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We report a method for microfluidic multiple trapping and continuous sorting of microparticles using an optical potential landscape projected by a Dammann grating, enabling a high power-efficient approach to forming a composite two-dimensional spots array with high uniformity. The Dammann grating is fabricated in a photoresist by optical lithography. It is employed to create an optical lattice for multiple optical trapping and sorting in a mixture of polymer particles (n = 1.59) and silica particles (n = 1.42) with the same diameters of 3.1 [micro]m. In addition to the exponential selectivity by the projected optical landscapes, the proposed microfluidic sorting system has advantages in terms of high power efficiency and high uniformity due to the Dammann grating. OCIS codes: 350.4855, 120.4610.

The extinction efficiency factor associated with the scattering of a plane electromagnetic wave impinging on a basal face of a dielectric disk or a cylindrical particle is investigated by employing the physical-geometric optics hybrid (PGOH) method and the discrete-dipole approximation (DDA) method. It is found that the derived extinction efficiency factor from the PGOH is a function of the thickness of the disk, or the length of the cylinder, and the refractive index, but is independent of the diameter and shape of the cross section of the basal face of the particle. Furthermore, the oscillations of the extinction efficiency factor versus the thickness or length of the particle do not diminish if the particle is not absorptive. The values of the extinction efficiency factor simulated from the DDA method are quite different from those computed from the PGOH, although the size parameter of the particle is in the commonly recognized geometric optics regime. To explain the difference, the concept of the edge effect associated with the tunneling rays in the semiclassical scattering theory is generalized from the case of spherical particles to that of nonspherical particles based on the localization principle. Accordingly, the edge-effect contribution can be distinguished and removed from the extinction cross section calculation by the DDA method. The remaining part of the extinction cross section, associated with the interference between the transmitted rays and incident rays, agrees well with the results computed from the PGOH, and the agreement illustrates the presence of the edge effect in the case of nonspherical particles with surfaces that have no curvature along the incident direction. It is found that the asymptotic extinction efficiency factor may not necessarily converge to 2, but it depends on the specific physical processes of the interference between diffracted and transmitted light and of the edge effect. [c] 2010 Optical Society of America OCIS codes: 290.1310, 010.0010.

The backscattering linear depolarization ratios of major types of tropospheric aerosol particles (Asian and Saharan mineral dust, sea salt, and ammonium sulfate) were measured using a laboratory chamber for interpreting the polarization lidar measurement of tropospheric aerosols. The values obtained from Asian and Saharan mineral particles were 0.39 [+ or -] 0.04 to 0.05 (mean [+ or -] standard deviation) for a high number of concentrations in the supermicrometer range and 0.17 [+ or -] 0.03 to 0.14 [+ or -] 0.03 in the submicrometer range. The values were 0.08 [+ or -] 0.01 for sea-salt crystals, 0.04 [+ or -] 0.003 for ammonium sulfate crystals, and 0.01 [+ or -] [less than or equal to] 0.001 for both liquid droplets in the submicrometer range. These values can serve as a reference for estimating aerosol type using lidar measurement. OCIS codes: 010.3640, 010.1100.

We propose a direct method of partitioning the particulate spectral scattering coefficient of the marine hydrosol based on the concurrent determination of the concentrations of particulate mineral and organic matter (the total mass of optically active scattering material exclusive of water) with the particulate spectral scattering coefficient. For this we derive a Model II multiple linear regression model. The multiple linear regression of the particulate spectral scattering coefficient against the independent variables, the concentrations of particulate inorganic matter and particulate organic matter, yields their mass-specific spectral scattering cross sections. The mass-specific spectral scattering cross section is simply the particle scattering cross section normalized to the particle mass, a fundamental optical efficiency parameter for the attenuation of electromagnetic radiation [Absorption and Scattering of Light by Small Particles, (Wiley-Interscience, 1983), pp. 80-81, 289]. It is possible to infer the optical properties of the suspended matter from the mass-specific spectral scattering cross sections. From these cross sections we partition the particulate spectral scattering coefficient into its major components. OCIS codes: 010.4450, 010.4458, 290.5850, 280.1415, 280.4991, 010.4455.

We present the results of a study of optical scattering and backscattering of particulates for three coastal sites that represent a wide range of optical properties that are found in U.S. near-shore waters. The 6000 scattering and backscattering spectra collected for this study can be well approximated by a power-law function of wavelength. The power-law exponent for particulate scattering changes dramatically from site to site (and within each site) compared with particulate backscattering where all the spectra, except possibly the very clearest waters, cluster around a single wavelength power-law exponent of -0.94. The particulate backscattering-to-scattering ratio (the backscattering ratio) displays a wide range in wavelength dependence. This result is not consistent with scattering models that describe the bulk composition of water as a uniform mix of homogeneous spherical particles with a Junge-like power-law distribution over all particle sizes. Simultaneous particulate organic matter (POM) and particulate inorganic matter (PIM) measurements are available for some of our optical measurements, and siteaveraged POM and PIM mass-specific cross sections for scattering and backscattering can be derived. Cross sections for organic and inorganic material differ at each site, and the relative contribution of organic and inorganic material to scattering and backscattering depends differently at each site on the relative amount of material that is present. OCIS codes: 010.1350, 010.4450, 010.4458.

An experimental instrument for measuring a laser-induced fluorescence spectrum from a single aerosol particle is described. As a demonstration of instrument capabilities, the results of monodisperse 4.7 [miro]m sodium chloride particles doped with fluorescent riboflavin, produced with an inkjet aerosol generator, are presented. The fluorescence of the aerosol particles is excited in the wide range from 210 to 419 nm using a pulsed, tunable optical parametric oscillator laser. The maximum of the fluorescence emission of separately measured particles is detected at 560 nm. The dependence of the fluorescence on the excitation wavelength is studied and fluorescence cross sections are estimated. Agreement between the measured fluorescence data and the literature data for riboflavin is observed. OCIS codes: 170.6280, 300.2530.

The European Space Agency will launch the Atmospheric Laser Doppler Instrument (ALADIN) for global wind profile observations in the near future. The potential of ALADIN to measure the optical properties of aerosol and cirrus, as well, is investigated based on simulations. A comprehensive data analysis scheme is developed that includes (a) the correction of Doppler-shifted particle backscatter interference in the molecular backscatter channels (cross-talk effect), (b) a procedure that allows us to check the quality of the cross-talk correction, and (c) the procedures for the independent retrieval of profiles of the volume extinction and backscatter coefficients of particles considering the height-dependent ALADIN signal resolution. The error analysis shows that the particle backscatter and extinction coefficients, and the corresponding extinction-to-backscatter ratio (lidar ratio), can be obtained with an overall (systematic + statistical) error of 10%-15%, 15%-30%, and 20%-35%, respectively, in tropospheric aerosol and dust layers with extinction values from 50 to 200 [Mm.sup.-1]; 700-shot averaging (50 km horizontal resolution) is required. Vertical signal resolution is 500 m in the lower troposphere and 1000 m in the free troposphere. In cirrus characterized by extinction coefficients of 200 [Mm.sup.-1] and an optical depth of >0.2, backscatter coefficients, optical depth, and column lidar ratios can be obtained with 25%-35% relative uncertainty and a horizontal resolution of 10 km (140 shots). In the stratosphere, only the backscatter coefficient of aerosol layers and polar stratospheric clouds can be retrieved with an acceptable uncertainty of 15%30%. Vertical resolution is 2000 m. OCIS codes: 010.0010, 010.1100, 280.1120, 280.3640.

The extinction efficiencies as well as the scattering properties of particles of different porosity are studied. Calculations are performed for porous pseudospheres with small size (Rayleigh) inclusions using the discrete dipole approximation. Five refractive indices of materials covering the range from 1.20 + 0.00i to 1.75 + 0.58i were selected. They correspond to biological particles, dirty ice, silicate, and amorphous carbon and soot in the visual part of the spectrum. We attempt to describe the optical properties of such particles using Lorenz-Mie theory and a refractive index found from some effective medium theory (EMT) assuming the particle is homogeneous. We refer to this as the effective model. It is found that the deviations are minimal when utilizing the EMT based on the Bruggeman mixing rule. Usually the deviations in the extinction factor do not exceed ~5% for particle porosity P = 0 - 0.9 and size parameters [x.sub.porous] = 2[pi][r.sub.s,porous]/[lambda] [less than or equal to] 25. The deviations are larger for scattering and absorption efficiencies and smaller for particle albedo and the asymmetry parameter. Our calculations made for spheroids confirm these conclusions. Preliminary consideration shows that the effective model represents the intensity and polarization of radiation scattered by fluffy aggregates quite well. Thus the effective models of spherical and nonspherical particles can be used to significantly simplify the computations of the optical properties of aggregates containing only Rayleigh inclusions. OCIS codes: 290.0290, 290.5850.

We performed extensive bidirectional reflectance measurements on dry, wet, and submerged particulate layers with various albedos to investigate the darkening effect caused by wetting with fluids. It was found that, in addition to the reduction of the refractive index contrast when there is a pore liquid (wetted), the concentration of translucent grains in a particulate layer and the surface roughness conditions of the individual grains make important contributions to the wetting-induced darkening effect. Reflectance measurements on glass--sediment mixtures confirmed that, as the concentration of translucent particles increases, the reflectance of the dry layers increases while that of the wetted layers decreases. Measurements indicate that neither the prediction made by the theory of Twomey et al. [Appl. Opt. 25, 431 (1986)] nor that of Lekner and Dorf [Appl. Opt. 27, 1278 (1988)] is sufficient. OCIS codes: 010.4450, 280.0280, 120.5700, 290.4210, 030.5620.

Digital holography, which consists of both acquiring the hologram image in a digital camera and numerically reconstructing the information, offers new and faster ways to make the most of a hologram. We describe a new method to determine the rough size of particles in an in-line hologram. This method relies on a property that is specific to interference patterns in Fresnel holograms: Self-correlation of a hologram provides access to size information. The proposed method is both simple and fast and gives results with acceptable precision. It suppresses all the problems related to the numerical depth of focus when large depth volumes are analyzed. OCIS codes: 090.1760, 100.2000, 110.2960, 120.3940, 120.7250.

Most optical measurements in turbid media (including sprays, fogs, particulate and colloidal suspensions) assume single scattering of the detected photons. Multiple scattering introduces error, which has been quantified in very few systems. To quantify this error, we have written a flexible Monte Carlo photon transport simulation code capable of handling any three-dimensional geometry. Simulations of planar laser spray imaging with large, nonabsorbing particles show that up to 50% of the photons reaching the camera are multiply scattered. Because forward scattering dominates, the image is affected little. For particles with more absorption or with size closer to the wavelength of the light than those we have simulated, the effects are expected to be more serious. OCIS codes: 110.7050, 290.4210, 290.1090, 010.1310, 120.1740, 170.3660.

We present the development of a semi-analytical algorithm for optical particle sizing in disperse media. The algorithm is applied to the specific case of water clouds. However, it can be extended with minor modifications to other types of light-scattering medium. It is assumed that the optical thickness [tau] of the medium is large and the probability of photon absorption [beta] is small. Thus the optical particle-sizing problem is studied in the regime of highly developed multiple light scattering. It was found that the degree of polarization in visible and near-infrared channels provides us with information both on the effective size of droplets and on the optical thickness [tau]. OCIS codes: 010.0010, 030.5620.

Expressions for radiation-induced forces are presented for the case of a Rayleigh particle near the focus of a Gaussian laser beam at near-resonant conditions. Classical electromagnetic theory was used to obtain the dependence of the scattering and gradient forces on the incident laser frequency, the beam convergence angle, and the spatial position of the particle with respect to the focus. Approximative numerical analysis performed for particles with a single resonant absorption peak demonstrates the occurrence of up to 50-fold enhanced trapping forces at near-resonant frequencies. The use of this technique of gradient force enhancement may provide optical tweezers with enhanced trapping strengths and a degree of specificity. OCIS codes: 140.7010, 160.4760, 170.0180, 260.2030, 260.2110, 260.5740.

A systematic evaluation of the effects of polydispersity of chainlike aggregates in terms of primary particle number density and size on the scattering quantities and data inversion is presented. For aggregates with refractive index in the range |m-1| = 0.8-1.2, average size parameter x < 0.40, and primary particle number [N.sub.p] < 20, it is shown that the effects of polydispersity of primary particle size on the light-scattering quantities are much stronger than the polydispersity of the number of primary particles per aggregate. For aggregates with polydisperse primary particle size, the assumption of monodispersity tends to underestimate the real and imaginary parts of the refractive index and the number of primary particles. Specifically, for values of the distribution width [sigma] greater than 0.10, the effect of polydispersity of the size of primary particles must be considered in the data inversion schemes. Furthermore, in the same range of values for the refractive index, particle size parameter, and primary particle number, the assumption of monodispersity for aggregates with polydisperse particle number tends to underestimate the value of the real part of the refractive index and overestimate the value of the imaginary part of the refractive index and primary particle size. However, for values of the distribution width [sigma] less than 0.60, the effects of polydispersity of primary particle number can be neglected. In addition, the suitable pairing sets of the measured scattering quantities for data inversion are presented and discussed. OCIS codes: 010.1100, 010.1110, 010.1120, 010.1310, 290.1090, 290.3200.

We have constructed and tested a novel particle sizer that employs particle counting (the time-domain approach) rather than the ensemble-diffraction approach that currently dominates the market in atmospheric-dust particle sizers. The method does not depend on mechanical devices to restrict particles within the sampling volume but instead allows for optical isolation of the sampling volume. This technique is useful for atmospheric-dust measurements for which nonobtrusive measurement is often desirable.

The size and the position of individual particles in a falling spray crossing a horizontal plane are measured simultaneously with a shadowgraph imaging setup. An original method for measurement of drop sizes based on a prescribed analytical form of the luminance distribution of the objects (i.e., the drops) is presented. The processing time is strongly reduced compared with that for the usual inversion techniques. The turbulent dispersion of drops in a grid-generated turbulence is studied. Evidence for the presence of coalescence in the spray is presented.

We examine and compare near-forward light scattering that is caused by turbulence and typical particulate assemblages in the ocean. The near-forward scattering by particles was calculated using Mie theory for homogeneous spheres and particle size distributions representative of natural assemblages in the ocean. Direct numerical simulations of a passive scalar with Prandtl number 7 mixed by homogeneous turbulence were used to represent temperature fluctuations and resulting inhomogeneities in the refractive index of water. Light scattering on the simulated turbulent flow was calculated using the geometrical-optics approximation. We found that the smallest temperature scales contribute the most to scattering, and that scattering on turbulence typically dominates over scattering on particles for small angles as large as 0.1 [degrees]. The scattering angle deviation that is due to turbulence for a light beam propagating over a 0.25-m path length in the oceanic water can be as large as 0.1 [degrees]. In addition, we carried out a preliminary laboratory experiment that illustrates the differences in the near-forward scattering on refractive-index inhomogeneities and particles.

The Phase Doppler Anemometer (PDA) technique measures particle diameter assuming sphericity. A means for detecting nonsphericity has usually been implemented in commercial PDA systems to avoid sizing errors if the sphericity assumption is not valid. In the present research the response of standard and planar PDA systems is examined experimentally in more detail by passing nonspherical droplets of known shape through the measurement volume. The effectiveness of nonsphericity detection schemes can be evaluated, and furthermore the influence of the droplet oscillations on the frequency and phase evolution of individual signals can be quantified. The light scattering from such particles has been simulated by using geometric optics, and the computed response of standard and planar PDA systems agrees well with the experimental observations. We conclude with some remarks concerning the possibilities of characterizing the nonsphericity with PDA systems.

We propose a new method of particle size retrieval for mixed-phase and ice crystal clouds. The method enables us to identify each component of a bicomponent cloud composed of water droplets and ice crystals and to retrieve a size distribution separately for each cloud component. We explore the method's capability by using sythetic multiangular data of scattered-light intensity. We model cloud microphysical characteristics by assuming two noninteracting cloud components, such as liquid or supercooled droplets and cubic or hexagonal ice crystals, with regular simple geometrical shapes as first approximation. The sensitivity of the method is tested for different relative concentrations of the cloud components that are varied over a wide range. First, we investigate the applicability limit of the single-component cloud approximation in retrieving particle size distributions era bicomponent cloud. Second, we test the method to retrieve size distributions simultaneously for both components in mixed-phase clouds, and we discuss the conditions of its applicability.

The particle density of ground-state chromium atoms within one cross section of an arc plasma was measured spatially resolved, and the spatial distribution of the line shape of the chromium resonance line at 427.48 nm was partly determined. The measurements were performed with a newly developed setup that combines the methods of resonance interferometry and refractive tomography. The wavelength of a dye laser was scanned over the investigated transition, and the refractive index was measured spatially and spectrally resolved by use of tomography. For each spatial point the particle density and the local line shape were calculated from the measured spectral refractivity distribution by the method of resonance interferometry. We describe the physical principles, the optical arrangement, and the numerical apparatus, and we discuss the results and further possibilities. Key words: Plasma diagnostics, refractive tomography, resonance interferometry.

We obtain and analyze simple analytical formulas for asymmetry parameters and absorption cross sections of large, nonspherical particles. The formulas are based on the asymptotic properties of these characteristics at strong and weak absorption of radiation inside particles. The absorption cross section depends on parameter [Phi], which determines the value of the light-absorption cross section for weakly absorbing particles. It is larger for nonspherical scatterers. The asymmetry parameter depends on two parameters. The first is the asymmetry parameter [g.sub.o] of a nonspherical, transparent particle with the same shape as an absorbing one. The second parameter, [Beta], determines the strength of the influence of light absorption on the value of the asymmetry parameter. Parameter [Beta] is larger for nonspherical particles. One can find these three parameters ([Phi], [g.sub.o], and [Beta]) using a ray-tracing code (RTC) for nonabsorbing and weakly absorbing particles. The RTC can then be used to check the accuracy of the equations at any absorption for hexagonal cylinders and spheroids. It is found that the error of computing the absorption cross section and 1 - g (g is the asymmetry parameter) is less than 20% at the refractive index of particles n = 1.333. Values for asymmetry parameters of large, nonabsorbing, spheroidal particles with different aspect ratios are tabulated for the first time to our knowledge. They do net depend on the size of particles and can serve as an independent check of the accuracy of T-matrix codes for large parameters.

Illumination of an optically levitated particle with an intensity-modulated transverse beam induces a transverse vibration of a particle in an optical trap. based on this, the trapping force of a trap can be measured. Using an intensity-modulated longitudinal levitating beam causes a particle to move vertically, allowing for the determination of some aerodynamic parameters of a particle in air. The principles and the experimental phenomena are described and the initial results are given. Key words: Optical levitation, intensity-modulated beam.

A quantitative analysis of the fluctuations in the scattering associated with micrometer-size glycerol droplets that contain spherical latex inclusions are performed. Scattering intensities at two angles (the near-forward and the near-backward directions) are measured as functions of time. We analyze these signals using two techniques. We find that calculated autocorrelation time constants associated with these signals are not consistent with current models based on interference of light scattering from latex inclusions that exhibit Stokes-Einstein diffusion. The intensity fluctuations at different scattering angles display extended periods of both positive and negative correlations with characteristic time constants of the order of seconds. The time constants associated with the cross correlations provide information on the physical parameters of the inclusions.

Retrieval of the aerosol particle distribution function in the marine atmospheric boundary layer for a radius interval as great as 30 [[micro]meter] is considered with the use of simultaneous data on the spectral attenuation (in the spectral range of 0.4-5 [[micro]meter]) and small-angle phase function (in the angle interval of 0-8 [degrees]). An iterative procedure is constructed combining inversion algorithms for the spectral attenuation and phase function, each being efficient for a specific particle-size interval. Numerical experiments with two aerosol models are performed. The effect of random errors of the small-angle phase function is considered for different angular resolutions. It is shown that, given certain conditions, the inversion methodology under discussion makes it possible to retrieve the particle-size distribution function for the radius interval of 0.2-30 [[micro]meter] with a mean relative error of less than 10% and a maximum deviation not exceeding 20%.

The laws of light transmission by particle monolayers are investigated. The results of measurement of coherent transmission for monolayers formed by large non-absorbing particles are presented. The obtained results are compared to the calculation in the single-scattering approximation. Good agreement between experimental and calculated data is shown. Key words: Light scattering, coherent transmission, monolayer, discrete scatterers.

We analyze the relation between spherical particle parameters (size parameter. and relative refractive index m) and light-scattering indicatrix parameters (fringe pitch and visibility) for [Alpha] and m ranging from 7 to 88 and from 1.025 to 1.2, respectively. We consider formation of the indicatrix structure under variation of size parameter . and phase-shift parameter [Rho] = 2[Alpha](m - 1). We show that indicatrix visibility depends basically on the phase-shift parameter whereas fringe pitch depends on the size parameter. An analysis of these dependencies allows us to determine the region in the [Alpha] x [Rho] map where particle parameters can be derived unambiguously from indicatrix parameters. We clarify errors in determination of particle characteristics on the basis of the approximating equations that relate particle size and phase shift to indicatrix parameters. Key words: Light-scattering indicatrix, particles, sizing, refractive index, inverse problem.

A prominent characteristic of the light scattered from a microparticle containing inclusions is a fluctuation in the intensity that is due to the changing positions of the inclusions with respect to each other and the host droplet. We calculate the magnitude of these fluctuations for a host sphere containing a single eccentrically located spherical inclusion and experimentally measure the fluctuation amplitudes for host spheres containing multiple inclusions. We find that, for sufficiently small single inclusions, the amplitude of the scattering fluctuations increases approximately linearly with the area of the inclusion. For multiple inclusions, the fluctuation amplitude increases with concentration with an approximate power-law dependence.

An experimental study has been made of the angular structure of radiation scattered by monolayers of large nonabsorbing particles. We have investigated three media exhibiting different light-scattering properties: monodisperse polyvinyl toluene latex particles of 3.75-[[micro]meter] diameter suspended in water, polydisperse rice starch particles with a mean diameter of 6.4 [[micro]meter] suspended in water, and a mixture of ethyl and benzoic alcohols. It is shown that for large particles the structure of scattered radiation can be described in a single-scattering approximation. Analysis of the influence of polydispersity and the relative refractive index of particles on the intensity scattered by the monolayer has been performed. Key words: Light scattering, high concentration of scatterers, monolayer.

We used a real-time joint transform correlation technique for sizing opaque particles. The scheme can be used to estimate the size of both nonspherical and spherical particles. Computer simulation results are presented to illustrate the performance of this technique. Key words: Particle sizing, joint transform correlation.

The scattering phase functions of micrometer-sized glycerol droplets containing spherical latex inclusions undergo random fluctuations with time. We measure scattering intensities in the near-forward and near-backward scattering directions and find them to have strong positive correlations during some time periods and strong negative correlations during other time periods. The characteristic time constants of these correlations are of the order of seconds. We calculate scattering correlations from two types of scattering system. Correlations from a two-sphere system generally are positive, whereas correlations from a sphere containing a single spherical inclusion may be both positive and negative. Calculations of correlations from our experimental data are consistent with diffusion of inclusions within the host droplet, rather than interference effects between the inclusions.

A comparative study of statistical particle model theory of diffuse reflectance has been made. Theories have been applied to six particulate samples having different optical characteristics and average particle sizes that vary from 42 to 106 [[micro]meter]. We made an overall assessment of each theoretical model by determining the CIELAB color difference using experimentally measured and theoretically predicted diffuse reflectance spectra in the visible spectral range. We discuss the performance ratings of the models of other researchers and discovered numerous typographical errors in Fresnel reflection coefficient expressions. We provide the correct versions for these expressions.

Light-scattering measurements of optically levitated microdroplets containing three components, glycerin, water, and ammonium sulfate, are presented. Evaporation of the microdroplet is studied by means of morphology-dependent resonances observed in both Raman spectra as well as elastically scattered light and by the simultaneous measurement of the laser power. The phase transition from the liquid to the solid state of ammonium sulfate inside the microdroplet is observed by means of morphology-dependent resonances and Raman scattering. Key words: Optical levitation, morphology-dependent resonances, microdroplet, phase transition, evaporation.

The standard ultraviolet through short-wave infrared (200-2500-nm) diffuse-reflectance material, Halon PTFE, type G-80, is no longer available. Therefore an equivalent diffuse-reflectance standard material must be found. Algoflon F6 is shown here to be an appropriate replacement through the presentation of measurements of various spectral-reflectance properties of Halon and Algoflon F6. The measurements include spectral hemispherical reflectance, spectral bidirectional reflectance factor (BRF), sample BRF repeatability, and sample lifetime. Key words: Hemispherical reflectance, bidirectional reflectance factor, Halon, Lambertian, polytetrafluoroethylene, reflectance standard.

A simple method for determining the mean size, the concentration, and the refractive index of the monodispersion and the polydispersion of particles has been presented. The method is based on the empirical inversion of measurements of forward-angle light-scattering transmittance. The effects of particle size distribution and optical constants on forward-angle-scattering transmittance have been considered by using Mie theory. The proposed method has been used successfully for single latex spheres in water and polydispersed weakly absorbing particles of [Al.sub.2][O.sub.3] and Si[O.sub.2] in the flow of the propane-air flame combustion products. Key words: Optical particle sizing, light-transmittance measurements.

Theoretical procedures are presented for the determination of internal and external electromagnetic fields for the plane two-dimensional problem of an arbitrary monochromatic field (e.g., a focused laser light sheet) incident upon an irregularly shaped, layered cylindrical particle. Equations for the arbitrary illumination of a layered circular cylindrical particle are also given as a special case of the general solution. Key words: Internal and near-surface electromagnetic fields, layered noncircular cylindrical particle, focused light sheet, laser-particle interactions.

Particle-size distribution and the concentration of polystyrene particles suspended in water were accurately recovered from the inversion of spectral extinction data measured with a commercial spectrophotometer. The instrument was modified by placing a spatial filter in the collection optics to prevent low-angle scattered light from affecting the measurement of transmitted power. The data were inverted by use of a nonlinear iterative algorithm. When the extinction coefficient is measured in the k range of 0.3-1.1 [[micro]meter], the particle distributions can be retrieved over a diameter range of 0.6-2.8 [[micro]meter] for a wide interval of sample concentrations. The average diameters are recovered with a precision of better than [+ or -]1% and with accuracies consistent with the uncertainties by which the nominal diameters are known. The relative standard deviations of distributions corresponding to monodisperse samples are [+ or -]5-10%, whereas the accuracy on the measured concentrations is [approximately]5%. Key words: Particle sizing, inversion algorithm, spectral extinction.

The range of validity of the Rayleigh-Debye-Gans approximation for the optical cross sections of fractal aggregates (RDG-FA) that are formed by uniform small particles was evaluated in comparison with the integral equation formulation for scattering (IEFS), which accounts for the effects of multiple scattering and self-interaction. Numerical simulations were performed to create aggregates that exhibit mass fractallike characteristics with a wide range of particle and aggregate sizes and morphologies, including [x.sub.p] = 0.01-1.0, [absolute value of m - 1] = 0.1-2.0, N = 16-256, and [D.sub.f] = 1.0-3.0. The percent differences between both scattering theories were presented as error contour charts in the [absolute value of m - 1][x.sub.p] domains for various size aggregates, emphasizing fractal properties representative of diffusion-limited cluster-cluster aggregation. These charts conveniently identified the regions in which the differences were less than 10%, between 10% and 30%, and more than 30% for easy to use general guidelines for suitability of the RDG-FA theory in any scattering applications of interest, such as laser-based particulate diagnostics. Various types of aggregate geometry ranging from straight chains ([D.sub.f] [approximately equal to] 1.0) to compact clusters ([D.sub.f] [approximately equal to] 3.0) were also considered for generalization of the findings. For the present computational conditions, the RDG-FA theory yielded accurate predictions to within 10% for [absolute value of m - 1] to approximately 1 or more as long as the primary particles in aggregates were within the Rayleigh scattering limit ([x.sub.p] [less than or equal to] 0.3). Additionally, the effect of fractal dimension on the performance of the RDG-FA was generally found to be insignificant. The results suggested that the RDG-FA theory is a reasonable approximation for optics of a wide range of fractal aggregates, considerably extending its domain of applicability. Key words: Rayleigh-Debye-Gans, optical cross sections, fractal aggregates, laser diagnostics.

The problem of scattering by a spherical particle whose refractive index arbitrarily depends on the distance from its center has been solved. A computational scheme for determining the scattering coefficients for the refractive-index profiles given by some piecewise smooth function is constructed, and the models to use it are presented. The simple algorithm for evaluating the scattered and internal field vectors is elaborated. The exact expression for the scattering cross section in terms of the generated Debye partial potentials that are dependent on the given refractive index has been obtained.

A solution of the electromagnetic scattering problem for confocal coated spheroids has been obtained by the method of separation of variables in a spheroidal coordinate system. The main features of the solution are (i) the incident, scattered, and internal radiation fields are divided into two parts: an axisymmetric part independent of the azimuthal angle [Psi] and a nonaxisymmetric part that with integration over [Psi] gives zero; the diffraction problems for each part are solved separately; (ii) the scalar potentials of the solution are chosen in a special way: Abraham's potentials (for the axisymmetric part) and a superposition of the potentials used for spheres and infinitely long cylinders (for the nonaxisymmetric part). Such a procedure has been applied to homogeneous spheroids [Differential Equations 19, 1765 (1983); Astrophys. Space Sci. 204, 19, (1993)] and allows us to solve the light scattering problem for confocal spheroids with an arbitrary refractive index, size, and shape of the core or mantle. Numerical tests are described in detail. The efficiency factors have been calculated for prolate and oblate spheroids with refractive indices of 1.5 + 0.0i, 1.5 + 0.05i for the core and refractive indices of 1.3 + 0.0i, 1.3 + 0.05i for the mantle. The effects of the core size and particle shape as well as those of absorption in the core or mantle are examined. It is found that the efficiency factors of the coated and homogeneous spheroids with the volume-averaged refractive index are similar to first maximum. Key words: Light scattering, nonspherical particles, inhomogeneous particles.

Dynamic light scattering from protein solutions can be applied to the detection of conformational changes and to the measurement of particle size. Because accurate results can be adversely affected by experimental perturbations, careful procedures are necessary both in data acquisition and in data analysis. Autocorrelation functions (ACF's) of scattered light are simulated here to evaluate the role of the perturbations affecting measured signals from dilute protein solutions. The analysis of measured and simulated ACF's has been performed both by cumulant expansion and by a nonlinear least-squares fit, thereby allowing the definition of criteria for the optimization of the fitting parameters and of the measuring conditions. Moreover, by comparing experimental data from hemoglobin solutions and computer simulations, we show how to evaluate the contributions of polydispersity and statistical noise affecting the measurements. Key words: Dynamic light scattering, polydispersity, small particle sizing, autocorrelation function.

To assess the efficiency and accuracy of light-scattering calculations based on the discrete dipole approximation (DDA) for particles with a real relative refractive index smaller than unity, differential scattering cross sections and scattering efficiency factors were calculated for spherical particles. We performed the calculations for oxide particles and voids embedded in glass and silicon, using the exact scattering theory (Mie scattering) and the DDA. A comparison of the results shows that the DDA is applicable in the above refractive-index regime, and the conditions under which DDA-based calculations can provide scattering data with good accuracy are discussed. Key words: Light scattering, discrete dipole approximation.

Generalized Lorentz-Mie formulas are used to study the scattering characteristics when a chirped femtosecond pulse illuminates a spherical particle. For a linear chirped Gaussian pulse with the envelope function g([Tau]) = exp[-[Pi](1 + ib)[[Tau].sup.2]], dimensionless parameter b is defined as a chirp. The calculation illustrated that even for pulses with a constant carrier wavelength ([[Lambda].sub.0] = 0.5 [[micro]meter]) and pulse-filling coefficient ([l.sub.0] = 1.98), the efficiencies for extinction and scattering differ very much between the carrier wave and the different chirped pulses. The slowly varying background of the extinction and the scattering curves is damped by the chirp. When the pulse is deeply chirped, the maxima and minima of the background curves reduce to the point where they disappear, and the efficiency curves illustrate a steplike dependence on the sphere size. Another feature is that the chirped-pulse scattering seems blind: it depends only on the amount of chirp ([absolute value of b]), regardless of upchirp (b > 0) or downchirp (b < 0). Key words: Scattering of spherical particle, chirp, pulse, generalized Lorentz-Mie theory.

The software code SKYRAD.pack for retrieval of aerosol size distribution and optical thickness from data of direct and diffuse solar radiation is described; measurements are carried out with sky radiometers in the wavelength range 0.369-1.048 [[micro]meter]. The treatment of the radiative transfer problem concerning the optical quantities is mainly based on the IMS (improved multiple and single scattering) method, which uses the delta-M approximation for the truncation of the aerosol phase function and corrects the solution for the first- and second-order scattering. Both linear and nonlinear inversion methods can be used for retrieving the size distribution. Improved calibration methods for both direct and diffuse radiation, the data-analysis procedure, the results from the proposed code, and several connected problems are discussed. The results can be summarized as follows: (a) the SKYRAD.pack code can retrieve the columnar aerosol features with accuracy and efficiency in several environmental situations, provided the input parameters are correctly given; (b) when data of both direct and diffuse solar radiation are used, the detectable radius interval for aerosol particles is approximately from 0.03 to 10 [[micro]meter]; (c) besides the retrieval of the aerosol features, the data-analysis procedure also permits the determination of average values for three input parameters (real and imaginary aerosol refractive index, ground albedo) from the optical data; (d) absolute calibrations for the sky radiometer are not needed, and calibrations for direct and diffuse radiation can be carried out with field data; (e) the nonlinear inversion gives satisfactory results in a larger radius interval, without the unrealistic humps that occur with the linear inversion, but the results strongly depend on the first-guess spectrum; (f) aerosol features retrieved from simulated data showed a better agreement with the given data for the linear inversion than for the nonlinear inversion.

Estimation of aerosol size distributions from measurements of scattered light intensity by the use of a bistatic system with a multiwavelength laser is presented. We investigated the effects of inversion of the scattered intensity on calculated aerosol size distribution in a numerical experiment. Two model aerosol size distributions were used, one a Junge type widely known as a typical example of the size distribution of suspended particles in the atmosphere and the other a log-normal type as an example of the monodisperse distribution. A singular value decomposition was applied to the inversion to infer the size distribution from the kernel function and the scattered light intensity. In the physical experiment, the size distributions were successfully inferred from analysis of the scattered light intensity from an artificial polystyrene latex aerosol. Key words: Inversion, aerosol, size distribution, bistatic system, multiwavelength laser.

The contribution of multiple scattering to a spaceborne lidar return from clear molecular atmosphere obscured by transparent upper-level crystal clouds is assessed by the use of the variance-reduction Monte Carlo technique. High anisotropy of scattering in the forward direction by polydispersions of ice crystals is the basis of a significant effect of multiple scattering for small values of the lidar receiver field of view. Because of scattering by large nonspherical crystal particles, the lidar signal backscattered from the molecular atmosphere under the cloud increases significantly compared with the single-scattering return. The ratio of the multiple-to-single-scattering contributions from the clear atmosphere hidden by the clouds is greater than from the crystal clouds themselves, and it is proportional to the values of cloud optical thickness. Key words: Lidar in space, crystal clouds, multiple scattering, Monte Carlo.

Large quantities of chlorine and alumina particles are injected directly into the stratosphere by the current fleet of launch vehicles. Environmental concerns have been raised over the impact of the rocket exhaust on the ozone layer. Recently, differential absorption lidar (DIAL) was selected for remote sensing of ozone density within the plumes of Titan IV launch vehicles. The application of DIAL to this very challenging problem is described, and an implementation of UV-ozone DIAL is discussed that holds promise for this application. Key words: Differential absorption lidar (DIAL), stratospheric ozone, rocket exhaust, chlorine, alumina.

An analytical technique has been developed for calculating the angle-resolved light scattering by contaminant particles on smooth opaque surfaces. The analytical method was tested by a comparison of measured and calculated bidirectional reflectance distribution function (BRDF) values for contaminated surfaces. BRDF values were calculated from particle sizes, shapes, and areal densities obtained from scanning electron microscope images of the contaminated surfaces by a Princeton gamma-tech image analyzer. Measured and calculated BRDF values agreed to within the uncertainty associated with the particle characterization process for most scattering angles. Key words: Bidirectional reflectance distribution function, particulate contaminants, optical surfaces.

The problem of the reconstruction of the spectrum of a dispersed system from data on its spectral attenuation is studied. The numerical algorithm for obtaining the particle size distribution by the use of the concept of regularization is thoroughly treated. The applicability of this method to the reconstruction of the particle size distribution of a typical marine aerosol is tested. A method of choosing the regularization parameter of the solution for the inverse problem based on an objective estimate of the validity of the obtained solution is proposed. Results are presented for a set of numerical experiments in which the radius interval for which the distribution function can be obtained with a satisfactory accuracy is estimated. The validity of solutions is estimated depending on the measuring spectral range for the attenuation, the radius interval, and the number and position of points within this interval. The possibility of extending the radius interval for which the distribution function can be obtained by the use of extrapolation of the distribution function tail is discussed.

An analytic inversion method, based on the anomalous diffraction approximation for nonabsorbing spherical particles, was developed to retrieve the size distribution from the optical turbidity or extinction spectrum. This method makes use of a differential Fourier cosine transform approach and provides a simple and fast inversion by means of fast Fourier transform and the Savitzky-Golay filter. The applicability of this algorithm was tested on the extinction data generated by the Mie solution. The effects of noise, modality, band limits, and data set size were analyzed by comparison with simulated data. This method can be used to reconstruct the original monomodal and bimodal distributions from 10% noise-corrupted data. The peak position and ratio of peak heights can be recovered with 10% or less deviation. The experiments with latex spheres showed that the inversion result from this method compares favorably with that from the dynamic light scattering measurement. Key words: Particle size measurement, turbidity, optical characterization, inverse problem and light scattering.

An experimental procedure for the determination of the specific backscattering and total scattering coefficients of mineral particles suspended in water is described. The procedure combines measurements performed on samples of particles retained in glass-fiber filters and suspended in water, using a dual-beam spectrophotometer provided with an integrating-sphere attachment.