Inelastic scattering on spherical microparticles with inclusions

The subject of the paper is scattering at spherical microparticles with inclusions. The inclusions are represented as dipoles for both elastic and inelastic scattering. For elastic scattering the dipoles are computed iteratively, and sequence transformations are used to accelerate this iteration. Mie theory is used to calculate the cross sections for scattering on spherical microparticles with inclusions as well as on agglomerates.     

KDP晶体缺陷形成机理的研究

采用激光散射层析术及 X 射线形貌术研究了 KDP(KH_2PO_4)晶体中散射颗粒及位错等缺陷的形成机理。作者采用微分干涉衬差显微镜(DICM)装置、通过录相放大系统观察研究了晶体生长过程中有机和无机固态包杂物的成因。     

Effective medium theories for irregular fluffy structures: aggregation of small particles

The extinction efficiencies as well as the scattering properties of particles of different porosity are studied. Calculations are performed for porous pseudospheres with small size (Rayleigh) inclusions using the discrete dipole approximation. Five refractive indices of materials covering the range from 1.20+0.00i to 1.75+0.58i were selected. They correspond to biological particles, dirty ice, silicate, and amorphous carbon and soot in the visual part of the spectrum. We attempt to describe the optical properties of such particles using Lorenz-Mie theory and a refractive index found from some effective medium theory (EMT) assuming the particle is homogeneous. We refer to this as the effective model. It is found that the deviations are minimal when utilizing the EMT based on the Bruggeman mixing rule. Usually the deviations in the extinction factor do not exceed approximately 5% for particle porosity P = 0 - 0.9 and size parameters x(porous) = 2 pi r(s,porous)/lambda < or approximately = 25. The deviations are larger for scattering and absorption efficiencies and smaller for particle albedo and the asymmetry parameter. Our calculations made for spheroids confirm these conclusions. Preliminary consideration shows that the effective model represents the intensity and polarization of radiation scattered by fluffy aggregates quite well. Thus the effective models of spherical and nonspherical particles can be used to significantly simplify the computations of the optical properties of aggregates containing only Rayleigh inclusions.     

CdSiP2晶体中光散射颗粒的研究

采用单温区法合成了CdSiP₂ (CSP)多晶原料, 然后采用垂直布里奇曼法生长了大尺寸的CSP单晶。采用扫描电子显微镜、EDS对晶体中光散射颗粒的尺寸、形貌和成分进行了观察和检测。测试结果表明, 所生长的CSP晶体中的光散射颗粒呈近椭圆形, 尺寸为2~8 μm, 主要成分为Si, 含量占88%以上。对CSP多晶合成的反应机理研究表明, 此第二相颗粒是由于合成时多晶料中残留有少量未反应的Si单质所致。通过合成工艺的改进, 有效地减少了晶体中Si散射颗粒的残留, 制备出了高透明性的CSP单晶体。     

Quantitative light-scattering angular correlations of conglomerate particles

A quantitative analysis of the fluctuations in the scattering associated with micrometer-size glycerol droplets that contain spherical latex inclusions are performed. Scattering intensities at two angles (the near-forward and the near-backward directions) are measured as functions of time. We analyze these signals using two techniques. We find that calculated autocorrelation time constants associated with these signals are not consistent with current models based on interference of light scattering from latex inclusions that exhibit Stokes-Einstein diffusion. The intensity fluctuations at different scattering angles display extended periods of both positive and negative correlations with characteristic time constants of the order of seconds. The time constants associated with the cross correlations provide information on the physical parameters of the inclusions.     

Qualitative light-scattering angular correlations of conglomerate particles

The scattering phase functions of micrometer-sized glycerol droplets containing spherical latex inclusions undergo random fluctuations with time. We measure scattering intensities in the near-forward and near-backward scattering directions and find them to have strong positive correlations during some time periods and strong negative correlations during other time periods. The characteristic time constants of these correlations are of the order of seconds. We calculate scattering correlations from two types of scattering system. Correlations from a two-sphere system generally are positive, whereas correlations from a sphere containing a single spherical inclusion may be both positive and negative. Calculations of correlations from our experimental data are consistent with diffusion of inclusions within the host droplet, rather than interference effects between the inclusions.     

Elastodynamic response of a coplanar periodic layer of elastic spherical inclusions

Reflection and transmission spectra of a plane longitudinal wave normally incident on a coplanar periodic array of identical spherical elastic inclusions in a solid (polyester) matrix are measured at wavelengths that are comparable to the inter-particle distance. These spectra exhibit pronounced Wood's anomalies i.e., a sharp variations in amplitude at the onset of a shear wave diffraction order as well as a drop in the transmission and a corresponding maximum in the reflection coefficients due to an enhancement of the resonance of the particles (for the case reported herein, this is the rigid body translational “dipole” resonance). An approximate low frequency (ka<1) self-consistent model is developed in which multiple scattering is explicitly taken into account by adding appropriate terms to the well-known solution for the scattering of a plane longitudinal wave by a single spherical particle in an unbounded matrix. The results of the numerical calculations show excellent agreement with the experimental data.     

Wear particles deposit formation on the polishing tool working surface

Based on the quantum-mechanical theory of scattering, the paper describes interaction between workpiece debris particles and tool wear particles in the contact zone in polishing. It is shown that the forward scattering of debris particles occurs mostly on the debris particles, and the probability of their scattering on wear particles is insignificant. The distribution function of the total cross-section of debris particles scattering along the radius of circular zones of the tool working surface has been determined together with coordinates of the deposit localization zone as well as approximate number and dimensions of the deposit fragments. The results of experimental verification of the theoretical calculations are given.     

Experimental test of a perturbation model for time-resolved imaging in diffusive media

We report what to our knowledge is a novel perturbation approach for time-resolved transmittance imaging in diffusive media, based on the diffusion approximation with extrapolated boundary conditions. The model relies on the method of Padé approximants and consists of a nonlinear approximation of time-resolved transmittance curves in the presence of an inclusion. The proposed model is intended to extend the range of applicability of perturbation models when applied to inclusions that are non-point-like. We test the model on different tissue phantoms with scattering only, absorbing only, and both scattering and absorbing inclusions. Maps of the optical properties are displayed, and the results are compared with those obtained by means of the usual linear approximation of time-resolved transmittance curves. We found that the nonlinear approach gives a better prediction for absolute values of the scattering and absorption coefficients of inclusions, when the inclusion optical properties are higher than the surrounding background. Furthermore, better-resolved spots and a reduced cross talk between the two parameters are found in the reconstructed maps. Because the range of the optical properties spanned by the considered phantoms covers the values expected for optical mammography, the application of the reported reconstruction method to in vivo images of a breast appears promising from a diagnostic viewpoint.     

Scattering of elastic waves by spherical inclusions with applications to low frequency wave propagation in composites

Scattering of plane elastic waves by a spherical inclusion is considered. A unified method of solution is presented which treats compressional and shear incidence on a similar basis. Explicit results are given for Rayleigh scattering. We apply the results of the single scattering problem to the propagation of low frequency waves in a composite containing a dilute concentration of spherical inclusions. Explicit formulae are given for the effective wave speeds and attenuations when the inclusions are voids. Both the compressional and shear wave speeds decrease initially as a function of frequency.     

Estimation of scattering error in spectrophotometric measurements of light absorption by aquatic particles from three-dimensional radiative transfer simulations

We present an approach based on three-dimensional Monte Carlo radiative transfer simulations for estimating scattering error in measurements of light absorption by aquatic particles with a typical laboratory double-beam spectrophotometer. The scattering error is calculated by combining the weighting function describing the angular distribution of photon losses that are due to scattering on suspended particles with the volume scattering function of particles. We applied this method to absorption measurements made on marine phytoplankton, a diatom Thalassiosira pseudonana and a cyanobacterium Synechococcus. Assuming that the scattering phase function is described by the Henyey-Greenstein formula, we determined the backscatter probability of phytoplankton, which yields the best correction for scattering error at a light wavelength of 750 nm, where true absorption is null. The backscattering ratio estimated for both phytoplankton species is significantly higher than previously reported data based on Mie-scattering calculations for homogeneous spheres. Depending on the type of particles, the corrected absorption spectra obtained with our method may be similar or significantly different from spectra obtained with the null-point correction based on wavelength-independent scattering error.     

Inclusion characterization in a scattering slab with time-resolved transmittance measurements: perturbation analysis

A procedure for the time-domain optical characterization of an inclusion in a scattering slab is investigated theoretically and experimentally. The method relies on the measurement of a contrast function, which is defined as the time-dependent relative change in the transmitted signal resulting from the presence of the inclusion. Analytical expressions for the contrast functions of absorptive and diffusive inclusions are obtained through a perturbation solution of the diffusion equation. This procedure is used successfully to determine the optical properties of absorptive, diffusive, and mixed inclusions located at midplane in a scattering slab by use of time-resolved transmittance measurements.     

The influence of tool wear particles scattering in the contact zone on the workpiece surface microprofile formation in polishing quartz

The paper describes the interaction and scattering of wear particles in the tool-workpiece contact zone in the course of polishing and explains the oscillatory structure of scatter of the tool wear particles on debris particles and on wear particles. The differential cross-section of scattering of the wear particles on the debris particles as well as on the wear particles is shown to be maximum in the case of forward scattering on the central segments of the contact zone. We have calculated the coordinate dependence of the differential cross-section of scattering of tool wear particles and the dependence of the polished surface microprofile height on the radius of circular zones. The theoretical curve of polished surface profile microirregularities is shown to fit well the experimental one for a quartz workpiece.     

A Modified Born Approximation for Scattering in Isotropic and Anisotropic Elastic Solids

A new modified Born approximation (MBA) is presented that significantly extends the range of validity of the Born approximation to include the pulse-echo responses of strongly scattering inclusions in an elastic solid. The MBA also improves on the doubly distorted Born approximation (DDBA), a similar modification of the Born approximation that has been recently developed. These improvements are demonstrated by comparing the MBA, the Born approximation and the DDBA with the exact separation of variables solution for spherical inclusions in isotropic media. Furthermore, it is shown that the form of the MBA remains valid even for the pulse-echo scattering of an anisotropic inclusion in a general anisotropic elastic medium so that it is potentially applicable to a wide class of flaws and materials.     

Fluorescence lifetime optical tomography in weakly scattering media in the presence of highly scattering inclusions

We consider the problem of fluorescence lifetime optical tomographic imaging in a weakly scattering medium in the presence of highly scattering inclusions. We suggest an approximation to the radiative transfer equation, which results from the assumption that the transport coefficient of the scattering media differs by an order of magnitude for weakly and highly scattering regions. The image reconstruction algorithm is based on the variational framework and employs angularly selective intensity measurements. We present numerical simulation of light scattering in a weakly scattering medium that embeds highly scattering objects. Our reconstruction algorithm is verified by recovering optical and fluorescent parameters from numerically simulated datasets.     

Mechanical anisotropy in the zirconia toughened alumina

The two kinds of the hydrothermally crystallised zirconia powders were used to toughen alumina matrix. The one composed of isometric crystallites of tetragonal symmetry, the other one of elongated monoclinic particles. In the sintered ZTA material either isometric or elongated particles form tetragonal disk shaped inclusions. Zirconia inclusions originating from the elongated particles tend to arrange crystallographically on the uniaxial compaction. This resulted in the material showing different ultrasonic wave velocity, Young modulus, crack lengths and fracture toughness along directions perpendicular and parallel to the compaction force. An explanation of this phenomenon is suggested. Zirconia inclusions originating from the powder composed of isometric crystallites lead to the material of isotropic mechanical properties.     

Rayleigh like scattering from silica–titania core-shell particles and their application in protection against harmful ultraviolet rays

In this article we report experimental and theoretical results of angle-dependent laser light scattering of nano titanium dioxide nucleated on silica particles. It was observed that the experimental scattering profile from nano-titania coated silica (TCS) particle resembles that of a Rayleigh scattering. It can be inferred from the light scattering profile that nucleating fine particles onto a surface of a bigger particle (core), the resulting scattering profile is dominated by the smaller particles. Thin film transmittance measurement of TCS particles also supports this claim. The theoretical scattering predictions do not match with the experimental findings and the reasons for the discrepancies are addressed. This Rayleigh-like scattering property of TCS particles can be used in cosmetic formulations as a replacement for nanoparticles to provide protection from harmful ultraviolet rays. This study helps to provide insights into these systems for their potential usage in cosmetics.     

Light-scattering intensity fluctuations in microdroplets containing inclusions

A prominent characteristic of the light scattered from a microparticle containing inclusions is a fluctuation in the intensity that is due to the changing positions of the inclusions with respect to each other and the host droplet. We calculate the magnitude of these fluctuations for a host sphere containing a single eccentrically located spherical inclusion and experimentally measure the fluctuation amplitudes for host spheres containing multiple inclusions. We find that, for sufficiently small single inclusions, the amplitude of the scattering fluctuations increases approximately linearly with the area of the inclusion. For multiple inclusions, the fluctuation amplitude increases with concentration with an approximate power-law dependence.     

Discrete-dipole-approximation-based light-scattering calculations for particles with a real refractive index smaller than unity

To assess the efficiency and accuracy of light-scattering calculations based on the discrete dipole approximation (DDA) for particles with a real relative refractive index smaller than unity, differential scattering cross sections and scattering efficiency factors were calculated for spherical particles. We performed the calculations for oxide particles and voids embedded in glass and silicon, using the exact scattering theory (Mie scattering) and the DDA. A comparison of the results shows that the DDA is applicable in the above refractive-index regime, and the conditions under which DDA-based calculations can provide scattering data with good accuracy are discussed.     

Effect of orienting fields on agglomeration in dilute dispersions of magnetic fine particles

Static light scattering was used to investigate dilute dispersions of fine gamma -Fe/sub 2/O/sub 3/ magnetic particles. The particles were acicular and on average 0.39 mu m long and 0.056 mu m in diameter. They were dispersed in organic solvents at concentrations of approximately 10/sup -4/ vol%, corresponding to an average interparticle separation of 9 mu m. Computer programs using a coupled dipole algorithm to predict the scattering from the particles were written. Experimental results do not agree with computer calculations of the light scattering from single particles, but are consistent with scattering from thick ropelike agglomerates of particles. The size of these agglomerates was estimated after 10 s to be less than 100 particles, while the thickness of the ropes is at least 5 particles.<>