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The study of light scattering by particles has become fundamental and applied interests in the fields of chemistry, biology, and most importantly in physics. In this context, this thesis focuses on understanding the optical properties of dye layers adsorbed onto metallic nanoparticles (NP), which is essential for interpreting the results of plasmon-dye coupling experiments. To model such a system, Mie theory is often used to solve for the exact solution to Maxwell’s equations for spherical homogeneous and isotropic coated NP. The effects of the NP’s plasmon resonances on the optical properties of the adsorbed dye layer have been predicted using an effective medium model, where the dye-layer is treated as an isotropic layer with an effective dielectric function accounting for the dye resonance. However, this isotropic shell model is inadequate as it cannot account for the dye surface concentration and the anisotropy of the optical response of the dye layer. In this thesis, we introduce anisotropic effects within Mie theory and develop microscopic models to define effective dielectric functions which explicitly include the dye-concentration effect in the shell model. Combining anisotropic Mie theory with a concentration-dependent effective shell model allows us to form new theoretical tools to model the optical properties of adsorbed dye layers on metallic NPs of spherical shape. With this new refined effective medium model, we are then able to study shell models for elongated particles beyond the quasi-static approximation. This is implemented using the finite element method (FEM) to numerically solve Maxwell’s equations. The FEM implementation is then used to investigate how the NP’s plasmon resonance can be affected by the dye’s orientation and location on the NP’s surface. We show that the orientation and location of the dye molecules on the NP determine how strongly the plasmon resonance is shifted. The results of this work will improve our ability to accurately model the optical properties of anisotropic molecules adsorbed on metallic NPs. This is important in a number of applications including the development of localised surface plasmon resonance (LSPR) sensing and the design of plasmonic devices.

Multiple scattering theory is used to develop a method for computing the velocity of an electromagnetic wave (light) propagating in a medium with inclusions. A model of light scattering by particles placed in a waveguide on its axis is investigated.

Standard synthesis protocols produce silicon dioxide (SiO2) particles with an inhomogeneous material distribution, which defines their optical properties. The inner structure and effective refractive index of the particles can be investigated by light scattering and optical contrast variation techniques. The standard analysis relies on scattering models for particles smaller than the wavelength of the scattering probe, thus restricting its use for a large variety of particle systems of academic and industrial interest. However, to overcome this difficulty should be possible by using the appropriate scattering model in the analysis. Here, SiO2 particles of size comparable to the wavelength of the illuminating source are dispersed at low particle number concentration in different mixtures of polar solvents to study the optical contrast. The angle-dependent scattered intensity from SiO2 particles suspended in different mixtures of water and DMSO are obtained by static light scattering (SLS) and the effective refractive index of the particles is estimated from refractometry experiments. The measured angle-dependent scattered intensity is well described by the Aden-Kerker theory for coated polydisperse spherical particles. Fitting of experimental data is performed by using a non-linear least squares routine assuming that the core-to-shell ratio remains constant from where the refractive index and radius of the particles shell are obtained. Additionally, we use the structural characterization to estimate the effective refractive index of SiO2 particles, which allows identification of the solvent composition that produces the minimal optical contrast between colloids and suspending medium. This is, to our knowledge, the first report describing the interplay between internal structure and optical properties of core-shell spherical colloids of size comparable to the wavelength of the scattering probe. Consequently, our study provides an experimental scheme that could be useful in the structural and optical characterization of large complex colloids.

A mathematical model for the analysis of the near field intensity distribution in problems of light scattering by particles on the substrate is developed based on the Discrete Sources Method. The influence of the size and material of the particles and the refractive index of the ambient medium on the distribution of the field intensity inside the substrate near the particle is examined.

The simulation of light scattering by particles on a substrate with the $T$-matrix method relies on the expansion of the scattered field in spherical waves, followed by a plane wave expansion to allow the evaluation of the reflection from the substrate. In practice, the plane wave expansion (i.e., the Sommerfeld integrals) needs to be truncated at a maximal in-plane wavenumber $\kappa_\mathrm{max}$. An appropriate selection of $\kappa_\mathrm{max}$ is essential: counter-intuitively, the overall accuracy can degrade significantly if the integrals are truncated with a too large value. In this paper, we propose an empirical formula for the selection of $\kappa_\mathrm{max}$ and discuss its application using a number of example simulations with dielectric and metallic oblate spheroids on dielectric and metallic substrates. The computed differential scattering cross sections are compared to results obtained from the discrete-sources method., Comment: Accepted manuscript. \copyright 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license, http://creativecommons.org/licenses/by-nc-nd/4.0/

The measurement of the shape and size distributions of small atmospheric ice particles (i.e. less than about 100 μm in size) is still an unresolved problem in atmospheric physics. This paper is composed of two parts, each addressing one of these measurements. In the first part, we report on an application of a new open-source electromagnetic boundary element method (BEM) called “BEM++” to characterise the shape of small ice particles through the simulation of the two-dimensional (2D) light scattering patterns of extreme Chebyshev ice particles. Previous electromagnetic studies of Chebyshev particles have concentrated upon high Chebyshev orders, but with low Chebyshev deformation parameters. Here, we extend such studies by concentrating on the 2D light scattering properties of Chebyshev particles with extreme deformation parameters, up to 0.5, and with Chebyshev orders up to 16, at a size parameter of 15, in a fixed orientation. The results demonstrate the applicability of BEM++ to the study of the electromagnetic scattering properties of extreme particles and the usefulness of measuring the light scattering patterns of particles in 2D to mimic the scattering behaviours of highly irregular particles, such as dendritic atmospheric ice or hazardous biological and/or aerosol particles. In the second part, we demonstrate the potential application of remotely sensed very-high-resolution brightness temperature measurements of optically thin cirrus between wavelengths of about 8.0 and 12.0 µm to resolve the current atmospheric physics issue of determining the number concentration of small ice particles with size less than about 100 μm.

Single particle Mie calculations of near micron-sized TiO2 particles predict strong light scattering dominating the visible range that would give rise to a white appearance. We demonstrate that a polydisperse collection of these “white” particles can result in the generation of visible colors through ensemble scattering. The weighted averaging of the scattering over the particle size distribution modifies the sharp, multiple, high order scattering modes from individual particles into broad variations in the collective extinction. These extinction variations are apparent as visible colors for particles suspended in organic solvent at low concentration, or for a monolayer of particles supported on a transparent substrate viewed in front of a white light source. We further exploit the color variations on optical sensitivity to the surrounding environment to promote micron-sized TiO2 particles as stable and robust agents for detecting the optical index of homogeneous media with high contrast sensitivities. Su...

The work presents the solution for the light scattering problem by arbitrarily-shaped particles in the vicinity of the backward scattering direction. The solution was obtained within the framework of the geometrical optics approximation. The refractive index was equal to 1.3116. It was shown that the general contribution of scattering light for arbitrarily-shaped particles in the vicinity of the backscattering direction consists of the specular reflection of the particles and two types of non-specular optical beams. It is shown that the optical characteristics of the ice particles with arbitrary shapes correspond to experimental data.

The polarization characteristics of light scattered by particles are sensitive to the morphology of the scatterers. In this study, we employed the finite element method (FEM) with a finite element software (COMSOL multiphysics) to retain the potentiality to extend the theoretical study of scattering in this work to single particles with more complex morphology and arbitrary orientation. The angular distribution profiles of the scattering field components perpendicular and parallel to the incident polarization direction are obtained for spherical and spheroidal particles. By comparison with the spheres’ preservation of the polarization, cross-polarization effects for differently oriented spheroidal particles are revealed. The question how to experimentally discriminate the particles with smooth surface moving freely in the detected area at single-particle level according to polarization is addressed. To this end, polarizing devices are inserted into an interference particle imaging (IPI) system. By detecting the orthogonally polarized components of the light, the preservation of the polarization state after scattering by spheres and the occurrence of cross-polarization effects after scattering by spheroids are verified experimentally with the fringes in the IPI system as a reference. A feasible method for distinguishing a spheroidal from a spherical shape at the single-particle level based on the existence of a cross-polarized component of the scattered light is proposed.

We design polystyrene-poly(N'-isopropylacrylamide-co-acrylic acid) core-shell particles that exhibit dynamically tunable scattering. We show that under normal solvent conditions the shell is nearly index-matched to pure water, and the particle scattering is dominated by Rayleigh scattering from the core. As the temperature or salt concentration increases, both the scattering cross-section and the forward scattering increase, characteristic of Mie scatterers. The magnitude of the change in the scattering cross-section and scattering anisotropy can be controlled through the solvent conditions and the size of the core. Such particles may find use as optical switches or optical filters with tunable opacity.

Q-space analysis is applied to extensive simulations of the single-scattering properties of ice crystals with various habits/shapes over a range of sizes. The analysis uncovers features common to all the shapes: a forward scattering regime with intensity quantitatively related to the Rayleigh scattering by the particle and the internal coupling parameter, followed by a Guinier regime dependent upon the particle size, a complex power law regime with incipient two dimensional diffraction effects, and, in some cases, an enhanced backscattering regime. The effects of significant absorption on the scattering profile are also studied. The overall features found for the ice crystals are similar to features in scattering from same sized spheres.

The dependence of the electric potential on the absorption and scattering of light by small particles has emerged as an interesting research topic, as the unexpected amplified optical signatures of a system of electrically charged particles were satisfactory predicted recently for homogeneous, uniformly charged spheres. However, natural particles are rarely of spherical shape. A comprehensive understanding of how arbitrarily shaped, charged particles interact with electromagnetic radiation has been missing. The approach we present here attempts to fill this gap by introducing a numerical formulation of the electromagnetic scattering problem for these particles. The first results from the intercomparison of numerical and analytical solutions for a pseudosphere show that the resonance features found are largely consistent, except for the magnitude and width of the peak amplitude, which may be due to inherent differences in the approaches used.

The computation of the light scattering properties of size and shape distributed interstellar graphite dust analogues using discrete dipole approximation (DDA) is presented. The light scattering properties of dust particles of arbitrary shapes having sizes ranging from 0.5 to 5.0 μm were computed using DDSCAT 7.3.0 software package and an indigenously developed post-processing tool for size and shape averaging. In order to model realistic samples of graphite dust and compute their light scattering properties using DDA, different target geometries were generated to represent the graphite particle composition in terms of surface smoothness, surface roughness and aggregation or their combination, for using as the target for DDSCAT calculations. A comparison of the theoretical volume scattering function at 543.5 nm and 632.8 nm incident wavelengths with laboratory simulation is also presented in this paper.

In this paper, an experimental apparatus for the analysis of biological cells light scattering in liquid suspensions has been presented. Firstly, an algorithm of the discrete sources method (DSM) is applied to model light scattering from a cell particle. In our model, a monochromatic laser beam scattered by cell particles, which can be inorganic, organic, or biological cells (animal cells and bacteria) and the scattering characteristic is analyzed with morphology and the refractive index of the cell particles. In contrast to traditional volume-based methods which are widely used for light scattering simulation, DSM allows calculation of scattering for all incident angles and polarizations at once. This leads to an essential reduction of the computing time. The DSM algorithm allows using a lower number of elementary sources which results in an increased accuracy of approximation for every harmonic. Secondly, in order to study light scattering in biological cells close to the actual situation, we focus on non-spherical particles in the cell-culture medium. Finally, we demonstrate the light scattering results of bovine kidney cells suspended in the cell-culture medium, and compares with the simulated results.

Light scattering by particles immersed in an absorbing host medium has been an important issue in many fields, such as ocean optics, atmospheric radiation, remote sensing and so on. The traditional theory ignores the effect of host medium absorption on particle scattering, which may result in inaccurate results. In this paper, the scattering coefficient, extinction coefficient and phase function of the dispersed medium consisting of optically soft particles are investigated with considering the effect of host medium absorption on particle scattering. The results are based on the recently developed Mie theory for the absorbing host medium. It is found that neglecting the host medium absorption on particle scattering will result in a small change in extinction coefficients but a great change in scattering coefficients. Meanwhile, the relative error of scattering coefficients caused by using the conventional Mie theory increases obviously with the increase of particle size and the absorption index of the host medium, while the relative error of extinction coefficients fluctuates with the particle size. Moreover, the relative error of scattering coefficients of polydisperse particles is more significant than that of monodisperse particles.

The equations for frequency-domain multiple scattering are derived for a scalar or electromagnetic plane wave incident on a collection of particles at known positions, and in the time-domain for a plane wave pulse incident on the same collection of particles. The calculation is carried out for five different combinations of wave types and particle types of increasing geometrical complexity. The results are used to illustrate and discuss a number of physical and mathematical characteristics of multiple scattering in the frequency- and time-domains. We argue that frequency-domain multiple scattering is a purely mathematical construct since there is no temporal sequencing information in the frequency-domain equations and since the multi-particle path information can be dispelled by writing the equations in another mathematical form. However, multiple scattering becomes a definite physical phenomenon in the time-domain when the collection of particles is illuminated by an appropriately short localized pulse.

The Gaussian sphere has been widely used as a model to study light scattering by irregular particles; and, despite extensive numerical studies, the optical properties are not thoroughly understood. Based on Gaussian spheres and using a combination of the invariant imbedding T-matrix method and an improved geometric-optics method, the single-scattering properties (namely, the 4×4 phase matrix, extinction cross section, single-scattering albedo, and asymmetry factor) are computed in the Rayleigh to geometric optics regimes. The simulations are performed with various degrees of irregularity, and the effects of particle irregularities are investigated over a wide range of particle sizes. Furthermore, the theoretical simulations based on Gaussian spheres are used to fit the measured optical properties of feldspar particles from the well-known Amsterdam–Granada light scattering database. A mixture of several shapes is shown to closely reproduce the measured phase matrices. The results may be potentially useful for remote-sensing and radiative-transfer applications involving dust aerosol.

The effect of inhomogeneous mineralogical composition on the optical properties of mineral dust particles is investigated. More specifically, spheres composed of a non-absorbing mineral with multiple spherical hematite inclusions are considered. The size of the particles, the number of inclusions, and the hematite volume fraction are varied, and the differential and integral optical properties are compared to those computed for homogeneous spheres. The effective refractive index of the homogeneous spheres is obtained (i) by use of four conventional effective medium approximations; and (ii) by freely varying the real and imaginary parts of the refractive index until a best-fit of the scattering matrix elements is achieved for all scattering angles and particle sizes. Among the integral radiometric observables, the single scattering albedo is most sensitive to particle inhomogeneity, while the extinction and scattering efficiency and the asymmetry parameter are rather insensitive. The phase function, the degree of linear polarisation, the linear depolarisation, and, indeed, all elements of the scattering matrix are strongly modulated by particle inhomogeneity. None of the effective medium approaches, not even the best-fit method, are able to reproduce the single scattering albedo and the scattering matrix elements over the entire range of particle sizes.

Large ice hydrometeors are usually present in intense convective clouds and may significantly affect the upwelling radiances that are measured by satellite-borne microwave radiometers – especially, at millimeter-wavelength frequencies. Thus, interpretation of these measurements (e.g., for precipitation retrieval) requires knowledge of the single scattering properties of ice particles. On the other hand, shape and internal structure of these particles (especially, the larger ones) is very complex and variable, and therefore it is necessary to resort to simplifying assumptions in order to compute their single-scattering parameters. In this study, we use the discrete dipole approximation (DDA) to compute the absorption and scattering efficiencies and the asymmetry factor of two kinds of quasi-spherical and non-homogeneous soft-ice particles in the frequency range 50–183 GHz. Particles of the first kind are modeled as quasi-spherical ice particles having randomly distributed spherical air inclusions. Particles of the second kind are modeled as random aggregates of ice spheres having random radii. In both cases, particle densities and dimensions are coherent with the snow hydrometeor category that is utilized by the University of Wisconsin – Non-hydrostatic Modeling System (UW-NMS) cloud-mesoscale model. Then, we compare our single-scattering results for randomly-oriented soft-ice hydrometeors with corresponding ones that make use of: a) effective-medium equivalent spheres, b) solid-ice equivalent spheres, and c) randomly-oriented aggregates of ice cylinders. Finally, we extend to our particles the scattering formulas that have been developed by other authors for randomly-oriented aggregates of ice cylinders.

The scattering properties of ice crystals at centimeter and millimeter wavelengths are fundamental for their measurement with radars or radiometers as well as for many other applications in remote sensing. Only the scattering properties of homogeneous spheres can be computed in a mathematically exact way using the Mie theory. Therefore, for many approaches ice crystals and other frozen hydrometeors are approximated by ice spheres that have the same volume as the crystal or hydrometeor – so called equal volume spheres. However, many frozen hydrometeors are non-spherical. They exist in a huge variety of shapes and exhibit different mixtures of ice, water and air. Therefore it is desirable to accurately compute scattering from non-spherical particles in order to clearly understand the effect the shape of a hydrometeor has on its scattering pattern. In this study, single scattering parameters like scattering cross section (Csca) and absorption cross section (Cabs) were calculated for six pristine ice crystals by means of the Discrete Dipole Approximation (DDA). The calculations were carried out for frequencies from 1 GHz to 300 GHz – leading to size parameters of up to 4. The study calculates the scattering parameters for randomly oriented ice crystals and investigates to what extent the exact scattering parameters can differ from an approximation by equal volume spheres.

Despite a long history, light scattering by particles with size comparable with the light wavelength still unveils surprising optical phenomena, and many of them are related to the Fano effect. Originally described in the context of atomic physics, the Fano resonance in light scattering arises from the interference between a narrow subradiant mode and a spectrally broad radiation line. Here, we present an overview of Fano resonances in coated spherical scatterers within the framework of the Lorenz-Mie theory. We briefly introduce the concept of conventional and unconventional Fano resonances in light scattering. These resonances are associated with the interference between electromagnetic modes excited in the particle with different or the same multipole moment, respectively. In addition, we investigate the modification of the spontaneous-emission rate of an optical emitter at the presence of a plasmonic nanoshell. This modification of decay rate due to electromagnetic environment is referred to as the Purcell effect. We analytically show that the Purcell factor related to a dipole emitter oriented orthogonal or tangential to the spherical surface can exhibit Fano or Lorentzian line shapes in the near field, respectively.

Light scattering by particles large compared to the wavelength of incident light is traditionally solved using ray optics which considers absorption inside the particle approximately, along the ray paths. To study the effects rising from this simplification, we have updated the ray-optics code SIRIS to take into account the propagation of light as inhomogeneous plane waves inside an absorbing particle. We investigate the impact of this correction on traditional ray-optics computations in the example case of light scattering by ice crystals through the extended near-infrared (NIR) wavelength regime. In this spectral range, ice changes from nearly transparent to opaque, and therefore provides an interesting test case with direct connection and applicability to atmospheric remote-sensing measurements at NIR wavelengths. We find that the correction for inhomogeneous waves systematically increases the single-scattering albedo throughout the NIR spectrum for both randomly-oriented, column-like hexagonal crystals and ice crystals shaped like Gaussian random spheres. The largest increase in the single-scattering albedo is 0.042 for hexagonal crystals and 0.044 for Gaussian random spheres, both at λ = 2.725 µm. Although the effects on the 4 × 4 scattering-matrix elements are generally small, the largest differences are seen at 2.0 µm and 3.969 µm wavelengths where the correction for inhomogeneous waves affects mostly the backscattering hemisphere of the depolarization-connected P22/P11, P33/P11, and P44/P11. We evaluated the correction for inhomogeneous waves through comparisons against the discrete exterior calculus (DEC) method. We computed scattering by hexagonal ice crystals using the DEC, a traditional ray-optics code (SIRIS3), and a ray-optics code with inhomogeneous waves (SIRIS4). Comparisons of the scattering-matrix elements from SIRIS3 and SIRIS4 against those from the DEC suggest that consideration of the inhomogeneous waves brings the ray-optics solution generally closer to the exact result and, therefore, should be taken into account in scattering by absorbing particles large compared to the wavelength of incident light.

В работе предлагается математическая модель на основе векторного метода конечных элементов для исследования распределения электромагнитного поля в ближней зоне пары сферических наночастиц. Данная модель позволила разработать алгоритмы и соответствующее программное обеспечение. Была проведена верификация, показавшая, что расхож- дение результатов исследования предлагаемой математической модели и имеющихся данных расчётов по аналитическим формулам согласно теории Ми (G. Mie) для однородных сферических наночастиц не превышает 10 %. С помощью созданного программного обеспечения проведён вычислительный эксперимент с целью определения расположения пары металлических наночастиц, при котором интенсивность электромагнитного поля в ближней зоне будет достигать наибольшего значения. Достоинством предлагаемой математической модели и методики её применения является использование в качестве конечных элементов тетраэдров, позволяющих с достаточной для практических целей точностью аппроксимировать неоднородную структуру наноматериала. Кроме того, обеспечивается непрерывность во всей расчётной области тангенциальной компоненты электромагнитного поля. Here we propose a mathematical model based on a vector finite-element method for modeling the distribution of the electromagnetic field in the near zone of spherical particles. This model has allowed us to develop algorithms for the appropriate software. The verification of the model shows that the discrepancy between the research results of the proposed model and the available calculation results based on analytical formulas derive d from the Mie theory for homogeneous spherical nanoparticles does not exceed 10 percent. Calculations were carried out to determine the relative positions of a pair of metal nanoparticles at which the intensity of the electromagnetic field reaches the maximum value in the near zone. The advantage of the proposed mathematical model and approach consists in the use of tetrahedrons as finite-elements. The tetrahedron finite-elements allow one to approximate the heterogeneous structure of the nanomaterial with the accu racy sufficient for the practical use. Furthermore, in this way the continuity of the tangential component of the electromagnetic field in the entire calculation region can be achieved.

Using the discrete dipole approximation (DDA), we compute light scattering from irregularly shaped particles with three different types of agglomerate morphologies. The packing density of materials in the model particles spans the range from 0.169 through 0.336. We investigate four different refractive indices m =1.313+0 i , 1.6+0.0005 i , 1.5+0.1 i , and 1.855+0.45 i , which are representative of various cosmic and terrestrial materials in the visible. In each case, we consider a wide range of size parameters that makes it possible to average the light-scattering response over particle size with a power-law size distribution. We find that despite noticeable differences in particle morphology, their light-scattering responses are remarkably similar; the difference in light scattering often does not exceed the error bars occurring in laboratory measurements of micron-sized particles. On the contrary, the impact of refractive index and size distribution on light scattering appears to be much stronger compared with the morphology of complex, agglomerate particles. This finding may simplify considerably the interpretation of photo-polarimetric observations of atmospheric aerosols, cosmic dust particles, etc., because the precise specification of target-particle shape is unnecessary for the analysis.

Scattering methods are widespread used to characterize the structure and constituents of matter on small length scales. This motivates this introductory text on identifying prospective approaches to scattering-based methods for granular media. A survey to light scattering by particles and particle ensembles is given. It is elaborated why the established scattering methods using X-rays and visible light cannot in general be transferred to granular media. Spectroscopic measurements using Terahertz radiation are highlighted as they to probe the scattering properties of granular media, which are sensitive to the packing structure. Experimental details to optimize spectrometer for measurements on granular media are discussed. We perform transmission measurements on static and agitated granular media using Fourier-transform spectroscopy at the THz beamline of the BessyII storage ring. The measurements demonstrate the potential to evaluate degrees of order in the media and to track transient structural states in agitated bulk granular media., Comment: 12 Pages, 9 Figures, 56 References

We define the partial scattering cross section and partial efficiencies to demonstrate that the total scattering is the sum of two roughly equal parts: approximately half from the forward scattering lobe due to 2D diffraction by the projected sphere and half from the 2D to 3D diffraction crossover. The first part is at angles such that θ≲λ/D, a result previously known, which can be quite small for large particles. The second part is in a new regime we call the "hump," visible in q-space, which to a good approximation contains the other half of the scattered light. The hump disappears when the imaginary part of the refractive index is significant.

Purpose – The purpose of this paper is to discuss the light scattering of nonspherical particles that is very important for the research on the aerosol optical properties. Design/methodology/approach – In this paper, the authors use the spheroid model as the characteristic particle shape to study the single scattering albedo of real nonspherical particles. Meanwhile, the extinction and scattering cross section of spheroids are calculated with the T matrix method combined with the improved geometric optics approximation method (IGOM). Findings – Through this combination, the extinction and scattering cross section of spheroids can be obtained in the larger size range and aspect ratio range. Furthermore, the comparison of the single scattering albedo for the spheroids and their equivalent spheres is conducted in order to investigate the difference of the spherical and nonspherical particles. Originality/value – Simulation experiments indicate that the single scattering albedo of spheroids can be calculated well with this combination, and it has some obvious influence on the variation of the aspect ratio, incident wavelength, and complex refractive index of spheroid particles.

The analysis of optical scattering data of interstellar carbonaceous graphite dust analog at 543.5 nm, 594.5 nm and 632.8 nm laser wavelengths by using an original laboratory light scattering setup is presented. The setup primarily consisted of a laser source, optical units, aerosol sprayer, data acquisition system and associated instrumentation. The instrument measured scattered light signals from 10° to 170° in steps of 1°. The results of the measurements of the volume scattering function β(θ) and degree of linear polarization P(θ) of the carbonaceous graphite dust particles that were sprayed in front of the laser beam by using an aerosol sprayer were subsequently compared with theoretically generated Mie plots with estimated parameters.

Development of an online web application to simulate and display plane wave scattering from small particles is presented. In particular, the computation of angular variation of the scattering properties (scattering matrix elements, scattering coefficients, single scattering albedo etc.) of particulate matter by using the Mie theory and the T-matrix method was incorporated in the application. Comparison of the results generated by using the web application with other reported benchmark results has shown that the web application is accurate and reliable for electromagnetic scattering computations.

Atmospheric aerosol particles may undergo phase separation due to differences in miscibility. This alters the morphology of particles such that they are no longer well-mixed, simple spheres. As a result, scattering and absorption of sunlight in Earth’s atmosphere could be affected. In turn, this may alter direct climate forcing by aerosols. In this work we examine the impact of phase separation on aerosol optics for the bi-sphere, core–shell, and engulfed morphologies. We find bi-spherical particles often exhibit very different scattering and absorption cross-sections for a mid-visible wavelength (0.53 lm) relative to an equivalent, volume-weighted spherical case. Optical differences are largely driven by the particle shape, rather than differences in refractive index between phases. However, when averaged across a typical urban particle size distribution, the differences in light scattering largely vanish and bi-sphere and volume equivalent models generally agreed to within 10% for dielectric particles. For particles that are light absorbing, the bi-sphere and volume averaged cases often yielded dissimilar results with the volume-averaged case reflecting absorption >10% more than the phase separated particles. This was particularly true for bi-spheres in which one component particle is strongly light absorbing. Core–shell and engulfed morphologies yield volume scattering efficiencies within a few percent of volume-weighted spheres. However, modeled light absorption between the phase separated and volume averaged models frequently differ by >20% when inclusions absorb light strongly. Therefore, modeling light absorption of mixed-phase particles through the volume-mixing rule cannot be recommended. 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

The study of light scattering by various particles is an active and important subject of research with myriad practical applications. During the years the scattering of plane wave by various particles has been investigated extensively. In recent years, with the development of laser sources and the tremendous expansion of their application, there has been a growing interest in the study of light scattering by various particles illuminated by a focused Gaussian beam. Since the analytical methods are only suitable for the analysis of Gaussian beam scattering by some regular particles, for complex particles with arbitrary shape and structure, one has to resort to the numerical methods. In this article, we review the recent numerical investigation on the scattering of Gaussian beam by systems of complex particles, including arbitrarily shaped conducting particles, dielectric particles, composite particles with inclusions, as well as random discrete particles and fractal soot aggregates. The essential formulations of the proposed numerical methods are outlined and the numerical results for some complex particles are also presented. This review is expected to provide useful help for the study of the interaction between the laser beams and the complex particles.

The dynamics of light scattering by minerogenic particles in the upper waters of Cayuga Lake, New York, were characterized for the spring–autumn interval of 8 yr (1999–2006) at pelagic and nearshore sites with a scanning electron microscope interfaced with automated image and x-ray analyses (SAX). SAX results were used to estimate the minerogenic scattering coefficient (bm) through Mie theory calculations. SAX–Mie supported a twocomponent model for particulate scattering (bp) that included an organic component of scattering (bo), estimated from a bio-optical model. The credibility of the bm estimates and the two-component modeling approach was demonstrated through good closure of the modeling results with bulk values of bp (estimated from measurements of the beam attenuation coefficient at 660 nm). The average of the ratio bp:(bm + bo) was 1.03 (average relative error 19.4%). Two minerogenic particle types were important in regulating the dynamics of bm—clay minerals that increased in concentration in response to runoff events, and calcium carbonate precipitated mostly on small organic particles during short-term late-summer whiting events. bm was attributed to particles in the size range of 1–10 mm. Variations in bm dominated the overall variations in bp and Secchi disk depth; differences in bo explained well those observed in bp during dry weather intervals of low bm. Higher bm values, mainly associated with clay mineral particles, were observed at the nearshore site as opposed to the pelagic location; there was a positive linkage between these levels and tributary flow rate. Light scattering by particles, a fundamental process regulating radiative transfer in water (Kirk 2011), is important in determining apparent optical properties (AOPs, depend on geometry of the light field) of interest, including clarity (Preisendorfer 1986) and the remote )

Light scattering by single, inhomogeneous mineral dust particles was simulated based on shapes and compositions derived directly from measurements of real dust particles instead of using a mathematical shape model. We demonstrate the use of the stereogrammetric shape retrieval method in the context of single-scattering modelling of mineral dust for four different dust types – all of them inhomogeneous – ranging from compact, equidimensional shapes to very elongated and aggregate shapes. The three-dimensional particle shapes were derived from stereo pairs of scanning-electron microscope images, and inhomogeneous composition was determined by mineralogical interpretation of localized elemental information based on energy-dispersive spectroscopy. Scattering computations were performed for particles of equal-volume diameters, from 0.08 μm up to 2.8 μm at 550 nm wavelength, using the discrete-dipole approximation. Particle-to-particle variation in scattering by mineral dust was found to be quite considerable and was not well reproduced by simplified shapes of homogeneous spheres, spheroids, or Gaussian random spheres. Effective-medium approximation results revealed that particle inhomogeneity should be accounted for even for small amounts of absorbing media (here up to 2% of the volume), especially when considering scattering by inhomogeneous particles at size parameters 3

This paper applies the Q-space analysis method to the scattering phase function of small irregular particles. Q-space analysis involves plotting the scattered intensity versus the magnitude of the scattering wave vector q =(4 π / λ ) sin( θ /2) on a double log plot. Four types of irregularly shaped particles were studied: strongly damaged spheres, rough surface spheres, pocked spheres, and agglomerated debris particles. The angular scattering phase function was calculated using the discrete dipole approximation (DDA). The Q-space analysis uncovered power law descriptions of the scattering as it has previously for aggregates, spheres and dusts, although in some situations the description is marginal. It also showed that the forward scattering lobe has Rayleigh functionalities on size and refractive index. These results imply that Q-space analysis can yield a comprehensive description of scattering in terms of power laws with quantifiable exponents for a wide variety of particle shapes. However, a theoretical explanation of the power laws and the values of the numerical exponents is lacking.

An experimental apparatus for the analysis of biological cells light scattering in liquid suspensions has been presented. Characterization is based on the scattering of a monochromatic laser beam by particles [which can be inorganic, organic, or biological (such as animal cells and bacteria)] and on the strong relation between the light-scattering pattern and the morphology and refractive index of the particles. In order to study light scattering in biological cells close to the actual situation, we focus on non-spherical particles in the cell-culture medium. Finally, we demonstrate the light scattering results of bovine kidney cells suspended in the cell-culture medium, and compares then with the simulated results.

The scattering waves by two elastic spheres in solid are studied. The incident wave, the scattering waves in the host and the transmitted waves in the elastic spheres are all expanded in the series form of spherical wave functions. The total waves are obtained by addition of all scattered waves from individual elastic sphere. The addition theorem of spherical wave function is used to perform the coordinates transform for the scattering waves from different spheres. The expansion coefficients of scattering waves are determined by the interface condition between the elastic spheres and the solid host. The scattering cross section is computed as numerical examples.

The scattering of particles with a small number of internal degrees of freedom is considered. Billiard formalism is used to study the scattering of two such structurally complex particles. The main scattering characteristics are found. Various types of scattering modes are revealed. In particular, a mode is detected when the velocity of motion of such particles away from each other is higher than their approach velocity before the collision. The scattering of such particles is shown to occur after a finite number of collisions. A generalized Newton law is proposed for the collision of particles with a small number of degrees of freedom, and the form of the effective coefficient of restitution is found.

Light scattering by particles located in a divergent beam is developed recently as a new method for particle size measurement, which has the characteristics of broadening the range of measurable particle sizes and reducing the requirements for experimental equipment system. In this paper, a theoretical model is presented which takes into account the refraction of the light while passing across the interfaces of the media. Analytical expression, based on the ray propagation, is deduced to describe the scattered light distribution on the detector. In the experimental parts, particle size distributions are extracted from the measurements by using the inverse algorithm. The experimental evidence shows that all the measurements give reasonable results on the particle size distribution. The results are insensitive to the parameters of the optical arrangement.

The study of cirrus clouds, which significantly affect the climate, is carried out using lidars. Interpretation of the lidar data is based on the direct solution of the problem of light scattering by particles of crystal clouds. Optical characteristics of perfect ice hexagonal columns, obtained previously, poorly agree with the lidar observation results. The work describes calculations of the optical characteristics of irregular hexagonal ice columns, which are in a good agreement with the experimental results. The calculations for particles with deformation of a dihedral angle of 90° are presented. It is shown that the logarithm of the scattering matrix can be linearly approximated well by the logarithm of the particle size. This can significantly accelerate the calculations of the optical characteristics of clouds. It is ascertained that the optical characteristics are in a good agreement with the lidar observation results throughout the range of sizes calculated even at deformation angles of a few degrees.

Angle-resolved Mueller matrix element from unpolarized light scattering by micro-bubble in water is simulated using Mie scattering and discrete dipole approximation (DDA) method. This element of Mueller matrix can be used to determine the scattered light intensity to study the possibility of distinguishing the size of micro-bubble. The scattering of unpolarized light beam is simulated for three various wavelengths, 425, 625, and 825 nm. We consider the micro-bubbles sphere 1 - 10 μm with relative refractive indices to water as medium 0.75. The The result show that both Mie and DDA scattering simulation produce similar result and the result shows promising potential of using light scattering to distinguish and measure the micro-bubble sphere diameter size. Clear distinction is shown for 60 – 80 degree of detection angle.

In order to analyze the scattering characteristics of suspended particles in water, a detail research about the intensity distribution of scattering light based on T-matrix theory is presented in this paper. Two kinds of suspended particles: alga and sands are taken into consideration and three kinds of non-spheroid shape model: spheroid, finite circular cylinder and generalized Chebyshev are simulated. The relationship between intensity of scattering light and scattering angle, complex refractive index of suspended particle, wavelength of incident light, size, etc. are calculated. Numerical results show that most scattering light mainly focus on the forward direction and there is a decreasing trend with the increase of scattering angle and wavelength. And when the particles size and the wavelength of incident light changes, the scattered light intensity is significantly changed accordingly for all shape models.

[EN] Cosmic dust particles are mostly responsible for polarization of the light that we observe from astrophysical objects. They also lead to color-extinction, thermal re-emission and other scattering related phenomena. Micrometric dust particles are often made of smaller constituent (nanometric grains). They are characterized by their size (average radius), chemical composition and morphology (including porosity). In the present work, we address the question of the role of the dust particle porosity on light polarization and color, using Discrete Dipole Approximation (DDA) light scattering code. To this purpose, we develop an algorithm to generate dust particles of arbitrary values of porosity. In brief, starting from a compact spherical ensemble of dipoles,randomly the dipoles are removed one by one, such that the remaining dipoles remain connected within their neighbours. We stop the removal process when the desired porosity is obtained. Then we compute and study the optical properties of the porous dust particle. The main objective of this paper is to develop a tool to generate dust particles with an arbitrary value of porosity and to study the effect of porosity on their light scattering properties. As a possible application, we simulate cometary polarization and color values which grossly match with the observed ones for the comet 1P/Halley, leaving scope for future work., R.B. thanks the Assam University, Silchar, for hospitality in the framework of 'Global Initiative for Academic Network' (GIAN) programme from MHRD, April 2016. The authors AKS and RV thank Erasmus Mundus - NAMASTE programme for funds to do this collaborative work. Finally, we are thankful to anonymous referees of this paper, due to whose comments we believe the quality of paper has improved.

The effect of ice crystal surface roughness on light scattering by ice crystals which are large compared to the wavelength was studied, in particular changes to the 2D scattering patterns, azimuthally averaged phase functions, degree of linear polarisation patterns and asymmetry parameters for a range of orientations and roughness scales. It was found that roughness has an effect on light scattering by hexagonal prisms, particularly when the roughness features are of comparable size to the wavelength. The roughness model that has the most effect on light scattering takes account of more than one roughness scale. Rough geometry was implemented by a Gaussian roughness method that took roughness parameters derived from sand grains, which have been reported to be suitable proxies for rough ice crystals. Light scattering data for these geometries was computed using the ADDA discrete dipole approximation method.

Dielectric-plasmonic composite media are interesting systems as far as light trapping is considered owing to their enhanced interaction with light. Core-shell particles are of particular interest due to their strong scattering and geometry-dependent plasmon resonances which are tunable from visible to IR region. Design of random media with such highly scattering particles increases the probability of light getting trapped inside the medium due to the enhanced multiple scattering. Here we investigate the light scattering scenario in ZnS-Au core-shell random medium experimentally and also provide theoretical basis using Finite Difference Time Domain (FDTD) simulations. Back scattering and transmission simulations are carried out at standard wavelengths 405, 445, 532 and 632 nm. Effect of geometry on light scattering is also investigated by varying the aspect ratios of the particles. Scattering and absorption efficiency is calculated for particles in this size range using Mie theory. Strength and tunability of plasmon resonances are explained in terms of plasmon hybridization model. Core shell particles with core radius 100 nm and shell thickness of 6 nm are found to be optimal for light trapping over the entire visible region. Dielectric-plasmonic random media consisting of ZnS-Au core shell particles with optimized aspect ratio appear to be efficient candidate materials for light harvesting, sensing and optoelectronics.

The discrete dipole approximation (DDA) is a general method to simulate light scattering by arbitrary particles. This talk reviews the DDA with focus on its application to very large particle systems, typically consisting of large numbers of particles with sizes comparable to or larger than the wavelength. Overall, the DDA is a viable option for such problems - it is conceptually simple, can naturally handle arbitrary inhomogeneous particles, and benefits from the availability of open-source codes. However, the major limitation is the computational complexity rapidly increasing with the size of the system. A few ideas to alleviate this issue are discussed, including the fast multipole method and the multi-grid DDA. While the DDA is equally applicable to both connected and disconnected particle systems, when applied to the latter it provides some insights into the notion of multiple scattering.

Starting from radiative transport theory, analytical and numerical methods are discussed that allow a quantification of light scattering properties from different experimental approaches. Several examples for the elucidation of, e.g. particle size, by application of Mie theory under consideration of dependent scattering effects and potential applications for chemical process monitoring are given.

By means of numerical solutions of Maxwell’s equations, we model the complex light scattering phenomenon. Light propagation through scattering medium is a deterministic process; with specific amplitude and phase, light can propagate to the target position via multiple scattering. By means of numerical solutions of Maxwell’s equations, the complex light scattering phenomenon can be accurately analyzed. The reported simulation enables qualitative and quantitative analyses of the effectiveness of directing light through turbid media to a targeted position