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

Sensors ◽  
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.

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

2012 ◽  
Vol 516 ◽  
pp. 90-95
Author(s):  
Bing Hui Liu ◽  
Li Jun Yang ◽  
Yang Wang
Keyword(s):  
Near Field ◽  
Fdtd Method ◽  
Laser Wavelength ◽  
Nano Particles ◽  
Minimum Size ◽  
Fiber Probe ◽  
Circular Shape ◽  
Optical Fiber Probe ◽  
Fibre Probe ◽  
Difference Time

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.

scholarly journals Optical Vortices Sharp Focusing by Silicon Ring Gratings Using High-Performance Computer Systems

2021 ◽  
Author(s):  
Dmitry Savelyev
Keyword(s):  
Time Domain ◽  
Finite Difference Time Domain ◽  
High Performance ◽  
Light Propagation ◽  
Longitudinal Component ◽  
Laser Beams ◽  
Minimum Size ◽  
Sharp Focusing ◽  
Direction Of Polarization ◽  
Difference Time

The diffraction of vortex laser beams with circular polarization (with different direction of polarization rotation) by silicon ring gratings was investigated in this paper. The silicon diffractive axicons with different numerical apertures (NA) were considered as such ring gratings. The considered diffractive axicons are compared with single silicon circular protrusion (cylinder). The finite difference time domain method was used for Light propagation (3D) through the proposed silicon ring gratings and silicon cylinder. The possibility of subwavelength focusing by varying the height of the elements is demonstrated. In particular, it is numerically shown that a silicon cylinder forms a light spot with the minimum size (intensity) of the longitudinal component of the electric field FWHM is 0.32λ.

Influence of the Nano-mesh Metal Electrode to Light Excitation of Carriers in Semiconductor

2012 ◽  
Vol 1391 ◽  
Author(s):  
Kumi Masunaga ◽  
Kenji Nakamura ◽  
Ryota Kitagawa ◽  
Eishi Tsutsumi ◽  
Tsutomu Nakanishi ◽  
...  
Keyword(s):  
Near Field ◽  
Fdtd Method ◽  
Surface Region ◽  
Metal Electrode ◽  
Infrared Region ◽  
Thin Metal Film ◽  
Infrared Light ◽  
Light Excitation ◽  
Theoretical Simulations ◽  
Difference Time

ABSTRACTA thin metal film with nano-apertures, called “nano-mesh electrode,” generates near-field lights near the electrode. We investigated carrier excitations in semiconductors by the near-field light. Finite-difference time-domain (FDTD) method revealed that when the infrared light irradiates the Au nano-mesh electrode on Ge, near-field lights are generated and absorbed in the surface region of the Ge. In order to measure the photocurrent involved by near-filed lights, we fabricated a Schottky cell and applied a Au nano-mesh electrode on the n-type Ge. The efficiency of the Schottky cell with the Au nano-mesh electrode improved in infrared region compared to plain the Au-film Schottky cell. The agreement between theoretical simulations and experiments indicates that near-field lights enhance the carrier excitation in the semiconductor.

Nano-Particle Manipulated with Near-Field Optical Tweezers

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.

Efficiency of Implicit Symplectic Finite-Difference Time-Domain Method for Near-Field Optics

2012 ◽  
Author(s):  
Ikuo Saitoh ◽  
Makoto Naruse
Keyword(s):  
Finite Difference ◽  
Time Domain ◽  
Finite Difference Time Domain ◽  
Near Field ◽  
Fdtd Method ◽  
Conservation Of Energy ◽  
Near Field Optics ◽  
Polarization Control ◽  
Metal Nanostructure ◽  
Difference Time

We proposed a new method, implicit symplectic finite difference time domain (FDTD) method) which inherits the good properties from the conventional FDTD method, simplecticity and the conservation of energy. The proposed method is free from the Courant-Friedrics-Lewy condition at the same time. In this paper, we show our method is more efficient than the conventional FDTD method using a typical problem, a polarization control in optical near and far fields of the designing the shape of a metal nanostructure.

scholarly journals The investigation of the features of focusing vortex super-Gaussian beams with a variable-height diffractive axicon

2021 ◽  
Vol 45 (2) ◽  
pp. 214-221
Author(s):  
D.A. Savelyev
Keyword(s):  
Gaussian Beam ◽  
Circular Polarization ◽  
Focal Spot ◽  
Near Field ◽  
Optical Element ◽  
Spot Size ◽  
Minimum Size ◽  
Focal Spot Size ◽  
Diffractive Axicon ◽  
Difference Time

Spatial intensity distributions of the Laguerre-superGauss modes (1,0) as well as a super-Gaussian beam with radial and circular polarization were investigated versus changes in the height of a diffractive axicon. The height of the relief of the optical element varied from 0.25λ to 3λ. The modeling by a finite-difference time-domain method showed that variations in the height of the diffractive axicon significantly affect the diffraction pattern in the near field of the axicon. The smallest focal spot size for a super-Gaussian beam was obtained for radial polarization at a height equal to two wavelengths. The minimum size of the focal spot for the Laguerre-superGauss mode (1,0) was obtained for circular "–" polarization with an element height equal to a quarter of the wavelength.

CHERENKOV RADIATION INDUCED BY COSMOGENIC NEUTRINOS IN NEAR-FIELD

2013 ◽  
Vol 28 (02) ◽  
pp. 1340006
Author(s):  
CHIA-YU HU ◽  
CHIH-CHING CHEN ◽  
PISIN CHEN
Keyword(s):  
Near Field ◽  
Fdtd Method ◽  
Field Approximation ◽  
High Energy ◽  
Dense Medium ◽  
Numerical Code ◽  
Peak Structure ◽  
Alternative Approach ◽  
Radiation Induced ◽  
Difference Time

The radio technique of cosmogenic neutrino detection, which relies on the Cherenkov signals coherently emitted from the particle showers in dense medium, has now become a mature field. We present an alternative approach to calculate such Cherenkov pulse by a numerical code based on the finite difference time-domain (FDTD) method that does not rely on the far-field approximation. We show that for a shower elongated by the LPM (Landau-Pomeranchuk-Migdal) effect and thus with a multi-peak structure, the generated Cherenkov signal will always be a bipolar and asymmetric waveform in the near-field regime regardless of the specific variations of the multi-peak structure, which makes it a generic and distinctive feature. This should provide an important characteristic signature for the identification of ultra-high energy cosmogenic neutrinos.

FDTD Study of the Surface Waves Detection in Apertureless Scanning Near-Field Microscopy

2008 ◽  
Author(s):  
G. Parent ◽  
S. Fumeron ◽  
D. Lacroix
Keyword(s):  
Surface Waves ◽  
Near Field ◽  
Fdtd Method ◽  
Three Dimensional ◽  
Far Field ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Experimental Tool ◽  
Field Transformation ◽  
Difference Time

Recent studies have shown the importance of surface waves in heat transfer near interfaces. The scanning near field optical microscopy (SNOM) provides an experimental tool to investigate the thermal electromagnetic field near surfaces. In this work, we present a three dimensional model of SNOM devices. This model is based on the finite-difference-time domain (FDTD) method associated to a near to far field transformation. Near field and far field scattered by a silicon tetrahedral tip and by a pecfectly conducting one are presented and discussed.

scholarly journals Modified Finite-Difference Time-Domain Method for Hertzian Dipole Source under Low-Frequency Band

Electronics ◽  
2021 ◽  
Vol 10 (22) ◽  
pp. 2733
Author(s):  
Minhyuk Kim ◽  
SangWook Park
Keyword(s):  
Finite Difference ◽  
Frequency Band ◽  
Time Domain ◽  
Finite Difference Time Domain ◽  
Near Field ◽  
Fdtd Method ◽  
Low Frequency ◽  
Dipole Source ◽  
Static Approximation ◽  
Difference Time

In this paper, a modified finite-difference time-domain (FDTD) method is proposed for the rapid analysis of a Hertzian dipole source in the low-frequency band. The FDTD technique is one of the most widely used methods for interpreting high-resolution problems such as those associated with the human body. However, this method has been difficult to use in the low-frequency band as the required number of iterations has increased significantly in such cases. To avoid this problem, FDTD techniques using quasi-static assumptions in low-frequency bands were used. However, this method was applied only to plane wave excitation, making it difficult to apply to near-field problems. Therefore, a modified approach is proposed, involving the application of the FDTD technique with a quasi-static approximation to an electric and magnetic dipole problem. The results when using the proposed method are in good agreement with those from a theoretical solution. An example of comparison with the standard FDTD method is shown for illustrating the proposed method’s performance.

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