Showing papers on "Light scattering published in 1974"

Light scattering in planetary atmospheres

Abstract: This paper reviews scattering theory required for analysis of light reflected by planetary atmospheres. Section 1 defines the radiative quantities which are observed. Section 2 demonstrates the dependence of single-scattered radiation on the physical properties of the scatterers. Section 3 describes several methods to compute the effects of multiple scattering on the reflected light.

Light scattering by pores in polycrystalline materials: Transmission properties of alumina

Abstract: The in‐line transmission of polycrystalline high‐density ceramics is discussed in terms of light scattering by pores. The Mie theory for light scattering is applied to calculate scattering coefficients using generalized parameters. Results are shown for scattering by spherical pores with uniform size and with a lognormal size distribution. Specific examples are given of the calculated transmission of alumina in the wavelength region 0.4–5 μm. Experimentally determined transmission curves of normally sintered and of hot‐pressed alumina are compared with calculated curves. The porosity, the position of the maximum, and the width of the lognormal distribution are treated as variables in the calculation. Good agreement with the experimental data is obtained.

Effects of intermacromolecular interactions on diffusion. II. Three‐component solutions

Abstract: The effect on the diffusion coefficient of nondissipative interactions between diffusing macromolecules is considered for three‐component solutions containing solvent and two species of macromolecules. The spectrum of light scattered quasielastically from a system containing two species of interacting Brownian molecules is calculated. Treatment of a dilute minimum‐salt protein solution as a three‐component system indicates a possible way of performing light scattering measurements on charged species which do not scatter light. Extension of the techniques of paper I of this series to include the effect of interspecies interactions clarifies the relation between the tracer and mutual diffusion coefficients as these have been defined by different authors. This extension also provides a criterion for phase separations in three‐component solutions.

Sodium D-line emission from Io - Sputtering and resonant scattering hypothesis

Abstract: A model is presented in explanation of the observation of sodium D-line emission from Io. The model involves: (1) charged-particle sputtering of sodium from Io's surface, (2) ejection of sodium into a cloud surrounding Io, and (3) resonant scattering of incident sunlight. Observational consequences and tests of the proposed model are also discussed.

Mie scattering by spheres in an absorbing medium.

Abstract: Equations are developed for Mie scattering by spheres (particles, bubbles, or voids) embedded in an absorbing medium. Computations demonstrate that under certain conditions the extinction-efficiency factor, Qext, can be less than the scattering-efficiency factor, Qs. In fact, Qext, as commonly defined, can be negative. Also, results are shown for the angular scattering distribution by a void, which indicate that the intensity of the backward-scattered light can be greater than the forward-scattered light.

Scattering from side-illuminated clad glass fibers for determination of fiber parameters

Abstract: The theoretical characteristics of the scattered-light pattern from a clad glass fiber illuminated by a laser beam perpendicular to its axis agree closely with results of experimental measurements of the scattered light. A simplified geometric ray-tracing technique shows that for fibers with medium and small core sizes, specific angle ranges of the scattering pattern provide determinations of fiber diameter independent of core parameters. Measurements of the fringe modulation give relatively sensitive determinations of core diameter. Light scattering is a useful technique for determining the diameters of both clad and unclad fiber. Total-diameter determinations have accuracies of ±0.2 μm and core diameters, ±0.5 μm for 0.02 refractive-index difference between core and cladding.

Anharmonic lattices, structural transitions and melting

Abstract: Phase Transitions, Anharmonic Solids and Liquids.- Neutron Scattering Studies of Soft Mode Dynamics.- Slow Local Fluctuations near Tc in SrTio3 Studied by EPR.- Hydrodynamics near Phase Transitions of Second Order.- Review of Methods for Obtaining a Central Mode.- Nonlinear Fluctuations and the Central Mode.- Some Further Observations of Soft Phonon Line Shapes in KMnF3.- Critical Sound Velocity and Attenuation in KMnF3.- Raman Spectral Study of the Upper Phase Transition in KMnF3.- Soft Mode and Critical Opalescence in SrTio3.- Phonon Transport Theory and the Central Mode.- Phase Transitions in Solid CD4.- The Jahn-Teller Effect as a Mechanism for Structural Phase Transitions.- Soft Modes at First and Second Order Phase Transitions.- A Qualitative Picture of the Tricritical Point.- Tricritical Studies of ND4Cl.- Computer Simulation of a Discontinuous Phase Transition in the Two-Dimensional One-Spin-Flip Ising Model.- Continuous versus Discontinuous Phasetransitions.- Dynamics of Fluids Near the Critical Point: Light Scattering Investigations.- Neutron Scattering in Solid and Liquid H2.- Neutron Scattering by a Liquid Crystal at Temperatures Close to Its Melting Point.- X-Ray Studies of the Smectic Structure and the Solid-Smectic Transition.- High-Frequency Dynamics of Simple Solids and Liquids Near Their Melting Points.- Analysis of the Approach to the Convective Instability Point.- Melting: Theories and Recent Computer Simulations.- Volume Expansion, Thermal and Electrical Conductivities and Sound Velocities of Sodium at Temperatures Very Close to Its Melting Point.- List of Participants.

Wind dependence of quasi-specular microwave sea scatter

Abstract: It is shown that a specular-point scattering model adequately predicts the relation between the average quasi-specular microwave scattering cross section of the sea and the mean wind speed. The mean-square sea slope required in this model varies with both the upper and lower ends of the waveheight spectrum, which in themselves are functions of wind speed. Optical measurements of slopes confirm this physical relationship. Finally, the resultant scattering cross section predicted by the slope-dependent specular-point model is compared with a set of recent measurements, lending credence to the model and interpretation suggested here.

Study of Phase Separation in a Critical Binary Liquid Mixture: Spinodal Decomposition

Abstract: Light scattering has been used to study phase separation near the critical point in a binary mixture of methanol and cyclohexane. The intensity measurements are in conformity with the spinodal decomposition theory of Cahn. Measurements were also made of the spectral width of the scattered light in the phase separation process.

Low-angle laser light scattering - rayleigh factors and depolarization ratios.

Abstract: The Rayleigh factors and depolarization ratios at 6328 A have been measured for carbon disulfide, toluene, benzene, chloroform, carbon tetrachloride, cyclohexane, butanone, acetone, methanol, and water using an improved model of the low-angle laser light-scattering (LALLS) photometer. Small errors in some of the Rayleigh factors published using an earlier model of this instrument have been revealed. Depolarization ratios are measured by a new method involving detection of the full cone of forward scattered light.

Analysis of Gaussian beam propagation and diffraction by inhomogeneous wave tracking

Abstract: Inhomogeneous waves behave locally like A(r) exp[ikS(r)], where A and S are spatially dependent complex amplitude and phase functions, and k is the (large) free-space wavenumber. A previously developed asymptotic theory for high-frequency propagation and scattering of such waves is here applied to the propagation and scattering of paraxial Gaussian beams. Attention is given to Gaussian beams in free space, to beams in a lens-like medium with parabolic variation of the refractive index, and to beam reflection by a cylindrical obstacle. In the latter instance, the obstacle size may be comparable to the incident beamwidth, thereby introducing substantial distortion into the reflected beam. The results obtained from the asymptotic theory are verified by comparison with rigorously derived solutions, thereby confirming the validity of the theory, which can also be applied to more general medium and obstacle configurations.

Pulse-induced critical scattering (pics) from polymer solutions

Abstract: Pulse-induced critical scattering (PICS) is a new, fast technique for determining thermodynamic and kinetic parameters of polymer solutions. Relative intensities of scattered laser light are measured over periods of seconds after a fast temperature step into the region of Debye critical opalescence. In the mode of operation using thermal pulses to progressively lower temperatures, the intensity pulse shape gives sensitive information on the fluctuation equilibrium and on the kinetics of phase separation with formation of emulsions of sub-wavelength particles, Spinodal and critical loci for the system polystyrenecyclohexane (PS–CH) are measured about 10 times faster and more accurately than in recent work based respectively on conventional light scattering equipment and on turbidimetry. The classical Debye theory of scattering near a critical point, or Scholte's extension to spinodal points, gives excellent semi-empirical extrapolations to spinodal temperatures T s . Though there are signs that the classical theory needs amendment in the sense of the generalized nonlinear theory of Fisher, Chu, and co-workers, this would generally give results on T s in close agreement with the simpler classical theory in the experimental range accessible to PICS. The effects of heterodispersity on the phase diagram are studied, comparing data by Scholte and new data by PICS on PS–CH. The evidence suggests that spinodal loci are governed mostly by M w (as suggested by recent theories). Marked secondary effects seem, however, to arise, not (as recently suggested) from M n , but from M z . Results obtained by the technique of approaching phase equilibrium from the heterogeneous side, using an emulsion carefully ‘seeded’ by a thermal step, suggest that supercooling is more serious in cloud-point determinations of dilute polymer solutions than hitherto thought. The formation of sub-wavelength droplets follows kinetics bearing more than formal resemblance to that for the nucleation and growth of spherulitic crystals in bulk.

Multiple scattering calculation of the middle ultraviolet reaching the ground.

Abstract: An investigation is conducted regarding the increase in the UV radiation as a function of wavelength due to changes in the amounts of ozone and various other parameters affecting the radiation in the atmosphere. Attention is given to the methods that can be used to solve the problem of the transfer of radiation through an absorbing and scattering atmosphere which includes aerosols. The multiple channel solution reported by Mudgett and Richards' (1971) is extended to vertically inhomogeneous atmospheres.

Application of complex ray tracing to scattering problems

Abstract: Representations and geometric constructions associated with complex points, complex lines, and complex rays are introduced. They are applied to the problem of scattering of an evanescent plane wave by a conducting circular cylinder. This problem has an exact solution, which provides a check of the validity of complex ray tracing and suggests more general applications. An important role is played by the transformation that maps the point of reflection, on the complex extension of the scattering surface, onto the trace in real space of the complex reflected ray. For the particular problem considered, the phase and amplitude of the reflected field are computed and the "phase paths" and "phase fronts" are constructed. The reflected field and phase paths obtained in this manner are not to be taken in their entirety because some reflection points are not "illuminated" by the incident wave, and because the reflector may be only part of the cylinder. Tentative selection and truncation rules are used which yield good agreement with the exact solution over some regions. The disagreement, where it occurs, comes-as it does for real rays-from neglecting the diffracted field such as the creeping waves around smooth surfaces and, in the case of truncation, the edge waves from the discontinuity. Some consideration is given to scattering by an arbitrary smooth conductor. Some problems peculiar to the use of complex rays are stated.

Stray Light Suppression in Optical Space Experiments

Abstract: Measurements of stray light suppression with mirrors, lenses, and baffle systems from four zodiacal light and one noctilucent cloud space experiments are reported. The method used to derive the total stray light suppression from these measurements is given. The predicted residual stray light intensity of about 10−11 sr−1 to 10−10 sr−1 corresponds to ≈1% of the zodiacal light intensity and is confirmed by the available inflight results. Therefore accurate photometry of the zodiacal light is possible from a sunlit rocket or satellite.

Theory of the propagation of high-power laser radiation in a nonlinear medium

Abstract: The propagation of high-power laser beams in media with the Kerr nonlinearity is discussed allowing for various types of nonlinear absorption. A parabolic equation for the complex amplitude of the electric field is derived from the Maxwell equations under conditions of greatest practical interest. This equation is analyzed under steady-state conditions and for laser pulses of 10-8 sec or shorter duration. A numerical solution of the steady-state problem shows that a multifocus structure appears in a beam of supercritical power. It is shown that this multifocus structure is universal, i.e., it appears irrespective of the nature of the nonlinear absorption in the medium and of other factors allowed for in the theory. The structure of the foci is studied in detail. Within light beams such foci usually move at velocities close to that of light. A theory of moving foci is presented. The trajectories of the motion of the foci and their parameters are calculated and the broadening of the laser pulse spectra due to the motion of the foci is evaluated. Explanations are given of various experimental data on the stimulated scattering, optical breakdown, and broadening of the laser radiation spectra.

Study of structural phase transitions by techniques of nonlinear optics

Abstract: The paper is intended to illustrate that nonlinear optical phenomena yield useful information about structural phase transitions in crystals. Emphasis is placed on collinear second harmonic generation (SHG) and on second harmonic scattering (SHS). The temperature dependence of higher-rank tensors describing SHG is discussed in detail and is related to variations of long- and short-range order. Several kinds of SHS are considered and explained by modulations of the nonlinear optical susceptibility. Particular attention is paid to results obtainable by SHS, but not by ordinary scattering of light.

Size–Refractive Index Distribution of Clear Coastal Water Particulates from Light Scattering

Abstract: Simultaneous measurements of the size distribution and volume scattering function of particles in clear coastal water are used to estimate a particle size-refractive index distribution. Various possibilities of the refractive index distribution and the observed particle distribution are studied systematically using Mie theory. The resulting model has minerals in mid-sizes and organic material in large and small sizes, but does not yield the correct dependence of scattering on wavelength. By assuming the existence of minerals or organics in sizes too small to be measured by the particle counter, two other models are developed, both of which yield acceptable wavelength dependence of scattering. The results of the three models are combined to provide limits on the size-refractive index distribution of the particles. Within these limits, volume scattering functions computed for the particles show good agreement with the measurements.