Strong and High-Precision Manipulation of Nanoparticle with Graphene-Coated Fiber Systems

Shu Yang, Kang Zhao, Zhengtian Xu

Two kinds of graphene-coated fiber systems are proposed and studied for optical trapping. Their plasmonic modes in uniform environment and close to the substrate are studied in the finite element method. The optical forces exerted on dielectric nanoparticle by these systems are calculated by standalone waveguide approximation. It is found that for the dielectric particle with diameter of 1 nm, the maximal optical forces generated by certain modes are more than 107 fN/W whereas their force ranges are only one to several nanometers. These results may have important applications in strong and high-precision optical tweezers.

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Rotating Ag-Fe3O4-Au Nanograin by Optical Torque with a Monochromatic Light Beam

Xiaoqin Mao, Yan Li, Weiyan Jiao, Xinshun Wang, Benyang Wang

Optical torques of asymmetrical Ag–Fe3O4–Au nanograins were investigated by the method of discrete dipole approximation (DDA). The results show that surface plasmon resonance (SPR) causes the optical torques which can keep the nanograins rotating clockwise or counterclockwise. When the power density of optical radiation is I = 109 W/m2, the angular velocities of the hybrid sphere and cube heterotrimers can reach to about 104 rad/s in the ranges of 360–374 nm and 403–426 nm, which is ten times larger than that of Brownian rotation. The peak widths at half height of angular velocity curves for two kinds of grains are in the ranges of 31–47 nm and 54–70 nm, respectively. When light radiation force offers a regular driving force, such grains can serve as potential nanoscale optical wrench or microscopic mixers. In addition, the influences of Brownian rotation and photophoresis were discussed.

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New Characterization of Plasmons in Nanowire Dimers by Optical Forces and Torques

R. M. Abraham Ekeroth
In a previous work, unexpected optical torques were found on metallic dimers of infinite nanowires. The dimers were illuminated with linearly polarized plane waves. Here, the study is extended to bigger systems: the spin torques are induced independently of scale, shape details, and dielectric corrections. New properties appear in the dynamics as the breaking of the action-reaction law, changes in the radiation pressures, or the detection of forbidden modes—dark plasmons—by optical forces. Furthermore, the spectra of spin torques show more resolved resonances than typical far-field spectra. The numerical study is based on an exact method. New possibilities are suggested for the detection of asymmetries in nanostructures. The results are thought for the design of nanorotators and nanodetectors, or simply approach the movement of coupled particles with more accuracy.

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Optical Manipulation of Dielectric Nanoparticles with Au Micro-racetrack Resonator by Constructive Interference of Surface Plasmon Waves

Mingrui Yuan, Lin Cheng, Pengfei Cao, Xu Li, Xiaodong He, Xiaoping Zhang

We design a gold micro-racetrack resonator (Au-MRR) which can tightly trap and drive the dielectric nanoparticle to rotate around the circuit of racetrack with an adjustable velocity. Since the surface plasmon waves can be excited and obey the resonance condition of the Au-MRR, the optics force can be strengthened observably due to the resonance. The optical forces applied on dielectric nanoparticle are discussed by utilizing the Maxwell’s stress tensor integration with a numerical finite element method. The depth of longitudinal trapping potential well in the Au-MRR is four times as large as that of a straight waveguide. At the same level of input power, the velocity of particle with radius of 50 nm driven by optical forces on Au-MRR is 200 times larger than that on a straight waveguide. Further, we explore the motion behavior of single nanoparticle lies on different position of Au-MRR, which can provide the details to trap and manipulate multiple nanoparticles and predict their trace of movement. This optimum geometry of Au-MRR allows further enhancement of the optical forces which is expected to realize all-optical on-chip manipulation of nanoparticles, biomolecules, and many other nanomanipulation applications.

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Theoretical Modeling of Average Force Acted on Nano Plasma Spheres in Presence of Radiation of Long Wavelength Point Source

Z. Hajijamali-AraniB. Jazi, S. Jahanbakht

Using the solutions of field equation, due to the electromagnetic wave scattering phenomena from a nano plasma sphere(NPS), the inserted force on nano plasma sphere is simulated. For this purpose, with using suitable Green’s function, the scattering phenomena of long wavelength electromagnetic waves from a nano plasma sphere will be investigated. A point electromagnetic source is considered in finite distance from the NPS. The computations will be generalized to two monopole point sources with the same strength but with opposite sign in two sides of sphere to simulating a NPS in presence of a plane electromagnetic wave. The resonance frequency and pattern scattering for these problems will be presented. The graphs of variations of inserted force with respect to wave frequency and geometrical dimension variations are presented.

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Fano Resonance-Assisted Plasmonic Trapping of Nanoparticles

Noor Uddin, Guangqing Du, Feng Chen, Yu Lu, Qing Yang, Hao Bian, Jiale Yong, Xun Hou

Plasmonic optical trapping is widely applied in the field of bioscience, microfluidics, and quantum optics. It can play a vital role to extend optical manipulation tools from micrometer to nanometer scale level. Currently, it is a challenge to obtain the highly stable optical trapping with low power and less damage. In this paper, we propose Fano resonance-assisted self-induced back-action (FASIBA) method, through which a single 40-nm gold particle can be trapped in hole-slit nano-aperture milled on metallic film. It is used to achieve ultra-accurate positioning of nanoparticle, metallic nanostructures at wide infrared wavelength range, quite effectively and evidently. The stable plasmonic trapping is achieved by tuning the transmission wavelengths and modifications of nanoslit, indicating that the depth of potential well can be increased from minus 8KT to 12KT, with the input power of 109 W/m2. This can be attributed to great modifications in Fano resonance transmissions according to self-induced back-action (SIBA) theory. The results are basically helpful to facilitate the trapping with lower power and less damage to the objects, which enables new scenario for the treatment of undesirable spread of a single nanoscale creature, such as virus.

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Plasmonic Nanoparticle Aggregates in High-Intensity Laser Fields: Effect of Pulse Duration

A. E. Ershov, A. P. Gavrilyuk, S. V. Karpov

We use an optodynamic model to study the interaction of pulsed laser radiation of different duration with mono- and polydisperse dimers and trimers of plasmonic nanoparticles as resonant domains of colloid Ag multiparticle aggregates. A comparative analysis of the influence of pulse duration on the kinetic characteristics of domains accompanied by the change in their local structure was carried out taking into account the intensity of incident radiation. The obtained results explain the reasons for laser photochromic reactions in materials containing colloidal aggregates of plasmonic nanoparticles.

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Optical Forces on Silver Homogeneous Nanotubes: Study of Shell Plasmonic Interaction

R. M. Abraham Ekeroth, M. F. Lester

In previous works (Abraham et al., Plasmonics 6(3):435–444 (2011); Abraham Ekeroth and Lester, Plasmonics 7(4):579–587, (2012); Abraham Ekeroth and Lester, Plasmonics 8:1417–1428 (2013)), we performed an exhaustive study about optical properties of metallic realistic nanotubes, hollow or with dielectric cores. Based on rigorous calculations, involving experimental-interpolated dielectric functions, we pointed out the importance of using an adequate size-corrected dielectric function in homogeneous bidimensional metallic shells when their thicknesses are about several nanometers. In this paper, we compute optical forces induced by electromagnetic plane waves on these kind of nanostructures. We focus the study under p polarisation, in order to observe plasmonic-related behaviour. The optical forces are calculated by the Maxwell’s stress tensor without any kind of approximation. We show three examples of mechanical effects on silver thin shells. The characteristics of the electromagnetic interaction in these structures, from the point of view of forces, allow us to comprehend the problem of the plasmonic interaction in the shell in a new way. We show numerically, for the first time, the nature of bonding/antibonding of surface plasmons in nanotubes made of realistic materials, in a way independent of approximations related to scale. The behaviour of the realistic silver shells is compared with the features deduced from the plasmon hybridization model, which are predicted from a quasi-static approximation of electromagnetic response. Our results conceive a full retarded problem and can only contain numerical errors. In addition, we compare rigorous calculations for the optical forces with those ones obtained from the far field approach, when specified for shell geometry.

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Field Enhancement and Gradient Force in the Graphene-Coated Nanowire Pairs

Bofeng Zhu, Guobin Ren, Yang Yang, Yixiao Gao, Beilei Wu, Yudong Lian, Jing Wang, Shuisheng Jian

We investigate the field enhancement and gradient force in the graphene-coated nanowire pairs in this paper. The real part of modal index, normalized propagation lengths, surface charge distributions and field distributions of the six lowest orders’ plasmon modes in the graphene-coated nanowire pairs is presented. Studies have shown that the six lowest orders’ modes can be divided into two groups due to the monopole-monopole hybridizations or the dipole-dipole interactions. The field enhancement in the slot region of the graphene-coated nanowire pairs can be as large as 107 times, which is six orders’ magnitude larger than the counterpart in silver nanowire pairs. Meanwhile, gradient force between the two nanowires can be as high as 20 nN·μm−1·mW−1, which is more than one order of magnitude (∼50 times) larger than the silver nanowire pairs and the previous results from other slot waveguides or coupled waveguides. The field enhancement or gradient force in the graphene-coated nanowire pairs may have applications in single biomolecule manipulation or detection.

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Numerical study of nanoparticle sensors based on the detection of the two-photon-induced luminescence of gold nanorod antennas

Zaoshan Huang, Qiaofeng Dai, Sheng Lan, Shaolong Tie

We investigate numerically the modification of the nonlinear optical properties of a nanoantenna in the trapping of nanoparticles (NPs) by using both the discrete dipole approximation method and the finite-difference time-domain technique. The nanoantenna, which is formed by two gold nanorods (GNRs) aligned end to end and separated by a small gap, can emit strong two-photon-induced luminescence (TPL) under the excitation of a femtosecond laser light which is resonant with its longitudinal surface plasmon resonance. In addition, the excited antenna can stably trap small NPs which in turn induce modifications in the emitted TPL. These two features make it a promising candidate for building highly sensitive detectors for NPs of different materials and sizes. It is demonstrated that sensors built with antennas possess higher sensitivities than those built with single GNRs and nanorod-based antennas are more sensitive than nanoprism-based antennas. In addition, it is found that the trapping probability for a second NP is significantly reduced for the antenna with a trapped NP, implying that trapping of NPs may occur sequentially. A relationship between the TPL of the system (antenna + NP) and the optical potential energy of the NP is established, enabling the extraction of the information on the optical potential energy and optical force by recording the TPL of the system. It is shown that the sequential trapping and releasing of NPs flowing in a microfluid channel can be realized by designing two different antennas arranged closely.

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Plasmonic Nanostructures as Accelerators for Nanoparticles: Optical Nanocannon

Alexander S. Shalin and Sergey V. Sukhov

We suggest a model of an optical structure that allows to accelerate nanoparticles to velocities on the order of tens of centimeters per second using low-intensity external optical fields. The nano-accelerator system employs metallic V-grooves which concentrate the electric field in the vicinity of their bottoms and creates large optical gradient forces for the nanoparticles in that groove. The conditions are found when this optical force tends to eject particles away from the groove.

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