Light scattering

About: Light scattering is a research topic. Over the lifetime, 37721 publications have been published within this topic receiving 861581 citations.

Magnetic excitations in layered media: Spin waves and the light-scattering spectrum

Abstract: We present an analysis of the spin-wave spectrum of a semi-infinite stack of ferromagnetic films, each of which is separated by a gap filled by a nonmagnetic medium. This is done within a formalism which includes the Zeeman and dipolar contributions to the spin-wave energy, with exchange omitted. We then calculate the spin-wave contribution to the Brillouin spectrum of such a system, in the backscattering geometry. The aim is to compare the spectrum for scattering from a sample with this geometry, with that from an isolated film. Two features unique to the stack appear in the spectrum. Each film, in isolation, possesses surface spin waves on its boundaries (Damon-Eshbach waves). In the layered geometry these interact to form a band of excitations of the array, which has nonvanishing component of wave vector normal to the stack. We find a feature in the spectrum associated with scattering from this band of modes; the position of the peak is controlled by dispersion introduced by interfilm interactions. Under certain conditions, the semi-infinite stack possesses a surface spin wave, whose eigenfunction is a linear superposition of individual film states, with amplitude that decays to zero as one moves down into the stack interior. This mode also produces a distinct feature in the light-scattering spectrum. These points are illustrated with a series of calculations of the spectrum, for parameters characteristic of layered ultrathin coherent structures.

Elastic wave scattering by a random medium and the small‐scale inhomogeneities in the lithosphere

Abstract: In this paper we use Born approximations to derive the mean square amplitudes of the scattered field for P-P, P-S, S-P, and S-S scattering by an elastic random medium characterized by perturbations of elastic constants and density. We also obtain the total scattered power or the scattering coefficient for the case of an incident P wave. We find that, in both the spatial scattering pattern and the frequency dependence of the scattering coefficient, there are some significant differences between scalar wave scattering and elastic wave scattering. These differences are most striking when the wavelength is comparable to the size of inhomogeneities, which is often encountered in the study of short-period seismic body waves. Under certain conditions, the perturbations of the medium parameters can be decomposed into an impedance term and a velocity term. In the forward direction, scattered waves are primarily controlled by the velocity perturbations. For backscattering, scattered waves are generated mainly by impedance perturbations. We derive low- and high-frequency asymptotic forms of the directional and total scattering coefficients. In the low-frequency range, Rayleigh scattering with fourth-power frequency dependence occurs. For the high-frequency range the scattered power for common-mode scattering has a second-power frequency dependence, which is attributed to velocity perturbations. The scattered power of converted waves reaches a maximum, for the case of an exponential correlation function, in the high-frequency range. We find that the scalar wave theory can be only approximately used for the forward scattering problem in the high-frequency range, such as the phase and amplitude fluctuations in large seismic arrays. The case of coda wave excitation by local earthquakes, which is a backscattering or a large-angle-scattering problem, must be handled by the full elastic wave theory. A preliminary analysis of past observations using our theory suggests that the lithosphere may have multiple-scale inhomogeneities. Besides the 10–20 km scale velocity inhomogeneities revealed by the forward scattering observations at LASA and NORSAR, the lithosphere in tectonically active regions may be rich in small-scale (less than 1 km) inhomogeneities.

Laboratory and Ambient Particle Density Determinations using Light Scattering in Conjunction with Aerosol Mass Spectrometry

Abstract: A light scattering module has been integrated into the current AMS instrument. This module provides the simultaneous measurement of vacuum aerodynamic diameter (d va) and scattered light intensity (RLS) for all particles sampled by the AMS above ∼180 nm geometric diameter. Particle counting statistics and correlated chemical ion signal intensities are obtained for every particle that scatters light. A single calibration curve converts RLS to an optical diameter (d o). Using the relationship between d va and d o the LS-AMS provides a real-time, per particle measurement of the density of the sampled aerosol particles. The current article is focused on LS-AMS measurements of spherical, non-absorbing aerosol particles. The laboratory characterization of LS-AMS shows that a single calibration curve yields the material density of spherical particles with real refractive indices (n) over a range from 1.41 < n < 1.60 with an accuracy of about ±10%. The density resolution of the current LS-AMS system is also shown...

Monte Carlo Calculation for Electromagnetic-Wave Scattering from Random Rough Surfaces

Abstract: A Monte Carlo calculation for light intensities scattered from a random Gaussian-correlated surface is presented for the first time. It is shown that small randomness on a grating surface can considerably change the intensities and, in particular, the surface polariton resonances. These results should be used to check perturbation-theory calculations.