Showing papers on "Light scattering published in 1977"
TL;DR: Extinction for the scattering by small particles embedded in an absorbing medium is defined and a generalized form of an optical theorem is derived in this article, where the extinction is related to both the forward and the backward scattering amplitude.
Abstract: Extinction for the scattering by small particles embedded in an absorbing medium is defined and a generalized form of an optical theorem is derived. In general, the extinction is related to both the forward and the backward scattering amplitude.
300 citations
TL;DR: In this paper, a method for calculating the surface brightness distribution on a plane-parallel reflection nebula of uniform density illuminated by a star located either in front of, behind, or arbitrarily inside the scattering medium is proposed.
Abstract: A method for calculating the surface brightness distribution on a plane-parallel reflection nebula of uniform density illuminated by a star located either in front of, behind, or arbitrarily inside the scattering medium is proposed. The Monte Carlo technique is used to find solutions to the radiative transfer problem. The scattering properties of the nebular particles are parameterized by the albedo for single scattering and a three-parameter analytic phase function. Calculations are then presented for the surface brightness distribution across the face of such nebulae with (1) a foreground star and (2) immersed stars. The calculations include the full effects of multiple scattering, are independent of a particular assumed grain material or size distribution, and are applicable to any wavelength region for which observations can be obtained.
211 citations
TL;DR: In this paper, a series of experiments on steam condensation have been made in a Laval nozzle over a variety of starting conditions such that the onset of condensation occurs in the range -40 to 40 C.
Abstract: : A series of experiments on steam condensation have been made in a Laval nozzle over a variety of starting conditions such that the onset of condensation occurs in the range -40 to 40 C. The homogeneous nucleation and growth of the new phase is documented with both static pressure and laser light scattering. Since even at onset the majority of the condensed phase is due to droplet growth the nucleation and growth are coupled and the availability of two measured quantities is helpful in comparing a particular combination of nucleation rate and growth law. For detailed calculations on one of the experiments there is excellent agreement with both measurements throughout the condensation zone and a theoretical calculation using the classical nucleation rate expression due to Volmer and a droplet growth law due to Gyarmathy.
188 citations
TL;DR: In this article, the authors discussed the measurement of the finish of diamond-turned surfaces by differential light scattering and analyzed the two-dimensional power spectral density of the surface roughness, which can then be used to specify surface finish and predict scattering under a variety of conditions.
Abstract: This paper discusses the measurement of the finish of diamond-turned surfaces by differential light scattering. Experimental scattering data are analyzed by electromagnetic theory to give the two-dimensional power spectral density of the surface roughness. These spectral densities are direct functional measures of the surface quality, and may be characterized in terms of topographic finish parameters. These parameters can then be used to specify surface finish, to predict scattering under a variety of conditions, and to aid in studies of other functional properties of these surfaces. Scattering spectra are separated in-to three groups corresponding to three classes of surface roughness: periodic tool marks and one- and two-dimensional random roughness. Periodic tool marks give rise to discrete diffraction lines in the scattering spectrum and are characterized by their surface periods and their Fourier amplitudes. Random one- and two-dimensional roughness give rise to one- and two-dimensional continua underlying the diffraction lines and are characterized by band-limited values of the rms surface heights and slopes, and transverse length parameters. Using HeNe light, vertical roughnesses are measured from a fraction of an Angstrom to several hundred Angstroms, for transverse spatial wavelengths from a fraction of a micron to several hundred microns. We re-view experimental techniques for making these measurements with emphasis on the scatterometer developed in our laboratory, which uses a fixed source-detector geometry and a rotating sam-ple. Results are illustrated by a number of scattering spectra taken with this instrument.
144 citations
TL;DR: In this article, the relations between surface statistics and the near and far-field scattered light statistics are surveyed, mainly using scalar diffraction theory, and the methods which have been proposed and used are grouped and described according to whether they operate in the near or the far field and whether they use monochromatic or polychromatic light.
Abstract: The relations between surface statistics and the near- and far-field scattered light statistics are surveyed, mainly using scalar diffraction theory. The methods which have been proposed and used are grouped and described according to whether they operate in the near-field or the far-field and whether they use monochromatic or polychromatic light. Several methods emerge as promising for practical application to non-contacting and non-destructive testing.
122 citations
107 citations
94 citations
TL;DR: In this paper, light-scattering experiments on thermal acoustic spin waves in EuO were conducted and two peaks which can be shifted by an external magnetic field were identified as due to a modified bulk spin wave of the material.
Abstract: We present results of light-scattering experiments on thermal acoustic spin waves in EuO. The Brillouin spectra show two peaks which can be shifted by an external magnetic field. One of these is identified as due to a modified bulk spin wave of the material. The other one, by its anomalous behavior on reversal of the magnetic field or change of the scattering geometry, reveals itself as a spin wave propagating along the surface of the crystal.
89 citations
TL;DR: A method is presented for high-range resolution measurement of the backscatter from a scattering medium located in one arm of an interferometer that relies on the availability of a cw laser with a significant linewidth.
Abstract: A method is presented for high-range resolution measurement of the backscatter from a scattering medium located in one arm of an interferometer. The technique is interferometric in nature and relies on the availability of a cw laser with a significant linewidth. The measurement is based on observing coherent interference (equivalent to white-light fringes) between the return from the two arms of the interferometer for the portion of the backscatter that makes the path lengths equal. Experimental results are presented for backscatter from a turbid medium and from a stack of glass plates.
84 citations
TL;DR: Formulas are derived, using first-order perturbation theory, which predict light scattering from substrates coated with multiple dielectric overlayers, to model low efficiency rectangular groove gratings as beam sampling optical components and multilayer-overcoated metallic mirror substrates.
Abstract: Formulas are derived, using first-order perturbation theory, which predict light scattering from substrates coated with multiple dielectric overlayers. The scattering is assumed to result from surface irregularity. Numerical analysis is given for three types of dielectric stack configurations designed to typify experimental situations. The three configurations are substrate profile replicated at each dielectric interface, profile present at outermost dielectric layer only, and random roughness present at each interface. The formulas and configurations are used to model low efficiency rectangular groove gratings as beam sampling optical components and multilayer-overcoated metallic mirror substrates. Consideration is given to thermal expansion and fabrication error of thicknesses of the dielectric layers.
83 citations
TL;DR: In this paper, the optical properties of aggregated noble metal films have been studied in the spectral range from 0.35 to 1.0 μm, and the effective optical constants were derived from measurements of reflectance and transmittance.
Abstract: The optical properties of aggregated noble metal films have been studied in the spectral range from 0.35 to 1.0 μm. From the measurements of reflectance and transmittance, the effective optical constants were derived. These constants were then compared to those given by a model considering the films as formed by small rotational ellipsoids. In the model, the dipole/dipole interactions between particles have been taken into account together with the influence of the substrate. Careful measurements of film structures have shown that the assumptions concerning the size and shape of particles are reasonable. When p-polarized incident light is used, the resonance wavelength observed in the visible for the noble metal films is shifted to shorter wavelengths as the angle of incidence is increased.
TL;DR: In this paper, a review is given on a variety of liquid-crystal optical switches or modulators and specific work is described on the analysis and experiment on thin-film nematic liquidcrystal guides with propagation constant controlled by means of an applied voltage across the films.
Abstract: Liquid-crystal optical waveguides may be modulated or switched with high sensitivity by electrooptic, magnetooptic or acoustooptic effects. Such guides, however, have relatively slow response times and relatively high scattering losses so that they currently appear limited to special-purpose applications. A review is given on a variety of liquid-crystal optical switches or modulators. Specific work is then described on the analysis and experiment on thin-film nematic liquid-crystal guides with propagation constant controlled by means of an applied voltage across the films. A dynamic scattering switch is also demonstrated. Recent results show switchable grating directions in films having mixtures of nematic and cholesteric liquid crystals. The controlling variable is the frequency of the applied electric field.
01 Jan 1977
TL;DR: In this article, the use of a forward scattering laser anemometer system for the measurement of particle diameters larger than the fringe spacing is investigated and a systematic calibration experiment demonstrates a direct relationship between signal amplitude and particle diameter for transparent particles between 30 microns and 240 microns in diameter.
Abstract: The use of a forward scattering Laser Anemometer system for the measurement of particle diameters larger than the fringe spacing is investigated. A systematic calibration experiment demonstrates a direct relationship between signal amplitude and particle diameter for transparent particles between 30 microns and 240 microns in diameter. A light scattering analysis confirms these measurements and indicates how the range of particles which can be measured using the peak (mean) signal depends on the optical arrangement and particle properties. On the basis of this work a real time Laser Anemometer signal processor is modified so that the peak of the mean of each signal can be measured. A method of correcting data for the effect of particles which do not go through the center of the measurement volume is derived. Good agreement is found between particle size distributions measured in sprays by using the Laser Anemometer and size distributions measured by collecting the particles on a slide and using an image analysis computer.
TL;DR: In this paper, the absorption coefficient of liquid sulfur was measured in the energy range of 1.2 − 2.6 eV and no discontinuous behavior in the temperature dependence of the optical edge was observed at polymerization temperature if the increase in light scattering occurring at the onset of the polymerization process is taken into account.
Abstract: The absorption coefficient of liquid sulfur was measured in the energy range of 1.2–2.6 eV. No discontinuous behavior in the temperature dependence of the optical edge was observed at the polymerization temperature if the increase in light scattering occurring at the onset of the polymerization process is taken into account. Therefore, the electronic states that determine the optical edge appear to be insensitive to higher-order structural correlations.
TL;DR: It is concluded that unambiguous and fairly precise estimates of both size and refractive index for cell-like particles can be obtained from a single (perpendicular) scatter signal in a flow system using line-focused illumination.
Abstract: We have investigated the properties of three forward angle light scattering signals in a flow cytophotometer (Bio/Physics FC-200) using a line focused illuminating beam of about 5 ,z half-intensity width: (a) extinction of the illuminating beam; (b) scattering in the direction parallel to the focal line, integrated between 2 and 20#{176}; (c) scattering perpendicular to the focal line, integrated between 5 and 25#{176}. Signals were compared qualitatively in terms of pulse shape, and quantitatively in terms of total intensity (time integral) and pulse width (integral rise time) measurements, with respect to variations in particle diameter and refractive index at two wavelengths (488 or 633 nm). Test particles were transparent, spherical dextran gel (Sephadex) beads, having diameters continuously distributed between about 10 and 40 �z of several distinct refractive indices in the range 1.01-1.04, relative to water- comparable to fixed (hydrated) and living cells. Parallel and perpendicular scatter signals exhibit different, characteristic pulse shapes which remain distinctive over the whole range of diameter, refractive index and wavelength studied. These shapes evidently depend on geometrical factors which are different for the two scattering directions. Parallel scatter pulses rise and fall rapidly at the edges, but their amplitudes change relatively little while the center of the particle traverses the beam. Perpendicular scattering arises primarily from the edges of the particle, each of which produces a sharp pulse as it passes through the beam. Leading and trailing edge pulses are detected unequally and mirror-symmetrically on opposite sides of the beam. Perpendicular scatter pulsewidth (i.e. , the separation in time of these two pulses) is accurately proportional to particle diameter (at constant flow velocity) and independent of refractive index and wavelength within experimental error. Integrated extinction intensity is comparable to extinction under uniform, parallel illumination; its dependence on diameter, refractive index and wavelength is in good agreement with the predictions of anomalous diffraction theory. This permits a simple absolute calibration ofthe pulsewidth scale. Perpendicular scatter intensity increases smoothly with bead diameter, and also depends strongly on refractive index in the range studied. Parallel scatter intensity shows a more complex dependence on these parameters, but is relatively much less sensitive to refractive index. These results are discussed in terms of an approximate separation of refractive from diffractive effects due to the undirectionally focused illumination. We conclude that unambiguous and fairly precise estimates of both size and refractive index for cell-like particles can be obtained from a single (perpendicular) scatter signal in a flow system using line-focused illumination.
TL;DR: In this article, the rotational and vibrational relaxation times of acetonitrile-carbon tetrachloride solutions were investigated as a function of concentration, viscosity, and temperature using depolarized Rayleigh and Raman scattering.
Abstract: The rotational and vibrational relaxation times of acetonitrile–carbon tetrachloride solutions were investigated as a function of concentration, viscosity, and temperature using depolarized Rayleigh and Raman scattering. Using a Fabry‐Perot interferometer and single frequency laser source, we have shown that reliable results for the single particle orientational correlation times (τs) for CH3CN can be obtained by carrying out a concentration dependent depolarized Rayleigh scattering study. Raman scattering was shown to yield inconsistent results for τs in CH3CN. At constant viscosity, it was found that the Rayleigh scattering relaxation time (τRay) of CH3CN in CCl4 does not change with CH3CN concentration, indicating that the orientational pair correlation factor of liquid CH3CN is close to unity. This result suggests that the dynamic pair correlation in CH3CN is just as important as the static pair correlation. The experimental data were also compared with the predictions of the hydrodynamic stick and sl...
TL;DR: In this paper, the principal band features were found to be due to light scattering from at least three independent modes, each of which appear to result from a different hydroxyl (deuteroxyl) genus.
Abstract: Radiation‐induced compound formation in vitreous silica has been observed with Raman light scattering. The compounds were observed to form in silica samples that were impregnated with hydrogen (deuterium) gas and irradiated with gamma rays. Neither impregnation nor irradiation alone produced Raman‐active compounds. The combination, however, did produce compounds that were identified as silicon hydrides (deuterides) and hydroxyls (deuteroxyls). In addition, the hydroxyl (deuteroxyl) band shapes differed between as received and impregnated/irradiated samples and among the different impregnated/irradiated silica samples. The principal band features were found to be due to light scattering from at least three independent modes, each of which appear to result from a different hydroxyl (deuteroxyl) genus. In contrast, the hydride (deuteride) bands behave as though they were due to scattering from a single vibrational mode.
TL;DR: A simple multiple scattering model of a leaf is shown to account well for its measured optical properties and a method is proposed for finding accurate absorption spectra of pigment-containing cells.
Abstract: The optical properties of turbid media are formulated in terms of the diffusion equation approximation to linear transport theory. In particular the important effects of specular reflection at bounding surfaces are accurately accounted for by means of explicit boundary conditions at these surfaces. Applications of these results to two problems of biological interest are made. In one a simple multiple scattering model of a leaf is shown to account well for its measured optical properties. In another a method is proposed for finding accurate absorption spectra of pigment-containing cells.
TL;DR: In this article, the scattered electric field amplitude autocorrelation function of a dilute solution of large rigid anisotropic particles is computed in the Rayleigh-Debye approximation.
Abstract: The scattered electric field amplitude autocorrelation function of a dilute solution of large rigid anisotropic particles is computed in the Rayleigh–Debye approximation. The autocorrelation function for cylindrically symmetric particles is an infinite series of decaying exponentials with time constants τ−1l=q2D +l (l+1) Θ⊥ containing both translational and rotational diffusion coefficients. The dynamical terms are weighted by particle form factors and also by experimental geometry factors which are given in coordinate independent form. Explicit formulas for the form factors of spheres, rods, and thin disks are given. The general formulas reduce to the correct expressions for similar optically isotropic scattering systems.
TL;DR: In this paper, the elastic energy propagation in a three dimensional elastic medium, in which scatterers are distributed homogeneously and randomly, is studied from the point of view of the scattering theory.
Abstract: The elastic energy propagation in a three dimensional elastic medium, in which scatterers are distributed homogeneously and randomly, is studied from the point of view of the scattering theory. The isotropic scattering is assumed and the scattering process is considered up to the first order. It is assumed that not only the P-wave to P-wave scattering and the S-wave to S-wave scattering but also the S-wave to P-wave conversion scattering and the P-wave to S-wave conversion scattering take place. Green functions corresponding to these single isotropic scatterings are obtained and their properties are exhibited when the elastic energy is radiated spherically from a source. A space-time distribution of the energy density of the single scattered elastic waves is obtained. This model is applied to the short period body wave propagation of a small local earthquake near a hypocenter in the earth, when heterogeneities are interpreted as the scatterers. The temporal development of the seismic energy density, which is closely related to the seismogram, may be explained qualitatively.
TL;DR: The depolarization ratio delta and backscatter coefficients from an altostratus cloud illustrate the potential of these quantities for the study of cloud structure and phase.
Abstract: A lidar system that can measure multiple scattering and depolarization in the atmosphere is being used to study the climatic effects of cirrus clouds and to perform other investigations. The lidar system and its novel aspects are described in this paper. The influence of multiple scattering on noise, signal, and SNR is considered. Special receiver field stops incorporated for multiple scattering measurements, use of low voltage to control the photomultiplier tube gain, and a precision power/energy monitor are described. A technique for aligning transmitter and receiver axes and measuring transmitter beamwidth is presented. The multiple-scattered components of backscattered light are determined by inserting a center-blocked field stop to restrict the receiver field of view to the region outside of the diverging transmitted beam. Typical returns with and without the opaque field stop indicate the amplitude of multiple scattering from cirrus clouds and prove the feasibility of this technique. The depolarization ratio delta and backscatter coefficients from an altostratus cloud illustrate the potential of these quantities for the study of cloud structure and phase.
TL;DR: A value for the dipole–quadrupole polarizability A of methane is obtained by attributing the excess scattering over that implied by the Dipole–induced-dipole model to A.
Abstract: The long tails at low and high frequency in the Rayleigh scattering by gases comprising tetrahedral molecules is attributed to rotational Raman scattering. The rotating part of the collision-induced polarizability is due to the dipole–quadrupole polarizability A and varies as the inverse fourth power of the separation of the two interacting molecules. The rotational section rules are ΔJ = 0, ±1, ±2, ±3, and quantitative agreement is obtained with the observed frequency dependence of the tail in methane. Contributions due to hyperpolarizability are found to be small. A value for the dipole–quadrupole polarizability A of methane is obtained by attributing the excess scattering over that implied by the dipole–induced-dipole model to A.
TL;DR: In this article, the use of a forward scattering laser anemometer system for the measurement of particle diameters larger than the fringe spacing is investigated and a systematic calibration experiment demonstrates a direct relationship between signal amplitude and particle diameter for transparent particles between 30 microns and 240 microns in diameter.
Abstract: The use of a forward scattering Laser Anemometer system for the measurement of particle diameters larger than the fringe spacing is investigated. A systematic calibration experiment demonstrates a direct relationship between signal amplitude and particle diameter for transparent particles between 30 microns and 240 microns in diameter. A light scattering analysis confirms these measurements and indicates how the range of particles which can be measured using the peak (mean) signal depends on the optical arrangement and particle properties. On the basis of this work a real time Laser Anemometer signal processor is modified so that the peak of the mean of each signal can be measured. A method of correcting data for the effect of particles which do not go through the center of the measurement volume is derived. Good agreement is found between particle size distributions measured in sprays by using the Laser Anemometer and size distributions measured by collecting the particles on a slide and using an image analysis computer.
TL;DR: Light scattering from chicken red blood cells has been used as a model system to identify the asymmetry of cells and a dual orthogonal scatter system is used to conclusively demonstrate the orientational variation in signal.
Abstract: Light scattering from chicken red blood cells has been used as a model system to identify the asymmetry of cells. The histogram for forward angle light scattering for these cells is bimodal, the signal size being dependent on the cell orientation. A dual orthogonal scatter system is used to conclusively demonstrate this orientational variation in signal. A third scattering system, using a single incident beam with two orthogonal detectors, is used to further characterize the orientational variation of the scatter signal. In this third system it is shown that the signal in a detector set 90 degrees from the incident beam collects light reflected from the cell surface. The optical selection of cells in specific orientations using these systems may circumvent the need to physically orient cell in flow systems.
TL;DR: In this article, the absorption of intense laser light is reduced when targets are irradiated by 1.06-m light with long pulse widths (150-400 ps) and large focal spots (100-250 m).
Abstract: The absorption of intense laser light is found to be reduced when targets are irradiated by 1.06-\ensuremath{\mu} m light with long pulse widths (150-400 ps) and large focal spots (100-250 \ensuremath{\mu}m). Estimates of Brillouin scatter which account for the finite heat capacity of the underdense plasma predict this reduction. Spectra of the back-reflected light show red shifts indicative of Brillouin scattering.
TL;DR: In this paper, the Kirkwood-Yvon dielectric theory is generalized to the case of fluids consisting of molecules possessing arbitrary polarizability densities, and a simplified version of the general theory, in which each atom in a polyatomic is given a POI, is proposed, and worked out in detail for homonuclear diatomics.
Abstract: The Kirkwood-Yvon dielectric theory is generalized to the case of fluids consisting of molecules possessing arbitrary polarizability densities. The theory is used to find expressions for the equilibrium dielectric constant, the polarized scattering intensity, and the depolarized scattering intensity, which we have previously calculated under the approximation (PPA) that molecules have point polarizabilities. A simplified version of the general theory, in which each atom in a polyatomic is given a point polarizability (PAPA), is proposed, and worked out in detail for the case of homonuclear diatomics. A discussion is given of how we hope to obtain numerical results in the near future for liquids composed of model homonuclear diatomics considered by us previously.
TL;DR: Scalar diffraction theory and experimental data are presented to show how the size information in the forward- scattered light is dependent on the collection optics geometry, including the size and shape of source beam stops, which have been neglected in previous analyses.
Abstract: The theory and conditions are summarized under which single spherical particles in the size range of a few micrometers and larger may be sized using the observed fringe visibility in a cross-beam laser velocimeter. Scalar diffraction theory and experimental data are presented to show how the size information in the forward-scattered light is dependent on the collection optics geometry, including the size and shape of source beam stops, which have been neglected in previous analyses. Experimental data are also presented to show that backscattered light may not be usable for this method of sizing in the range of sizes examined.
TL;DR: In this article, the magnitude of orientational pair correlations (OPC) in liquids is measured by combining high pressure and depolarized Rayleigh light scattering techniques, and it is shown that the magnitude correlates well with the square of the molecular dipole moment.
Abstract: The nature of the intermolecular forces which are important in determining the magnitude of orientational pair correlations (OPC) in liquids is studied by combining high pressure and depolarized Rayleigh light scattering techniques. For molecules of similar shape (toluene, bromobenzene, and nitrobenzene) we find that the magnitude of the OPC as measured by depolarized light scattering is not simply a function of the packing of the molecules. For 16 monosubstituted derivatives of benzene, we find that the magnitude of the OPC correlates well with the square of the molecular dipole moment. This correlation of OPC with dipole moment is understood by relating both the molecular dipole moment and the magnitude of the OPC to the detailed distribution of molecular electronic charge. The light scattering reorientational relaxation times for toluene, bromobenzene, and nitrobenzene as a function of pressure have also been measured and found to be linear functions of viscosity.