Light scattering

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

Neutron scattering from charge stabilized suspensions undergoing shear

Abstract: Small angle neutron scattering(SANS) is used to investigate the local order in aqueous, charge stabilized suspensions of 103 A diameter polystyrene latexspheres at ∼14 wt. % solids. These samples which evidence a close packed close packed structure in equilibrium are observed to undergo a transition to an amorphous order when sustaining a sufficiently large and steady shear. The shear melting phenomonology is different from that observed by light scattering for very dilute (0.16 wt. % solids) suspensions of polystyrene particles which form bcc lattices in equilibrium. Furthermore, neutron scattering reveals more detail than light scattering for concentrated suspensions and indicates a larger degree of three‐dimensional ordering under steady shear flow than is implied by sliding layer models for similar systems.

Collision-Induced Light Scattering in Gaseous Ar and Kr

Abstract: Light scattering attributable to a change in polarizability produced in colliding pairs of atoms is observed in gaseous Ar and Kr. The experimental results are qualitatively accounted for by relations between the integrated intensity and the collision-induced polarizability.

Brillouin and raman scattering study of borate glasses

Abstract: We report light scattering results obtained from Brillouin and Raman scattering experiments in a series of B 2 O 3 − x M 2 O glasses (M  Li, Na, K, Rb, Cs and Tl). Raman lines related to the internal vibrations of structural units give information on the composition and concentration dependence of the short range arrangement in the glasses. The “Boson peak” is analysed on the basis of the Martin-Brenig model. The short correlation range is lower than 10 A and increases with the cation radius. From these experiments the very low frequency light scattering (Light Scattering Excess) is extracted. The temperature dependence of the LSE intensity in pure B 2 O 3 glass as well as its variation with composition at room temperature are studied. The Theodorakopoulos-Jackle theory relates this intensity to the acoustic attenuation deduced here from Brillouin linewidth measurements. While a theoretical description of the relation between the temperature variation of both quantities agrees well with experimental results, disagreement is apparent in their composition dependence. Finally, the sound velocity plotted versus concentration gives evidence of the contradictory influence of the hardening due to the change of the boron atom coordination number and the softening related to the distortion of the network by large cations.

Path-length-resolved dynamic light scattering in highly scattering random media : the transition to diffusing wave spectroscopy

Abstract: Dynamic light scattering ~DLS! has been used extensively during the past few decades for characterization of the structural and dynamical properties of materials that weakly scatter light @1,2#. DLS is based on measuring fluctuations in the intensity of the scattered light arising from phase and/or amplitude fluctuations induced by particle dynamics. This technique is applicable to media in which the detected light has scattered no more than once. In highly scattering materials the scattering angle and the polarization of the scattered wave are not well defined due to multiple scattering events and details about the sample properties are lost. However, the intensity of the multiply scattered light is accurately predicted by the photon diffusion equation and therefore the theory of diffusing wave spectroscopy ~DWS! can be applied for quantitative analysis of the angle averaged dynamic properties @3,4#. Although both DLS and DWS provide information about the structural and dynamical properties of the sample, they are only valid in the two extreme cases of single scattered and diffusive light respectively. Durian @5# and Kaplan et al. @6# have studied conditions under which DWS is valid, but still little is known about the intermediate regime between DLS and DWS. Since the detection of multiply scattered light causes degradation of image contrast and resolution in confocal @7# and optical coherence microscopy @8#, a clear understanding of the transition from ballistic to diffusive light will permit a quantitative analysis of scattering media that do not satisfy the single scattering or light diffusion criteria and can lead to the development of new techniques for image quality improvement. In this paper we show how low coherence interferometry ~LCI! can be used to make path-length-resolved measurements of particle Brownian motion within highly scattering media. LCI uses a coherence gate to select light that has traveled a specific path length in the medium. Thus it is possible to detect light that has scattered only once within a turbid medium and to apply DLS for the determination of the sample dynamical properties or to select only diffusive light and apply DWS theory. We experimentally demonstrate these two extremes in highly scattering samples of polystyrene microspheres, as well as the smooth transition between them. We show experimentally that this transition depends on the scattering properties of the medium and the measurement geometry. In particular, we find that the transition to the diffusing light regime occurs at shorter path lengths for either higher scattering anisotropy or a larger numerical aperture ~NA! of the collection optics. A schematic of our LCI system is shown in Fig. 1. The single-mode fiber optic interferometer is illuminated with an 850-nm superluminescent diode ~25-nm spectral bandwidth, 1.2-mW output power!. The optical properties of the sample generate a distribution of optical path lengths in the sample arm, while the path length in the reference arm is determined solely by the position of the retroreflector. Interference is observed only when the optical path-length difference between the reference and the sample arms is within the coherence length of the source. Thus a coherence gate is used to select specific path lengths within the sample. The amplitude of the interference signal is therefore proportional to the path-length-dependent reflection/scattering properties of the sample. In the single scattering regime the axial resolution is determined by the source coherence length, while the lateral resolution depends on the focusing optics. The position of the reference mirror ~retroreflector ! is adjusted in such a way as to align the coherence gate with the beam waist, thus optimizing the rejection of multiply scattered light @8#. As demonstrated in our previous studies @9#, particle dynamics of highly scattering media can be imaged and quantified in the single scattering regime with dynamic LCI by examining the intensity fluctuations of the backscattered light and extracting information from the photocurrent power spectrum. For a fixed position of the reference mirror of the

Theoretical and computational concepts for periodic optical waveguides

Abstract: We present a general, rigorous, modal formalism for modeling light propagation and light emission in three-dimensional (3D) periodic waveguides and in aggregates of them. In essence, the formalism is a generalization of well-known modal concepts for translation-invariant waveguides to situations involving stacks of periodic waveguides. By surrounding the actual stack by perfectly-matched layers (PMLs) in the transverse directions, reciprocity considerations lead to the derivation of Bloch-mode orthogonality relations in the sense of E×H products, to the normalization of these modes, and to the proof of the symmetrical property of the scattering matrix linking the Bloch modes. The general formalism, which rigorously takes into account radiation losses resulting from the excitation of radiation Bloch modes, is implemented with a Fourier numerical approach. Basic examples of light scattering like reflection, transmission and emission in periodic-waveguides are accurately resolved.