Young's interference in light scattering by spheres

Young's interference pattern was observed in laser light scattering by spheres on the backside of a glass plate, but not on the frontside of the substrate. This was because that former method eliminated or reduced the influence of light scattering from a substrate on interference fringes. Young's interference makes the prediction of integrated scattering cross section of spheres complicated for the case of high number density of deposited particles. A modified Bohbert-Vlieger model that takes interference effect into consideration is proposed. Analysis shows that this model is reasonable to describe light scattering cross section of spheres.     

溶剂密度对β胡萝卜素拉曼散射截面的影响

测量了含有9个CC共轭双键的链状多烯类生物分子β胡萝卜素在9种溶剂中的紫外—可见吸收和拉曼光谱.结果表明,β胡萝卜素C—C,CC键拉曼散射截面随溶剂体密度增加而线性增加,其机理是β胡萝卜素分子在体密度大的溶剂中受浮动干扰小,分子结构有序性高,π电子离域扩展,产生强的相干弱阻尼CC键振动,而产生大的拉曼散射截面.密度对分子拉曼散射截面影响研究还没见过报道,本文为多烯类链状分子的光散射理论研究提供了实验线索,也对多烯类链状分子性能研究及光电器件研制有参考价值. 关键词： 拉曼散射截面 多烯分子 吸收光谱 分子结构有序     

Elastic light scattering by semiconductor quantum dots of arbitrary shape

Elastic light scattering by low-dimensional quantum objects without a change in the frequency is theoretically investigated in terms of the quantum perturbation theory. The differential cross section of resonance light scattering from any excitons in any quantum dots is calculated. It is demonstrated that, when the light wavelengths considerably exceed the quantum-dot size, the polarization and angular distribution of the scattered light do not depend on the shape, the size, or the configuration of quantum dots. In this case, the total light scattering cross section is independent of the quantum-dot size. If the radiative damping of an exciton exceeds the nonradiative damping, the total light scattering cross section at resonance is of the order of the light wavelength squared. The radiative damping associated with the long-range exchange interaction between electrons and holes is calculated for any excitons and any quantum dots.     

Estimation of Velocities and Energy Densities of GHz Domain Shear Fluxes Propagating in Sapphire by Brillouin Scattering Technique

Energy densities and velocities of GHz domain shear fluxes in sapphire were estimated using the Brillouin scattering theory. The Brillouin scattering cross section was calculated from sapphire’s material parameters. The experiment was done using CdS domain shear fluxes. Direct contact was used to mirror surfaces of the CdS and the sapphire. Injection efficiency of shear fluxes ranging from 0.2 GHz to 1.1 GHz into the sapphire from CdS was measured by this method. In addition, energy density distributions of domain fluxes in the sapphire were estimated from scattering light intensities by employing the scattering cross section of the sapphire.     

Influence of entropy-fluctuation on the Rayleigh spectrum

We discuss the light scattering cross section due to entropy-fluctuation on the region of the central peak of the spectrum. A back-scattering oblique incidence geometry is used in our theoretical calculations which are based on the linear response function approach. Our results show that the power spectrum varies significantly with the incident angle and frequency and so does the light scattering cross section. The results are illustrated with numerical calculations for silicon.Work partially supported by the Brazilian Research Agencies CNPq and FINEP     

Direct Detection of Dark Matter with Resonant Annihilation

In the scenario where the dark matter (DM) particles χχ pair annihilate through a resonance particle R, the constraint from DM relic density makes the corresponding cross section for DM-nuclei elastic scattering extremely small, and can be below the neutrino background induced by the coherent neutrino-nuclei scattering, which makes the DM particle beyond the reach of the conventional DM direct detection experiments. We present an improved analytical calculation of the DM relic density in the case of resonant DM annihilation for s- and p-wave cases and invesitgate the condition for the DM-nuclei scattering cross section to be above the neutrino background. We show that in Higgs-portal type models, for DM particles with s-wave annihilation, the spin-independent DM-nucleus scattering cross section is proportional to Γ_R/m_R, the ratio of the decay width and the mass of R. For a typical DM particle mass ～50 GeV, the condition leads to Γ_R/m_R ≥O(10^-4). In p-wave annihilation case, the spin-independent scattering cross section is insensitive to Γ_R/m_R, and is always above the neutrino background, as long as the DM particle is lighter than the top quark. The real singlet DM model is discussed as a concrete example.     

Spectral power determinations of compressibility and density variations in model media and calf liver using ultrasound

A model of scattering is used to relate average differential scattering cross section and power spectra of scattering medium variations. The model expresses the average differential scattering cross section as a sum of the power spectrum of medium compressibility variations, the power spectrum of density variations weighted by the square of the cosine of the scattering angle, and the cross-power spectrum of compressibility and density variations weighted by twice the cosine of the scattering angle. Known values of the average differential scattering cross section at a minimum of three different scattering angles and temporal frequencies corresponding to the same spatial frequency are used to calculate each of the three power spectra. Since noise and statistical fluctuations are present in actual measurements of average differential scattering cross section, the calculations of power spectra are obtained from an overdetermined set of equations to which a solution is found by using a singular value decomposition. Data derived from a model for scattering from a cloud of correlated particles are employed to show the influence of additive noise. Calculations are also made from measurements of scattering from three suspensions of particles that have a different average radius in each suspension but are similarly modeled by scattering from a cloud. Additionally, the calculations are applied to measurements of average differential scattering cross section of calf liver. The results show that determination of the power spectra of scattering medium variations can be made under practical conditions, and also imply that density variations contribute significantly to scattering by calf liver.     

Theory of scattering of electromagnetic waves of the microwave range in a turbid medium

The coefficient of extinction of electromagnetic waves of the microwave range due to their scattering from clusters suspended in an amorphous medium and responsible for turbidity is calculated. Turbidity resembles the case when butter clusters transform water into milk. In the case under investigation, the clusters are conductors (metallic or semiconducting). The extinction coefficient is connected in a familiar way with the cross section of light scattering from an individual cluster. A new formula is derived for the light scattering cross section in the case when damping of oscillations of an electron is due only to spontaneous emission of light quanta. In this case, the resonant scattering cross section for light can be very large. It is shown that this can be observed only in a whisker nanocluster. In addition, the phonon energy on a whisker segment must be higher than the photon energy, which is close to the spacing between the electron energy levels in the cluster.     

Electron-induced scattering dynamics of Boron,Aluminium and Gallium trihalides in the intermediate energy domain

This article is focused on the calculation of electron-induced ionisation and total scattering cross sections by Boron, Aluminium and Gallium trihalide molecules in the intermediate energy domain. The computational formalism, spherical complex optical potential has been employed for the study of these two scattering cross sections. The ionisation cross section has been derived from the inelastic cross section using a semi-empirical method called complex scattering potential-ionisation contribution (CSP-ic) method. We have also calculated the ionisation cross section using the BEB theory with Hartree–Fock and density functional theory (DFT- ωB97XD) orbitals so that a comparison can be made with the cross sections predicted by CSP-ic method. For this theoretical study, we have also calculated polarisability and bond length of some targets which were not found in literature using DFT/B3LYP in Gaussian 09 software.     

颗粒溶液颗粒尺寸及浓度的差分偏振弹性散射光谱在线分析方法

偏振弹性散射光谱技术的基本原理为在偏振光入射条件下,根据出射光的偏振特性不同可以筛选出浅表层组织的单次散射光信息和深层组织的漫散射光信息。该研究的创新点在于将这种方法应用于颗粒溶液检测,目的是在颗粒溶液原始状态下实现对颗粒尺寸及浓度的同时检测。设计了一个共轴笼式光学系统,测量了聚苯乙烯微球颗粒溶液某一角度的背向散射信号,通过控制入射端和收集端偏振片的偏振方向获得了颗粒溶液的偏振平行光谱与偏振垂直光谱,两者之差即偏振差分光谱对应颗粒的单次散射信息,将该单次散射信息与Mie散射数据库进行比对获得颗粒的尺寸,然后在颗粒尺寸作为已知的条件下进一步分析偏振垂直光谱,将该垂直光谱对应的颗粒溶液的漫散射信息代入光漫散射下的近似表达式拟合得到颗粒的浓度信息。将实验结果与样品提供值进行了比对,并进一步分析了在获取颗粒数浓度时,颗粒直径的方差分布对结果的影响,最终验证了该实验方法的可行性。该方法的潜在应用包括对标准颗粒制造厂商的产品在线检测以及对牛奶制品中脂肪和蛋白质的浓度检测研究。     

Monte Carlo simulation of elastic and quasielastic nucleus-nucleus scattering

The amplitude of elastic nucleus-nucleus scattering is calculated in framework of the multiple scattering theory. We consider the dependence of the amplitude on slope and cross section ofNN scattering, and on nuclear matter density. The results are compared to approximate calculations. The total inelastic nucleus-nucleus cross sections as well as the cross sections of quasielastic processes are calculated. Predictions are given for the case of superhigh energies.     

Analytical techniques for addressing forward and inverse problems of light scattering by irregularly shaped particles

Understanding light scattering by nonspherical particles is crucial in modeling the transport of light in realistic structures such as biological tissues. We report the application of novel analytical approaches based on modified Wentzel-Kramers-Brillouin and equiphase-sphere methods that facilitate accurate characterization of light scattering by a wide range of irregularly shaped dielectric particles. We also demonstrate that these approaches have the potential to address the inverse-scattering problem by means of a spectral analysis of the total scattering cross section of arbitrarily shaped particles.     

Theory of interband and intraband light scattering in semiconductors in an external electric field

A theory is developed for interband and intraband light scattering in semiconductors in an external electric field. Explicit results are given for a simple two-band model. The field induced change of the interband scattering cross section shows oscillation close to the scattering edge. Intraband scattering being approximately elastic without an external electric field becomes inelastic in the presence of the field. A numerical estimation of the field influence on the scattering cross section is given in both cases.     

Cross photoelastic and thermorefractive light scattering in continuous media

Two additional types of light scattering in continuous media are considered. One is the cross photoelastic scattering from density fluctuations caused by thermodynamic temperature fluctuations and the other is the cross thermorefractive scattering from temperature fluctuations caused by density fluctuations, which manifest themselves in propagation of elastic sound waves. Expressions for the light scattering coefficients for these two types of scattering are obtained. The integral intensities of scattered light are shown to be comparable with the well-known integral intensities of light scattering by fluctuations of density (pressure) and temperature (entropy) for some substances.     

基于Mie散射理论的铌酸锂晶粒散射特性

基于Mie散射理论,对铌酸锂晶粒光散射特性进行了理论分析与数值计算,得到了散射强度分布、偏振度与散射角、散射强度与粒子尺寸参数,以及光学截面与粒子半径的关系。研究表明:前向散射占优势,并随粒子半径的增大而增强;当粒子半径为0.1 μm 左右,散射截面和吸收截面达到最大值。     

The effect of a layer of varying density on spatial correlation of sea-bottom backscattering signal

The research is about the effect of a layer of varying density of sea-bottom sediments on spatial correlation of sea-bottom backscattering.The relationship between scattering cross section and spatial correlation is that backscattering cross section decreases quickly and the spatial correlation becomes stronger as the incident angle increases.Therefore,the densitydepth profile is introduced into sea-bottom high-frequency backscattering echo model,which is used to simulate sea-bottom backscattering and calculate the function of spatial correlation.The influence of the density gradient on spatial correlation of sea-bottom backscattering is investigated by analyzing the relations between vertical gradient of density and the scattering cross section.As can be seen from the simulation results,the impact of the density gradient on the spatial correlation is found more significant.While the density gradient increases,the scattering cross-section and the radius of the spatial correlation broaden,the spatial correlation becomes stronger.At the same time,the scattering cross-section decreases more quickly as the incident angle increases.     

Theory of indirect resonant inelastic X-ray scattering

We express the cross section for indirect resonant inelastic X-ray scattering in terms of an intrinsic dynamic correlation function of the system that is studied with this technique. The cross section is a linear combination of the charge response function and the dynamic longitudinal spin density correlation function. This result is asymptotically exact for both strong and weak local core-hole potentials. We show that one can change the relative charge and spin contribution to the inelastic spectral weight by varying the incident photon energy.     

Correlation effects in electron-ion collisions in a strong laser field

We examine elastic and inelastic scattering of electrons by ions in intense laser light. A method of numerical investigation of the scattering characteristics based on regularizing the Coulomb singularity is proposed. We show that over a broad range of parameter values the transport scattering cross section is weakly dependent on the intensity of the high-frequency field. We detect a significant modification of the dependence of the effective inelastic scattering cross section. We also show that the energy exchange with the field is determined by a fairly small group of electrons, called the representative electrons. Finally, we propose a qualitative model that explains our results by the fact that the leading contribution is provided by inelastic collisions of electrons with relatively small impact parameters traversing the region important for the interaction at large angles. Zh. éksp. Teor. Fiz. 115, 463–478 (February 1999)     

Effect of finite terms on the truncation error of Mie series

The finite sum of the squares of the Mie coefficients is very useful for addressing problems of classical light scattering. An approximate formula available in the literature, and still in use today, has been developed to determine a priori the number of the most significant terms needed to evaluate the scattering cross section. Here, we obtain an improved formula, which includes the number of terms needed for determining the scattering cross section within a prescribed relative error. This is accomplished using extended precision computation for a wide range of commonly used size parameters and indices of refraction. The revised formula for the finite number of terms can be a promising and valuable approach for efficient modeling light scattering phenomena.