FDTD analysis of optical forces on bowtie antennas for high-precision trapping of nanostructures (original) (raw)

Optical forces in plasmonic nanoantennas

Quantum Electronics, 2012

The optical forces acting on nanoparticles in V-shaped plasmonic resonators with a high local-field gain have been investigated. Two versions are considered, which make it possible to implement either attractive or repulsive gradient optical forces. A plasmonic resonator is proposed, which can focus 350-nm radiation and implement a repulsive gradient force. It has been shown for the first time that a perturbation induced by a nanoparticle redistributes the field in the resonator so that additional intensity peaks arise in both versions to hold the nanoparticle in the resonator by forming an optical trap.

Electromagnetic forces for an arbitrary optical trapping of a spherical dielectric

Optics Express, 2006

Analytical solution for optical trapping force on a spherical dielectric particle for an arbitrary positioned focused beam is presented in a generalized Lorenz-Mie and vectorial diffraction theory. In this case the exact electromagnetic field is considered in the focal region. A double tweezers setup was employed to perform ultra sensitive force spectroscopy and observe the forces, demonstrating the selectively couple of the transverse electric (TE), transverse magnetic (TM) modes by means of the beam polarization and positioning, and to observe correspondent morphology-dependent resonances (MDR) as a change in the optical force. The theoretical prediction of the theory agrees well with the experimental results. The algorithm presented here can be easily extended to other beam geometries and scattering particles.

Near-field photonic forces

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2004

A review of recent advancements in photonic forces is presented. We discuss in detail the interaction of light and sub-wavelength particles on a substrate illuminated by total internal reflection, and we study the optical forces experienced by the particles. The effects of plasmon-mode excitations on the resulting photonic forces on metallic particles are also addressed. Moreover, we explore the possibility of using the metallic tip of a classical apertureless microscope to create optical tweezers, and thus to achieve a selective manipulation of nanoparticles.

Optical trapping and sensing with plasmonic dipole antennas

Plasmonics: Metallic Nanostructures and Their Optical Properties Viii, 2010

In this work, we study how to use a plasmonic dipole antenna as a multifunctional nanodevice for surface-enhanced Raman spectroscopy (SERS), localized surface plasmon resonance (LSPR)-based sensing and optical trapping. An analytical model is implemented to link the local electric field enhancement with the gradient forces, as well as the resonance shift caused by the presence of the analyte which can be a molecule or a nanoparticle. We find that a higher local field enhancement induces stronger trapping forces and a larger resonance wavelength shift. Experiments were also performed using plasmonic dipole antennas. Strong SERS signals were observed from the nanogap of an antenna, trapping of Au nanoparticles as small as 10 nm was achieved with a moderate laser power, and evident resonance shifts of the antenna associated with the trapping events were also observed. These results are consistent with our theoretical result that the giant field enhancement generated by a plasmonic dipole antenna also generates strong gradient forces and a high spectral sensitivity.

Field Computations of Optical Antennas

Antenna-based near-field optical microscopy and spectroscopy makes use of locally enhanced optical fields created near laser-irradiated metal nanostructures acting as local probes. Using threedimensional simulations based on the finite element method we study the electromagnetic fields near various optical antennas and we optimize their geometry in order to bring out a strong enhancement in a selected frequency range. Our results provide clear guidelines for the fabrication of efficient antenna structures and for improving the sensitivity of current near-field microscopy schemes.

Optical Forces on Non-Spherical Nanoparticles Trapped by Optical Waveguides

International Journal of Optomechatronics, 2011

Numerical simulations of a solid-core polymer waveguide structure were performed to calculate the trapping efficiencies of particles with nanoscale dimensions smaller than the wavelength of the trapping beam. A three-dimensional (3-D) finite element method was employed to calculate the electromagnetic field. The inlet and outlet boundary conditions were obtained using an eigenvalue solver to determine the guided and evanescent mode profiles. The Maxwell stress tensor was considered for the calculation of the transverse and downward trapping efficiencies. A particle at the center of the waveguide showed minimal transverse trapping efficiency and maximal downward trapping efficiency. This trend gradually reversed as the particle moved away from the center of the waveguide. Particles with larger surface areas exhibited higher trapping efficiencies and tended to be trapped near the waveguide. Particles displaced from the wave input tended to be trapped at the waveguide surface. Simulation of an ellipsoidal particle showed that the orientation of the major axis along the waveguide's lateral z-coordinate significantly influenced the trapping efficiency. The particle dimensions along the z-coordinate were more critical than the gap distance (vertical displacement from the floor of the waveguide) between the ellipsoid particle and the waveguide. The present model was validated using the available results reported in the literature for different trapping efficiencies.

Optical Trapping and Manipulation of Nano-objects with an Apertureless Probe

Physical Review Letters, 2002

We propose a novel way to trap and manipulate nano-objects above a dielectric substrate using an apertureless near-field probe. A combination of evanescent illumination and light scattering at the probe apex is used to shape the optical field into a localized, three dimensional optical trap. We use the coupled-dipole method and the Maxwell stress tensor to provide a self-consistent description of the optical force, including retardation and the influence of the substrate. We show that small objects can be selectively captured and manipulated under realistic conditions.

Nearā€field analysis of discrete bowtie plasmonic nanoantennas

Microwave and Optical Technology Letters, 2019

A discrete antenna is a discretized version of a traditional antenna design which enhances the antenna properties (such as field intensity, multi-band, compact size, and low sidelobe levels) of its traditional counterpart. In this work, a classical bowtie antenna is discretized using circular elements of different sizes. Numerical simulations and near-field optical scanning microscopy are performed on classical and discrete bowtie antennas in the infrared. Simulations show that discrete antennas have an increased bandwidth and an increased number of electric-field hotspots and near-field measurements confirm the increment of hotspots. These characteristics make discrete antennas potentially useful in applications where an extended region of localized electric field enhancements is of interest.

Nanometric plasmonic optical trapping on gold nanostructures

The European Physical Journal Applied Physics, 2019

The precise noninvasive optical manipulation of nanometer-sized particles by evanescent fields, instead of the conventional optical tweezers, has recently awaken an increasing interest, opening a way for investigating phenomena relevant to both fundamental and applied science. In this work, the optical trapping force exerted on trapped dielectric nanoparticle was theoretically investigated as a function on the trapping beam wavelength and as a function of several plasmonic nanostructures schemes based on numerical simulation. The maximum optical trapping forces are obtained at the resonance wavelength for each plasmonic nanostructure geometry. Prominent tunabilities, such as radius and separation of gold nanoparticles as well as the numerical aperture of objective lens were examined. This work will provide theoretical support for developing new types of plasmonic sensing substrates for exciting biomedical applications such as single-molecule fluorescence.