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Material point method for simulating nonequilibrium thermal transport in metals irradiated by ultrafast lasers

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2017年第11期34卷 2334-2342页

作者： Gan, Yong Lei, Chunxia Sun, Zheng Zhejiang Univ Fac Engn Hangzhou 310027 Zhejiang Peoples R China Beijing Inst Technol State Key Lab Explos Sci & Technol Beijing 100081 Peoples R China

A material point method (MPM) for the analysis of two-step heating of metals subjected to ultrafast laser irradiation is developed based on the weak formulation of the two-temperature model (TTM). The electron and lattice subsystems in the metallic targets are both represented by a finite number of Lagrangian material points to discretize the TTM equations, while a background Eulerian grid mesh is used to solve the spatially discrete TTM equations for the electron and lattice temperatures carried by the material points. The verification, convergence, and robustness of the proposed MPM method are demonstrated using representative examples for femto/picosecond laser heating of a gold thin film. In addition to avoiding the numerical difficulties due to the mesh distortion and entanglement in the mesh-based method, the presented MPM algorithm automatically handles the adiabatic boundary condition without requiring additional boundary treatments and could achieve higher computational efficiency than the mesh-based approaches at a comparable level of accuracy, showing its advantage over the mesh-based methods for modeling energy transfer in metals irradiated by ultrafast lasers. (C) 2017 Optical Society of America

关键词： computation methods Energy transfer Frequency division multiplexing Laser energy Laser irradiation Ultrafast lasers

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Robust, efficient computational methods for axially symmetric optical aspheres

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OPTICS EXPRESS 2010年第19期18卷 19700-19712页

作者： Forbes, G. W. QED Technol Inc Rochester NY 14627 USA

Whether in design or the various stages of fabrication and testing, an effective representation of an asphere's shape is critical. Some algorithms are given for implementing tailored polynomials that are ideally suited to these needs. With minimal coding, these results allow a recently introduced orthogonal polynomial basis to be employed to arbitrary orders. Interestingly, these robust and efficient methods are enabled by the introduction of an auxiliary polynomial basis. (C) 2010 Optical Society of America

关键词： Algorithms Beam foil spectroscopy computation methods Optical surfaces Optical testing Zernike polynomials

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Second harmonic scattering from small particles using Discrete Dipole Approximation

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OPTICS EXPRESS 2010年第21期18卷 21603-21611页

作者： Balla, Naveen K. So, Peter T. C. Sheppard, Colin J. R. Natl Univ Singapore Computat & Syst Biol Program Singapore MIT Alliance Singapore 117576 Singapore Natl Univ Singapore Div Bioengn Singapore 117574 Singapore MIT Dept Biol Engn Cambridge MA 02139 USA MIT Dept Mech Engn Cambridge MA 02139 USA Natl Univ Singapore Dept Biol Sci Singapore 117543 Singapore

We extend a simple dipole approximation model to predict nonlinear scattering from small particles. This numerical method is known as Discrete Dipole Approximation (DDA) and has been extensively used to model linear scattering by small particles of various shapes and sizes. We show here that DDA can be used to efficiently model second harmonic scattering by small particles. Our results are compared with experimental data and other computational methods. (C) 2010 Optical Society of America

关键词： computation methods Hyper Rayleigh scattering Light matter interactions Light scattering Optical force Particle scattering

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Monte Carlo approach for solving the radiative transfer equation over mountainous and heterogeneous areas

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APPLIED OPTICS 1999年第36期38卷 7419-7430页

作者： Miesch, C Briottet, X Kerr, YH Cabot, F Off Natl Etud & Rech Aerosp Dept Opt Theor & Appl F-31400 Toulouse France Ctr Etud Spatiales Biosphere F-31400 Toulouse France Ctr Natl Etud Spatiales F-31400 Toulouse France

An algorithm based on the Monte Carlo method is developed to solve the radiative transfer equation in the reflective domain (0.4-4 mu m) of the solar spectrum over rugged terrain. This algorithm takes into account relief, spatial heterogeneity, and ground bidirectional reflectance. The method permits the computation of irradiance components at ground level and radiance terms reaching an airborne or satelliteborne sensor. The Monte Carlo method consists of statistically simulating the paths of photons inside the Earth-atmosphere system to reproduce physical phenomena while introducing neither analytical modeling nor assumption. The potentialities of the code are then depicted over different types of landscape, including a seashore, a desert region, and a steep mountainous valley. (C) 1999 Optical Society of America OCIS codes: 010.1300, 280.0280, 000.5490.

关键词： Atmospheric scattering computation methods Forward scattering Irradiance Particle scattering Radiative transfer

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Comparison of Monte Carlo ray-tracing and photon-tracing methods for calculation of the impulse response on indoor wireless optical channels

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OPTICS EXPRESS 2011年第3期19卷 1997-2005页

作者： Gonzalez, Oswaldo Rodriguez, Silvestre Perez-Jimenez, Rafael Mendoza, Beatriz R. Ayala, Alejandro Univ La Laguna Dept Fund & Expt Phys Elect & Syst San Cristobal la Laguna 38203 Tenerife Spain Univ Las Palmas Gran Canaria Dept Signals & Commun Gran Canaria 35017 Las Palmas Spain

We present a comparison between the modified Monte Carlo algorithm (MMCA) and a recently proposed ray-tracing algorithm named as photon-tracing algorithm. Both methods are compared exhaustively according to error analysis and computational costs. We show that the new photon-tracing method offers a solution with a slightly greater error but requiring from considerable less computing time. Moreover, from a practical point of view, the solutions obtained with both algorithms are approximately equivalent, demonstrating the goodness of the new photon-tracing method. (C) 2011 Optical Society of America

关键词： Algorithms computation methods Optical wireless communication Reflection Reflection coefficient Signal collection

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Fractional finite Fourier transform

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 2004年第7期21卷 1179-1185页

作者： Khare, K George, N Univ Rochester Inst Opt Rochester NY 14627 USA

We show that a fractional version of the finite Fourier transform may be defined by using prolate spheroidal wave functions of order zero. The transform is linear and additive in its index and asymptotically goes over to Namias's definition of the fractional Fourier transform. As a special case of this definition, it is shown that the finite Fourier transform may be inverted by using information over a finite range of frequencies in Fourier space, the inversion being sensitive to noise. Numerical illustrations for both forward (fractional) and inverse finite transforms are provided. (C) 2004 Optical Society of America.

关键词： computation methods Fourier transforms Fractional Fourier transforms Fresnel diffraction Inverse problems Transforms

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Photoelastic coupling in gallium arsenide optomechanical disk resonators

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OPTICS EXPRESS 2014年第12期22卷 14072-14086页

作者： Baker, Christopher Hease, William Dac-Trung Nguyen Andronico, Alessio Ducci, Sara Leo, Giuseppe Favero, Ivan Univ Paris Diderot Sorbonne Paris Cite Lab Mat & Phenomenes Quant CNRS UMR 7162 F-75013 Paris France

We analyze the magnitude of the radiation pressure and electrostrictive stresses exerted by light confined inside GaAs semiconductor WGM optomechanical disk resonators, through analytical and numerical means, and find the electrostrictive stress to be of prime importance. We investigate the geometric and photoelastic optomechanical coupling resulting respectively from the deformation of the disk boundary and from the strain-induced refractive index changes in the material, for various mechanical modes of the disks. Photoelastic optomechanical coupling is shown to be a predominant coupling mechanism for certain disk dimensions and mechanical modes, leading to total coupling g(om) and g(0) reaching respectively 3 THz/nm and 4 MHz. Finally, we point towards ways to maximize the photoelastic coupling in GaAs disk resonators, and we provide some upper bounds for its value in various geometries. (C) 2014 Optical Society of America

关键词： computation methods Distributed Bragg reflectors Effective refractive index Radiation pressure Refractive index Total internal reflection

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Self-learning based Fourier ptychographic microscopy

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OPTICS EXPRESS 2015年第14期23卷 18471-18486页

作者： Zhang, Yongbing Jiang, Weixin Tian, Lei Waller, Laura Dai, Qionghai Tsinghua Univ Grad Sch Shenzhen Shenzhen Key Lab Broadband Network & Multimedia Shenzhen 518055 Peoples R China Univ Calif Berkeley Dept Elect Engn & Comp Sci Berkeley CA 94709 USA Tsinghua Univ Dept Automat Beijing 100084 Peoples R China

Fourier Ptychographic Microscopy (FPM) is a newly proposed computational imaging method aimed at reconstructing a high-resolution wide-field image from a sequence of low-resolution images. These low-resolution images are captured under varied illumination angles and the FPM recovery routine then stitches them together in the Fourier domain iteratively. Although FPM has achieved success with static sample reconstructions, the long acquisition time inhibits real-time application. To address this problem, we propose here a self-learning based FPM which accelerates the acquisition and reconstruction procedure. We first capture a single image under normally incident illumination, and then use it to simulate the corresponding low-resolution images under other illumination angles. The simulation is based on the relationship between the illumination angles and the shift of the sample's spectrum. We analyze the importance of the simulated low-resolution images in order to devise a selection scheme which only collects the ones with higher importance. The measurements are then captured with the selection scheme and employed to perform the FPM reconstruction. Since only measurements of high importance are captured, the time requirements of data collection as well as image reconstruction can be greatly reduced. We validate the effectiveness of the proposed method with simulation and experimental results showing that the reduction ratio of data size requirements can reach over 70%, without sacrificing image reconstruction quality. (C) 2015 Optical Society of America

关键词： computation methods Fast Fourier transforms Image quality Image reconstruction LED sources Phase imaging

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Moire flat bands in strongly coupled atomic arrays

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OPTICAL MATERIALS EXPRESS 2023年第7期13卷 2003-2019页

作者： Dams, D. Beutel, D. Garcia-Santiago, X. Rockstuhl, C. Alaee, R. Karlsruhe Inst Technol Inst Theoret Solid State Phys Wolfgang Gaede Str 1 D-76131 Karlsruhe Germany Karlsruhe Inst Technol Inst Nanotechnol Wolfgang Gaede Str 1 D-76131 Karlsruhe Germany

Moire effects arise from stacking periodic structures with a specific geometrical mismatch and promise unique possibilities. However, their full potential for photonic applications has yet to be explored. Here, we investigate the photonic band structure for an atomic stack of strongly coupled linear arrays in the dipolar regime. A moire parameter 0 is used to parameterize a relative lattice constant mismatch between the two arrays that plays the role of a 1D twist angle. The system's interaction matrix is analytically diagonalized and reveals the presence of localized excitations which strongly enhance the density of optical states in spectral regions that can be controlled via the moire parameter. We also confirm our findings by numerical simulations of finite systems. Our work provides a better understanding of photonic moire effects and their potential use in photonic devices such as optical sensors and light traps.

关键词： computation methods Field enhancement Light matter interactions Numerical simulation Optical sensing Photonic bandgap structure

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ITERATIVE SCHEME FOR COMPUTING EXACTLY THE TOTAL FIELD PROPAGATING IN DIELECTRIC STRUCTURES OF ARBITRARY SHAPE

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 1994年第3期11卷 1073-1080页

作者： MARTIN, OJF DEREUX, A GIRARD, C FAC UNIV NOTRE DAME PAIX INST STUDIES INTERFACE SCIB-5000 NAMURBELGIUM UNIV FRANCHE COMTE CNRSUNITE 772PHYS MOLEC LABF-25030 BESANCONFRANCE

We present a new approach to the computation of an electrical field propagating in a dielectric structure. We use the Green's-function technique to compute an exact solution of the wave equation. No paraxial approximation is made, and our method can handle any kind of dielectric medium (air, semiconductor, metal, etc.). An original iterative numerical scheme based on the parallel use of Lippman-Schwinger and Dyson's equations is demonstrated. The influence of the numerical parameters on the accuracy of the results is studied in detail, and the high precision and stability of the method are assessed. Examples for one and two dimensions establish the versatility of the method and its ability to handle structures of arbitrary shape. The application of the method to the computation of eigenmode spectra for dielectric structures is illustrated.

关键词： computation methods Finite difference time domain First order optics Integrated optical devices Integrated optics Semiconductors

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