Patterns in the ripple structure of Mie scattering.

We study the ripple structure in the scattered intensity predicted by Mie scattering theory in the angular behavior of the scattered intensity for homogeneous, dielectric spheres. We find that for small values of the phase shift parameter rho = 2kR absolute value(m - 1), where k = 2 pi/lambda, R is the sphere radius, and m is the relative refractive index, the ripples are periodic with spacing equal to pi when plotted versus the dimensionless qR, where q = 2k sin(theta/2) and theta is the scattering angle. However, as rho increases, this outcome switches to nonuniform spacing of approximately pi cos(theta/2). The latter spacing is equivalent to a uniform spacing of pi/kR when plotted versus theta.     

Near-field magnetooptics in resonant light scattering by a linear nanoprobe

A theory of the magnetooptical scattering of light by a near-field linear probe parallel to the surface of a magnet is presented. The probe is modeled by a cylindrical nanowire supporting long-lived surface plasmons. The scattering of light is considered in the longitudinal magnetooptical Kerr effect geometry (with magnetization parallel to the sample surface and the plane of light incidence). The resonant interaction of the probe + image system is taken into account in the self-consistent approximation of the multiple scattering theory, while the magnetooptical interaction is described in the linear approximation with respect to magnetization. Polarization characteristics of the scattered light and the magnetooptical modulation of light intensity, which are resonantly enhanced by the surface plasmons, have been studied.     

Photonic-plasmonic scattering resonances in deterministic aperiodic structures

In this paper, we combine experimental dark-field scattering spectroscopy and accurate electrodynamics calculations to investigate the scattering properties of two-dimensional plasmonic lattices based on the concept of aperiodic order. In particular, by discussing visible light scattering from periodic, Fibonacci, Thue-Morse and Rudin-Shapiro lattices fabricated by electron-beam lithography on transparent quartz substrates, we demonstrate that deterministic aperiodic Au nanoparticle arrays give rise to broad plasmonic resonances spanning the entire visible spectrum. In addition, we show that far-field diffractive coupling is responsible for the formation of characteristic photonic-plasmonic scattering modes in aperiodic arrays of metal nanoparticles. Accurate scattering simulations based on the generalized Mie theory approach support our experimental results. The possibility of engineering complex metal nanoparticle arrays with distinctive plasmonic resonances extending across the entire visible spectrum can have a significant impact on the design and fabrication of novel nanodevices based on broadband plasmonic enhancement.     

Debye series for light scattering by a multilayered sphere

We have derived the formula for the Debye-series decomposition for light scattering by a multilayered sphere. This formulism permits the mechanism of light scattering to be studied. An efficient algorithm is introduced that permits stable calculation for a large sphere with many layers. The formation of triple first-order rainbows by a three-layered sphere and single-order rainbows and the interference of different-order rainbows by a sphere with a gradient refractive index, are then studied by use of the Debye model and Mie calculation. The possibility of taking only one single mode or several modes for each layer is shown to be useful in the study of the scattering characteristics of a multilayered sphere and in the measurement of the sizes and refractive indices of particles.     

Near-field microscopy by elastic light scattering from a tip

We describe ultraresolution microscopy far beyond the classical Abbe diffraction limit of one half wavelength (lambda/2), and also beyond the practical limit (ca. lambda/10) of aperture-based scanning near-field optical microscopy (SNOM). The 'apertureless' SNOM discussed here uses light scattering from a sharp tip (hence scattering-type or s-SNOM) and has no lambda-related resolution limit. Rather, its resolution is approximately equal to the radius a of the probing tip (for commercial tips, a < 20 nm) so that 10 nm is obtained in the visible (lambda/60). A resolution of lambda/500 has been obtained in the mid-infrared at lambda = 10 microm. The advantage of infrared, terahertz and even microwave illumination is that specific excitations can be exploited to yield specific contrast, e.g. the molecular vibration offering a spectroscopic fingerprint to identify chemical composition. S-SNOM can routinely acquire simultaneous amplitude and phase images to obtain information on refractive and absorptive properties. Plasmon- or phonon-resonant materials can be highlighted by their particularly high near-field signal level. Furthermore, s-SNOM can map the characteristic optical eigenfields of small, optically resonant particles. Lastly, we describe theoretical modelling that explains and predicts s-SNOM contrast on the basis of the local dielectric function.     

Ray scattering by an arbitrarily oriented spheroid. II. Transmission and cross-polarization effects

Transmission of an arbitrarily polarized plane wave by an arbitrarily oriented spheroid in the short-wavelength limit is considered in the context of ray theory. The transmitted electric field is added to the diffracted plus reflected ray-theory electric field that was previously derived to obtain an approximation to the far-zone scattered intensity in the forward hemisphere. Two different types of cross-polarization effects are found. These are (a) a rotation of the polarization state of the transmitted rays from when they are referenced with respect to their entrance into the spheroid to when they are referenced with respect to their exit from it and (b) a rotation of the polarization state of the transmitted rays when they are referenced with respect to the polarization state of the diffracted plus reflected rays.     

Numerical study of light scattering by a boundary-layer flow

Temperature inhomogeneities in free, isotropic turbulence have the effect of scattering light in near-forward angles. We investigate numerically modifications of free turbulence by a rigid wall and its effect on the propagation of light through turbulence. The wall is a 5 cm optical window placed at the leading edge of an instrument towed with speeds of 0.1 and 1 m/s in free turbulence. The turbulent flow field presents inhomogeneities of an embedded passive scalar (Pr = 7, temperature in water), which are modified by the boundary layer developing on the window. We find that the developing laminar boundary layer has a negligible effect on light scattering for the investigated geometry when considered in terms of the volume-scattering function (differential cross section). This indicates that the boundary layer is not an obstacle for optical measurements of turbulence.     

Ray scattering by an arbitrarily oriented spheroid. I. Diffraction and specular reflection

Diffraction and reflection of an arbitrarily polarized plane wave by an arbitrarily oriented spheroid in the short-wavelength limit are considered in the context of ray theory. A closed-form solution for both diffraction and reflection is obtained, and the polarization character of the diffracted plus reflected electric field is obtained. It is found that the magnitude of the reflected electric field is multivalued for forward scattering. This is interpreted in terms of the variation of the spheroid's Gaussian curvature at the points where grazing ray incidence occurs.     

Improved recursive algorithm for light scattering by a multilayered sphere

An improved recurrence algorithm to calculate the scattering field of a multilayered sphere is developed. The internal and external electromagnetic fields are expressed as a superposition of inward and outward waves. The alternative yet equivalent expansions of fields are proposed by use of the first kind of Bessel function and the first kind of Hankel function instead of the first and the second kinds of Bessel function. The final recursive expressions are similar in form to those of Mie theory for a homogeneous sphere and are proved to be more concise and convenient than earlier forms. The new algorithm avoids the numerical difficulties, which give rise to significant errors encountered in practice by previous methods, especially for large, highly absorbing thin shells. Various calculations and tests show that this algorithm is efficient, numerically stable, and accurate for a large range of size parameters andrefractive indices.     

Underwater light polarization and radiance fluctuations induced by surface waves

The underwater light field is an ever-changing environment. Surface waves induce variability in the radiance and the light's polarization. We examined the dependence of the polarization fluctuations associated with diffuse light (not including contribution from direct skylight) on the viewing zenith angle (30 degrees, 70 degrees, and 90 degrees), solar zenith angle (23 degrees -72 degrees), depth of 0.5-3 m, and light wavelength (380-650 nm) while observing within the azimuthal plane in the wind-wave direction. Polarization and radiance fluctuated with time. Light variability (presented by the coefficient of variation calculated over a series of fluctuations in the radiance and percent polarization, and by the standard deviation calculated over a series of fluctuations in the e-vector orientation) was highest at a viewing zenith angle of 70 degrees , depended positively on the solar zenith angle, and decreased with depth at viewing zenith angles of 30 degrees and 70 degrees . Additionally, the variability of the percent polarization was significantly higher than that of the radiance. The temporal light fluctuations offer possibilities, such as enhancing the detection of transparent and reflecting objects; however, they set constraints on the optimal underwater polarization vision by both animals and by the use of instruments.     

Null-field BIEM for solving a scattering problem from a point source to a two-layer prolate spheroid

In this paper, the acoustic scattering problem from a point source to a two-layer prolate spheroid is solved by using the null-field boundary integral equation method (BIEM) in conjunction with degenerate kernels. To fully utilize the spheroidal geometry, the fundamental solutions and the boundary densities are expanded by using the addition theorem and spheroidal harmonics in the prolate spheroidal coordinates, respectively. Based on this approach, the collocation point can be located on the real boundary, and all boundary integrals can be determined analytically. In real applications of a two-layer prolate spheroidal structure, it can be applied to simulate the kidney-stone biomechanical system. Here, we consider the confocal structure to simulate the kidney-stone system since its analytical solution can be analytically derived. The parameter study for providing some references in the clinical medical treatment is also considered. To check the validity of the null-field BIEM, a special case of the acoustic scattering problem of a point source by a rigid scatterer is also done by setting the density of the inner prolate spheroid to infinity. Results of the present method are compared with those obtained using the commercial finite element software ABAQUS.     

Single scattering of light by circular cylinders

We consider two topics pertaining to light scattering by circular cylinders. (A) Scattering properties of cylinders with increasing aspect ratio are studied. It is shown that the solution for finite cylinders does not converge to the solution for infinitely long cylinders if the aspect ratio increases. This is due to differences in the treatment of diffraction for finite and infinite cylinders. (B) Finite cylinders have sharp edges, so their scattering properties differ from those of spheroids having the same aspect ratio. To illustrate these differences we present scattering matrix elements of cylinders and spheroids for a large set of aspect ratios. To handle the large amount of data, the scattering matrix elements as functions of aspect ratio and scattering angle are presented in so-called three-dimensional figures.     

Viscosity of liquidn-heptane by dynamic light scattering

The dynamic viscosity of liquidn-heptane was measured in the temperature range 293–353 K by dynamic light scattering employing a newly designed optical setup. Commercial stearyl-coated silica particles were used as a seed, where a calibration of particle sizes to obtain absolute viscosity values was performed in other alkanes. The measurements included experimental runs at various particle concentrations and scattering vectors and in both a heating and a cooling cycle with a total standard deviation of 0.8–0.9%. As established reference values exist for alkane viscosities, from which the deviations were below 1% over the whole range of relevant temperatures, the experiments may also be regarded as a successful test of the accuracy of the method.     

Hydrodynamic surface fluctuations of polymer films by coherent X-ray scattering

We have applied X-ray photon correlation spectroscopy (XPCS) to measure the surface dynamics of polymer films of thicknesses down to a few times of the polymer radius of gyration. XPCS is currently the only technique to measure selectively dynamics of surface and/or interfacial fluctuations of the films thanks to high brilliance and coherence of the third generation synchrotron source. The results show the behavior of the capillary waves expected in viscous liquid when the film thickness is thicker than four times of the radius of gyration. However, thinner films show a deviation indicating the need to account for viscoelasticity. We present also the theory for surface dynamics of the thermally excited fluctuations on homogenous single-layer film with arbitrary depth is generalized to describe surface and interfacial dynamics of polymeric liquid bilayer films in terms of susceptibilities, power spectra and characteristic relaxation time constants. The effects on surface dynamics originating from viscosity inhomogeneities close to surface region are investigated by the bilayer theory and compared with the surface dynamics from homogeneous single-layer films under non-slip and slip boundary conditions.     

Elastic laser light scattering by GaAs surfaces

Angle-resolved scattering (ARS) intensities were measured in the backscattering hemisphere for the (1 0 0) and (1 1 1) faces of GaAs single crystals. Three epitaxial layers were deposited onto the GaAs (1 0 0) single-crystalline wafers. The laser elastic light scattering shows the presence of a regular surface microrelief whose orientation corresponds to the crystallographic axes in the surface plane. We studied the statistical properties of this microrelief and determined the parameters that characterize the surface. We propose to use the ARS ratio for two wavelengths (in our case, 632.8 and 441.6 nm) to determine the topographical properties of scattering and to study crystal surface defects.     

Enhanced Raman scattering in a colloidal crystal observed by a tunable laser light source

The Raman scattering intensity was measured for a colloidal crystal composed of polystyrene micro spheres and a polymer gel with a tunable continuous-wave dye laser as an excitation light source. Enhancement of the Raman scattering caused by both the electric field enhancement at the excitation frequency and the increase in the local photon density of states at the scattering frequency was expected. The observed Raman scattering intensity as a function of the excitation frequency showed a reasonable agreement with the theoretical prediction.     

Measurements of light scattering from glass substrates by total integrated scattering

A total integrated scattering (TIS) measurement was performed to investigate the surface and volume scattering of K9 glass substrates with low reflectance. Ag layers with thicknesses of 60 nm were deposited on the front and back surfaces of the K9 glass substrates by the magnetron sputtering technique. Surface scattering of the K9 glass substrate was obtained by the TIS measurement of the Ag layers on the assumption that the Ag layers and the K9 substrate had the same surface profile. Volume scattering of the substrates was deduced by subtracting the front and back surface scattering from the total scattering of the substrates.     

Heterodyne measurements of laser light scattering by a turbulent phase screen

We report experiments in which a fiber-coupled heterodyne laser system operating at a wavelength of 1.5 microm is used to measure the phase fluctuations induced on a laser beam by passage through a thin layer of turbulent air and subsequent propagation through free space. We investigate the statistical properties and power spectra of the phase and its rate of change, in addition to the intensity statistics. We find that the power spectrum of the rate of change of phase has a simple negative exponential form. We discuss our results in the context of the problem of detection of phase variations over an extended turbulent atmospheric path.