Interaction of acoustic scatterers

The interaction of scatterers under steady-state acoustic irradiation is studied for the case of scatterers in the form of elliptic cylinders taken as an example. The angular scattering characteristics of two interacting cylinders are calculated and compared with the angular characteristics of a single cylinder in a wide frequency band and in a wide angular range of irradiation. The parameters of interacting bodies (the angle of irradiation, the size with respect to the wavelength, and the distance between the bodies) at which the interaction is negligibly small are determined.     

Extension of the generalized multipole technique to three-dimensional anisotropic scatterers

New expansions are derived for the simulation of three-dimensional anisotropic scatterers with the generalized multipole technique (GMT). This extension of the GMT makes possible the investigation of subtle phenomena such as the interaction of light with realistic crystals or magneto-optic materials.     

Condensation of interacting bosons in a random potential

We study the effects of random scatterers on the ground state of the one-dimensional Lieb-Liniger model of interacting bosons on the unit interval. We prove that, in the Gross-Pitaevskii limit, Bose Einstein condensation takes place in the whole parameter range considered. The character of the wave function of the condensate, however, depends in an essential way on the interplay between randomness and the strength of the two-body interaction. For low density of scatterers or strong interactions the wave function extends over the whole interval. High density of scatterers and weak interaction, on the other hand, leads to localization of the wave function in a fragmented subset of the unit interval.     

The reflection of ultrasound from partially contacting rough surfaces

Ultrasound is commonly used to detect and size cracks in a range of engineering components. Modeling techniques are well established for smooth and open cracks. However, real cracks are often rough (relative to the ultrasonic wavelength) and closed due to compressive stress. This paper describes an investigation into the combined effects of crack face roughness and closure on ultrasonic detectability. A contact model has been used to estimate the size and shape of scatterers (voids) at the interface of these rough surfaces when loaded. The response of such interfaces to excitation with a longitudinal ultrasonic pulse over a wide range of frequencies has been investigated. The interaction of ultrasound with this scattering interface is predicted using a finite-element model and good agreement with experiments on rough surfaces is shown. Results are shown for arrays of equi-sized scatterers and a distribution of scatterer sizes. It is shown that the response at high frequencies is dependent on the size, shape, and distribution of the scatterers. It is also shown that the finite-element results depart from the mass-spring model predictions when the product of wave number and scatterer half-width is greater than 0.4.     

T-matrix method for electromagnetic scattering from scatterers with complex structure

We describe a T-matrix program for light scattering calculations from particles with complex structure. The code treats the cases of homogeneous, layered and composite scatterers. These results are combined with basic results concerning the scattering by inhomogeneous scatterers and aggregates to apply to more general types of scatterers. Some numerical simulations are presented.     

光通过纳米颗粒随机散射体透射光强的计算及分析

光通过随机散射体后透射光强的估算,对于提取散射体内部无法直接测量或者无法直接观察的信息至关重要。在分析平行光束通过纳米圆形颗粒随机散射体出射面上光强组成的基础上推导了透射光强的计算公式,并指出多重散射理论、一阶多重散射理论和朗伯-比尔定律在一定近似程度上可以相对精确地估算透射光强。这三种方法的估算结果之间会出现四种相对关系。根据这些相对关系,分析了光在散射体内部传输时散射过程的特征以及各种散射过程对出射面光强的贡献大小。     

Ultraslow-light effects in symmetric and asymmetric waveguide structures with moon-like scatterers

Ultraslow-light effects in two-dimensional hexagonal-lattice coupled waveguide with moon-like scatterers were theoretically studied using the plane-wave expansion method. For symmetric structures, simulations showed that slow light with high group index can be achieved by shifting the scatterers and adjusting the radius of moon-like scatterers. The maximum group index was over 8:0 × 10⁴. For asymmetric structures, simulations showed that slow light with flat band and high group index can be obtained by shifting the scatterers, adjusting the radius of moon-like scatterers, and rotating the scatterers. The maximum group index was over 5:7 × 10⁵ with a “saddle-like” relationship between the frequency and group index.     

Light scattering by closely packed clusters: Shielding of particles by each other in the near field

Equations of the theory of light scattering by clusters (aggregates) of spherical particles are analyzed, and peculiarities of interaction of scatterers in the near field are discussed. It is shown that one of the manifestations of the near field is a mutual shielding of particles. For simple clusters consisting of two identical spherical particles (bisphere), the mutual shielding leads to a decrease in the intensity of light scattered along the axis of the bisphere. If the bispheres are small as compared to the wavelength, shielding is caused by electrostatic interaction of charges induced in the particles by the external field. Calculations of the intensity of light scattered by randomly oriented clusters of spherical particles show that for the model ignoring the near field the intensity is significantly larger than for the model with the near field taken into account.     

Application of 2D graded eye-shape scatterers for slow light effect in photonic crystal line defect waveguide

With operating frequency f = 1thz, two-dimensional (2D) graded eye-shape scatterers were firstly applied into photonic crystal waveguide (PCW) for slow light effect in two ways: (1) selecting group index n_g from 31.4 to 95.0, low-dispersion bandwidth (n_g varies within a 10% range) was got from 0.736 μm to 2.334 μm, and ultralow-dispersion bandwidth (n_g varies within a 1% range) was got from 0.438 μm to 0.945 μm by grading the eye-shape scatterers along the longitudinal direction; (2) selecting group index n_g from 32.1 to 98.3, low-dispersion bandwidth was got from 0.559 μm to 1.765 μm, and ultralow-dispersion bandwidth was got from 0.296 μm to 0.661 μm by grading the eye-shape scatterers along the transverse direction. The 2D graded structures can also used in asymmetrical structures and heterostructures for slow light effect.     

Electromagnetic radiation from filamentary sources in the presence of axially magnetized cylindrical plasma scatterers

Electromagnetic radiation from filamentary electric-dipole and magnetic-current sources of infinite length in the presence of gyrotropic cylindrical scatterers in the surrounding free space is studied. The scatterers are assumed to be infinitely long, axially magnetized circular plasma columns parallel to the axis of the filamentary source. The field and the radiation pattern of each source are calculated in the case where the source frequency is equal to one of the surface plasmon resonance frequencies of the cylindrical scatterers. It is shown that the presence of even a single resonant magnetized plasma scatterer of small electrical radius or a few such scatterers significantly affects the total fields of the filamentary sources, so that their radiation patterns become essentially different from those in the absence of scatterers or the presence of isotropic scatterers of the same shape and size. It is concluded that the radiation characteristics of the considered sources can efficiently be controlled using their resonance interaction with the neighboring gyrotropic scatterers.     

Slow light effect with high group index and wideband by saddle-like mode in PC-CROW

Slow light with high group index and wideband is achieved in photonic crystal coupled-resonator optical waveguides (PC-CROWs). According to the eye-shaped scatterers and various microcavities, saddle-like curves between the normalized frequency f and wave number k can be obtained by adjusting the parameters of the scatterers, parameters of the coupling microcavities, and positions of the scatterers. Slow light with decent flat band and group index can then be achieved by optimizing the parameters. Simulations prove that the maximal value of the group index is > 10⁴, and the normalized delay bandwidth product within a new varying range of n _g > 10² or n _g > 10³ can be a new and effective criterion of evaluation for the slow light in PC-CROWs.     

Angular intensity distribution of scattered light in systems of closely spaced particles

The results of experimental and computational investigations of the dependence of the angular intensity distribution of scattered light on the concentration of scatterers are discussed. It is shown that a high density of small and large scatterers in a three-dimensional system results in a deformation of the scattering indicatrix. The changes in the angular distribution of intensity of the scattered light at large concentrations are explained by the appearance of fields of multiply scattered waves at significantly lower optical thicknesses than for independent scatterers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 99–103, March, 1976.     

Propagation of light through a monolayer of particles: Analysis of phase and coherent transmittance

Phase variations of a wave transmitted through a monolayer of spherical scatterers are studied as functions of size, optical constants, and particle concentration for light incident normally to the surface of the layer. The analysis is performed in the quasi-crystal approximation of the theory of multiple scattering of waves and in the single scattering approximation. The results obtained allow one to estimate the limits of applicability of the single scattering approximation to layers with partial ordering of scatterers in analysis of the transmitted wave phase. The variations of the phase of the wave in the range of the parameters where the coherent component of the transmitted beam exhibits quenching are studied. It is shown that small variations in the refractive index of the particles may give rise to strong variations of the phase. This effect can be used for phase modulation of light beams, e.g., in liquid crystal films controlled by an electric (or magnetic) field.     

Reflectance properties of finite-size turbid media

Analytic expressions for the position-dependent reflectance of light were derived from a classical diffusion propagator. A modified transport propagator which describes the crossover from the ballistic to the diffusive propagation, and a cross-polarized component propagator. The theoretical reflectances are compared with the experimental ones and their potential for describing finite-size turbid media is discussed. It is found that the cross-polarized propagator provides the best agreement with the experimental data at the low volume fraction of scatterers, for a wide range of separation distances.     

Polarization-based range-gated imaging in birefringent medium:Effect of size parameter

We have investigated the effect of size parameter of the scatterer on the image quality obtained with polarization-based range-gated imaging in birefringent turbid medium. Both linearly and circularly polarized light were utilized for imaging.The simulated results indicate that the improvement of visibility is more pronounced using circularly polarized light for the birefringent medium composed of smaller-sized scatterers at lower values of optical thickness and the birefringent medium comprising larger-sized scatterers. In contrast, linearly polarized light provides better image quality for the birefringent medium composed of smaller-sized scatterers at larger values of optical thickness. The evolution of the polarization characteristics of backscattered light and target light under the conditions mentioned above was measured to account for these numerical results.     

Mie theory interpretations of light scattering from intact cells

We present a Mie theory-based analysis of angularly resolved light scattering from intact cells that involves the product of a particle size distribution rho and the scattering cross section sigma. The analysis shows that the ability to size intracellular organelles depends strongly upon the assumed functional form of the particle size distribution; however, the product sigma rho extracts the dominant light scatterers regardless of this choice. We examine goniometer measurements from our own and another laboratory and find that this analysis reconciles seemingly conflicting results and confirms that mitochondrial-sized organelles dominate scattering from intact cells in the angular range 50 degrees - 90 degrees.     

Extension of the generalized multipole technique to anisotropic medias

This paper presents an extension of the generalized multipole technique (GMT) for 2D anisotropic scatterers. New expansions similar to the Bessel multipole expansion are derived for arbitrary anisotropic media. Numerical simulations prove the accuracy and the rapid convergence of these expansions. As the results obtained are extremely accurate, this technique is most helpful for the evaluation of reference solutions and for the understanding of the physical interaction of light with arbitrary anisotropic media.     

Transport mean free path for magneto-transverse light diffusion: an alternative approach

This paper presents a derivation of the transport mean free path for magneto-transverse light diffusion, ℓ*_⊥, in an arbitrary random mixture of Faraday-active and non-Faraday-active Mie scatterers. This derivation is based on the standard radiative transfer equation. The expression of the transport mean free path obtained previously from the Bethe-Salpeter equation, for the case where only Faraday-active scatterers are present, is recovered. This simpler formulation can include the case of homogeneous mixtures of Faraday-active and non-Faraday-active scatterers.     

Anomalous polarization effects during light scattering in random media

The dependence of the intensity of light backscattered from a layer of a randomly inhomogeneous medium on the polarization of incident light and the size of scatterers has been investigated. The results of numerical simulation have demonstrated that the direction of rotation of the plane of polarization is different in systems with small- and large-scale inhomogeneities. It is shown for the first time that the dependence of the sign of the residual circular polarization on the size of scatterers can be observed in systems described by the Henyey-Greenstein phase function used in simulating biological tissues. A similar anomalous polarization effect, which consists in changing the direction of rotation of the plane of polarization of backscattered light with an increase in the scattering angle, is revealed in studying the coherent backscattering component. These polarization effects are observed in light backscattering from optically active media.     

Enhanced observation of number fluctuations by use of structured light

The point statistics of light scattered from structured, incoherent illumination of a random and fluctuating population of identical scatterers are derived. Theoretical predictions for a two-beam illumination pattern in which the relative beam intensity is modulated are compared with computer simulations and experiments performed by illumination of a rotating mask of identical but random apertures. The use of structured light is found to enhance the size of fluctuations, and quantitative comparisons between theory and practical measurement are made. The structured-light technique introduces flexibility in fluctuation measurement, permitting optimal control of the dynamic range, and is relevant to the development of instrumentation for particle and flow analysis.