Light scattering by an inhomogeneous spherical particle with intermediate layers

A model of a radially inhomogeneous multilayer spherical particle with a continuously varying refractive index in the intermediate layers between the shells of the particle and between the particle and the surroundings is proposed. Such a particle scatters light much like a dust particle with a rough and ragged surface of the layers, which is simulated with the help of the discrete dipole approximation method. For dust particles whose surface shape deviates from the spherical one, the refractive index profile and the behavior of the extinction Q _ext(x) and absorption Q _abs(x) efficiency factors with increasing thickness of the intermediate layers are studied. Properties of such particles in dependence on the number of layers are also studied. It is revealed that, as the number of shells increases, the order of the relative position of substances ceases to play a role, as is also the case for a multilayer spherical particle without intermediate layers. It is shown that, upon an increase in the number of shells at the same percentages of substances in the intermediate layers, the difference of the values of Q _ext(x) and Q _abs(x) from the corresponding values calculated with the model without intermediate layers decreases.     

铁电液晶MBOPDOB相变的光散射研究

我们对铁电液晶 MBOPDOB 进行了温度有关的拉曼散射研究。在低频范围记录了三条拉曼谱线(15,49,93cm~(-1))。其中15和49cm~(-1)谱线消失于 C-Sm C相变温度,没有检测到任何频移现象。93cm~(-1)拉曼线产生部分频移,消失于各向同性相,联系着偶极-偶极互作用。高频范围四个振动模(1178和1116cm~(-1),1710和1738cm~(-1))之间能量转移归于由电子转移引起的 C=0键硬化和 C-0健的弱化。同时也讨论了该液晶 Sm C-Sm A 相变的二级连续型特征。     

Light scattering study of a twist grain boundary liquid crystal

Dynamic light scattering is used to probe the fluctuation modes of a liquid crystal exhibiting twist grain boundary (TGB) structure. At the chiral nematic to proposed "chiral line liquid" phase transition, anomalous temperature dependence in the fluctuation spectrum and an instability in the helicoidal director structure signify developing TGB order. At lower temperatures, the behavior of the smectic layer-director fluctuations ("soft" mode) indicates that the previously identified commensurate TGB(A) phase may in fact be a TGB(C) phase with an unusually small tilt angle.     

Three-dimensional problem of inverse scattering in stratified randomly inhomogeneous media

Conclusions The problem with a stratified medium is of immediate interest in acoustics (in particular, marine acoustics), just as it is in radiophysics [8], but its importance consists primarily of the fact that it permits closely fitting a solution of a problem with three-dimensional inhomogeneities.One can isolate the characteristic facts associated with IS in stratified media. In the first place, spatial-temporal scales arise which restrict the region of applicability of the approximate methods. Outside this region the approximate methods do not work due to accumulating effects, and, secondly, fluctuations of the IS intensity increase there. It would be very timely to investigate, in this respect, media with three-dimensional inhomogeneities, which is necessary for problems of probing randomly inhomogeneous media by the IS method.Pacific Ocean Oceanological Institute, Far East Scientific Center, Academy of Sciences of the USSR. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 25, No. 9, pp. 1032–1040, September, 1982.     

Light scattering studies of crossover to a liquid crystal tricritical point

We have used light scattering to study nematic elastic constantsK ₂ andK ₃ in the alkyl-cyanobiphenyl (n CB) system. As the average alkyl chain lengthn increases, the temperature range of the nematic phase decreases and the system approaches a tricritical point. Our data are analyzed to determine the parallel and perpendicular correlation lengths and critical exponents for smectic short-range order. We find a continuous decrease in the critical exponentsv andv as the tricritical point, which occurs at 9.1 CB, is approached. There is also a significant decrease in the magnitude of the parallel correlation length at a fixed reduced temperature.     

Optical depth and multiple scattering depolarization in liquid clouds

In this paper, we calculate multiply scattered lidar signals with Monte Carlo method for measuring optical depth (extinction coefficient), effective size of water droplets, and liquid water content of clouds, and present algorithms that implement our method. We calculated multiply scattered lidar signals for various water droplet sizes and liquid water contents using a Monte Carlo method. A simple correspondence between water droplet optical depth and the degree of polarization in a modified gamma size distribution (C₁ cloud) is found. We also calculated the degree of polarization of a lidar signal for a given liquid water content, finding that the degree of polarization is only dependent on optical depth. Since the Raman lidar signal of liquid water depends on the total volume of the water droplet, the effective radius of the water droplet can thus be recovered from the degree of polarization of the lidar signal and the Raman signal of the liquid water.     

Photoluminescence and Raman scattering in spatially inhomogeneous heteroepitaxial InGaN layers

Spatial inhomogeneities of the indium distribution in In _x Ga_1–x N epitaxial layers grown on sapphire substrate with a GaN buffer layer were investigated using photoluminescence (PL) in addition to confocal scanning Raman spectroscopy (RS) and PL. Broad emission bands from In-enriched InGaN nanoclusters (700–900 nm) and from the volume outside the clusters (about 460 nm) were observed in PL spectra of an epitaxial InGaN layer with an average In content of 25.7%. It was established that larger micro-PL intensities corresponded to energetically shallower clusters. The observed broadly asymmetric A₁(LO) RS band of InGaN confirmed that the In concentration in the layer was highly variable. Modeling the LO phonon band by two Lorentzian curves gave an average In concentration of 21% in the volume outside the clusters and 37% in the nanoclusters, which was considerably higher than the average concentration in the layer and agreed well with their PL band positions.     

Light scattering on random dielectric layers

Scattering of light by a random stack of dielectric layers represents a one-dimensional scattering problem, where the scattered field is a three-dimensional vector field. We investigate the dependence of the scattering properties (band gaps and Anderson localization) on the wavelength, strength of randomness and relative angle of the incident wave. There is a characteristic angular dependence of Anderson localization for wavelengths close to the thickness of the layers. In particular, the localization length varies non-monotonously with the angle. In contrast to Anderson localization, absorptive layers do not have this characteristic angular dependence.     

Multiple scattering and intensity fluctuations in optical coherent tomography of randomly inhomogeneous media

An expression for signal intensity fluctuations in optical coherent tomography has been obtained for the first time in the framework of the theory of the multiple scattering of low-coherent optical radiation in a random medium. The contribution of the multiple scattering of low-coherent radiation backscattered from a randomly inhomogeneous layer, as well as the speckles of the interference component in optical coherent tomography, has been calculated.     

Rayleigh scattering induced by static bends of layers in a smectic A liquid crystal

We observe the anisotropy and the polarization properties of the Rayleigh scattered light for a planar smectic A texture of butoxyl benziledene-p-n anilino-acetophenone (BBAA). This scattering is attributed to static bends of the smectic layers, with wave vectors parallel to the smectic planes. This effect gives a simple method to measure the ratio of the extraordinary to the ordinary indices: n_e/n₀ = 1.18 at 89°C.     

Small-angle light scattering symmetry breaking in polymer-dispersed liquid crystal films with inhomogeneous electrically controlled interface anchoring

We have described the method of analyzing and reporting on the results of calculation of the small-angle structure of radiation scattered by a polymer-dispersed liquid crystal film with electrically controlled interfacial anchoring. The method is based on the interference approximation of the wave scattering theory and the hard disk model. Scattering from an individual liquid crystal droplet has been described using the anomalous diffraction approximation extended to the case of droplets with uniform and nonuniform interface anchoring at the droplet–polymer boundary. The director field structure in an individual droplet is determined from the solution of the problem of minimizing the volume density of the free energy. The electrooptical effect of symmetry breaking in the angular distribution of scattered radiation has been analyzed. This effect means that the intensities of radiation scattered within angles +θ _s and–θ _s relative to the direction of illumination in the scattering plane can be different. The effect is of the interference origin and is associated with asymmetry of the phase shift of the wavefront of an incident wave from individual parts of the droplet, which appears due to asymmetry of the director field structure in the droplet, caused by nonuniform anchoring of liquid crystal molecules with the polymer on its surface. This effect is analyzed in the case of normal illumination of the film depending on the interfacial anchoring at the liquid crystal–polymer interface, the orientation of the optical axes of droplets, their concentration, sizes, anisometry, and polydispersity.     

Light scattering in photopolymerizing layers under laser irradiation

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 2, pp. 215–221, February, 1990.     

In-plane bistatic backward scattering from seabottom with randomly inhomogeneous sediment and rough interface

1 Introduction Backward scattering of sound due to sediment is the main source of shallow waterreverberation. In order to predict the reverberation or detect sediment properties frommeasured reverberation data, a reasonable in-plane bistatic backward scattering (BBS)model is essential. The scattering can be caused by the roughness of water-sediment in-terface or by inhomogeneities within the volume of sediment. A great deal of researchhas been done on sediment backscattering, most of which h…     

Comparative characteristics of coherent and incoherent microwave scattering in dense inhomogeneous layers

Results of experiments on measuring forward scattering of waves in the range 88–100 GHz propagating in dense inhomogeneous layers consisting of grainy polymer materials are presented. Experiments were carried out with coherent and incoherent radiation. A comparison of the results demonstrates that incoherent radiation averages the depolarization effects and is preferable in comparison with coherent radiation for diagnostics of dense inhomogeneous materials. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 11–14, September, 2006.     

Equivalent volume-averaged light scattering behavior of randomly inhomogeneous dielectric spheres in the resonant range

Finite-difference time-domain numerical experiments and supporting analyses demonstrate that the spectral dependence of the total scattering cross sections of randomly inhomogeneous dielectric spheres of sizes in the resonant range closely resemble those of their homogeneous counterparts that have a volume-averaged refractive index. This result holds even for the extreme case in which the refractive index within an inhomogeneous sphere varies randomly over the range 1.0-2.0.     

Tunnelling through randomly inhomogeneous barriers as a special problem of the scattering theory

The tunnelling of electrons through an inhomogeneous delta barrier is considered. The strength of the barrier is defined as a function oscillating around a constant mean value along a plane. Owing to deviations from this value, the tunnelling through such a delta barrier has to be interpreted as a scattering. A simple model is discussed when circular windows of a given radius b representing themselves delta barriers of a given strength γ₀ are embedded in a homogeneous delta barrier defined with another strength . When the centers of the windows are distributed randomly in the barrier plane, the potential energy of the electrons is a random function of two space coordinates. The perpendicular incidence is discussed with emphasis on the angular probability density of the tunnelled electrons. The derivation of the angular probability density proves that three basic quantum-mechanical phenomena can be described by one simple formula: tunnelling, diffraction and scattering.