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Modeling optical properties of particles with small-scale surface roughness: combination of group theory with a perturbation approach

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OPTICS EXPRESS 2011年第12期19卷 11138-11151页

作者： Kahnert, Michael Rother, Tom Swedish Meteorol & Hydrol Inst Res Dept S-60176 Norrkoping Sweden German Aerosp Ctr DLR D-17235 Neustrelitz Germany

A T-matrix method for scattering by particles with small-scale surface roughness is presented. The method combines group theory with a perturbation expansion approach. Group theory is found to reduce CPU-time by 4-6 orders of magnitude. The perturbation expansion extends the range of size parameters by a factor of 5 compared to non-perturbative methods. An application to optically hard particles shows that small-scale surface roughness changes scattering in side-and backscattering directions, and it impacts the single-scattering albedo. This can have important implications for interpreting remote sensing observations, and for the climate impact of mineral aerosols. (C) 2011 Optical Society of America

关键词： computation methods Electromagnetic scattering Light wavelength Particle scattering Refractive index Remote sensing

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Iterative approach to self-adapting and altitude-dependent regularization for atmospheric profile retrievals

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OPTICS EXPRESS 2011年第27期19卷 26696-26709页

作者： Ridolfi, Marco Sgheri, Luca CNR Ist Appl Calcolo Florence Italy Univ Bologna Dipartimento Fis I-40126 Bologna Italy

In this paper we present the IVS (Iterative Variable Strength) method, an altitude-dependent, self-adapting Tikhonov regularization scheme for atmospheric profile retrievals. The method is based on a similar scheme we proposed in 2009. The new method does not need any specifically tuned minimization routine, hence it is more robust and faster. We test the self-consistency of the method using simulated observations of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). We then compare the new method with both our previous scheme and the scalar method currently implemented in the MIPAS on-line processor, using both synthetic and real atmospheric limb measurements. The IVS method shows very good performances. (C) 2011 Optical Society of America

关键词： Algorithms Atmospheric measurement computation methods Michelson interferometers Ozone Troposphere

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Discrete dipole approximation for time-domain computation of optical forces on magnetodielectric scatterers

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OPTICS EXPRESS 2011年第3期19卷 2466-2475页

作者： Chaumet, Patrick C. Belkebir, Kamal Rahmani, Adel Univ Paul Cezanne Inst Fresnel UMR 6133 F-13397 Marseille 20 France Univ Technol Sydney Dept Math Sci Broadway NSW 2007 Australia

We present a general approach, based on the discrete dipole approximation (DDA), for the computation of the exchange of momentum between light and a magnetodielectric, three-dimensional object with arbitrary geometry and linear permittivity and permeability tensors in time domain. The method can handle objects with an arbitrary shape, including objects with dispersive dielectric and/or magnetic material responses. (C) 2011 Optical Society of America

关键词： computation methods Light scattering Optical force Spontaneous emission Surface plasmon resonance Transient phenomena

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Angular spectrum calculations for arbitrary focal length with a scaled convolution

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OPTICS EXPRESS 2011年第15期19卷 14268-14276页

作者： Odate, Satoru Koike, Chiaki Toba, Hidemitsu Koike, Tetsuya Sugaya, Ayako Sugisaki, Katsumi Otaki, Katsura Uchikawa, Kiyoshi Nikon Inc Core Technol Ctr Shinagawa Ku Tokyo 1408601 Japan

Nyquist sampling theorem in an image calculation with angular spectrum method restricts a propagation distance and a focal length of a lens. In order to avoid these restrictions, we studied suitable expressions for the image computations depending on their conditions. Additionally, a lateral scale in an observation plane can be magnified freely by using a scaled convolution in each expression. (C)2011 Optical Society of America

关键词： computation methods Discrete Fourier transforms Fast Fourier transforms Fourier transforms Propagation methods

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Characterization of complex plasmonic modes in two-dimensional periodic arrays of metal nanospheres

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2011年第6期28卷 1446-1458页

作者： Fructos, Ana L. Campione, Salvatore Capolino, Filippo Mesa, Francisco Univ Calif Irvine Dept Elect Engn & Comp Sci Irvine CA 92697 USA Univ Seville Coll Phys Dept Elect & Electromagnetism E-41012 Seville Spain Univ Seville ETS Ingn Informat Dept Appl Phys 1 E-41012 Seville Spain

Two-dimensional periodic arrays of noble metal nanospheres support a variety of optical phenomena, including bound and leaky modes of several types. The scope of this paper is the characterization of the modal dispersion diagrams of planar arrays of silver nanospheres, with the ability to follow individual modal evolutions. The metal spherical nanoparticles are described using the single dipole approximation technique by including all the retarded dynamic field terms. Polarizability of the nanospheres is provided by the Mie theory. Dispersion diagrams for both physical and nonphysical modes are shown for a square lattice of Ag nanospheres for the case of lossless and lossy metal particles, with dipole moments polarized along the x, y, and z directions. Though an array with one set of parameters has been studied, the analysis method and classification are general. The evolution of modes through different Riemann sheets and analysis of guidance and radiation are studied in detail. (C) 2011 Optical Society of America

关键词： Analytical techniques computation methods Mie theory Modal dispersion Optical properties Raman spectroscopy

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Bonding, antibonding and tunable optical forces in asymmetric membranes

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OPTICS EXPRESS 2011年第3期19卷 2225-2241页

作者： Rodriguez, Alejandro W. McCauley, Alexander P. Hui, Pui-Chuen Woolf, David Iwase, Eiji Capasso, Federico Loncar, Marko Johnson, Steven G. MIT Dept Math Cambridge MA 02139 USA Harvard Univ Sch Engn & Appl Sci Cambridge MA 02138 USA MIT Dept Phys Cambridge MA 02139 USA

We demonstrate that tunable attractive (bonding) and repulsive (anti-bonding) forces can arise in highly asymmetric structures coupled to external radiation, a consequence of the bonding/anti-bonding level repulsion of guided-wave resonances that was first predicted in symmetric systems. Our focus is a geometry consisting of a photonic-crystal (holey) membrane suspended above an unpatterned layered substrate, supporting planar waveguide modes that can couple via the periodic modulation of the holey membrane. Asymmetric geometries have a clear advantage in ease of fabrication and experimental characterization compared to symmetric double-membrane structures. We show that the asymmetry can also lead to unusual behavior in the force magnitudes of a bonding/antibonding pair as the membrane separation changes, including nonmonotonic dependences on the separation. We propose a computational method that obtains the entire force spectrum via a single time-domain simulation, by Fourier-transforming the response to a short pulse and thereby obtaining the frequency-dependent stress tensor. We point out that by operating with two, instead of a single frequency, these evanescent forces can be exploited to tune the spring constant of the membrane without changing its equilibrium separation. (C) 2011 Optical Society of America

关键词： computation methods Guided mode resonance Optical force Planar waveguides Resonant modes Waveguide modes

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Variational estimation of inhomogeneous specular reflectance and illumination from a single view

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 2011年第2期28卷 136-146页

作者： Hara, Kenji Nishino, Ko Kyushu Univ Fac Design Dept Visual Commun Design Minami Ku Fukuoka 8158540 Japan Drexel Univ Coll Engn Dept Comp Sci Philadelphia PA 19104 USA

Estimating the illumination and the reflectance properties of an object surface from a few images is an important but challenging problem. The problem becomes even more challenging if we wish to deal with real-world objects that naturally have spatially inhomogeneous reflectance. In this paper, we derive a novel method for estimating the spatially varying specular reflectance properties of a surface of known geometry as well as the illumination distribution of a scene from a specular-only image, for instance, recovered from two images captured with a polarizer to separate reflection components. Unlike previous work, we do not assume the illumination to be a single point light source. We model specular reflection with a spherical statistical distribution and encode its spatial variation with a radial basis function (RBF) network of their parameter values, which allows us to formulate the simultaneous estimation of spatially varying specular reflectance and illumination as a constrained optimization based on the I-divergence measure. To solve it, we derive a variational algorithm based on the expectation maximization principle. At the same time, we estimate optimal encoding of the specular reflectance properties by learning the number, centers, and widths of the RBF hidden units. We demonstrate the effectiveness of the method on images of synthetic and real-world objects. (C) 2011 Optical Society of America

关键词： computation methods Inverse problems Laser ranging Light sources Polarizers Spatial resolution

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Full-automatic self-calibration of color digital cameras using color targets

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OPTICS EXPRESS 2011年第19期19卷 18164-18174页

作者： Yilmazturk, F. Aksaray Univ Aksaray Turkey

In photogrammetric applications, camera calibration and orientation procedures are a prerequisite for the extraction of precise and reliable 3D metric information from images. This study presents a method for full automatic calibration of color digital cameras using color targets. Software developed using Borland C + + Builder programming language is used to apply the method. With this software, the calibration process is carried out in 3 stages: firstly, at least four of six color targets (whose 3D object coordinates are known) on each image of the overall test field are detected and the approximate exterior orientation parameters are computed. Then, the remaining target points are measured using the approximate image locations, determined using these parameters and the 3D object point coordinates parameters. Finally, calibration parameters are determined using a self-calibration bundle adjustment technique. The colored targets within the test field are assigned labels corresponding to their color. For the detection of color targets and computation of approximate exterior orientation elements, HSV color space was used together with space resection computation method for all the possible color labels of targets. To test the proposed method, full automatic calibration was carried out using six different digital cameras. The calibration accuracies achieved in object space were within the range 0.006 to 0.030 mm;the accuracies achieved in image space were within the range 0.14 to 0.51 mu m. (C) 2011 Optical Society of America

关键词： Camera calibration CCD cameras Color detection Color spaces computation methods Image processing

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Approximate Fourier phase information in the phase retrieval problem: what it gives and how to use it

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 2011年第10期28卷 2124-2131页

作者： Osherovich, Eliyahu Zibulevsky, Michael Yavneh, Irad Technion Israel Inst Technol Dept Comp Sci IL-32000 Haifa Israel

This work evaluates the importance of approximate Fourier phase information in the phase retrieval problem. The main discovery is that a rough phase estimate (up to pi/2 rad) allows development of very efficient algorithms whose reconstruction time is an order of magnitude faster than that of the current method of choice-the hybrid input-output (HIO) algorithm. Moreover, a heuristic explanation is provided of why continuous optimization methods like gradient descent or Newton-type algorithms fail when applied to the phase retrieval problem and how the approximate phase information can remedy this situation. Numerical simulations are presented to demonstrate the validity of our analysis and success of our reconstruction method even in cases where the HIO algorithm fails, namely, complex-valued signals without tight support information. (C) 2011 Optical Society of America

关键词： computation methods Fourier transforms Numerical simulation Phase estimation Phase retrieval Reconstruction algorithms

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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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