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ABSTRACT: In this paper the discrete sources method is applied to analyze the extreme scattering effect for particles located both inside and on a gold film deposited on a glass prism. The extreme scattering effect is an effect of the sharp increase of the scattered intensity for P-polarized excitation which occurs in the evanescent wave region behind the critical angle. Moreover, the intensity enhancement appears not only in the transmission direction but in the backscattering direction as well. The effect does not depend on the thickness of the metal film or particle diameter, but it is strongly affected by the film material. Different scattering characteristics, such as transmission cross section and reflection cross sections and their correlation with the surface plasmon resonance in the film, are investigated and discussed in this paper. The analysis of the influence of a thin transparent spacer layer between particle and gold film on the scattering characteristics has been performed. The differential scattering cross section is considered to examine the field distribution in the forward and backscattering directions.
Journal of optics 12/2011; 14(1):015001. · 1.57 Impact Factor
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ABSTRACT: We embark on this preliminary study of the suitability of the discrete dipole
approximation with surface interaction (DDA-SI) method to model electric field scattering
from noble metal nano-structures on dielectric substrates. The refractive index of noble
metals, particularly due to their high imaginary components, require smaller lattice spacings
and are especially sensitive to the shape integrity and the volume of the dipole model.
The results of DDA-SI method are validated against those of the well-established finite element
method (FEM) and the finite difference time domain (FDTD) method.
AAPP Physical, Mathematical, and Natural Sciences. 01/2011; 89:C1V89S1P060-1.
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ABSTRACT: The discrete sources method has been applied to perform a computer simulation analysis of different total internal reflection microscopy schemes. It has been found that the positioning of the objective lens beneath a glass prism can provide a considerable advantage for determination of the particle–film distance.
J. Opt. 01/2010; 12:95703-7.
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ABSTRACT: The effect of extreme light transmission through a nanohole in metal film deposited on a glass prism has been investigated. The Discrete Sources Method has been applied for computer simulation analysis of this effect in the evanescent wave area. It has been found that the effect appears together with Plasmon resonance of the film. The dependence of the transmitted intensity on the wavelength, incident angle, film materials and hole's filling has been analyzed.
Journal of Computational and Theoretical Nanoscience 02/2009; 6(3):795-803. · 0.91 Impact Factor
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ABSTRACT: In this paper the scattering spectrum of evanescent light scattering from a nanoshell particle deposited on a plane surface is investigated. We analyze the spectrum dependence of a nanoshell on the core materials and on the polarization of an external excitation. For this analysis the Discrete Sources Method (DSM) is chosen. Based on its rigorous theoretical model, DSM allows to account for all features of the scattering problem such as the medium with frequency dispersion, the presence of the interface, the objective aperture and its location and the core-shell asphericity. Computer simulated results are presented in the final part of the paper.
Journal of Computational and Theoretical Nanoscience 10/2008; 5(11):2186-2193. · 0.91 Impact Factor
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ABSTRACT: This paper describes the generation of small water droplets in the size range down to a few microns. Commercially available inkjet printing devices are not suitable for producing such droplets since they produce satellite droplets. Furthermore, standard drop-on-demand devices are normally restricted to the generation of droplets with the same size as the orifice diameter. Using a new and more sophisticated computer-based signal generation system, smaller-sized droplets can be generated from the same orifice. A key feature of the design is the generation of freely definable pulses. This enables the generation of acoustic modes within the fluid of the droplet generator, which leads to the generation of droplets without satellites. Only very few pulse forms enable the generation of suitable acoustic modes. Therefore, it is necessary to look for the specific pulse corresponding to the chosen droplet generator. Flexible pulse form generation appears to be more suitable than simple pulse forms for the generation of such droplets.
Particle and Particle Systems Characterization 04/2008; 25(2):176 - 182. · 0.49 Impact Factor
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ABSTRACT: In this paper we consider electromagnetic wave scattering by aggregated fibres using a multiple scattering approach. Scattering by particles of complex shape such as concave particles, torus, or clusters of fibres can not normally be computed using the T-matrix method. In this paper we are proposing a decompositioning approach to handle this scattering problem. A scattering particle is decomposed into a number of basic units and scattering by such an ensemble of basic constituents is computed using a multiple scattering T-matrix approach. The range of validity of this approach is investigated by providing exemplary computation results for single fibres and aggregated fibres.
Particle and Particle Systems Characterization 03/2008; 25(1):74 - 83. · 0.49 Impact Factor
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ABSTRACT: Total internal reflection microscopy (TIRM) is a method for the precise measurement of interaction potentials between a spherical colloidal particle and a wall. The method is based on single-particle evanescent wave light scattering. The well-established model used to interpret TIRM data is based on an exponential relation between scattering intensity and particle wall distance. However, applying this model for a certain range of experimental parameters leads to significant distortions of the measured potentials. Using a TIRM setup based on a two-wavelength illumination technique, we were able to directly measure the intensity distance relation revealing deviations from an exponential decay. The intensity-distance relations could be compared to scattering simulations taking into account exact experimental parameters and multiple reflections between a particle and the wall. Converging simulation results were independently obtained by the T-matrix method and the discrete sources method (DSM) and show excellent agreement with experiments. Using the new scattering model for data evaluation, we could reconstruct the correct potential shape for distorted interaction potentials as we demonstrate. The comparison of simulations to experiment intrinsically yields a new method to determine absolute particle-wall distances, a highly desired quantity in TIRM experiments.
Langmuir 02/2008; 24(1):1-4. · 4.19 Impact Factor
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ABSTRACT: The discrete sources method has been extended to analyze the scattering behavior of a core-shell nanoparticle (nanoshell) deposited near a plane surface in an evanescent wave field. The rigorous computer model based on DSM, which allows one to take into account all features of the scattering problem, has been realized. The dependence of the scattering spectra of core-shell particles on size, shell thickness and core-shell asphericity is discussed.
Journal of Modern Optics 01/2008; 55(2):297-310. · 1.17 Impact Factor
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ABSTRACT: Inhomogeneous droplets including small spherical inclusions are characterized by the estimation of droplet diameter, inclusion concentration and inclusion diameter and a measure for the polydispersity of the inclusions. In most cases, it is reasonable to assume that the material parameters are known and therefore the index of refraction and the shape of inclusions. In this paper, the results from a measurement technique are investigated. The method will be evaluated on the basis of light scattering measurements for a range of scattering angles. These measurements have been taken with a fast CCD line scan camera and appropriate optics. An attempt is made to derive information from these measurements only. The continuous wavelet transform, speckle image analysis and turbidity measurement methods are used to estimate the concentration and the diameter of the monodisperse polystyrene particles within a droplet. The droplets, generated by a drop-on-demand droplet generator, are nearly monodisperse. The volume concentration of the inclusions within the suspensions varies between 0.01% and 9%. The inclusions are monodisperse. However, it seems to be possible that they coagulate due to the fast fluid flows at the droplet generation. As a result, the technique may be used only for the estimation of average values of size and concentration of inclusions from the measurements.
Meas. Sci. Technol. 01/2007; 18:2209-2218.
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ABSTRACT: In the paper we applied a variant of the T-matrix method, the null-field method with discrete sources (NFM-DS) and the discrete sources method (DSM) to model light scattering by a particle near a plane surface in an evanescent wave field. Such investigations have a great practical value for total internal reflection microscopy (TIRM). The numerical algorithms of DSM and NFM-DS have been modified to model the specific conditions of real measurement experiments carried out in Stuttgart University. Objective response and scattering cross-section have been calculated. Numerical results of both methods have been compared and demonstrate good agreement with measurements.
Journal of Quantitative Spectroscopy and Radiative Transfer 01/2007; 106:464-474. · 3.19 Impact Factor
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ABSTRACT: We simulate and measure light scattering of a micrometer-sized spherical particle suspended in solution close to a glass substrate. The model, based on the discrete sources method, is developed to describe the experimental situation of total internal reflection microscopy experiments; i.e., the particle is illuminated by an evanescent light field originating from the glass-solvent interface. In contrast to the well-established assumption of a simple exponential decay of the scattering intensity with distance, we demonstrate significant deviations for a certain range of penetration depths and polarization states of the incident light.
Applied Optics 11/2006; 45(28):7299-308. · 1.41 Impact Factor
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ABSTRACT: In this paper the nullfield method with discrete sources (NFM-DS) is applied to analysis of light scattering by biconcave Cassini-like particles, which can be described as oblate discspheres with central concavities on their top and bottom. As far as we know this is a first attempt to apply a modification of the T -matrix method to model such a nonconvex object. The numerical results for different particles under different incident angles obtained by the NFM-DS are presented in the last section of the paper. For result verification the discrete source method (DSM) has been chosen. The comparison of results obtained by using both methods shows very good agreement.
J. Opt. A: Pure Appl. Opt. 01/2006; 8:1-9.
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ABSTRACT: The discrete sources method has been extended to analyse P or S polarized evanescent wave scattering by a dielectric particle located on a layered interface. This was done to develop a light scattering simulation model for total internal reflection microscopy. The influence of metallic layers on the prism surface is investigated. Numerical results for the objective response versus particle height and the scattering cross-section are presented.
J. Opt. A: Pure Appl. Opt. 01/2006; 8:999-1006.
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ABSTRACT: In this paper the discrete source method (DSM) is applied to analyse light scattering from nano-particles on a prism surface. Results of a comparison of an approximate Mie model and the rigorous DSM model, which accounts for the light scattering interaction of the particle with the prism surface, are presented. It is shown that taking into account the particle–prism interaction plays a significant role for a correct interpretation of spectroscopic measurements.
Journal of Optics A Pure and Applied Optics 10/2005; 7(12):706. · 1.92 Impact Factor
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ABSTRACT: Light scattering computations for cylindrical fibers of high aspect ratios are needed in designing instruments for the optical characterization of airborne fibers. Long airborne fibers may also appear in a bent shape. In this paper computational results for bent fibers of various radii of bending will be presented using the multiple multipole technique (MMP).
Particle and Particle Systems Characterization 08/2003; 20(4):243 - 249. · 0.49 Impact Factor
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ABSTRACT: In this paper we analyse suspension droplet light scattering with respect to measuring the size of the host particle and the inclusion concentration. The light-scattering simulations show significant changes in the scattering distribution of suspension droplets with different inclusion concentrations. The evaluation reduces to only two parameters, namely angular fringe spacing and the slope in the scattering domain 30-70°. This method relies on the simulation of scattering with parameters such as the refractive indices of the host and the inclusions and the size of the inclusions.
Measurement Science and Technology 02/2002; 13(3):276. · 1.49 Impact Factor
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ABSTRACT: In this paper we analyse the scattering by a spherical particle with multiple spherical inclusions. Our analysis is focused on the equivalence between the inhomogeneous sphere and a homogeneous sphere with an equivalent refractive index. The equivalent sphere reproduces the differential scattering cross section of the inhomogeneous sphere reasonably accurately. This equivalence is investigated for small and large size parameters of the inclusions.
Journal of Optics A Pure and Applied Optics 04/2001; 3(3):204. · 1.92 Impact Factor
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ABSTRACT: Using phase Doppler anemometry (PDA) to investigate sprays of optically inhomogeneous liquids leads to blurred measured size distributions. The blurring function is formed by performance of PDA measurements on single-size droplets generated by a piezoelectric droplet generator. To obtain the undistorted droplet-size distributions, a constrained iterative inversion algorithm is applied. The number of iteration steps to achieve the best possible restoration is determined by the use of synthetically generated data that has noise properties similar to the measured histograms. The obtained size distributions are checked by comparison with undistorted measurement results of an atomized optical homogeneous liquid.
Applied Optics 05/1996; 35(15):2537-43. · 1.41 Impact Factor
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ABSTRACT: Current international research needs efficient exchange of information. To constantly keep information for the light-scattering community up to date, a project for a new Scattering Information Portal has been proposed. The history and the concept of the project will be described to invite interested scientists to contribute to the project.
Journal of Quantitative Spectroscopy and Radiative Transfer.
