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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.

Optical measurements of particle size and composition in granular samples are difficult to make due to complex light scattering from particles. These multiple scattering events bias absorption estimates and complicate the calculation of scattering and absorption coefficients used to estimate sample properties. Time series data, such as chromatograms and photon time-of-flight (TOF) profiles, contain self-repeating (fractal) characteristics. Power law analysis of photon TOF profiles allows the determination of absorption coefficients and particle sizes in a single experiment. A correlation dimension algorithm was used on photon TOF data from scattering samples. MLR models were then obtained from correlation dimension plots for the estimation of sample properties. Estimates of particle sizes and absorption coefficients were shown to agree well with theoretical values when compared using independent validation sets. Results show close to a 3-fold and up to a 5-fold decrease in the errors of estimation of dye concentration and particle size, respectively, as compared to steady-state measurements. The power law approach provides a useful means of determining sample properties in highly scattering media.

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.

The coupling of field-flow fractionation (FFF) and multiangle light scattering (MALS) detectors is complementary in that the MALS system allows particle characterization when a narrow dispersity particle population is present in the detector. The fractionation process provides this narrow dispersity. Utilizing discrete particle simulations of FFF and optical calculations based on both the Mie theory of particle scattering and Rayleigh-Gans-Debye (RGD) scattering theory, the extent of polydispersity that can be tolerated for accurate particle quantitation is explored. It is found that flow, electrical, and sedimentation FFF provide adequate separation for accurate particle quantitation by MALS. The Mie theory is more accurate than the RGD theory, which is known to deviate at higher particle size. Low error in the measurement of mean diameters is found when only the particle diameter is of interest. It is shown that the reconstruction of the particle size distribution from time slice data is distorted due to errors in concentration, which result from finite polydispersity and other effects. A number of procedures are evaluated in restoring the size distribution to higher accuracy. None of these procedures is deemed of general purpose and none of these is reliable. The best results are obtained when fractionation is conducted under the minimal possible outlet polydispersity and when steric effects are minimized. In addition, best results are had for inherently narrow dispersity colloidal materials.

The indirect effect of aerosols on water clouds, whereby aerosol particles change cloud optical properties, is caused by aerosol-induced changes of the size and number of cloud droplets. This affects the lifetime of the water clouds as well as their shortwave radiative properties. In addition, anthropogenic aerosols may change the properties of ice-forming nuclei. To investigate the potential effect of aerosol-ice cloud interactions by contact freezing, a prognostic equation for the number concentration of ice crystals is introduced into the ECMWF-Hamburg (ECHAM4) GCM. A simulation in which the number of contact ice nuclei is considered to be only temperature dependent is compared to simulations in which contact ice nuclei are considered to be dust aerosols. If dust aerosols are assumed to lose their nucleability by forming an internally mixed aerosol with sulfate, then the ice formation is slightly inhibited. On the contrary, if all contact nuclei are assumed to be insoluble carbonaceous aerosols, as found in contrails and some cirrus clouds, then contact nucleation is more important so that the liquid water path is smaller and the ice water path larger. These changes are, however, small compared to the extreme assumptions of having either no ice nuclei at all or so many ice nuclei that no supercooled cloud water exists.

Described is an improved algorithm that uses channel 1 and 2 radiances of the Advanced Very High Resolution Radiometer (AVHRR) to retrieve the aerosol optical thickness and Angstrom exponent over the ocean. Specifically discussed are recent changes in the algorithm as well as the results of a sensitivity study analyzing the effect of several sources of retrieval errors not addressed previously. Uncertainties in the AVHRR radiance calibration (particularly in the deep-space count value) may be among the major factors potentially limiting the retrieval accuracy. A change by one digital count may lead to a 50% change in the aerosol optical thickness and a change of 0.4 in the Angstrom exponent. On the other hand, the performance of two-channel algorithms weakly depends on a specific choice of the aerosol size distribution function with less than 10% changes in the optical thickness resulting from replacing a power law with a bimodal modified lognormal distribution. The updated algorithm is applied to a 10-yr period of observations (Jul 1983-Aug 1994), which includes data from NOAA-7, NOAA-9 (Feb 1985-Nov 1988), and NOAA-11 satellites. (The results are posted online at http://gacp.giss.nasa.gov/retrievals.) The NOAA-9 record reveals a seasonal cycle with maxima occurring around January-February and minima in June-July in the globally averaged aerosol optical thickness. The NOAA-7 data appear to show a residual effect of the El Chichon eruption (Mar 1982) as increased optical thickness values in the beginning of the record. The June 1991 eruption of Mt. Pinatubo resulted in a sharp increase in the aerosol load to more than double its normal value. The NOAA-9 record shows no discernible long-term trends in the global and hemisphere averages of the optical thickness and Angstrom exponent. On the other hand, there is a discontinuity in the Angstrom exponent values derived from NOAA-9 and NOAA-11 data and a significant temporal trend in the NOAA-11 record. The latter is unlikely to be related to the Mt. Pinatubo eruption and may be indicative of a serious calibration problem. The NOAA-9 record shows that the Northern Hemisphere mean optical thickness systematically exceeds that averaged over the Southern Hemisphere. Zonal means of the optical thickness exhibit an increase in the tropical regions of the Northern Hemisphere associated with annual desert dust outbursts and a springtime increase at middle latitudes of the Northern Hemisphere. Increased aerosol loads observed at middle latitudes of the Southern Hemisphere are probably associated with higher sea salt particle concentrations. Reliable extension of the retrieval record beyond the NOAA-9 lifetime will help to corroborate these findings.

Aerosol optical depth measurements over Bahrain acquired through the ground-based Aerosol Robotic Network (AERONET) are analyzed. Optical depths obtained from ground-based sun/sky radiometers showed a pronounced temporal trend, with a maximum dust aerosol loading observed during the March-July period. The aerosol optical depth probability distribution is rather narrow with a modal value of about 0.25. The Angstrom parameter frequency distribution has two peaks. One peak around 0.7 characterizes a situation when dust aerosol is more dominant, the second peak around 1.2 corresponds to relatively dust-flee cases. The correlation between aerosol optical depth and water vapor content in the total atmospheric column is strong (correlation coefficient of 0.82) when dust aerosol is almost absent (Angstrom parameter is greater than 0.7), suggesting possible hygroscopic growth of fine mode particles or source region correlation, and much weaker (correlation coefficient of 0.45) in the presence of dust (Angstrom parameter is less than 0.7). Diurnal variations of the aerosol optical depth and precipitable water were insignificant. Angstrom parameter diurnal variability (~20%-25%) is evident during the April-May period, when dust dominated the atmospheric optical conditions. Variations in the aerosol volume size distributions retrieved from spectral sun and sky radiance data are mainly associated with the changes in the concentration of the coarse aerosol fraction (variation coefficient of 61%). Geometric mean radii for the fine and coarse aerosol fractions are 0.14 [micro]m (std dev = 0.02) and 2.57 [micro]m (std dev = 0.27), respectively. The geometric standard deviation of each fraction is 0.41 and 0.73, respectively. In dust-free conditions the single scattering albedo (SSA) decreases with wavelength, while in the presence of dust the SSA either stays neutral or increases slightly with wavelength. The changes in the Angstrom parameter derived from a ground-based nephelometer and a collocated sun photometer during the initial checkout period were quite similar.

A technique for modification of the microtiter reader plates well with a polyaniline (PANI) film sensitive for ascorbic acid is presented. The principle of the analyte detection is based on monitoring the changes in optical absorption of the PANI film resulting from the reduction process initiated by ascorbic acid. The detection limit for ascorbic acid is 1 mg/L. Testing with real samples (soft drinks, fruit juices) gave good correlation of the method with iodimetric titration. High sensitivity, stability, and good reproducibility of the measurements make the proposed system an attractive alternative to traditional assays, used in medicine, ecology, and biotechnology.

The review focuses on the chemistry of phase transitions in concentrated aqueous salt particles as they occur in the atmosphere. Discussion on the laboratory work on the phase transitions of deliquescence and efflorescence salts as influenced by relative humidity, ice formation in the upper troposphere, and in polar stratophere is presented.

We present a simple laboratory experiment to illustrate some aspects of the soliton theory in discrete lattices with a system that models the dynamics of dislocations in a crystal or the properties of adsorbed atomic layers. The apparatus not only shows the role of the Peierls-Nabarro potential but also illustrates the hierarchy of depinning transitions and the importance of the collective motion in mass transport.

Research concerning the production of trimetallic particles of silver-gold-platinum is presented. The process involves the catalytic use of gold-platinum core-shell particles in an aqueous solution of silver ions.

A theoretical study of the near-field optical properties of subwavelength resonant metallic particles deposited on a surface was conducted. Stable solutions for both magnetic and electric fields inside and outside metallic particles of arbitrary shape were derived using the Green's dyadic method. The real-space technique is apparently well suited to describe the nontrivial near-field optical phenomena close to resonant metallic particles supported by dielectric surfaces.

The function of the film elongation was studied through the analysis of the polarization spectra of template-synthesized colloidal gold rods with aspect ratios ranging from L/d=1.8 to 49 embedded in poly(vinyl alcohol) films. Only one resonance band instead of two absorbance bands as found for randomly distributed gold rods were shown by the polarization absorbance spectra of aligned systems. The rods were completely oriented when the film was stretched 4-6 times its original length as revealed by the visible and near-infrared spectra.

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.

An experimental apparatus to measure the scattering properties of hexagonal icelike particles in the analog manner at the helium neon laser wavelength of 0.633 [[micro]meter] has been designed and built. The instrument consists of an array of 36 highly sensitive and linear photodiode detectors that are positioned to measure the light between the scattering angles of 2.8 [degrees] and 177.2 [degrees] in approximately 2.5 [degrees] increments and at any desired azimuthal angle. This array is calibrated such that the retrieved light signals are corrected to the actual light seen by the detectors to within approximately 6% at all applicable scattering and azimuthal angles. A system of electro-mechanical positioners places the sample at the desired and known position. A glass sphere and a glass fiber configured to scatter light like an infinite cylinder was used to test the operational effectiveness and calibration of the experimental apparatus. The phase functions for the parallel and perpendicular components determined from the experimental results match closely with the results computed from Mie theory.

Colloidal suspensions or colloids consist of small particles that are not visible to the naked eye. The opal is a primary example of an ordered colloid that is formed from silica spheres over geological timescales. One characteristic feature is that the particles are subject to Brownian motion.

Laser-induced fluorescence (LIF) is one of the most sensitive techniques for analysis of traces of polycyclic aromatic compounds in liquids. Application of this method to on-line monitoring requires solution of problems related to the presence of particulate materials. Thus, understanding the analytical effects associated with the suspension of microparticles is of considerable importance for both environmental and industrial applications. Here, LIF of perylene in acetonitrile solutions was studied for different light-scattering/-absorbing microparticle matrixes. With increasing suspension mass of efficiently light absorbing black-colored particles, the intensity of the associated LIF signals was found to obey an apparently exponential decrease. Their white-colored counterparts, however, have initially produced a sizable, [approximately]20%, signal increase of the respective LIF responses. An exponential decrease then became predominant, too. A model that explains the observations in terms of absorption and scattering coefficients is developed and examined. The quantitative effect of the particulate mass is correctly reproduced by the model, as well as the laser wavelength dependence. A possible application of a calibrating algorithm is addressed.

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 optical nonlinear response of a Bragg diffracting polyacrylamide crystalline colloidal arrays (PCCA) of dyed poly(1H,1H-heptafluorobutyl methacrylate) were described and characterized. Matching of the refractive index of the particles and the diffracted probe energy change was measured as a function of pump beam heating of the PCCA. The system was expected to switch on diffraction in the nanosecond time regime. However, the refraction of incident light was smaller than 97% due to crystalline colloidal array disorder.

Inhalation toxicologists are studying atmospheric ultrafine particles, which have a diameter of less than 0.1 micrometer, to discover whether they are hazardous to public health. Toxicologists are examining the chemical composition of atmospheric ultrafine particles, the number of concentration and size distribution, under the wintertime conditions in Pasadena, CA. The experiments are conducted with the use of a scanning differential mobility analyzer, a laser optical counter and two micro-orifice impactors. Toxicologists believe that the biggest contributors to the concentration of ultrafine particles are organic compounds.

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.

The potential application of nanometer-scale colloidal particles in optoelectronic devices and single-molecule detection initiated scientific interest on their size and shapes. A study was conducted on a population of novel nanoparticles in heterogeneous silver colloids. Surface-enhanced Raman scattering (SERS) analysis was performed. The findings illustrate that nanoparticle enhancement in the colloidal samples was correlated with particle size. Moreover, the optical enhancement can achieve a maximum of 10%-15% using size-selective fractionation techniques.

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.