Cui Xudong, Erni Daniel, Hafner Christian
Faculty of Engineering, General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, D-47057 Duisburg, Germany.
Opt Express. 2008 Sep 1;16(18):13560-8. doi: 10.1364/oe.16.013560.
We investigate the optical forces acting on a metallic nanoparticle when the nanoparticle is introduced within a photonic nanojet (PNJ). Optical forces at resonance and off-resonance conditions of the microcylinder or nanoparticle are investigated. Under proper polarization conditions, the whispering gallery mode can be excited in the microcylinder, even at off resonance provided that scattering from the nanoparticle is strong enough. The optical forces are enhanced at resonance either of the single microcylinder or of the nanoparticle with respect to the forces under off-resonant illuminations. We found that the optical forces acting on the nanoparticle depend strongly on the dielectric permittivity of the nanoparticle, as well as on the intensity and the beam width of the PNJ. Hence, metallic sub-wavelength nanoparticle can be efficiently trapped by PNJs. Furthermore, the PNJ's attractive force can be simply changed to a repulsive force by varying the polarization of the incident beam. The changed sign of the force is related to the particle's polarizability and the excitation of localized surface plasmons in the nanoparticle.
我们研究了将金属纳米颗粒引入光子纳米射流（PNJ）时作用在该纳米颗粒上的光学力。研究了微圆柱体或纳米颗粒在共振和非共振条件下的光学力。在适当的偏振条件下，即使在非共振情况下，只要纳米颗粒的散射足够强，微圆柱体内也能激发回音壁模式。相对于非共振照明下的力，单个微圆柱体或纳米颗粒在共振时的光学力会增强。我们发现，作用在纳米颗粒上的光学力强烈依赖于纳米颗粒的介电常数，以及PNJ的强度和光束宽度。因此，金属亚波长纳米颗粒可以被PNJ有效地捕获。此外，通过改变入射光束的偏振，PNJ的吸引力可以简单地变为排斥力。力的符号变化与颗粒的极化率以及纳米颗粒中局域表面等离子体激元的激发有关。
