表面增强光学力与光操纵研究进展

Advances in surface-enhanced optical forces and optical manipulations

金属纳米结构在光激发下产生的表面等离激元,可导致亚波长光场局域、近场增强等效应,在表面增强光谱、超灵敏传感、微流控芯片、光学力等方面有重要的应用.对于光学力而言,首先,由于表面等离激元共振及其导致的电场增强对于入射波长、几何结构等具有较强的依赖性,而光学力又与电场分布密切相关,所以可利用光镊(会聚光束)来操纵或筛选金属纳米颗粒;其次,入射光激发金属纳米颗粒聚集体后,在间隙形成的较大的近场增强和梯度,也可看作一种“等离激元镊”,用于操纵其他颗粒;最后,当入射光的偏振改变甚至为新型光束的情况下,光学操纵将具有更高的自由度.本文首先简要介绍了表面等离激元增强光学力的计算;之后围绕光镊作用于等离激元金属纳米颗粒,等离激元镊作用于其他颗粒,与偏振、新型光场或手性结构相关的等离激元光学力这三个方面,综述了近年来表面等离激元金属纳米颗粒光学力和光操纵的一些新进展;最后提出了表面增强光学力与光操纵的若干研究趋势.

The localized surface plasmons in metal nanostructures under optical excitation will lead to near-fieldlocalization and enhancement,which have shown important applications in surface enhancement spectroscopy,ultra-sensitive sensing,microfluidic chip,enhanced optical force,etc.The plasmon resonance and the resultingelectric field enhancement strongly depend on wavelength and structure geometry.As a result,the optical forcewill be closely related to the field distribution,that is,the optical force can be used to manipulate and sortplasmonic metal structures.The large near-field enhancement and gradient of metal nanoparticle aggregates canalso be used as a“plasmonic tweezer”to manipulate other particles.Furthermore,in the case of changing theincident polarization and even for a new type of structured laser beam,the optical manipulation has a higherdegree of freedom.In this review,having briefly introduced the plasmon-enhanced optical force,we focus on therecent advances in the following three aspects:1)the manipulation of plasmonic nanoparticles by opticaltweezer,2)the manipulation of other particles by plasmonic tweezer,and 3)dependence of plasmonic opticalforce on the polarization,optical angular momentum,structured light and the structured chirality.Comparingwith other topics of plasmon-enhanced light-interactions,there is plenty of room for further developing theplasmon-enhanced optical force and optical manipulation.Several research trends can be foreseen.1)Moreprecise optical manipulating and sorting of nanoparticles(even sub-nanometer).For example,more sensitivespecial resonant modes(e.g.Fano resonance)of plasmonic nanostructure can be utilized.For somenanostructures with small feature sizes,especially when the gap size is close to 1 nm,the non-local effect has acertain effect on the plasmon resonance.Therefore,when calculating the optical force in this case,non-localeffects and possibly other quantum effects should be considered.2)Richer laser fields,that is,using various newstructured fields and chiral structures provides a higher degree of freedom for the optical forces and opticalmanipulation.Also,the localized surface plasmons can be combined with propagating surface plasmons.3)Wider applications of plasmonic optical forces,especially in combination with other effects and eveninterdiscipline,e.g.enhanced spectroscopy,enhanced single particle chemical reactions,nonlinear optical effects,and photothermal manipulations.