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 lat...
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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
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 s...
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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
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 s...
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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
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 rel...
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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.
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 anal...
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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
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...
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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.
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...
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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
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 ...
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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
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 inv...
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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.
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 appro...
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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.
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