Effect of ultraviolet irradiation on the optical properties of silicon oxide films.
UV irradiation effect on optical properties, thickness and chemical composition of silicon oxide films
ULTRAVIOLET RADIATION↗
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Magnetic and Optical Properties of Au–Co Solid Solution and Phase-Separated Thin Films and Nanoparticles
The chemical composition and morphology of Au x Co 1–x thin films and nanoparticles are controlled via a combination of cosputtering, pulsed laser-induced dewetting (PLiD), and annealing, leading to tunable magnetic and optical properties. Regardless of chemical composition, the as-deposited thin films and as-PLiD nanoparticles are found to possess a face-centered cubic (FCC) Au x Co 1–x solid-solution crystal structure. Annealing results in large phase-separated grains of Au and Co in both the thin films and nanostructures for all chemical compositions. The magnetic and optical properties are characterized via vibrating sample magnetometry (VSM), ellipsometry, optical transmission spectroscopy, and electron energy loss spectroscopy (EELS). Despite the exceptionally high magnetic anisotropy inherent to Co, the presence of sufficient Au (72 atom %) in the Au x Co 1–x solid solution results in superparamagnetic thin films. Among the as-PLiD nanoparticle samples, an increased Co composition leads to a departure from traditional ferromagnetism in favor of wasp-waisted hysteresis caused by magnetic vortices. Phase separation resulting from annealing leads to ferromagnetism for all compositions in both the thin films and nanoparticles. The optical properties of Au x Co 1–x nanostructures are also largely influenced by the chemical morphology, where the Au x Co 1–x intermixed solid solution has significantly damped plasmonic performance relative to pure Au and comparable to pure Co. Phase separation greatly enhances the quality factor, optical absorption, and electron energy loss spectroscopy (EELS) signatures. The enhancement of the localized surface plasmon resonances (LSPRs) scales with the reduction in Co composition, despite EELS evidence that excitation of the Co portions of a nanoparticle can provide a similar, and in some instances enhanced, LSPR resonance compared to Au. This behavior, however, is seemingly limited to the LSPR dipole mode, while higher-order modes are greatly damped by a Co aloof position. As a result, this observed magneto-plasmonic functionality and tunability could be applicable in biomedicine, namely, cancer therapeutics.
annealing (metallurgy)↗
Optical Properties of Non-Spherical Particles of Size Comparable to the Wavelength of Light: Application to Comet Dust
Scattering Calculations of none-spherical particles have been carried out in order to explain observed optical properties of cometary dust. We focused on two optical properties of cometary dust sensitive to particle shape.
Optical Properties Non-Spherical Particles Comet D↗
A long path-length optical property measurement device for highly transparent detector media
Measurements of the optical properties of highly transparent liquids are necessary for large-scale detectors that seek to detect optical signatures in kiloton-scale or larger volumes. Detailed understanding of the attenuation and scattering properties of fill media is critical to the ability to accurately simulate detector performance, and yet is often unavailable until in-situ measurements can be performed. Moreover, in-situ measurements may rely on effective attenuation lengths or other approximations to characterize performance, rather than absolute measurements of attenuation and scattering. To better understand the optical properties of potential fill media and purification schemes, a system has been developed which provides simultaneous attenuation and differential scattering cross-section measurements for highly transparent liquids. This horizontal, adjustable path-length “long-arm” system provides excellent isolation from the atmosphere, a high degree of vibration insensitivity, and a simple and reliable method of calibration. Further, scattering measurements can be carried out simultaneously at ports along the beamline equipped with optics allowing the selection of scatter angle and polarization. This enables both reliable quantitative scatter measurements and phase-function separation. This system has been extensively tested using deionized (DI) water as a benchmark, and has demonstrated repeatable measurements of attenuation lengths exceeding 100 m and scattering lengths approaching 1 km.
47 OTHER INSTRUMENTATION↗
Optical properties of Peaked Spectrum radio sources
ABSTRACT In this work, we study the optical properties of compact radio sources selected from the literature in order to determine the impact of the radio-jet in their circumnuclear environment. Our sample includes 58 Compact Steep Spectrum (CSS) and GigaHertz Peaked Spectrum (GPS) and 14 Megahertz-Peaked spectrum (MPS) radio sources located at z ≤ 1. The radio luminosity (LR) of the sample varies between Log LR ∼ 23.2 and 27.7 W Hz−1. We obtained optical spectra for all sources from SDSS-DR12 and performed a stellar population synthesis using the starlight code. We derived stellar masses (M⋆), ages 〈t⋆〉, star formation rates (SFR), metallicities 〈Z⋆〉 and internal reddening AV for all young AGNs of our sample. A visual inspection of the SDSS images was made to assign a morphological class for each source. Our results indicate that the sample is dominated by intermediate to old stellar populations and there is no strong correlation between optical and radio properties of these sources. Also, we found that young AGNs can be hosted by elliptical, spiral and interacting galaxies, confirming recent findings. When comparing the optical properties of CSS/GPS and MPS sources, we do not find any significant difference. Finally, the Mid-Infrared WISE colours analysis suggests that the compact radio sources defined as powerful AGNs are, in general, gas-rich systems.
79 ASTRONOMY AND ASTROPHYSICS↗
Comprehensive anisotropic linear optical properties of the Weyl semimetals TaAs and NbAs
We report that TaAs and NbAs are two of the earliest identified Weyl semimetals that possess many intriguing optical properties, such as chirality-dependent optical excitations and giant second harmonic generation (SHG). Linear and nonlinear optics have been employed as tools to probe the Weyl physics in these crystals. Here, we extend these studies to address two important aspects: determining the complete anisotropic dielectric response and exploring if and how they can reveal essential Weyl physics. We determine the complete anisotropic dielectric functions of TaAs and NbAs by combining spectroscopic ellipsometry and density functional theory (DFT). Parameterized Lorentz oscillators are reported from 1.2 - 6 eV (experiment) and 0 - 6 eV (DFT), and good agreement is shown between them. Both linear and nonlinear optical properties have been previously reported to reveal Weyl physics. We suggest that strong optical resonances from trivial bands are the likely origin of the large optical SHG previously reported at these energies. Furthermore, by comparing the contribution of a small k -space centered around the Weyl cones with the total linear dielectric function, we find that these contributions are highly anisotropic and are < 25% of the total dielectric function below 0.5 eV; abov1 eV, these contributions are negligible. Thus, the study of Weyl physics using optical techniques requires very low energies, and even there, a careful assessment is required in distinguishing the much smaller contributions of the Weyl bands from the dominant contributions of the trivial bands and Drude response to the total dielectric function.
36 MATERIALS SCIENCE↗
Fundamental studies of the metallurgical, electrical, and optical properties of gallium phosphide Quarterly progress report, 1 Jan. - 31 Mar. 1965
Metallurgical, electrical, and optical properties of gallium phosphide
ELECTRIC PROPERTY↗
Thermophysical and Optical Properties of Semiconducting Ga2Te3 Melt
The majority of bulk semiconductor single crystals are presently grown from their melts. The thermophysical and optical properties of the melts provide a fundamental understanding of the melt structure and can be used to optimize the growth conditions to obtain higher quality crystals. In this paper, we report several thermophysical and optical properties for Ga2Te3 melts, such as electrical conductivity, viscosity, and optical transmission for temperatures ranging from the melting point up to approximately 990 C. The conductivity and viscosity of the melts are determined using the transient torque technique. The optical transmission of the melts is measured between the wavelengths of 300 and 2000 nm by an dual beam reversed-optics spectrophotometer. The measured properties are in good agreement with the published data. The conductivities indicate that the Ga2Te3 melt is semiconductor-like. The anomalous behavior in the measured properties are used as an indication of a structural transformation in the Ga2Te3 melt and discussed in terms of Eyring's and Bachinskii's predicted behaviors for homogeneous melts.
Li, Chao↗
Laboratory Studies of the Optical Properties and Condensation Processes of Cosmic Dust Grains
A laboratory facility for conducting a variety of experiments on single isolated dust particles of astrophysical interest levitated in an electrodynamics balance has been developed at NASA/Marshall Space Flight Center. The objective of the research is to employ this experimental technique for studies of the physical and optical properties of individual cosmic dust grains of 0.1-100 micron size in controlled pressure/temperatures environments simulating astrophysical conditions. The physical and optical properties of the analogs of interstellar and interplanetary dust grains of known composition and size distribution will be investigated by this facility. In particular, we will carry out three classes of experiments to study the micro-physics of cosmic dust grains. (1) Charge characteristics of micron size single dust grains to determine the photoelectric efficiencies, yields, and equilibrium potentials when exposed to UV radiation. (2) Infrared optical properties of dust particles (extinction coefficients and scattering phase functions) in the 1-30 micron region using infrared diode lasers and measuring the scattered radiation. (3) Condensation experiments to investigate the condensation of volatile gases on colder nucleated particles in dense interstellar clouds and lower planetary atmospheres. The condensation experiments will involve levitated nucleus dust grains of known composition and initial mass (or m/q ratio), cooled to a temperature and pressure (or scaled pressure) simulating the astrophysical conditions, and injection of a volatile gas at a higher temperature from a controlled port. The increase in the mass due to condensation on the particle will be monitored as a function of the dust particle temperature and the partial pressure of the injected volatile gas. The measured data will permit determination of the sticking coefficients of volatile gases and growth rates of dust particles of astrophysical interest. Some preliminary results based on measurements of photoelectric emission and radiation pressure on single isolated 0.2 to 6.6 micron size silica particles exposed to UV radiation at 120-200 nm and green laser light at 532 nm are presented.
Abbas, M. M.↗
Effect of halogenation on the nonlinear optical properties of porthyrin and substituted porphyrins
The effect that fluorine and chlorine substitution has on the nonlinear optical properties of porphyrin, tetramethylporphyrin and tetraphenylporphyrin has been theoretically studied. The calculations of nonlinear optical properties have been obtained by performing finite-field calculations on structures determined by semiempirical methods. In addition, tetra(p-chlorophenyl)porphyrin and tetra(p-bromophenyl)porphyrin were synthesized by the condensation of pyrrol and the appropriate aldehyde. Thin films of polymethylmethacrylate were obtained containing these materials, by spin coating onto glass substrates. The films were characterized by third-harmonic generation. It was determined that the experimental conditions enhance the third-order polarizability of the tetraphenylporphyrins by a factor of about 1.6.
Cardelino, Beatriz H.↗
Mineral Dust Optical Properties for Remote Sensing and Global Modeling: A Review
Dust plays a key role in many Earth system processes and is ubiquitous in the Martian atmosphere. Various intensive field campaigns, laboratory analyses, space-based remote sensing missions, and global modeling efforts aim to characterize dust optical properties. This is a bountiful time for dust scientists, and yet the interpretation of retrievals and comparison to models remains complicated by various conflicting assumptions that are part of each algorithm. For example, the conversion of satellite radiance measurements into products like aerosol optical depth for model evaluation depends upon aerosol properties like particle size and shape that are often prescribed and not part of the retrieval. Conversely, the model calculation of aerosol optical depth often uses different assumptions. The goal of this review is to first document algorithmic assumptions by various satellite retrieval products and models, and identify where there is consistency and where there are differences. In general, the differences documented in this paper reflect uncertainties resulting from incomplete observational characterization of dust aerosols and limitations in our understanding. Second, we note what observations might reduce uncertainties in our knowledge and bring greater consistency to retrievals and models, allowing for a more rigorous and harmonious comparison. The lack of comprehensive and realistic shape models for dust is an outstanding issue, such that closure between forward modeling from particle refractive index, shape, and size and observed optical properties cannot be achieved. Limitations in the computational methods that must be applied to model scattering from complex shapes also makes accurate optical modeling for dust challenging. Field observations indicate the persistence of coarse and giant dust particles at higher altitudes and farther downwind from their source than previously expected. Remote sensing retrieval algorithms based on observations at visible wavelengths have limited sensitivity to these particles and generally do not consider them, although a recent product based on longwave radiances is encouraging. Current measurements of the refractive index of bulk dust and fundamental dust minerology components such as hematite vary widely, inhibiting attempts to represent the variability in dust optical properties and forcing, as expected from different major dust source regions on Earth that have varying mineralogical composition. Some remote sensing retrieval algorithms allow for limited refractive index variability in their inversion solutions through mixing with other fine mode aerosol models, or optimizing the single scattering albedo, but Earth system models surveyed for this paper assume a globally uniform, size-invariant refractive index. Although no Martian dust samples have yet been returned to Earth, remote sensing observations indicate that Martian dust is globally homogenous in composition, and a single spectral refractive index assumption has been widely adopted to represent Martian dust. The lack of comprehensive, statistically representative measurements of dust particle microphysical properties (size distribution, morphology, complex index of refraction spectra, internal structure heterogeneity), and the resulting optical properties, limits our ability to verify the fidelity of these assumptions. A chain of measurements is needed, ranging from characterizing individual dust mineralogy components (e.g., pure hematite and goethite) to in situ sampling of complex atmospheric aerosol mixtures. Such results could be applied to both remote sensing retrievals that characterize the optical properties of the total aerosol burden in the atmosphere from total radiance measurements, and to global models that represent the total aerosol burden in the atmosphere by building it up from the balance of individual aerosol sources and sinks.
Aeolian dust↗
Temperature-dependent optical properties of Cd(1-x),Zn(x),Te substitute material
In this study, we report cryogenic optical properties of Cd(l-x), Zn(x), Te wafers that are used as substrate seed layers in the manufacturing of HgCdTe focal-plane array detectors. These studies are motivated by the fact that the substrate optical properties influence the overall detector performance. The studies consist of measuring the substrate frequency dependent transmittance T(W) and reflectance R(W) above and below the optical band-gap in the UV/Visible and infrared frequency ranges, and with temperature variation of the sample from 5 to 300 K. Determination of the optical absorption from these measurements show that the optical absorption energy gap near 1.6 eV shows a substantial increase as the temperature is reduced from 300 to 5 K. Furthermore, we observe the presence of infrared-active optical phonons whose peak frequency shifts as the temperature of the sample is varied over the measured temperature range. The theoretical frequency dependent optical conductivity, with allowance for redistribution of spectral weight among the interband transition charge carriers, will be discussed.
Quijada, Manuel A.↗
Optical property degradation of anodic coatings in the Space Station low earth orbit
The anodic coatings and optical properties to be used for passive thermal control of the SSF are studied. Particular attention is given to the beginning-of-life optical properties for aluminum alloys suitable for structural and radiator applications, the statistical variation in the beginning-of-life properties, and estimates of the end-of-life properties of the alloys based on ultraviolet radiation testing and flight test results. It is concluded that anodic coatings can be used for thermal control of long life, low earth orbit spacecraft. Some use restrictions are defined for specific cases. Anodic coatings have been selected as baseline thermal control coating for large portions of the SSF.
David, Kaia E.↗
End-of-Life Optical Property Predictions of White Conductive Thermal Control Coatings through Analysis of On-Orbit and Ground Based Testing Data
New system requirements pertaining to thermal optical properties and coating electrical properties are commonly specified on non-low earth orbit missions. An increasing number of projects are specifying coatings with a surface resistivity of less than lE-9 ohm/square to mitigate electrostatic charge buildup events over a range of operational temperatures. There are a limited number of coatings that. meet these electrical property requirements while having flight derived optical properties in representative environments. Goddard Space Flight Center Code 546, Contamination and Thermal Coatings Group has recently explored the variety of electrically conductive white coatings available through domestic vendors to evaluate properties to meet project requirements in a geostationary orbit. The lack of significant flight data in representative environments required the careful selection of samples in ground based tests to establish end of life thermal properties. Attention must be given to the origin and pedigree of samples used on past on-orbit experiments to insure that the present formulations for the materials are similar and will react in similar manner.
Hasegawa, Mark↗
Influence of substrate misorientation on the optical properties of Mg-doped GaN
The GaN substrate miscut angle has a significant effect on the optical properties of Mg-doped GaN grown by metal-organic chemical vapor deposition. We have studied the optical properties of epilayers grown on c-plane GaN wafers with nominal miscut angles of 0.3° and 4° toward the [11¯00] direction. Periodic surface steps are observed in thin films grown on 0.3° miscut substrates. The step separation and height, as well as the surface roughness, increase with layer thickness, leading to a decrease in Mg doping efficiency. For films grown on 4° miscut substrates, step bunching causes the formation of visually observable wavy features on the film surface with strong spatial variations in cathodoluminescence characteristics, indicating a significant effect of surface morphology on the nature of Mg incorporation and p-type characteristics.
Liu, Hanxiao (ORCID:0000000331067542)↗
Improving Pixel Level Cloud Optical Property Retrieval using Monte Carlo Simulations
The accurate pixel-by-pixel retrieval of cloud optical properties from space is influenced by radiative smoothing due to high order photon scattering and radiative roughening due to low order scattering events. Both are caused by cloud heterogeneity and the three-dimensional nature of radiative transfer and can be studied with the aid of computer simulations. We use Monte Carlo simulations on variable 1-D and 2-D model cloud fields to seek for dependencies of smoothing and roughening phenomena on single scattering albedo, solar zenith angle, and cloud characteristics. The results are discussed in the context of high resolution satellite (such as Landsat) retrieval applications. The current work extends the investigation on the inverse NIPA (Non-local Independent Pixel Approximation) as a tool for removing smoothing and improving retrievals of cloud optical depth. This is accomplished by: (1) Delineating the limits of NIPA applicability; (2) Exploring NIPA parameter dependences on cloud macrostructural features, such as mean cloud optical depth and geometrical thickness, degree of extinction and cloud top height variability. We also compare parameter values from empirical and theoretical considerations; (3) Examining the differences between applying NIPA on radiation quantities vs direct application on optical properties; (4) Studying the radiation budget importance of the NIPA corrections as a function of scale. Finally, we discuss fundamental adjustments that need to be considered for successful radiance inversion at non-conservative wavelengths and oblique Sun angles. These adjustments are necessary to remove roughening signatures which become more prominent with increasing absorption and solar zenith angle.
Oreopoulos, Lazaros↗
Regional Aerosol Optical Properties and Radiative Impact of the Extreme Smoke Event in the European Arctic in Spring 2006
In spring 2006 a special meteorological situation occurred in the European Arctic region giving record high levels of air pollution. The synoptic situation resulted in extensive transport of pollution predominantly from agricultural fires in Eastern Europe into the Arctic region and record high air-pollution levels were measured at the Zeppelin observatory at Ni-Alesun(78deg 54'N, 11deg 53'E) in the period from 25 April to 12 May. In the present study we investigate the optical properties of the aerosols from this extreme event and we estimate the radiative forcing of this episode. We examine the aerosol optical properties from the source region and into the European Arctic and explore the evolution of the episode and the changes in the optical properties. A number of sites in Eastern Europe, Northern Scandinavia and Svalbard are included in the study. In addition to AOD measurements, we explored lidar measurements from Minsk, ALOMAR (Arctic Lidar Observatory for Middle Atmosphere Research at Andenes) and Ny-Alesund. For the AERONET sites included (Minsk, Toravere, Hornsund) we have further studied the evolution of the aerosol size. Importantly, at Svalbard it is consistency between the AERONET measurements and calculations of single scattering albedo based on aerosol chemical composition. We have found strong agreement between the satellite dally MODIS AOD and the ground-based AOD observations. This agreement is crucial for the radiative forcing calculations. We calculate a strong negative radiative forcing for the most polluted days employing the analysed ground based data, MODIS AOD and a multi-stream model for radiative transfer of solar radiation.
Lund Myhre, C.↗
Prediction of nonlinear optical properties of large organic molecules
The preparation of materials with large nonlinear responses usually requires involved synthetic processes. Thus, it is very advantageous for materials scientists to have a means of predicting nonlinear optical properties. The prediction of nonlinear optical properties has to be addressed first at the molecular level and then as bulk material. For relatively large molecules, two types of calculations may be used, which are the sum-over-states and the finite-field approach. The finite-field method was selected for this research, because this approach is better suited for larger molecules.
Cardelino, Beatriz H.↗