Showing papers in "Journal of Quantitative Spectroscopy & Radiative Transfer in 2012"

New section of the HITRAN database: Collision-induced absorption (CIA)

Abstract: This paper describes the addition of Collision-Induced Absorption (CIA) into the HITRAN compilation. The data from different experimental and theoretical sources have been cast into a consistent format and formalism. The implementation of these new spectral data into the HITRAN database is invaluable for modeling and interpreting spectra of telluric and other planetary atmospheres as well as stellar atmospheres. In this implementation for HITRAN, CIAs of N2, H2, O2, CO2, and CH4 due to various collisionally interacting atoms or molecules are presented. Some CIA spectra are given over an extended range of frequencies, including several H2 overtone bands that are dipole-forbidden in the non-interacting molecules. Temperatures from tens to thousands of Kelvin are considered, as required, for example, in astrophysical analyses of objects, including cool white dwarfs, brown dwarfs, M dwarfs, cool main sequence stars, solar and extra-solar planets, and the formation of so-called first stars.

FORLI radiative transfer and retrieval code for IASI

Abstract: This paper lays down the theoretical bases and the methods used in the Fast Optimal Retrievals on Layers for IASI (FORLI) software, which is developed and maintained at the "Universite Libre de Bruxelles" (ULB) with the support of the "Laboratoire Atmospheres, Milieux, Observations Spatiales" (LATMOS) to process radiance spectra from the Infrared Atmospheric Sounding Interferometer (IASI) in the perspective of local to global chemistry applications. The forward radiative transfer model (RTM) and the retrieval approaches are formulated and numerical approximations are described. The aim of FORLI is near-real-time provision of global scale concentrations of trace gases from IASI, either integrated over the altitude range of the atmosphere (total columns) or vertically resolved. To this end, FORLI uses precalculated table of absorbances. At the time of writing three gas-specific versions of this algorithm have been set up: FORLI-CO, FORLI-O3 and FORLI-HNO3. The performances of each are reviewed and illustrations of results and early validations are provided, making the link to recent scientific publications. In this paper we stress the challenges raised by near-real-time processing of IASI, shortly describe the processing chain set up at ULB and draw perspectives for future developments and applications.

IASI on Metop-A: Operational Level 2 retrievals after five years in orbit

Abstract: Geophysical parameters from the IASI instrument on Metop-A are essential products provided from EUMETSAT's Central Facility in near real time. They include vertical profiles of temperature and humidity, related cloud information, surface emissivity and temperature, and atmospheric composition parameters (CO, ozone and several other trace gases). As compared to previous operational processor versions, the latest processor version 5 delivers significant improvements in retrieval performance for most major products. These include improvements to cloud properties products, cloud detection (with a positive impact on the knowledge of the sea surface temperature, SST), the temperature profile (especially in the mid and upper troposphere), and ozone and carbon monoxide total columns. This paper provides a comprehensive summary of the processing algorithms, the latest scientific developments, and the related validation studies and activities. It concludes with a discussion of the future outlook.

The Amsterdam–Granada Light Scattering Database

Abstract: The Amsterdam Light Scattering Database proved to be a very successful way of promoting the use of the data obtained with the Amsterdam Light Scattering apparatus at optical wavelengths. Many different research groups around the world made use of the experimental data. After the closing down of the Dutch scattering apparatus, a modernized and improved descendant, the IAA Cosmic Dust Laboratory (CoDuLab), has been constructed at the Instituto de Astrofisica de Andalucia (IAA) in Granada, Spain. The first results of this instrument for water droplets and for two samples of clay particles have been published. We would now like to make these data also available to the community in digital form by introducing a new light scattering database, the Amsterdam–Granada Light Scattering Database ( www.iaa.es/scattering ). By combining the data from the two instruments in one database we ensure the continued availability of the old data, and we prevent fragmentation of important data over different databases. In this paper we present the Amsterdam–Granada Light Scattering Database.

2.7 μm fluorescence radiative dynamics and energy transfer between Er3+ and Tm3+ ions in fluoride glass under 800 nm and 980 nm excitation

Abstract: A detailed study of the fluorescence radiative dynamics and energy transfer processes between Er and Tm ions in the Er3+/Tm3+ doped fluoride glass is reported. The fluorescence properties of 2.7 μm emission, other infrared and visible emissions are investigated under different selective laser excitations. Three Judd–Ofelt intensity parameters, energy transfer microparameters and efficiency have been determined and discussed. It is found that present Er3+/Tm3+ doped fluoride glass possesses large calculated emission cross section (8.98×10–21 cm2) around 2.7 μm. The more suitable pumping scheme for laser applications at 2.7 μm laser is 980 nm excitation for Er3+/Tm3+ doped fluoride glass.

Line lists for H218O and H217O based on empirical line positions and ab initio intensities

Abstract: New line lists for isotopically substituted water are presented. Most line positions were calculated from experimentally determined energy levels, while all line intensities were computed using an ab initio dipole moment surface. Transitions for which experimental energy levels are unavailable use calculated line positions. These line lists cover the range 0.05–20 000 cm−1 and are significantly more complete and potentially more accurate than the line lists available via standard databases. All lines with intensities (scaled by isotopologue abundance) greater than 10−29 cm/molecule at 296 K are included, augmented by weaker lines originating from pure rotational transitions. The final line lists contain 39 918 lines for H218O and 27 546 for H217O and are presented in standard HITRAN format. The number of experimentally determined H218O and H217O line positions is, respectively, 32 970 (83% of the total) and 17 073 (62%) and in both cases the average estimated uncertainty is 2×10−4 cm−1. The number of ab initio line intensities with an estimated uncertainty of 1% is 16 621 (42%) for H218O and 13 159 (48%) for H217O.

Calculation of the near fields for the scattering of electromagnetic waves by multiple infinite cylinders at perpendicular incidence

Abstract: The near field solution for the scattering of a plane monochromatic electromagnetic wave by an ensemble of parallel infinite dielectric cylinders at perpendicular incidence is presented in this paper. The solution is given for the calculation of the electric and magnetic near fields and the Poynting vector. A MATLAB program has been developed to solve the near field formulas which is introduced and validated. The near to far field transition as well as formation and transport of photonic nanojets have been calculated for multiple cylinder scattering.

MARVEL: Measured active rotational–vibrational energy levels. II. Algorithmic improvements☆

Abstract: When determining energy levels from several, in cases many, measured and assigned high-resolution molecular spectra according to the Ritz principle, it is advantageous to investigate the spectra via the concept of spectroscopic networks (SNs). Experimental SNs are finite, weighted, undirected, multiedge, rooted graphs, whereby the vertices are the energy levels, the edges are the transitions, and the weights are provided by transition intensities. A considerable practical problem arises from the fact that SNs can be very large for isotopologues of molecules widely studied; for example, the experimental dataset for the H2 16O molecule contains some 160,000 measured transitions and 20,000 energy levels. In order to treat such large SNs and extract the maximum amount of information from them, sophisticated algorithms are needed when inverting the transition data. To achieve numerical effectiveness, we found the following efficient algorithms applicable to very large SNs: reading the input data employs hash codes, building the components of the SN utilizes a recursive depth-first search algorithm, solving the linear least-squares problem is via the conjugate gradient method, and determination of the uncertainties of the energy levels takes advantage of the robust reweighting algorithm.

The electromagnetic effect in surface enhanced Raman scattering: Enhancement optimization using precisely controlled nanostructures

Abstract: This article presents an overview of surface enhanced Raman scattering (SERS) studies using substrates realized with fabrication techniques that provide a precise control of the geometry of metallic nanostructures. The role of the localized surface plasmons resonance (LSPR) in SERS is especially emphasized since it can be studied systematically thanks to the substrates produced by these fabrication techniques. We therefore explain why a precise control of the LSPR position is important in order to optimize the SERS intensity. The leading fabrication techniques (self-assembly and nanolithography) that ensure a precise control of all the geometrical parameters of the fabricated nanostructures and, as a consequence, a precise control of the LSPR are then described. The largest part of this article is focused on the identification of the main parameters governing the SERS intensity through the LSPR position such as nanoparticle size and shape (principally cylindrical, triangular, square, and elongated sections), higher orders LSPR, excitation polarization and excitation wavelength. The studies done on the optimization of the SERS intensity in the last 10 years is then summarized. We finally describe the studies made on the near-field coupling between the nanoparticles and emphasize its potential before exploring other kind of controlled nanostructures used to increase the SERS intensity.

Water in planetary and cometary atmospheres: H2O/HDO transmittance and fluorescence models

Abstract: We developed a modern methodology to retrieve water (H2O) and deuterated water (HDO) in planetary and cometary atmospheres, and constructed an accurate spectral database that combines theoretical and empirical results. On the basis of a greatly expanded set of spectroscopic parameters, we built a full non-resonance cascade fluorescence model and computed fluorescence efficiencies for H2O (500 million lines) and HDO (700 million lines). The new line list was also integrated into an advanced terrestrial radiative transfer code (LBLRTM) and adapted to the CO2 rich atmosphere of Mars, for which we adopted the complex Robert–Bonamy formalism for line shapes. We retrieved water and D/H in the atmospheres of Mars, comet C/2007 W1 (Boattini), and Earth by applying the new formalism to spectra obtained with the high-resolution spectrograph NIRSPEC/Keck II atop Mauna Kea (Hawaii). The new model accurately describes the complex morphology of the water bands and greatly increases the accuracy of the retrieved abundances (and the D/H ratio in water) with respect to previously available models. The new model provides improved agreement of predicted and measured intensities for many H2O lines already identified in comets, and it identifies several unassigned cometary emission lines as new emission lines of H2O. The improved spectral accuracy permits retrieval of more accurate rotational temperatures and production rates for cometary water.

Atmospheric validation of high accuracy CO2 absorption coefficients for the OCO-2 mission

Abstract: We describe atmospheric validation of View the MathML source and View the MathML source CO_2 absorption coefficient databases for use by the Orbiting Carbon Observatory (OCO-2). The OCO-2 mission will collect the measurements needed to estimate column-averaged CO_2 dry air mole fraction within 1 ppm accuracy without the region- or airmass-dependent biases that would significantly degrade efforts to understand carbon sources and sinks on a global scale. To accomplish this, the forward radiative transfer model used to generate synthetic atmospheric spectra for retrievals must achieve unprecedented spectroscopic fidelity within the short wave infrared CO_2 bands sampled by the sensors. The failure of Voigt line shapes and conventional line mixing formulations for such objectives has motivated significant revisions to line shape models used to generate the gas absorption cross sections for the OCO-2 forward model. In this paper, we test line mixing and speed dependent line shapes combined with improved experimental line parameters. We evaluate pre-computed absorption coefficients in the two spectral regions of CO_2 absorbtion using high resolution FT-IR laboratory spectra, atmospheric spectra from the Total Carbon Column Observing Network (TCCON), and medium resolution soundings from the space-based Greenhouse Gases Observing Satellite (GOSAT).

Extended line positions, intensities, empirical lower state energies and quantum assignments of NH3 from 6300 to 7000 cm−1

Abstract: Nearly 4800 features of ammonia between 6300 and 7000 cm−1 with intensities ≥4×10−24 cm−1/(molecule·cm−2) at 296 K were measured using 16 pure NH3 spectra recorded at various temperatures (296–185 K) with the McMath–Pierce Fourier Transform Spectrometer at Kitt Peak National Observatory, AZ. The line positions and intensities were retrieved by fitting individual spectra based on a Voigt line shape profile and then averaging the values to form the experimental linelist. The integrated intensity of the region was 4.68×10−19 cm−1/(molecule·cm−2) at 296 K. Empirical lower state energies were also estimated for 3567 absorption line features using line intensities retrieved from 10 spectra recorded at gas temperature between 185 and 233 K. Finally, using Ground State Combination Differences (GSCDs) and the empirical lower state energy estimates, the quantum assignments were determined for 1096 transitions in the room temperature linelist, along with empirical upper state energies for 434 levels. The assignments correspond to seven vibrational states, as confirmed from recent ab initio calculations. The resulting composite database of 14NH3 line parameters will provide experimental constraints to ab initio calculations and support remote sensing of gaseous bodies including the atmospheres of Earth, (exo)planets, brown dwarfs, and other astrophysical environments.

A critical assessment of the Hapke photometric model

Abstract: The photometric model developed by Hapke is commonly used to study surface structure and composition of atmosphereless celestial bodies using photometric measurements. However, this model has shortcomings that weaken its applications. For instance, some of the model parameters are empirical and mutually dependent. Moreover, the photometric model is eclectic and approximate; e.g., (1) the model simultaneously considers the single-scattering phase-function as backscattering and isotropic when describing, respectively, incoherent and coherent multiple scattering, which is physically impossible; (2) the approximation of the incoherent multiple scattering function takes into account the function anisotropy for the incident and emergent angles, but ignores the anisotropy for the azimuth angle that is of equal importance; (3) the model also ignores the dependence of the shadow-hiding effect of particles and coherent-backscattering enhancement on illuminating/viewing geometry, accounting only for the phase-angle component; (4) the azimuthal dependence of the shadow-hiding effect on random topographies is introduced ad hoc and is not verified; moreover, the shadow phase function may produce a non-physical maximum at large angles of viewing. We test the Hapke model using a computer simulation of ray-tracing in particulate surfaces, showing significant differences between the Hapke model and the ray-tracing results. We also apply the Hapke model to the interpretation of laboratory photometry of several well-characterized powdered samples measured in two wavelengths. The samples were measured in three states: as particles in air, as a particulate surface formed by freely spilled particles, and after compressing the particulate surface. The Hapke model parameters were completely inconsistent in the interpretation of these laboratory data. Our attempt to map the Hapke parameters using a series of telescopic calibrated images of the Moon acquired at different phase angles demonstrates that the model does not provide a physically meaningful distribution of its parameters. We also suggest that the small increase of the circular polarization ratio μC at decreasing phase angle (<10°), which is observed for lunar samples, is not evidence of the coherent-backscattering effect of the Moon. We suggest that Clementine observations carried out with the UV–Vis and NIR cameras demonstrate that the coherent-backscattering effect exists only for bright lunar surface areas with albedo higher than 30%.

The inter-comparison of MODIS, MISR and GOCART aerosol products against AERONET data over China

Abstract: Aerosols in East Asia have significant direct and indirect effects on the Earth's climate change. Several aerosol products have been generated to provide long-term monitoring of aerosol properties, but the discrepancies among them make the reliability of the products in doubt which leads to the uncertainty in the understanding of the long-time series of aerosols in East Asia, and especially in China. In this study, we investigate the applicability of Aerosol Optical Thickness (AOT) products derived from the measurements or model results of MODIS, MISR and GOCART through a statistical comparison, with Aerosol Robotic Network (AERONET) measurements over four sites located in China during a long-term period (2001–2011). Analysis shows that (1) only 43.06% of MODIS retrieved AOT values fall within ±(0.15τ+0.05) of the paired validation data from the AERONET for most sites, lower than the global averaged level (>66%) announced by Levy and Remer, in addition, MODIS/Terra shows a decreasing trend (−0.009/yr.) while MODIS/Aqua shows an increasing trend (+0.0012/yr.) and provides more stable AOT retrievals than MODIS/Terra during 2001–2011; (2) about 66.82% of MISR retrieved AOTs fall within the error envelop and MISR also shows a high correlation around 0.88 with AERONET data; (3) only 26.82% of GOCART model calculated AOTs fall within ±(0.15τ+0.05) of the paired validation data from the AERONET. GOCART also shows a low correlation (R=0.22–0.60) with AERONET data and thus cannot be well applied to total column AOT. Comparison of MODIS, MISR and GOCART products over the four sites in China and four sites located separately in Europe, North Africa and USA is carried out, which shows lower retrieval accuracy and larger discrepancy of products in China region. This is attributed to the fewer match-ups, larger aerosol load, moderate level of aerosol absorption and the complex nature of the aerosol mixtures. The analysis indicates the need for multiple-viewing-angle measurements of both intensity and polarization to provide the relevant aerosol parameters with sufficient accuracy for climate research.

Application of the pseudo-spectral time domain method to compute particle single-scattering properties for size parameters up to 200

Abstract: The applicability, efficiency, and accuracy of the pseudo-spectral time domain (PSTD) method are investigated with specific emphasis on the computation of the single-scattering properties of homogeneous dielectric particles. By truncating the high spectral terms, the Gibbs phenomenon is eliminated, and, consequently, the applicability of the PSTD is enhanced. The PSTD simulations for ice spheres, with moderate refractive indices and size parameters up to 200, are compared with the exact Lorenz–Mie solutions at three wavelengths. In addition, the comparison is extended to a case with an extremely large refractive index (7.150+i2.914) and size parameters up to 40. Furthermore, the single-scattering properties of randomly oriented spheroids and circular cylinders for size parameters up to 150 and 75, respectively, are calculated with the PSTD in comparison with those computed from the T-matrix method. The aspect ratio of the spheroid and the diameter-to-length ratio of the circular cylinder are 0.5 and 1, respectively. The relative errors, given by the PSTD for these randomly oriented non-spherical particles, are smaller than 2% for the extinction efficiencies and asymmetry factors and less than 30% for the phase function. The PSTD is also employed to compute the phase matrices of randomly oriented hexagonal columns with size parameters of 50 and 100. The simulations show the PSTD to be a robust method for simulating the single-scattering properties of particles with small-to-medium size parameters and for a wide range of refractive indices.

Diffraction patterns and nonlinear optical properties of gold nanoparticles

Abstract: Stable gold nanoparticles have been prepared by using soluble starch as both the reducing and stabilizing agents; this reaction was carried out at 40 °C for 5 h. The obtained gold nanoparticles were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy (TEM) and z-scan technique. The size of these nanoparticles was found to be in the range of 12–22 nm as analyzed using transmission electron micrographs. The optical properties of gold nanoparticles have been measured showing the surface plasmon resonance. The second-order nonlinear optical (NLO) properties were investigated by using a continuous-wave (CW) He–Ne laser beam with a wavelength of 632.8 nm at three different incident intensities by means of single beam techniques. The nonlinear refractive indices of gold nanoparticles were obtained from close aperture z-scan in order of 10−7 cm2/W. Then, they were compared with diffraction patterns observed in far-field. The nonlinear absorption of these nanoparticles was obtained from open aperture z-scan technique. The values of nonlinear absorption coefficient are obtained in order of 10−1 cm/W.

Imaging multiple colloidal particles by fitting electromagnetic scattering solutions to digital holograms

Abstract: Digital holographic microscopy is a fast three-dimensional (3D) imaging tool with many applications in soft matter physics. Recent studies have shown that electromagnetic scattering solutions can be fit to digital holograms to obtain the 3D positions of isolated colloidal spheres with nanometer precision and millisecond temporal resolution. Here we describe the results of new techniques that extend the range of systems that can be studied with fitting. We show that an exact multisphere superposition scattering solution can fit holograms of colloidal clusters containing up to six spheres. We also introduce an approximate and computationally simpler solution, Mie superposition, that is valid for multiple spheres spaced several wavelengths or more from one another. We show that this method can be used to analyze holograms of several spheres on an emulsion droplet, and we give a quantitative criterion for assessing its validity.

Spectroscopic study of plasma during electrolytic oxidation of magnesium- and aluminium-alloy

Abstract: We present the results of an optical emission spectroscopy study of Plasma during Electrolytic Oxidation (PEO) of magnesium- and aluminum-alloy Plasma electron number density Ne diagnostics is performed either from the Hβ line shape or from the width or shift of non-hydrogenic ion lines of aluminum and magnesium The line profile analysis of the Hβ suggests presence of two PEO processes characterized by relatively low electron number densities Ne≈12×1015 cm−3 and Ne≈23×1016 cm−3 Apart from these two low Ne processes, there is the third one related to the ejection of evaporated anode material through micro-discharge channels This process is characterized by larger electron density Ne=(12–16)1017 cm−3, which is detected from the shape and shift of aluminum and magnesium singly charged ion lines Two low Ne values detected from the Hβ and large Ne measured from the widths and shift of ion lines suggest presence of three types of discharges during PEO with aluminum- and magnesium-alloy anode On the basis of present and earlier results one can conclude that low Ne processes do not depend upon anode material or electrolyte composition The electron temperature of 4000 K and 33,000 K are determined from relative intensities of Mg I and O II lines, respectively The attention is drawn to the possibility of Ne application for Te evaluation using Saha equation what is of importance for PEO metal plasma characterization During the course of this study, difficulties in the analysis of spectral line shapes are encountered and the ways to overcome some of the obstacles are demonstrated

GRANADA: A Generic RAdiative traNsfer AnD non-LTE population algorithm

Abstract: We present in this paper the Generic RAdiative traNsfer AnD non-LTE population Algorithm (GRANADA). This model is able to compute non-LTE populations for vibrational, rotational, spin (i.e., NO and OH), and electronic (i.e., O 2 ) states in a given planetary atmosphere. The model is very flexible and can be used for computing very accurate non-LTE populations or for calculating reasonably accurate but at high speed non-LTE populations in order to implement it into non-LTE remote sensing retrievals. We describe the model in detail and present an update of the non-LTE collisional processes and their rate coefficients for the most important molecules in Earth's atmosphere. In addition, we have applied the model to the most important atmospheric infrared emitters including 13 species (H 2 O, CO 2 , O 3 , N 2 O, CO, CH 4 , O 2 , NO, NO 2 , HNO 3 , OH, N 2 , and HCN) and 460 excited vibrational or electronic energy levels. Non-LTE populations for all these energy levels have been calculated for 48 reference atmospheres expanding from the surface up to 200 km, including seasonal (January, April, July and October), latitudinal (75°S, 45°S, 10°S, 10°N, 45°N, 75°N) and diurnal (day and night) coverages. The effects of the most recent updates of the non-LTE collisional parameters on the non-LTE populations are briefly described. This climatology is available online to the community and it can be used for estimating non-LTE effects at specific conditions and for testing and validation studies.

Retrieving the size of particles with rough and complex surfaces from two-dimensional scattering patterns

Abstract: Scattered intensity measurement is a commonly used method for determining the size of small particles. However, it requires calibration and is subject to errors due to changes in incident irradiance or detector sensitivity. Analysis of two-dimensional scattering patterns offers an alternative approach. We test morphological image processing operations on patterns from a diverse range of particles with rough surfaces and/or complex structure, including mineral dust, spores, pollen, ice analogs and sphere clusters from 4 to 88 μm in size. It is found that the median surface area of intensity peaks is the most robust measure, and it is inversely proportional to particle size. The trend holds well for most particle types, as long as substantial roughness or complexity is present. One important application of this technique is the sizing of atmospheric particles, such as ice crystals.

Extension of the MIRS computer package for the modeling of molecular spectra: From effective to full ab initio ro-vibrational Hamiltonians in irreducible tensor form

Abstract: The MIRS software for the modeling of ro-vibrational spectra of polyatomic molecules was considerably extended and improved. The original version [Nikitin AV, Champion JP, Tyuterev VlG. The MIRS computer package for modeling the rovibrational spectra of polyatomic molecules. J Quant Spectrosc Radiat Transf 2003;82:239–49.] was especially designed for separate or simultaneous treatments of complex band systems of polyatomic molecules. It was set up in the frame of effective polyad models by using algorithms based on advanced group theory algebra to take full account of symmetry properties. It has been successfully used for predictions and data fitting (positions and intensities) of numerous spectra of symmetric and spherical top molecules within the vibration extrapolation scheme. The new version offers more advanced possibilities for spectra calculations and modeling by getting rid of several previous limitations particularly for the size of polyads and the number of tensors involved. It allows dealing with overlapping polyads and includes more efficient and faster algorithms for the calculation of coefficients related to molecular symmetry properties (6C, 9C and 12C symbols for C3v, Td, and Oh point groups) and for better convergence of least-square-fit iterations as well. The new version is not limited to polyad effective models. It also allows direct predictions using full ab initio ro-vibrational normal mode Hamiltonians converted into the irreducible tensor form. Illustrative examples on CH3D, CH4, CH3Cl, CH3F and PH3 are reported reflecting the present status of data available. It is written in C++ for standard PC computer operating under Windows. The full package including on-line documentation and recent data are freely available at http://www.iao.ru/mirs/mirs.htm or http://xeon.univ-reims.fr/Mirs/ or http://icb.u-bourgogne.fr/OMR/SMA/SHTDS/MIRS.html and as supplementary data from the online version of the article.

Linearized T-matrix and Mie scattering computations

Abstract: We present a new linearization of T-Matrix and Mie computations for light scattering by non-spherical and spherical particles, respectively In addition to the usual extinction and scattering cross-sections and the scattering matrix outputs, the linearized models will generate analytical derivatives of these optical properties with respect to the real and imaginary parts of the particle refractive index, and (for non-spherical scatterers) with respect to the ‘‘shape’’ parameter (the spheroid aspect ratio, cylinder diameter/height ratio, Chebyshev particle deformation factor) These derivatives are based on the essential linearity of Maxwell’s theory Analytical derivatives are also available for polydisperse particle size distribution parameters such as the mode radius The T-matrix formulation is based on the NASA Goddard Institute for Space Studies FORTRAN 77 code developed in the 1990s The linearized scattering codes presented here are in FORTRAN 90 and will be made publicly available

Spectral line parameters including temperature dependences of self- and air-broadening in the 2←0 band of CO at 2.3 μm

Abstract: Temperature dependences of pressure-broadened half-width and pressure-induced shift coefficients along with accurate positions and intensities have been determined for transitions in the 2←0 band of 12C16O from analyzing high-resolution and high signal-to-noise spectra recorded with two different Fourier transform spectrometers. A total of 28 spectra, 16 self-broadened and 12 air-broadened, recorded using high-purity (≥99.5% 12C-enriched) CO samples and CO diluted with dry air (research grade) at different temperatures and pressures, were analyzed simultaneously to maximize the accuracy of the retrieved parameters. The sample temperatures ranged from 150 to 298 K and the total pressures varied between 5 and 700 Torr. A multispectrum nonlinear least squares spectrum fitting technique was used to adjust the rovibrational constants (G, B, D, etc.) and intensity parameters (including Herman–Wallis coefficients), rather than determining individual line positions and intensities. Self- and air-broadened Lorentz half-width coefficients, their temperature dependence exponents, self- and air-pressure-induced shift coefficients, their temperature dependences, self- and air- line mixing coefficients, their temperature dependences and speed dependence have been retrieved from the analysis. Speed-dependent line shapes with line mixing employing off-diagonal relaxation matrix element formalism were needed to minimize the fit residuals. This study presents a precise and complete set of spectral line parameters that consistently reproduce the spectrum of carbon monoxide over terrestrial atmospheric conditions.

Interstellar extinction and interstellar polarization: old and new models

Abstract: The review contains an analysis of the observed and model curves of the interstellar extinction and polarization. The observations mainly give information on dust in diffuse and translucent interstellar clouds. The features of various dust grain models including spherical/non-spherical, homogeneous/inhomogeneous particles are discussed. A special attention is devoted to the analysis of the grain size distributions, alignment mechanisms and magnetic field structure in interstellar clouds. It is concluded that the interpretation of interstellar extinction and polarization is not yet complete.

Irregularly shaped ice aggregates in optical modeling of convectively generated ice clouds

Abstract: We propose a model of irregular shaped ice particles for satellite and ground-based cloud remote sensing applications. Microphysical observations have shown that ice particles generated in convective clouds tend to have highly irregular structures as a result of aggregation process. To simulate such complex structures, we used spatial Poisson–Voronoi tessellations. Furthermore, we adopted fractal-like shapes that were consistent with the proposed mass-dimension and area ratio-dimension relationships of measured cirrus particles. Single-scattering properties of the modeled “Voronoi aggregates” at visible wavelengths with size parameters up to 2246 were estimated from numerical calculations using the finite-difference time-domain method and the geometrical-optics integral-equation method. The phase functions for randomly oriented Voronoi aggregates showed features with no halos in the forward-scattering direction and a flat angular dependence in the side-to-backscattering directions. These characteristics and resultant asymmetry factors agreed with those of measured ice particles. Moreover, we confirmed the weak size and shape dependences of these scattering properties for the Voronoi aggregates, as well as high backscattering depolarization ratios and low linear polarizations.

Evanescent wave optical trapping and transport of micro- and nanoparticles on tapered optical fibers

Abstract: We investigate the manipulation of microscopic and nanoscopic particles using the evanescent optical field surrounding an optical fiber that is tapered to a micron-scale diameter, and propose that this scheme could be used to discriminate between, and thereby sort, metallic nanoparticles. First we show experimentally the concept of the transport of micron-sized spheres along a tapered fiber and measure the particle velocity. Having demonstrated the principle we then consider theoretically the application to the optical trapping and guiding of metallic nanoparticles, where the presence of a plasmon resonance is used to enhance optical forces. We show that the dynamics of the nanoparticles trapped by the evanescent field can be controlled by the state of polarization of the fiber mode, and by using more than one wavelength differently detuned from the nanoparticle plasmon resonance. Such a scheme could potentially be used for selectively trapping and transporting nano- or microscopic material from a polydisperse suspension.

High resolution analysis of the SO 2 spectrum in the 2600-2900cm -1 region: 2ν 3 , ν 2 +2ν 3 -ν 2 and 2ν 1 +ν 2 bands

Abstract: Infrared spectrum of the SO 2 molecule was recorded with high resolution in the 2600– 2900 cm − 1 region. Spectrum was recorded with the Fourier transform interferometer Bruker IFS-120 HR in Oulu (Finland) with the pressure of 111 Pa and the absorption path length of 163.2 m that allowed us to record 2 ν 3 and 2 ν 1 + ν 2 weak bands. The 2 ν 3 band discussed earlier by Lafferty et al., was re-analyzed, and considerably more information was extracted from the spectrum (more than 3800 transitions of the 2 ν 3 band were assigned in the experimental spectrum with maximum values of quantum numbers, J max . = 76 and K a max . = 26 ). On the basis of the procedure discussed in Ulenikov et al., about 760 transitions of the ν 2 + 2 ν 3 − ν 2 hot band ( J max . = 49 and K a max . = 13 ), were assigned, and the rotational structure of the (012) vibrational state was determined for the first time with high accuracy. Very weak band, 2 ν 1 + ν 2 , was analyzed also for the first time, and about 1250 transitions with J max . = 43 and K a max . = 17 were assigned in the spectrum. Information, obtained from the experimental data, was used in the fit for the determination of spectroscopic parameters of the states (002), (012), and (210). In this case, some earlier undiscussed sets of interacting ro-vibrational states were found, and resonance interactions between the states (002)/(130) and (012)/(140) were taken into account. Obtained from the fit, 36 parameters reproduce more than 5800 initial transitions of all three bands with the accuracy close to experimental uncertainties (rms deviation is 0.00021 cm − 1 , 0.00031 cm − 1 and 0.00014 cm − 1 for the 2 ν 3 , ν 2 + 2 ν 3 − ν 2 and 2 ν 1 + ν 2 bands, respectively).

Semiclassical calculations of half-widths and line shifts for transitions in the 30012←00001 and 30013←00001 bands of CO2 II: Collisions with O2 and air

Abstract: Calculations of the half-width, its temperature dependence, and the line shift are made for the rotational states J=0–120 for two of the Fermi-tetrad bands (30012←00001 and 30013←00001) of CO2 perturbed by N2. The calculations employ the semi-classical complex Robert–Bonamy method with no ad hoc scaling, J-dependent or otherwise, and an intermolecular potential (IP) comprised of an electrostatic part, an atom–atom part, and an isotropic London dispersion part. The averaging over the impact parameter b and relative speed v are explicitly carried out. Many interesting features about CO2 as the radiating molecule are elucidated. Effects of the trajectory model, the order of the expansion of the atom–atom component of the potential, and the inclusion of the imaginary terms are studied. It is shown that the results are very sensitive to the intermolecular potential. The final IP parameters give results that demonstrate excellent agreement with measurement for the three line shape parameters studied in this work.

Laser induced optical heating from Yb3+/Ho3+:Ca12Al14O33 and its applicability as a thermal probe

Abstract: Yb3+/Ho3+ co-doped calcium aluminate phosphor has been synthesized using solution combustion process. Multicolored (blue, green and red) strong upconversion emission (λexc=980 nm) due to Ho3+ ion is observed which shows a color tunability (from green to red) with a variation in input laser power. The color tunability has been attributed to be due to the induced heating in the local volume of the sample and the temperature produced has been estimated using the fluorescence intensity ratio (FIR) method. The sample shows temperature sensing behavior and more importantly the temperature could be sensed through two pairs of thermally coupled levels, one lying in the green region (5F4/5S2→5I8) and the other in the blue region (5G4/5G5→5I8). The temperature sensing through the blue pair of levels is novel in itself. The material thus prepared serves as temperature sensor as well as a source for the production of heat in a localized volume.

Infrared emission spectroscopy of CO2 at high temperature. Part II: Experimental results and comparisons with spectroscopic databases

Abstract: Measurements of CO2 emission spectra at high temperature in the 2.7 μ m and 4.3 μ m regions are presented and compared to predictions from the spectroscopic databases, CDSD-4000 (Tashkun SA, Perevalov VI. CDSD-4000: high-resolution, high-temperature carbon dioxide spectroscopic databank. Journal of Quantitative Spectroscopy and Radiative Transfer 2011;112:1403–10) and HITELOR (Scutaru D, Rosenmann L, Taine J. Approximate intensities of CO2 hot bands at 2.7, 4.3 and 12 μ m for high temperature and medium resolution applications. Journal of Quantitative Spectroscopy and Radiative Transfer 1994;52:765–81). The measurements near 2.7 μ m show that CDSD-4000 provides better agreement with experimental data, especially in the band wing corresponding to very hot band emission. In the 4.3 μ m region, experimental intensities are generally lower than theoretical predictions but the measurements are more affected by the use of sapphire confinement tubes. The two spectroscopic databases provide closer results than in the 2.7 μ m region although CDSD-4000 yields here also better agreement with experimental data in band wing. Analysis of the two spectroscopic databases is carried out in terms of vibrational and rotational energy cutoff and total band emissivities.