Mie Scattering

Radiative transfer is the dominant mode of heat transfer in many engineering problems, including combustion chambers, greenhouses, rocket plume sensing among others. A complete genuinely multi-dimensional discretization in two-dimensional discrete ordinates method is formulated to solve radiative heat transfer in a rectangular enclosure composed of diffusely emitting and reflecting boundaries and containing homogeneous media that absorbs, emits and scatters. The major objetive of this study is to use an efficient method capable of eliminating the ray effect in complex 2D situations. One new genuinely multidimensional differencing scheme is used to solve a radiative transfer equation with S4, S6, S8, T6, T7, T8 and T9 angular quadrature scheme. Different cases are analized and the results are compared, when possible, with those obtained by other researchers.

When lidar pulses travel through a short path that includes a relatively high concentration of aerosols, scattering phenomena can alter the power and temporal properties of the pulses significantly, causing undesirable effects in the received pulse. In many applications the design of the lidar transmitter and receiver must consider adverse environmental aerosol conditions to ensure the desired performance. We present an analytical model of lidar system operation when the optical path includes aerosols for use in support of instrument design, simulations, and system evaluation. The model considers an optical path terminated with a solid object, although it can also be applied, with minor modifications, to cases where the expected backscatter occurs from nonsolid objects. The optical path aerosols are characterized by their attenuation and backscatter coefficients derived by the Mie theory from the concentration and particle size distribution of the aerosol. Other inputs include the lidar system parameters and instrument response function, and the model output is the time-resolved received pulse. The model is demonstrated and experimentally validated with military fog oil smoke for short ranges (several meters). The results are obtained with a lidar system operating at a wavelength of 0:905 μm within and outside the aerosol. The model goodness of fit is evaluated using the statistical coefficient of determination whose value ranged from 0.88 to 0.99 in this study.

Scattering of microwave radiation by large particles-Mie scattering-makes possible an innovative method for observing precipitation using 94-Ghz Doppler radar M eteorologists are often impeded in their observational studies of the atmosphere by the inherent difficulty in making accurate measurements of key atmospheric variables. For example, difficulties in making accurate cloud temperature and liquid water estimates from aircraft have frustrated scientists for years. Even with sophisticated (and sometimes expensive) remote sensing systems capable of making accurate measurements of some fundamental quantity, it is not always possible to obtain accurate estimates of the desired atmospheric variables from the fundamental quantity measured. For example, wellcalibrated weather radars can be used to make accurate measurements of reflectivity, but transforming this reflectivity to accurate rainfall estimates for a wide AMERICAN METEOROLOGICAL SOCIETY range of conditions is inherently difficult. Likewise, radiometers used on satellites can make accurate radiance measurements, but accurate retrievals of cloud properties from these radiance measurements are more difficult. In fact, many remote sensing techniques are based on some fundamental measurement that must then be used to obtain the quantities of interest through a transfer function that inherently adds uncertainty. Given the uncertainty that meteorologists face in making many measurements of atmospheric variables, particularly using remote sensing techniques, there is a certain excitement that accompanies the discovery of new techniques for making accurate measurements of fundamental meteorological quantities. It is our own excitement about a method of making accurate measurements of vertical air motion and coincidentally raindrop spectra in precipitation Kollias et al. 1999 Kollias et al. , 2001) ) that prompts us to write this paper to expose the technique to the larger meteorological community. The remote sensing technique for the vertical motion retrieval is particularly appealing since it is based on fundamental physics without the need of a complicated transfer function other than the relationship between terminal velocity and raindrop size. The technique that we highlight in this paper represents yet another example of the visionary contributions that Dr. Roger Lhermitte has made to radar meteo-OCTOBER 2002 BAF15* I 1471

As urban development and population growth accelerate, more tunnel construction in seismic zones has been planned. A tunnel's behaviour under earthquake loading must be assessed using proper techniques, in which field tests must evaluate these techniques. However, the field measurements of actual tunnel responses during earthquakes are rare. Centrifuge tests, for example, may be modelled in laboratory settings to simulate the actual tunnel on a much smaller scale. These tests can provide valuable information on how tunnels respond to seismic events and represent a valuable reference for calibrating numerical approaches. Four sets of centrifuge experiments were conducted under the supervision of the ReLUIS research project at the Cambridge University engineering department. This project aimed to develop seismic design procedures through experimental validations of computational methods. The present study aims to numerically model the two series of centrifuge tests under 2D plane-strain conditions on the model scale. A hardening soil model with a small-strain stiffness overlay is implemented to calibrate the Leighton Buzzard sand characteristics. Detailed inspections of input parameters were performed before any simulations, and potential reasons for the possible deviations in results were discussed. Comparisons of numerical simulations and experimental test results reveal that, in most instances, numerically-calculated and experimentally obtained results are in good agreement. However, some of the obtained results deviate from the experimental ones. Poor calibration of the dynamic characteristics of the sand was primarily cited as the source of these differences. Nevertheless, these calibrations could accurately predict the laboratory's static results. Modifying the soil model's stiffness parameters brings the predicted results much closer to the experimental ones, but some unidentified deviations remain.

In the present article the classical problem of electromagnetic scattering by a single homogeneous sphere is revisited. Main focus is the study of the scattering behavior as a function of the material contrast and the size parameters for all electric and magnetic resonances of a dielectric sphere. Specifically, the Padé approximants are introduced and utilized as an alternative system expansion of the Mie coefficients. Low order Padé approximants can give compact and physically insightful expressions for the scattering system and the enabled dynamic mechanisms. Higher order approximants are used for predicting accurately the resonant pole spectrum. These results are summarized into general pole formulae, covering up to fifth order magnetic and forth order electric resonances of a small dielectric sphere. Additionally, the connection between the radiative damping process and the resonant linewidth is investigated. The results obtained reveal the fundamental connection of the radiative damping mechanism with the maximum width occurring for each resonance. Finally, the suggested system ansatz is used for studying the resonant absorption maximum through a circuit-inspired perspective.

The complex refractive indices of eight volcanic ash samples, chosen to have a representative range of SiO2 contents, were retrieved from simultaneous measurements of their spectral mass extinction coefficient and size distribution. The mass extinction coefficients, at 0.33–19 μm, were measured using two optical systems: a Fourier transform spectrometer in the infrared and two diffraction grating spectrometers covering visible and ultraviolet wavelengths. The particle size distribution was measured using a scanning mobility particle sizer and an optical particle counter; values for the effective radius of ash particles measured in this study varied from 0.574 to 1.16 μm. Verification retrievals on high‐purity silica aerosol demonstrated that the Rayleigh continuous distribution of ellipsoids (CDEs) scattering model significantly outperformed Mie theory in retrieving the complex refractive index, when compared to literature values. Assuming the silica particles provided a good analog...

To improve the parameterization of ice-phase microphysics in regional meteorological models, this study developed a triple-moment bulk scheme, which also tracks the variations in the shape and density of several hydrometeors. Solid-phase hydrometeors are classified into pristine ice, snow aggregates, rimed ice, and hailstones based on their physical mechanisms. The new scheme has been incorporated into the Weather Research and Forecasting Model and tested with an idealized two-dimensional simulation of a squall-line system. The simulation successfully revealed the smooth transition from the convective core to the stratiform anvil as well as the alternating pattern in the hydrometeor vertical distributions, as was similarly demonstrated in other similar studies. A few sensitivity tests were performed to reveal the importance of including shape and density variations, which strongly affect the mean particle size by up to 50% and fall speed by as much as 100% for individual hydrometeor categories. Furthermore, the inclusion of a third moment could enhance the diffusional growth rate of small crystals and reduce the ventilation effect of large particles compared with the conventional double-moment approach. These factors have a significant influence on cloud structure and precipitation amounts.

To improve the parameterization of ice-phase microphysics in regional meteorological models, this study developed a triple-moment bulk scheme, which also tracks the variations in the shape and density of several hydrometeors. Solid-phase hydrometeors are classified into pristine ice, snow aggregates, rimed ice, and hailstones based on their physical mechanisms. The new scheme has been incorporated into the Weather Research and Forecasting Model and tested with an idealized two-dimensional simulation of a squall-line system. The simulation successfully revealed the smooth transition from the convective core to the stratiform anvil as well as the alternating pattern in the hydrometeor vertical distributions, as was similarly demonstrated in other similar studies. A few sensitivity tests were performed to reveal the importance of including shape and density variations, which strongly affect the mean particle size by up to 50% and fall speed by as much as 100% for individual hydrometeor categories. Furthermore, the inclusion of a third moment could enhance the diffusional growth rate of small crystals and reduce the ventilation effect of large particles compared with the conventional double-moment approach. These factors have a significant influence on cloud structure and precipitation amounts.

The e ect of aggregation on soot radiative properties in the infrared region of the spectrum is numerically investigated using Rayleigh-Debye-Gans theory for fractal aggregates (RDG-FA). In order to use the RDG-FA theory for a wide range of aggregate sizes and wavelengths, the predicted phase functions, scattering and absorption coe cients are compared with a more accurate theory, the integral equation formulation for scattering-IEFS. The importance of scattering when compared with absorption is investigated, as well as the e ect of aggregation on the phase function shape and on the scattering cross section. It is concluded that in the case of small aggregates formed with small primary particles the scattering coe cient is negligible compared with the absorption coe cient, and scattering and aggregation of primary particles can be ignored. Thus, the Rayleigh approximation can be used leading to isotropic scattering. In the case of large aggregates constituted by large primary particles, aggregation becomes important and the scattering cross section is of the same order of magnitude of the absorption cross section. Moreover, the phase function becomes highly peaked in the forward direction. Therefore, the Rayleigh and the equivalent volume Mie sphere approximations are not valid, and the RDG-FA method emerges as a good compromise between accuracy and simplicity of application. However, radiative transfer calculations between two inÿnite, parallel, black walls show that scattering may always be neglected in the calculation of total radiative heat source and heat uxes to the walls. The minor in uence of scattering on the accuracy of the predictions is explained by the shift between the spectral region where scattering is important and the region where the spectral radiative heat source is large.

Light scattering by an evaporating water droplet several micrometers in size with spherical dielectric inclusions was investigated. The evolution of the droplet radius and the effective refractive index was determined. A deviation from predictions by standard effective-medium theories in the form of a resonance was encountered. Simple analysis of the phenomenon was conducted, and a qualitative explanation was proposed.

The dependence of the optical properties of large sodium clusters as a function of their size is studied. Clusters are light induced allowing observation of the smooth change of their sizes as a result of the spontaneous nucleation process. We combine the formalism of the classical Mie scattering theory for spheres of arbitrary large size and the concept of the collective electron oscillations (plasmons). The maxima in normalized intensities of light scattered by single cluster we attribute to resonant excitation of dipole and quadrupole plasmon oscillation respectively. We show that plasmon resonances take place for different cluster sizes when excited with different wavelength. We compare these results with expectations resulting from solving the problem of eigenfrequencies of free-electron sphere with the dielectric function described within the Lorentz-Drude model.

The evaporation and the thermal accommodation coefficients for water in nitrogen were investigated by means of the analysis of evaporation of pure water droplet as a function of temperature. The droplet was levitated in an electrodynamic trap placed in a climatic chamber. The levitation time was in the range of seconds, which corresponds to the characteristic time scales of cloud droplet growth. Droplet radius evolution and evaporation dynamics were studied as a function of temperature, by analyzing the angle-resolved light scattering Mie interference patterns. A model of droplet evolution, accounting for the kinetic effects near the droplet surface, was applied. The evaporation coefficient for the temperature range from 273.6 to 298.3 K was found to be between 0.054 and 0.12 with a minimum of 0.036 ± 0.015 seemingly coinciding with water maximum density at 277.1 K. The average value of thermal accommodation coefficient over the temperature range from 277 to 289 K was found to be 0....

The paper is devoted to numerical simulation of homogeneous images of dielectric, semiconductor and metal spherical nanoparticles in a flat plane situated in the near-field region. The influence of the particle radius, the distance to the image plane and the polarization direction of the illuminating light wave on image formation is illustrated on the basis of near-field Mie scattering theory.

To speed up the numerical computation of beam shape coefficients in the generalized Lorenz-Mie theory (GLMT) for cylinders, a cylindrical localized approximation has recently been introduced [J. Opt. Soc. Am. A 14, 3014 (1997)], in analogy with the localized approximation used for the GLMT for spheres. A rigorous justification of this cylindrical localized approximation is presented.

Monotonic relationships between scattered intensities and diameters in Lorenz-Mie theory are obtained with the aid of the SUPERMIDI computer program. The influence of the solid collection angle, scattered light, and of the real and imaginary parts of the complex refractive index on these relations is discussed. Results are given for typical opaque particles (aluminum) and transparent particles (glass). Emphasis is on the application of such relationships to simultaneous measurements of the velocity and the size of single particles embedded in flows.

Aerosols on Mars have an important impact on the radiative transfer properties of its atmosphere. Today their spectral properties and therefore their interaction with UV radiation are only poorly known. Improving the radiative transfer modeling requires a better knowledge of their characteristics, in particular of their phase function, single scattering albedo and opacity. We will show that such information can be accessed by using EPF observations.

We report the first experimental results on angle-resolved elastic light scattering in the soft X-ray regime, where free sub-micron particles in the size regime between 150 and 250 nm are studied in the gas phase by using a continuous particle beam. Two different types of studies are reported: (i) Angle-resolved elastic light scattering experiments provide specific information on the scattering patterns in the regime of element-selective inner-shell excitation near the Si 2p-edge (80-150 eV). In addition to intense forward scattering, we observe distinct features in the angle-resolved scattering patterns. These are modelled by using Mie theory as well as a model that includes contributions from diffuse and specular reflection. The results are primarily attributed to scattering from soft X-rays in the surface layer. (ii) Spectroscopic experiments are reported, where the photon detector is placed at a given scattering angle while scanning the photon energy near the Si 2p-absorption edge. These results are also analyzed by a Mie model, yielding accurate information of the size distribution.

We present a detailed evaluation of remotely sensed aerosol microphysical properties obtained from an advanced, multi-wavelength high-spectral-resolution lidar (HSRL-2) during the 2013 NASA DISCOVER-AQ field campaign. Vertically resolved retrievals of fine-mode aerosol number, surface-area, and volume concentration as well as aerosol effective radius are compared to 108 collocated, airborne in situ measurement profiles in the wintertime San Joaquin Valley, California, and in summertime Houston, Texas. An algorithm for relating the dry in situ aerosol properties to those obtained by the HSRL at ambient relative humidity is discussed. We show that the HSRL-2 retrievals of ambient fine-mode aerosol surface-area and volume concentrations agree with the in situ measurements to within 25 and 10 %, respectively, once hygroscopic growth adjustments have been applied to the dry in situ data. Despite this excellent agreement for the microphysical properties, extinction and backscatter coefficients at ambient relative humidity derived from the in situ aerosol measurements using Mie theory are consistently smaller than those measured by the HSRL, with average differences of 31 ± 5 % and 53 ± 11 % for California and Texas, respectively. This low bias in the in situ estimates is attributed to the presence of coarse-mode aerosol that are detected by HSRL-2 but that are too large to be well sampled by the in situ instrumentation. Since the retrieval of aerosol volume is most relevant to current regulatory efforts targeting fine particle mass (PM 2.5 ), these findings highlight the advantages of an advanced 3β + 2α HSRL for constraining the vertical distribution of the aerosol volume or mass loading relevant for air quality.

Retrievals of aerosol microphysical properties (effective radius, volume and surface-area concentrations) and aerosol optical properties (complex index of refraction and single-scattering albedo) were obtained from a hybrid multiwavelength lidar data set for the first time. In July 2011, in the Baltimore-Washington DC region, synergistic profiling of optical and microphysical properties of aerosols with both airborne (in situ and remote sensing) and ground-based remote sensing systems was performed during the first deployment of DISCOVER-AQ. The hybrid multiwavelength lidar data set combines ground-based elastic backscatter lidar measurements at 355 nm with airborne High-Spectral-Resolution Lidar (HSRL) measurements at 532 nm and elastic backscatter lidar measurements at 1064 nm that were obtained less than 5 km apart from each other. This was the first study in which optical and microphysical retrievals from lidar were obtained during the day and directly compared to AERONET and in situ measurements for 11 cases. Good agreement was observed between lidar and AERONET retrievals. Larger discrepancies were observed between lidar retrievals and in situ measurements obtained by the aircraft and aerosol hygroscopic effects are believed to be the main factor in such discrepancies.

Over 700 vertically-resolved retrievals of effective radii, number, volume, and surface-area concentrations of aerosols obtained from inversion of airborne multiwavelength High Spectral Resolution Lidar (HSRL-2) measurements are compared to vertically resolved airborne in situ measurements obtained during DISCOVER-AQ campaign from 2013 in California and Texas. In situ measurements of dry and humidified scattering, dry absorption, and dry size distributions are used to estimate hygroscopic adjustments which, in turn, are applied to the dry in situ measurements before comparison to HSRL-2 measurements and retrievals. The HSRL-2 retrievals of size parameters agree well with the in situ measurements once the hygroscopic adjustments are applied to the latter, with biases smaller than 25 % for surface-area concentrations, and smaller than 10 % for volume concentration. A closure study is performed by comparing the extinction and backscatter measured with the HSRL-2 with those calculated f...

Retrievals of aerosol microphysical properties (e.g. effective radius, volume and surface-area concentrations) and aerosol optical properties (e.g. complex index of refraction and single scattering albedo) were obtained from a hybrid multiwavelength lidar dataset for the first time. In July of 2011, in the Baltimore-Washington DC region, synergistic profiling of optical and microphysical properties of aerosols with both airborne in-situ and ground-based remote sensing systems was performed during the first deployment of DISCOVER-AQ. The hybrid multiwavelength lidar dataset combines elastic ground-based measurements at 355 nm with airborne High Spectral Resolution Lidar (HSRL) measurements at 532 nm and elastic measurements at 1064 nm that were obtained less than 5 km apart of each other. This was the first study in which optical and microphysical retrievals from lidar were obtained during the day and directly compared to AERONET and in-situ measurements for 11 cases. Good agreement ...

A time-lag and linear regression-based framework is developed and its performance is assessed for predicting temporally resolved spray number of droplets using flame chemiluminescence and a sparse number of droplets data. Separate pressure, interferometric laser imaging for droplet sizing, shadowgraphy, and flame chemiluminescence are performed for the spray characterization. Simultaneous 10 kHz flame chemiluminescence and 0.2 Hz Mie scattering measurements are performed for the purposes of the framework development and the number of droplets prediction. Both methane and/or Jet A-1 are used in the experiments. Three conditions corresponding to perfectly premixed methane and air, Jet A-1 spray, and Jet A-1 spray in premixed methane and air flames are examined. For all test conditions, the fuels and air flow rates are adjusted to produce a fixed power of 10 kW. The results show that the frequency of the spatially averaged flame chemiluminescence as well as the number and the mass of the droplets (for both reacting and non-reacting conditions) oscillations frequencies match; however, these frequencies do not match that of the pressure fluctuations. This suggests that the flame chemiluminescence dynamics is driven by the fuel injection system. For signals with matching frequency content, a data-driven framework is developed for predicting an objective signal (the spray number of droplets) using an input signal (the flame chemiluminescence). The performance of the developed framework is assessed for tested spray conditions and the predicted number of droplets agrees well with those measured. For gas turbine engine combustion research, the developed framework is of importance, as it facilitates understanding the time-resolved spray characteristics for instances that the spray data is available sparsely.

The 20-L dust explosion apparatus is widely used for dust explosion risk assessment, however the 1-m 3 apparatus remains the gold standard for explosion testing by generating a turbulent dust cloud consistent with industrial scenarios. Recent studies show a 1-m 3 dispersion leads to particle breakage, which can impact risk assessment. However, the effect of particle breakage on explosion risk assessment is not quantified. The focus of this work is to measure particle breakage in a 1-m 3 and to quantify the effect of resulting particle size distribution shift on the explosion risk assessment by measuring change in the minimum ignition energy (MIE). We observed Ascorbic Acid particle size reduction in a 1-m 3 , resulting in a reduced post-dispersion MIE as compared to the pre-dispersion sample. This work aims to create awareness of dust particle breakage to improve the risk assessment process, to better prevent incidents.

Tilted washboard potentials are periodic functions of potential energy whose graphs remind the profiles of inclined washboards for scrubbing clothes. Practically unknown until the 1970´s, washboard potentials are at present ubiquitous seminal landscapes across diverse physics researches and technologies now receiving significant attention. However, washboard potentials are still rarely presented to science and engineering undergraduates; perhaps they could hear about those when first studying Josephson junctions. Aiming to promote the presentation of such potentials to undergraduates, we here consider cases of washboard potentials in: classical mechanics, quantum physics and optics. The quantum case is the superconducting Josephson junction whose phase quasi-particle has a tilted washboard potential leading to important applications, e.g. the phase qubit in quantum computation. Optical cases are electro-optical potentials generated with laser beams in which thousands of atom electric dipoles may become confined or evolve, potentials being generated either with laser Bessel beams, or with laser standing waves, whose periodic potential profile is implicitly tilted or may be experimentally adjusted to become tilted. Electro-optical potentials are presently used in fast-paced fundamental research, e.g. Brownian particle motors, atom trapping in optical lattices, optical atomic clocks, protein transport in biological cells, and in condensed matter physics to name a few.

In the field of biomedical infrared spectroscopy it is often desirable to obtain spectra at the cellular level. Samples consisting of isolated single biological cells are particularly unsuited to such analysis since cells are strong scatterers of infrared radiation. Thus measured spectra consist of an absorption component often highly distorted by scattering effects. It is now known that the predominant contribution to the scattering is Resonant Mie Scattering (RMieS) and recently we have shown that this can be corrected for, using an iterative algorithm based on Extended Multiplicative Signal Correction (EMSC) and a Mie approximation formula. Here we present an iterative algorithm that applies full Mie scattering theory. In order to avoid noise accumulation in the iterative algorithm a curve-fitting step is implemented on the new reference spectrum. The new algorithm increases the computational time when run on an equivalent processor. Therefore parallel processing by a Graphics Pr...

Infrared spectra of single biological cells often exhibit the 'dispersion artefact' observed as a sharp decrease in intensity on the high wavenumber side of absorption bands, in particular the Amide I band at $1655 cm À1 , causing a downward shift of the true peak position. The presence of this effect makes any biochemical interpretation of the spectra unreliable. Recent theory has shed light on the origins of the 'dispersion artefact' which has been attributed to resonant Mie scattering (RMieS). In this paper a preliminary algorithm for correcting RMieS is presented and evaluated using simulated data. Results show that the 'dispersion artefact' appears to be removed; however, the correction is not perfect. An iterative approach was subsequently implemented whereby the reference spectrum is improved after each iteration, resulting in a more accurate correction. Consequently the corrected spectra become increasingly more representative of the pure absorbance spectra. Using this correction method reliable peak positions can be obtained.

We present an approach for estimating and correcting Mie scattering occurring in infrared spectra of single cells, at diffraction limited probe size, as in synchrotron based microscopy. The Mie scattering is modeled by extended multiplicative signal correction (EMSC) and subtracted from the vibrational absorption. Because the Mie scattering depends non-linearly on α, the product of the radius and the refractive index of the medium/sphere causing it, a new method was developed for estimating the Mie scattering by EMSC for unknown radius and refractive index of the Mie scatterer. The theoretically expected Mie contributions for a range of different α values were computed according to the formulae developed by Van de Hulst (1957). The many simulated spectra were then summarized by a six-dimensional subspace model by principal component analysis (PCA). This subspace model was used in EMSC to estimate and correct for Mie scattering, as well as other additive and multiplicative interferen...

The canonical studies on Mie scattering unravel strong electric/magnetic optical responses in nanostructures, laying foundation for emerging meta-photonic applications. Conventionally, the morphology-sensitive resonances hinge on the normalized frequency, i.e. particle size over wavelength, but non-paraxial incidence symmetry is overlooked. Here, through confocal reflection microscopy with a tight focus scanning over silicon nanostructures, the scattering point spread functions unveil distinctive spatial patterns featuring that linear scattering efficiency is maximal when the focus is misaligned. The underlying physical mechanism is the excitation of higher-order multipolar modes, not accessible by plane wave irradiation, via displacement resonance, which showcases a significant reduction of nonlinear response threshold, sign flip in all-optical switching, and spatial resolution enhancement. Our result fundamentally extends the century-old light scattering theory, and suggests new d...

Infrared spectra of single biological cells often exhibit the 'dispersion artefact' observed as a sharp decrease in intensity on the high wavenumber side of absorption bands, in particular the Amide I band at $1655 cm À1 , causing a downward shift of the true peak position. The presence of this effect makes any biochemical interpretation of the spectra unreliable. Recent theory has shed light on the origins of the 'dispersion artefact' which has been attributed to resonant Mie scattering (RMieS). In this paper a preliminary algorithm for correcting RMieS is presented and evaluated using simulated data. Results show that the 'dispersion artefact' appears to be removed; however, the correction is not perfect. An iterative approach was subsequently implemented whereby the reference spectrum is improved after each iteration, resulting in a more accurate correction. Consequently the corrected spectra become increasingly more representative of the pure absorbance spectra. Using this correction method reliable peak positions can be obtained.

A method is described for obtaining real-time in situ size and velocity measurements of spherical particles or droplets using crossed-beam interferometry. The optical arrangement, which is similar to a dual-scatter laser Doppler velocimeter (LDV), consists of two laser beams focused to a crossover region. Droplets passing through the focal volume scatter light to the collecting lens situated at some off-axis angle. The dualbeam light scatter is analyzed by the geometric optics theory to relate the scattered fringe pattern to the droplet diameter. Because the droplet size measurement is based on the relative phase shift between the two light waves passing through it, the method is independent of the incident intensity, droplet absorption, or absolute scattering intensity. Experimental measurements of monodisperse droplet streams show good agreement with the theory. The technique can be applied to spray-droplet measurements over the size range of 3 Am to 5 mm. By using large off-axis scatter detection angles, the measurement of the droplet size and velocity distributions in relatively dense spray environments is made possible.

By controlling interference of Mie resonance modes of various nanostructures, we can achieve a large number of nontrivial effects in nanophotonics. In this work, we propose a cylindrical structure in which the spectral overlap of the Mie-type modes can be controlled by drilling a hole parallel to the axis, thus changing unidirectional scattering. We further demonstrate that the scattering patterns can be tailored by rotating the structure to achieve almost arbitrary scattered wave direction.

Lorenz-Mie resonances produced by small spheres are analyzed as a function of their size and optical properties (ѥ0, ѥ 0). New generalized ͑ 1͒ approximate and compact expressions of the first four Lorenz-Mie coefficients (a 1 , b 1 , a 2 , and b 2 ) are calculated. With these expressions and for small particles with various values of and , the extinction cross section ͑Q ext ͒ is calculated and analyzed, in particular for resonant conditions. The dependence on particle size of the extinction resonance, together with the resonance shape (FWHM), is also analyzed. In addition to the former analysis, a study of the scattering diagrams for some interesting values of and is also presented.

The ultra-black skin of the deep-sea dragonfish consists of small pigment particles which together provide optimal light absorption to prevent detection from bioluminescent predators or prey. The mechanism of light absorption in these pigment particles resembles the nanophotonic approaches to increase solar cell efficiency via Mie scattering and resonances. In this work, the Mie resonance responses of dragonfish pigment particles were investigated with finite-difference time-domain (FDTD) simulations to elucidate the exact mechanism responsible for the ultra-black skin of the dragonfish. Ellipsoidal pigment particles were found to have superior light absorption over spherical pigment particles. The pigment particles were also shown to exhibit forward scattering, demonstrating an important feature for repeated light absorption in pigment-containing skin layers. Although this work contributes to a deeper understanding of the ultra-back skin of the dragonfish, the nanophotonic mechanis...

Spray formation has been studied in an optically accessible heavy-duty diesel engine for regular diesel, synthetic, oxygenated and biofuels using a high-speed digital camera. Images are analyzed with custom made algorithms to obtain spray penetration length and spray cone angle as function of time. Results from 2 out of the 8 nozzle sprays have been used in the data analysis. Variation in spray equilibrium length and angle is observed between the fuels tested. Modelling of the fuel injection, taking great care to account for individual fuel properties, shows good correspondence with experimental results.

Radar measurements of rainfall at different climatological conditions have been taken into account emphasizing rain rate and associated radar reflectivity. It is observed from the analysis that the reflectivity measurement is being consistent at high rain intensities. From the knowledge of radar reflectivity, the rain drop size distribution is examined. The most probable drop size diameter and rain rate have been calculated wherefrom it appears that the most probable rain drop size vary exponentially with radar reflectivity and also with rain rate. The theoretical model implemented by using the measured rain drop sizes over the tropical sites also show similar kind of variation. For estimating rain attenuation two important parameters, viz., the point rainfall rates and the vertical and horizontal structures of rain have been considered. The elevation angle we have chosen is ~ 56 0 as most of the stations in India have that value of elevation angle with geostationary satellite. Taking the frequencies 11 to 14 GHz separately and 0 0 C isotherm height as 5.0 km, the effective rain height values are determined. The attenuation of radio waves due to rain are calculated for different rain rates assigning different γ-values. The attenuation is found to vary significantly with the γ-values. Also the attenuation curves are closer when the γ-values are of low order. An increase in attenuation with the γ-values is found to be more prominent for higher rain rates.

An efficient new method of calculating spherical Bessel functions of complex argument based on continued fractions is developed. The method does not depend on recurrence relations and it a~lows accurate calculations on computers with differing word lengths. The method ma~ be easily extended to other types of Bessel functions and to complex orders.

We present measurements of the complete scattering matrix as a function of the scattering angle of randomly oriented irregular hematite and rutile particles. The measurements were made at a wavelength of 632.8 nm in the scattering angle range from 5-174 degrees. Apart from their astronomical interest, these two samples are extremely interesting from a theoretical point of view, because they both have high real parts of the refractive index (about 3.0 for the hematite and 2.73 for the rutile). In addition, the hematite sample has a high imaginary part of the refractive index k, with values between 10 -1 and 10 -2 , whereas rutile is a non-absorbing material (k ≈ 0) at the studied wavelength. The scattering patterns of these mineral particles are quite similar to each other but show remarkable differences when compared to the results obtained for irregular mineral particles with moderate real parts of the refractive index. The measured results for both samples were compared with results of Mie calculations for projected surface equivalent spheres and T-matrix calculations for various spheroidal and cylindrical shapes. Both the experimental and theoretical results presented in this work seem to indicate that the scattering behavior of irregular mineral particles that have a high real part of the refractive index is not very dependent on the shape of the particles. In this case, Mie theory may give reasonable results despite the irregular shapes of the particles.

We report the optical investigation and analysis of both nano-sized and micrometer size Cadmium Sulphide particles which is embedded in a transparent polyvinyl alcohol (PVOH) dielectric host material. A designed and fabricated laser based light scattering system using a He-Ne laser of wavelength 632.8nm was used for the measurement and study of the scattering properties of the particles as a function of the scattering angle at this wavelength. An attempt was made to experimentally determine the most significant elements of the Mueller scattering matrix using combinations of randomly and linearly polarized incident laser beam and subsequent analyzers in corresponding orientations. The analysis of the experimental data was done by the method of comparison with theoretically generated data. Novel computational technique, involving single scattering for spherical particles using Mie-theory, was developed and applied. The theoretical data was found to be in good agreement with the experimental data within an acceptable margin of error. The results have proved that the combination of the experimental setup and associated computational method is a highly efficient and reliable in-situ system for monitoring size growth of semiconductor particles in the laboratory.

This paper is concerned with the design and fabrication of a laser based air quality monitoring system combining the design principle of the nephelometer, transmissiometer and a point visibility meter The system is tested by investigations on water droplet formation in air having different concentration of different gases As such the work involves the theory of extinction and scattering, especially Mie scattering Essentially m the system light from a laser source passes through a simulation chamber and the extinction and angular scattering of the light is monitored by photo detector arrangement. The signals are digitized and interlaced with pc for data recording and processing. Finally a correlation is drawn between the experimental results and the theoretical work

Noble metal nanoparticle composed glasses attract significant attention due to the unique optical properties that they express in the near UV and visible spectral range. These are related to the high values of the extinction cross section and nonlinear optical characteristics. In this work we study the ability of laser irradiation to induce modification of the optical properties of borosilicate glasses that contain gold nanoparticles. The process is investigated by application of laser pulses of nanosecond Nd:YAG system on glasses that consist of nanoparticles with different size and shape. The results show that at certain conditions the glass optical properties can be modified as a change of the nanoparticles plasmon resonance wavelength is observed. The influence of the laser fluence and pulse number on this effect is studied. Two fluence regimes are defined: (i) at low fluences, close to the optical properties modification threshold the increase of the laser fluence results in a blue shift of the resonance wavelength; (ii) further increase of the laser fluences induces a red shift. Similar behavior is observed by changing the number of the applied pulses. Here after application of several thousand laser pulses additional, third regime of blue shift is realized. Theoretical models based on multiparticle Mie scattering theory and heat conduction equation are applied to explain the observed modifications. On their basis and performed analyses can be concluded that the induced optical properties variations are related to modification of the nanoparticles size and shape by melting, fragmentation and coalescence. The obtained results indicate an ability of nanoparticle size and shape modifications with a high spatial resolution in 3D and can be used for fabrication of integrated optical systems.

A significant fraction of the Argentinean population is seasonally exposed to elevated UV radiation, particularly during severe stratospheric ozone destruction episodes in Antarctica. In order to provide early alert, global monitoring and to improve our understanding of these phenomena, various Argentinean and international organizations maintain stratospheric composition remote sensing sites from the southern tip of Argentina (Patagonia) to Antarctica. The

We studied a Spherically Radially Anisotropic (SRA) multilayer sphere with an arbitrary number of layers. Within each layer permittivity components are different from each other in radial and tangential directions. Under the quasi-static approximation, we developed a more generalized mathematical model that can be used to calculate polarizability of the SRA multilayer sphere with any arbitrary number of layers. Moreover, the functionality of the SRA multilayer sphere as a cloak has been investigated. It has been shown that by choosing a suitable contrast between components of the permittivity, the SRA multilayer sphere can achieve threshold required for invisibility cloaking.

The limb darkening (LD) curve is the plot of radiance I as function of cosine of the emission angle (i.e. angle between the line of sight and the normal to the target). Its shape is related to atmospheric and cloud properties, such as opacity and scale height. These can be deduced also considering the plot of brightness temperature T as function of cos at some wavelengths . In this work, Venus clouds have been studied by means of a LD study on infrared images of the Venus nightside, provided by the VIRTIS-Venus Express instrument .