1 Kerker条件
除了增强近场的光与物质相互作用外，等离激元结构还可以作为光学纳米天线，将局域场的能量或信息，通过辐射转化至远场。同时，借助不同电磁共振模式之间的干涉，实现远场辐射分布的有效调控，最典型的例子如Kerker效应。早在1983年，Kerker预测磁性球颗粒中电偶和磁偶极共振模式的散射电磁场会在远场干涉叠加。并且，当两模式的强度相同，相位差相同或相反时，可在远场实现单一的后向或前向散射，即所谓的Kerker条件［63-64］。随后，更广义的Kerker条件被提出，适用范围也扩展到复杂结构光激发下，多个散射体通过多极模式间的干涉形成任意方向的单向散射。在等离激元研究中，光学八木天线［65］、V形纳米结构［66］、金纳米颗粒二聚体［67］等结构陆续被提出，为单向远场散射的灵活控制提供了便利，也拓展了等离激元在片上信号传输［13］、光学传感［68］、超分辨成像［69］等方面的应用。
现以核壳结构的金属-介质纳米球为例，来考察矢量光场调控的面内散射方向。根据Mie散射理论，面内的左、右向散射强度［70］分别为
式中：Itotal为总电磁场强度；
则σd，l=0，于是便可实现右向单向散射。类似地，实现左向单向散射的条件为
4.2 矢量光场对等离激元远场辐射的调控
如前所述，通过聚焦矢量光场的调控，可以设计矢量焦场各电磁分量的大小与相位，以此满足Kerker条件，实现等离激元核壳结构面内单向散射的目的。以聚焦的角向矢量光为例，如
图 9. 紧聚焦角向矢量光对等离激元核壳纳米球的散射方向调控［70］。（a）角向矢量光束焦场的不同电磁场分量在x轴上的分布；（b）角向矢量光的横向电场（|E⊥|2=|Ex|2+|Ey|2）和磁场强度（|ZH⊥|2=|ZHx|2+|ZHy|2）的分布；（c）核壳纳米球Mie散射系数a1和b1的相位差的谱分布；（d）核壳纳米球在1550 nm波长处的远场单向散射分布
Fig. 9. Manipulating scattering pattern of plasmonic core-shell nanosphere with tightly focused azimuthally polarized vector beam[70]. (a) Distributions of electromagnetic components of azimuthally polarized vector beam along x direction of focal plane; (b) in-plane electric field (|E⊥|2=|Ex|2+|Ey|2) and magnetic field intensity (|ZH⊥|2=|ZHx|2+|ZHy|2) of azimuthally polarized vector beam; (c) spectrum distribution of phase difference between Mie coefficients a1 and b1 of core-shell nanospheres; (d) far-field unidirectional scattering distribution of core-shell nanosphrere at λ=1550 nm
利用矢量光场调控等离激元结构的辐射方向，为提升纳米光子器件的光波收集效率，研发高灵敏度的传感器件提供了新的解决方案。2014年，Neugebauer等［12］研究了紧聚焦径向矢量光激发下金纳米球的远场散射特性，如
图 10. 矢量光场调控的金纳米结构的单向散射。（a）利用紧聚焦矢量光操控的金纳米球远场散射的示意图［12］；（b）金纳米球在焦场位置的变化可令面内辐射场由各向同性（中图）变为单向性散射（左、右图）［12］；（c）金纳米球单向散射在波导定向耦合中的应用［12］；（d）紧聚焦厄米-高斯光束激发槽孔天线表面等离激元的光路示意图［71］；（e）槽孔天线中磁偶模式的激发（上图）与单向传输的表面等离极化激元（下图）［71］；（f）非对称传输的表面等离极化激元在纳米位移传感中的应用［71］
Fig. 10. Unidirectional scattering of Au nanosctructure using vector beam control. (a) Schematic of far-field scattering of Au nanosphere controlled by tightly focused vector beam[12]; (b) change in focal field position of Au nanospheres can cause in-plane radiation field to shift from isotropic (center image) to unidirectional scattering (left and right images) [12]; (c) application of unidirectional scattering of Au nanospheres in waveguide directional coupling [12]; (d) optical path diagram of tightly focused Hermite-Gaussian beam exciting slotted antenna surface plasmon polariton[71]; (e) excitation of magnetic dipole modes in slot antennas (upper panel) and surface plasmon polaritons with unidirectional transmission (lower panel) [71]; (f) application of asymmetric transmission of surface plasmon polaritons in nanometric displacement sensing[71]
5 结论
本文综述了近年来矢量光场与等离激元模式作用的进展。简要讨论了矢量光场匹配激发等离激元模式的本征响应理论。从等离激元杂化理论和耦合谐振子模型角度，解释了矢量光场对模式耦合的调控机理。通过Mie散射理论和Kerker条件，论述了矢量光场对等离激元远场辐射分布的调控方法。以此为基础，详细介绍了矢量光场在调控等离激元模式激发、耦合、辐射中的暗模式、Fano共振和单向散射等过程中的新颖现象，以及在增强荧光和光学非线性、纳米尺度光操控、纳米位移传感等方面的应用。
需要指出的是，近十年来，基于矢量光场的等离激元模式调控得到了长足发展，但仍有许多问题亟待解决。典型地，由于衍射极限的存在，矢量光场与纳米尺度的等离激元结构存在较大的空间失配，导致偏振-偶极矩匹配的模式激发方法（特别是高阶模式）的效率较低。为此，需要发展极小尺度的聚焦场的产生方法，如借助镀金属膜的光纤探针生成纳米尺度的矢量光场［73］。再者，矢量光场等离激元模式耦合调控方面，多限于对称性较高的等离激元结构。如何在非对称金属结构中挑选并调控等离激元模式的耦合仍存在挑战。这需要发展更为精细、灵活的矢量光场的定制方法（如基于机器学习的光场调控技术［74］）来准确调控等离激元模式。
值得注意的是，近年来光场调控研究得到了飞速发展，一些新型光场不断涌现，如高度局域手性“光针”［75］、具有拓扑特性的斯格明子［76］、光学莫比乌斯环［77］等。这些为人们利用光场调控技术操纵等离激元提供了巨大的机遇。与此同时，以等离激元纳米腔为代表的超紧凑等离激元结构逐渐兴起，成为实现极端局域光场的理想选择。可以预见的是，如将两者相结合，可赋予人们操控等离激元物性（如超手性场、局域光子态密度、模体积等）更为丰富的手段［78-79］，从而为纳米甚至皮米尺度下研究室温强耦合、光学非线性、手性光力学等基本物理现象提供更为便利的条件，并有望拓展等离激元在信息、能源、生物等领域的应用。
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Article Outline
肖发俊, 赵建林. 基于矢量光场的等离激元模式调控[J]. 光学学报, 2023, 43(16): 1623002. Fajun Xiao, Jianlin Zhao. Plasmonic Mode Control Based on Vector Beams[J]. Acta Optica Sinica, 2023, 43(16): 1623002.
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