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Intensity distribution analysis of cathodoluminescence using the energy loss distribution of electrons

ULTRAMICROSCOPY 2016年 160卷 225-229页

作者： Fukuta, Masahiro Inami, Wataru Ono, Atsushi Kawata, Yoshimasa Shizuoka Univ Grad Sch Sci & Technol Hamamatsu Shizuoka 4328011 Japan Shizuoka Univ Elect Res Inst Naka Ku Hamamatsu Shizuoka 4328011 Japan Japan Sci & Technol Agcy CREST Kawaguchi Saitama 3320012 Japan

We present an intensity distribution analysis of cathodoluminescence (CL) excited with a focused electron beam in a luminescent thin film. The energy loss distribution is applied to the developed analysis method in order to determine the arrangement of the dipole locations along the path of the electron traveling in the film. Propagating light emitted from each dipole is analyzed with the finite-difference time-domain (FDTD) method. CL distribution near the film surface is evaluated as a nanometric light source. It is found that a light source with 30 nm widths is generated in the film by the focused electron beam. We also discuss the accuracy of the developed analysis method by comparison with experimental results. The analysis results are brought into good agreement with the experimental results by introducing the energy loss distribution. (C) 2015 Elsevier BY. All rights reserved.

关键词： Cathodoluminescence Monte Carlo simulation finite-difference time-domain method Nanometric light spot

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Use of a hybrid pseudospectral time-domain-finite-difference time-domain method for optical simulation of liquid crystals

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LIQUID CRYSTALS 2010年第3期37卷 241-246页

作者： Fang, Yun Li, Xi Zhang, Jian Wu, Liying Harbin Inst Technol Inst Ultra Precis Optoelect Instrument Engn Harbin 150001 Peoples R China Univ Sci & Technol China Dept Precis Machinery & Instrumentat Hefei 230026 Peoples R China

In order to reduce the computational cost of the finite-difference time-domain method, the pseudospectral time-domain method is applied to the glass substrate direction with a large surface and smooth internal media, while the finite-difference time-domain method is applied to the thickness direction of a cell with a small thickness and fine structures. A fast Fourier transform algorithm, instead of the central-difference in the finite-difference time-domain method, is used to represent the spatial derivatives in the pseudospectral time-domain method, which greatly reduces the spatial sampling rate in the glass substrate direction. Both the hybrid method and the finite-difference time-domain method are used to simulate the propagation of light through the same twisted nematic pixel in the on state for 100 fs. The maximum deviation of the transmittance obtained using both methods is less than 5.1%;the memory capacity and computational time required for the hybrid method are about 8.5% and 21% respectively compared with those required for the finite-difference time-domain method. The use of the hybrid method reduces the memory capacity and computational time required for the finite-difference time-domain method while its accuracy is preserved.

关键词： liquid crystal optical simulation finite-difference time-domain method pseudospectral time-domain method

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Effect of Shield Wires on the Lightning-Induced Currents on Buried Cables

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IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY 2016年第3期58卷 738-746页

作者： Tanaka, Hiroki Baba, Yoshihiro Barbosa, Celio Fonseca Doshisha Univ Dept Elect Engn Kyoto 6100321 Japan CPqD R&D Ctr Telecommun BR-13086902 Campinas SP Brazil

The effect of a shield wire, which is a bare conductor buried above an insulated metallic cable, on lightning-induced currents on the cable has been studied using the three-dimensional (3-D) finite-difference time-domain (FDTD) method. In the 3-D FDTD model, a 1-km-long insulated cable is buried at depth 0.6 m in 1850-Omega.m ground, and a 1-km-long shield wire is installed 0.3 m above the cable (at the depth 0.3 m from the ground surface). A 1-km-long vertical lightning return-stroke channel, attached to a 30-m-high tower or flat ground, is located 25 m away from the cable and the shield wire. The validity of this model has been shown by comparing the FDTD-computed lightning-associated currents on the cable and the shield wire with the corresponding measured currents associated with rocket-triggered lightning. The FDTD-computed results show that the presence of the shield wire reduces the induced current on the cable and the voltage across the outer insulation layer of the cable, as expected, but the series resistance of the shield wire has a negligible effect on this reduction. The presence of 30-m-high strike object slightly reduces the cable current. The ground permittivity and the return-stroke speed have negligible effects on the cable current, but the higher the ground resistivity, the higher is the cable current. The increase of bonding points between the cable sheath and the shield wire increases the cable current, but decreases the voltage across the outer insulation layer of the cable.

关键词： Buried cable finite-difference time-domain method lightning shield wire

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Effect of shape of scatterers and plasma frequency on the complete photonic band gap properties of two-dimensional dielectric-plasma photonic crystals

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PHYSICS LETTERS A 2016年第48期380卷 4092-4099页

作者： Khalkhali, T. Fathollahi Bananej, A. NSTRI Laser & Opt Res Sch Tehran Iran

In this study, we analyze complete photonic band gap properties of two-dimensional dielectric-plasma photonic crystals with triangular and square lattices, composed of plasma rods with different geometrical shapes in the anisotropic tellurium background. Using the finite-difference time-domain method we discuss the maximization of the complete photonic band gap width as a function of plasma frequency and plasma rods parameters with different shapes and orientations. The numerical results demonstrate that our proposed structures represent significantly wide complete photonic band gaps in comparison to previously studied dielectric-plasma photonic crystals. (C) 2016 Elsevier B.V. All rights reserved.

关键词： Photonic band gap material Plasma photonic crystals Anisotropic tellurium material finite-difference time-domain method

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Beyond the effective mass approximation: A predictive theory of the nonlinear optical response of conduction electrons

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Physical Review B 2017年第12期95卷 125201-125201页

作者： Shukai Yu Kate H. Heffernan Diyar Talbayev Department of Physics and Engineering Physics Tulane University 6400 Freret Street New Orleans 70118 LA United States

We present an experimental and computational study of the nonlinear optical response of conduction electrons to intense terahertz (THz) electric field. Our observations (saturable absorption and an amplitude-dependent group refractive index) can be understood on the qualitative level as the breakdown of the effective mass approximation. However, a predictive theoretical description of the nonlinear THz propagation has been missing. We propose a model based on the semiclassical electron dynamics, a realistic band structure, and the free electron Drude parameters to accurately calculate the experimental observables in InSb. Our results open a path to modeling of the conduction-electron optical nonlinearity that governs the THz propagation in semiconductors.

关键词： Nonlinear optics Optical conductivity Semiconductors Drude model Effective medium approach finite-difference time-domain method

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Modeling and analysis of the temperature sensitivity in two-dimensional photonic crystal microcavity

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JOURNAL OF NANOPHOTONICS 2016年第1期10卷

作者： Hocini, Abdesselam Harhouz, Ahlam Mohamed Boudiaf Univ Msila Lab Anal Signaux & Syst Dept Elect BP 166Route Ichebilia Msila 28000 Algeria

We propose a temperature sensor design based on the two-dimensional (2-D) photonic crystals (PhCs) microcavity coupled to two waveguides. We consider a Si 2-D PhC, and the refractive index (RI) of distilled water in holes has been taken as temperature dependent. The resonant wavelength will shift when temperature variation induces change in the RIs of the distilled water. The temperature variation causes the shifting of defect modes. The transmission characteristics of light in the sensor under different RIs that correspond to the change in temperatures are simulated by using the finite-difference time-domain method. A sensitivity of 84 pm/degrees C was achieved with the structure proposed. This property can be exploited in the design of a temperature sensor. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

关键词： two-dimensional photonic crystal temperature sensor microcavity waveguide finite-difference time-domain method refractive index

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Factorisation-splitting WLP-FDTD method of wave propagation in dispersive materials

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IET MICROWAVES ANTENNAS & PROPAGATION 2016年第15期10卷 1740-1746页

作者： Liu, Jiang-Fan Wu, Ji-Min Fang, Yun Xi, Xiao-Li Xian Univ Technol Dept Elect Engn Xian 710048 Peoples R China Wuhan Univ Dept Opt Informat Engn Wuhan 430072 Peoples R China

The authors present an efficient finite-difference time-domain (FDTD) method with weighted Laguerre polynomials (WLP) to simulate electromagnetic wave propagation in the general dispersive materials in 3D case. As compared with the original auxiliary differential equation WLP-FDTD method, the proposed method employed a factorisation-splitting scheme to translate the large sparse matrix equation into two and six tri-diagonal ones for 2D and 3D cases, respectively, which significantly improves the efficiency of the WLP-FDTD algorithm. The perfectly matched layer with complex frequency shifted factor is also implemented based on the stretched coordinate. The accuracy and efficiency of the proposed algorithm are validated by numerical examples.

关键词： finite difference time-domain analysis electromagnetic wave propagation sparse matrices factorisation-splitting WLP-FDTD method dispersive materials finite-difference time-domain method weighted Laguerre polynomials electromagnetic wave propagation large sparse matrix equation

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Exploring the superfocusing performance of plasmonic lenses formed by coupled nanoslits

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MICRO & NANO LETTERS 2016年第10期11卷 615-618页

作者： Zhu, Yechuan Yuan, Weizheng Yu, Yiting Wang, Ping Sun, Hao Northwestern Polytech Univ Minist Educ Key Lab Micro Nano Syst Aerosp Xian 710072 Peoples R China Northwestern Polytech Univ Key Lab Micro & Nanoelectromech Syst Shaanxi Prov Xian 710072 Peoples R China

A comprehensive investigation on the superfocusing performance of a plasmonic lens formed by coupled metallic nanoslits is carried out. Based on the geometrical optics and the wavefront reconstruction principle, the nanoslit array for a plasmonic lens is optimally designed to achieve the desired phase modulation by considering the influence of the coupling between adjacent aperiodic nanoslits on phase delay and the theory of periodic metallic nanoslits. The designed lens' focusing behaviour is verified by using the finite-difference time-domain method. Numerical results demonstrate that the superfocusing performance of a plasmonic lens has a close relationship with the lens size, focal length, working medium and incident wavelength. A larger lens size, a shorter focal length, a higher-index working medium can contribute to producing a higher-resolution superfocusing. Moreover, due to the material response, a shorter wavelength is not beneficial for an efficient focusing.

关键词： plasmonics lenses nanostructured materials nanophotonics optical focusing geometrical optics holography phase modulation optical modulation finite difference time-domain analysis superfocusing performance plasmonic lenses coupled metallic nanoslits geometrical optics wavefront reconstruction principle phase modulation adjacent aperiodic nanoslits phase delay periodic metallic nanoslit theory finite-difference time-domain method lens size focal length working medium incident wavelength

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A novel FDTD/WP-PML/NUFFT algorithm applied to the design of a printed metamaterial enhanced antenna

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AEU-INTERNATIONAL JOURNAL OF ELECTRONICS AND COMMUNICATIONS 2016年第9期70卷 1187-1191页

作者： Ramos, Glaucio L. Capovilla, Carlos E. Araujo, Humberto X. Rego, Cassio G. Casella, Ivan R. S. Pereira, Paulo T. Univ Fed Sao Joao del Rei GAPEA Antennas & Propagat Res Grp Sao Joao Del Rei MG Brazil Fed Univ ABC Santo Andre Brazil Fed Univ Tocantins Elect Engn Arraias TO Brazil Univ Fed Minas Gerais Dept Elect Engn Belo Horizonte MG Brazil

This paper presents the results for a FDTD/WP-PML/NUFFT algorithm developed to design and analyze printed antennas. To show the applicability of the developed code, a new metamaterial printed antenna array is designed for the S-Band operation. Results obtained are compared to those determined from conventional FFT based methods available in the scientific literature and to results obtained by measurements given evidence of the methodology applicability in an operational prototype. (C) 2016 Elsevier GmbH. All rights reserved.

关键词： finite-difference time-domain method Near-to-far-field transformation Non-uniform fast Fourier transform

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Physical Review B 2017年第5期96卷 054113-054113页

作者： Ruben Khachaturyan Jens Wehner Yuri A. Genenko Institut of Materials Science Technische Universität Darmstadt Jovanka-Bontschits-Str. 2 D-64287 Darmstadt Germany Max Planck Institute for Polymer Research Ackermannweg 10 55128 Mainz Germany

Analysis of statistical distributions and auto- and cross correlations of polarization and electric field during the field-driven polarization reversal in a bulk polycrystalline ferroelectric is performed. A mesoscopic switching model is used which accounts self-consistently for the development of depolarization fields. Correlations mediated by electrostatic fields are shown to be mostly isotropic and short range at the typical scale of the grain size which is explained by an effective screening via adapting bound charges. The short-range screening clarifies the paradoxical ability of common statistical concepts neglecting the feedback effect of depolarization fields to adequately describe the polarization switching kinetics. The statistical distribution of the local electric field magnitudes is continuously spreading in the course of the global polarization reversal due to mismatching of both dielectric tensor and spontaneous polarization at grain boundaries. The increasing field dispersion substantially contributes to the well-known deceleration of the polarization reversal at long times.

关键词： Electric polarization Ferroelectricity Ferroelectrics Polycrystalline materials finite-difference time-domain method

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