Trapping of Nano-Particles Using a Near-Field Optical Fiber Probe

By employing a generalization of the conservation law for momentum using the finite difference time domain (FDTD) method, the feasibility of using a near-field optical fibre probe to create near-field optical trapping is investigated. Numerical results indicate that the scheme is able to trap nanoparticles with diameters of tens of nanometres in a circular shape with lower laser intensity. Using the built system with a tapered metal-coated fibre probe, 120 nm polystyrene particles are trapped in a multi-circular shape with a minimum size of 400 nm. They are at a resolution of λ/7 (λ: laser wavelength) and d (d: tip diameter of fiber probe), respectively.

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Near-Field Vortex Beams Diffraction on Surface Micro-Defects and Diffractive Axicons for Polarization State Recognition

Sensors ◽

10.3390/s21061973 ◽

2021 ◽

Vol 21 (6) ◽

pp. 1973

Author(s):

Dmitry Savelyev ◽

Nikolay Kazanskiy

Keyword(s):

Light Propagation ◽

Near Field ◽

Polarization State ◽

Fdtd Method ◽

Minimum Size ◽

Size Change ◽

State Recognition ◽

Input Radiation ◽

Height Change ◽

Difference Time

The diffraction of vortex Gaussian laser beams by elementary objects of micro-optics (surface micro-defects) to recognize the type of polarization (linear, circular, radial, azimuthal) of the input radiation was investigated in this paper. We considered two main types of defects (protrusion and depression in the form of a circle and a square) with different sizes (the radius and height were varied). Light propagation (3D) through the proposed micro-defects was modeled using the finite difference time domain (FDTD) method. The possibility of recognizing (including size change) of surface micro-defects (protrusions and depressions) and all the above types of polarization are shown. Thus, micro-defects act as sensors for the polarization state of the illuminating beam. The focusing properties of micro-defects are compared with diffractive axicons with different numerical apertures (NAs). The possibility of sub-wavelength focusing with element height change is demonstrated. In particular, it is numerically shown that a silicon cylinder (protrusion) forms a light spot with a minimum size of the all intensity FWHM of 0.28λ.

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Nano-Particle Manipulated with Near-Field Optical Tweezers

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.299-300.1068 ◽

2011 ◽

Vol 299-300 ◽

pp. 1068-1071

Author(s):

Jing Tang ◽

Li Jun Yang ◽

Bing Hui Liu ◽

Yang Wang

Keyword(s):

Optical Tweezers ◽

Near Field ◽

Three Dimensional ◽

Direct Calculation ◽

Nano Particles ◽

Minimum Size ◽

Optical Manipulation ◽

Maxwell Stress Tensor ◽

Difference Time

By applying the direct calculation of Maxwell stress tensor using three-dimensional finite difference time domain method, the feasibility of using a metal-coated fiber probe to create near-field optical tweezers is investigated. Numerical results indicate that these schemes are able to trap nano-particles with lower laser intensity than that required by conventional optical tweezers. The near-field optical trapping systems that are more flexible than conventional optical tweezers are built. In experiments, 120-nm polystyrene particles are trapped in a multi-circular shape with a minimum size of 400 nm. The realization of trapping particles in the range of tens of nanometers largely promotes the role of near-field optical manipulation at the nanometer scale.

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