Light scattering in a finite multi-particle system

We use the discrete dipole approximation (DDA) to perform electromagnetic scattering calculations of particles in a 3D volume. We adjust the spacing between the particles to change the volume densities of the scattering systems from approximately 10% to 100%. For very large volume densities, e.g. >50%, it is difficult to assign unambiguously whether the system is composed of a single heterogeneous particle or of multiple particles. Our calculations demonstrate optical effects attributable to multiple scattering in systems having volume densities as high as ～90%. This suggests that heterogeneities within naturally occurring particle systems can produce multiple-scattering effects. We also see evidence of very deep negative polarization branches (NPBs) (～?6%) that may have implications in interpreting polarization phase curves of cometary circumnuclear halos.     

Highly sensitive multiple fano resonances excitation on all-dielectric metastructure

Optical Review - A multi-Fano resonances optical refractive sensor with high sensitivity and sharp Fano resonances is proposed in this paper. The unit cell of the designed structure consists of two...     

Light scattering by a finite cylinder containing a spherical cavity using Sh-matrices

We use the Sh-matrix formalism that contains the shape-dependent parameters of the T-matrix to derive an analytical solution for the light scattering from a finite cylinder containing a spherical cavity. The integral expressions for the Sh-matrix elements are simpler than those of the T-matrix elements and the case of a sphere embedded in a finite cylinder these integrals can be solved analytically.     

Optical fano resonances in photonic crystal slabs near diffraction threshold anomalies

Optical Fano resonances due to resonant eigenmodes in a layered periodically-modulated structure (photonic crystal slab) are investigated theoretically. The special attention is focused on the behavior of the resonances near a diffraction threshold. A new formulation of the resonant mode approximation for the optical scattering matrix near the diffraction threshold anomalies is proposed.     

Light scattering study of surface plasmon resonances in very thin silver films

The surface plasmon modes of Ag thin films were studied by the light scattering method in the thickness range down to 100 Å. The observed thickness dependence of the resonance peaks was analysed in detail by the theory of Kretschmann. It is shown that the coupled surface plasmon modes in the very thin films can be detected only in modified forms by the light scattering experiment.     

Bound states and scattering resonances induced by spatially modulated interactions

We study the two-body problem with a spatially modulated interaction potential using a two-channel model, in which the interchannel coupling is provided by an optical standing wave and its strength modulates periodically in space. As the modulation amplitudes increase, there will appear a sequence of bound states. Part of them will cause a divergence of the effective scattering length, defined through the phase shift in the asymptotic behavior of scattering states. We also discuss how the local scattering length, defined through short-range behavior of scattering states, modulates spatially in different regimes. These results provide a theoretical guideline for a new control technique in the cold atom toolbox, in particular, for alkaline-earth(-like) atoms where the inelastic loss is small.     

Theoretical investigation of giant resonances by inelastic proton scattering

A fully microscopic, antisymmetrized DWBA analysis of (p, p') spectra in the giant resonance region of ¹⁶O, ⁴⁰Ca and ²⁰⁸Pb is presented. The nuclear structure information is derived from RPA wave functions calculated in large configuration spaces. The theoretical spectra are in general in agreement with the experimental results. A new interpretation follows from our. investigation for the spectrum of the giant dipole region in the heavy nuclei: This resonance structure is mainly due to the breathing mode, whereas the electric dipole contribution is much smaller.     

Light scattering by needle-type and disk-type particles

A powerful tool to analyze light scattering by 3D arbitrary-shaped homogeneous or inhomogeneous obstacles located in free space is based on volume integral equation. In this paper we apply a weak form of volume integral equation to simulate light scattering by needle- and disk-type particles such as straight and curved cylinders, cylindrical plate and hexagonal prism with high aspect ratio and low and high values of refractive indexes. For problems where discrete sources method could be applied, we calculated differential scattering cross-section using both methods and got excellent agreement in results.     

Above barrier Dirac multiple scattering and resonances

We extend an above barrier analysis made with the Schrödinger equation to the Dirac equation. We demonstrate the perfect agreement between the barrier results and back to back steps. This implies the existence of multiple (indeed infinite) reflected and transmitted wave packets. These packets may be well separated in space or partially overlap. In the latter case interference effects can occur. For the extreme case of total overlap we encounter resonances. The conditions under which resonance phenomena can be observed is discussed and illustrated by numerical calculations.     

Light scattering by complex ice-analogue crystals

Angle-dependent light-scattering measurements on single ice analogues crystals are described. Phase functions and degree of linear polarization are measured for electrodynamically levitated crystals. A procedure for randomizing particle orientation during levitation is demonstrated. The dependence of scattering on the shape, complexity and surface roughness of the crystals is examined. The phase functions from complex crystals with smooth surfaces show little dependence on shape. There is close agreement between the measured functions and the analytic phase function for ice clouds. However, rosettes with rough surfaces have qualitatively different phase functions, with raised side and back scattering. The asymmetry parameter is typically about 0.8±0.04 and 0.63±0.05 for smooth and rough crystals, respectively. The 22° halo peak is present for smooth rosettes and aggregates but absent for rough rosettes. Two-dimensional scattering patterns from several crystals in fixed orientations are also shown. The results suggest that it may be possible to use such patterns to discriminate not only between crystals of different shape but also to obtain some information on surface properties.     

长柱状气溶胶粒子的光散射特性

以中纬度卷云中常见的长柱状冰晶为例,利用长柱状粒子光散射理论,探讨了入射光为线偏振时,电矢量平行和垂直于入射面情况下,单个长柱状粒子的散射光强度分布和偏振特性随入射角、尺度参数与偏振态的转化关系:随着入射角的增大,散射强度、偏振总体趋于对称且数值振荡频率降低,散射强度总体减小,偏振的改变程度总体增大;随着尺度参数的增大,散射强度、偏振的数值振荡频率增大,散射强度数值振荡峰的幅度整体减小,电矢量平行于粒子长轴时主偏振的数量、强度和位置皆有变迁,电矢量垂直于粒子长轴时前后主偏振位置相对固定;随着偏振度的减小,散射强度、偏振趋向于一致,两者的数值改变程度减小,当偏振度减小到0时,散射强度、偏振变得完全相同。选取火山尘埃和烟灰与冰晶对比,阐述了粒子散射光的强度分布和偏振特性随折射率的变化规律:折射率虚部不改变散射强度的整体趋势,但使散射强度和偏振的振荡峰幅度增大,当其数值较大时,使得偏振的数值振荡峰覆盖范围拓宽。     

Light scattering by axisymmetric multilayer particles

A new recursive algorithm for solving the problem of scattering a plane electromagnetic wave by axisymmetric dielectric multilayer particles is constructed. The approach that was proposed earlier and demonstrated for uniform axisymmetric particles is used. It has the following basic features: (1) the fields are represented in the form of a sum of two terms, one of which is independent of the azimuthal angle, whereas averaging of the second term over this angle gives zero; (2) the axisymmetric problem is solved by using the scalar potentials related to the azimuthal components of electromagnetic fields; and (3) the non-axisymmetric problem is solved by using the superposition of Debye potentials and vertical components of the magnetic and electric Hertz vectors. It is of principal importance for the solution proposed here that the scattering problem is formulated in the form of surface integral equations in these scalar potentials, which are represented in the form of expansions in wave spherical functions. Infinite systems of linear algebraic equations for unknown expansion coefficients are obtained, which are rather simple in structure. The reduced systems for multilayer particles have the same dimension as the systems for identical uniform particles. In the case of multilayer spherical particles, the algorithm gives an explicit solution to the problem, and the dependence on the radial spherical functions for the layers is specified in terms of the derivative of the logarithm (i.e., the ratio of the derivative to the function itself) and the ratio of the functions of neighboring layers. Numerical calculations demonstrated the high efficiency of the algorithm.     

Light absorption and scattering by a photolayer with closely packed particles

Light absorption and scattering by weakly absorbing layers of close-packed fine-grained silver halide particles was studied. Absorption characteristics of an elementary volume and a photolayer were found to have a nonlinear and nonmonotonic dependence on the concentration. Qualitative specific features of this dependence in the range of medium values of volume concentrations from 0.4 to 0.8 were expressed by an empirical formula. The average cosine of the depth brightness diagram and the probability of photon survival Λ in a concentrated photolayer were calculated. The analysis of changes in Λ in a close-packed medium in a more general case, irrespective of the size and the degree of absorption of particles, was carried out. A conclusion was made concerning the character of changes in the scattering indicatrix of a photolayer caused by an increase of its density.     

Radiation scattering by finite dielectric cyclinders

The volumetric integral equation formalism (VIEF) is used to determine characteristics of scattering of radiation falling along the axis of dielectric cylinders that scatter the radiation. The spectral dependence of the extinction efficiency factor Q is studied with changes in the length l of the cylinder (300–2200 nm), its width d (100–300 nm), and the refraction index m (1.33–1.65). In the range of angles θ=0–180°, for a cylinder with l=700 nm, d=100 nm, and m=1.33, angular intensity distribution functions i_i and i₂ are calculated for the components of the scattered radiation that are polarized perpendicular and parallel to the plane of observation, respectively. No effect of scattered-radiation depolarization is found. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 2, pp. 256–260, March–April, 1998.     

Light scattering by extraordinarily polarized polaritons

The objective of this work is to investigate how the anisotropy of the interaction between dipole-active vibrations of a crystal lattice and infrared electromagnetic waves is manifested in the spontaneous parametric light scattering spectra of polaritons (Raman scattering by small angles). The case where scattering occurs by extraordinarily polarized polaritons—quasiparticles formed as a result of the coupling of the wave polarized in the symmetry plane of a biaxial crystal simultaneously with two phonons possessing orthogonal dipolar moments—is studied. A series of spectra of equilibrium fluctuations of the electromagnetic (infrared) field, each of which represents an intensity distribution in frequency-wave number coordinates for a fixed direction of the wave vector, are constructed on the basis of a scattering model that takes account of the tensor character of the permittivity and the quadratic and cubic susceptibilities of the crystal. Analysis of the computed spectra identified the basic laws and dependences which are determined by the anisotropy of the electromagnetic susceptibilities of various orders and made it possible to explain previous experimental results which cannot be interpreted on the basis of the generally accepted model of transversely polarized polaritons. A method is proposed for determining the contributions of the dipole-active vibrations of the crystal lattice to the permittivity and the quadratic and cubic susceptibilities, as well as the absorption of the material from the spectra of the extraordinarily polarized polaritons.