3D structure of the H ii region Sh2-235 from tunable-filter optical observations
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M S Kirsanova↗
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Results for “optical structures”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Dish concentrators for solar thermal energy - Status and technology development
Comparisons are presented of point-focusing, or 'dish' solar concentrator system features, development status, and performance levels demonstrated to date. In addition to the requirements of good optical efficiency and high geometric concentration ratios, the most important future consideration in solar thermal energy dish concentrator design will be the reduction of installed and lifetime costs, as well as the materials and labor costs of production. It is determined that technology development initiatives are needed in such areas as optical materials, design wind speeds and wind loads, structural configuration and materials resistance to prolonged exposure, and the maintenance of optical surfaces. The testing of complete concentrator systems, with energy-converting receivers and controls, is also necessary. Both reflector and Fresnel lens concentrator systems are considered.
Jaffe, L. D.↗
Honeywell multispectral linear array (MLA) instrument design A system overview
In support of NASA's Experimental Land Observing System, a simple, reliable and relatively inexpensive multispectral linear array (MLA) instrument concept has been developed. The design satisfies requirements for multichannel radiometry and wide field imaging. A reflective off-axis anastigmat telescope is mounted in a highly strength-to-weight efficient truss structure, coupled to a solid beamsplitter assembly. Attention is given to the optical design of the MLA instrument, the telescope structure, the detector arrays, detector cooling, on-orbit calibration, signal processing electronics, the spacecraft interfaces, the modulation transfer function, the signal-to-noise ratio, radiometric accuracy, and spatial registration.
Eyring, D.↗
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↗
Optical Measurement System for Strain Field Ahead of a Crack Tip for Lattice Structures
The aim of the ARAMADAS project is to automate the construction of cuboctahedral lattice structures. Lattice materials are appealing for aerospace applications due to their strength and stiffness at ultra-light densities. However, in order for any material to be realistically considered for such environments, it must also be damage tolerant. The ability of a material to absorb damage is characterized by its fracture toughness, which remains poorly characterized for lattice materials. Consequently, the objective of this research is to develop an optical measurement system to experimentally validate the strain field ahead of a crack tip in architecture lattice materials. Although the ability to predict the strain field ahead of a crack tip has been investigated for continuum materials, such behaviour of three-dimensional architectures is under-investigated. As such, we will use a custom optical measurement system to track deformation of the voxels in a side-cracked plate fracture specimen. The system shall use 3D pose estimation, stereo imaging, and possibly color tracking, in combination with optical flow algorithms, to compute information regarding the three-dimensional movement movement of the lattice nodes during mechanical testing. Bench top experiments will validate the optical measurement system and characterize precision. Additionally, the effect of multiple cameras on precision, as well as system scalability will be investigated. Final results will compare measured lattice deformation with finite element predictions.
Lennig, Miriam↗
Pointing and figure control system for a space-based far-IR segmented telescope
A pointing and figure control system for two space-based far-IR telescopes, the 10-20 m Large Deployable Reflector and the 3.6 m Submillimeter Intermediate Mission, is described. The figure maintenance control system is designed to counter the optical elements translational and rotational changes induced by long-term thermal drifts that the support structure may experience. The pointing system applies optical truss to telescope pointing; a laser metrology system is used to transfer pointing informaton from an external fine guidance sensor to the telescope optical boresight, defined by the primary mirror, secondary mirror, and focal plane assembly.
Lau, Kenneth↗
Two-Stage Passive Vibration Isolator
The design and testing of a structural system were implemented to hold the optics of the planned Space Interferometry Mission (SIM) at positions and orientations characterized by vibrational translation and rotation errors of no more than a few nanometers or a few milliarcseconds, respectively. Much of the effort was devoted to a test bed for verifying the predicted behavior of a vibration- isolation structural subsystem working together with an active control system for positioning and orienting the SIM optics. There was considerable emphasis on the vibration-isolation subsystem, which was passive and comprised two stages. The main sources of vibration were six reaction wheels in an assembly denoted the "backpack." The first vibration-isolation stage consisted of hexapod isolator mounts - one for each reaction wheel - characterized by a natural vibration frequency of 10 Hz. The second stage was a set of three beams, disposed between the backpack and the structure that held the SIM optics, that were flexured such that they transmitted only bending loads, with a natural vibrational frequency and damping of about 5 Hz and 4 percent, respectively. Preliminary test results were presented and characterized as demonstrating the effectiveness of the two-stage vibration-isolation design.
Goullioud, Renaud↗
Band-gap Engineering in Sputter Deposited Amorphous/Microcrystalline Sc(x)Ga(1-x)N
Reactive sputtering was used to grow thin films of Sc(x)Ga(1-x)N with scandium concentrations of 20%-70% on quartz substrates at temperatures of 300-675 K. X-ray diffraction (XRD) of the films showed either weak or no structure, suggesting the films are amorphous or microcrystalline. Optical absorption spectra were taken of each sample and the optical band gap was determined. The band gap varied linearly with increasing Ga concentration between 2.0 and 3.5 eV. Ellipsometry was used to confirm the band gap measurements and provide optical constants in the range 250-1200 nm. ScN and GaN have different crystal structures (rocksalt and wurzite, respectively), and thus may form a heterogeneous mixture as opposed to an alloy. Since the XRD data were inconclusive, bilayers of ScN/GaN were grown and optical absorption spectra taken. A fundamental difference in the spectra between the bilayer films and alloy films was seen, suggesting the films are alloys, not heterogeneous mixtures.
Little, Mark E.↗
MPL-Net Measurements of Aerosol and Cloud Vertical Distributions at Co-Located AERONET Sites
In the early 1990s, the first small, eye-safe, and autonomous lidar system was developed, the Micropulse Lidar (MPL). The MPL acquires signal profiles of backscattered laser light from aerosols and clouds. The signals are analyzed to yield multiple layer heights, optical depths of each layer, average extinction-to-backscatter ratios for each layer, and profiles of extinction in each layer. In 2000, several MPL sites were organized into a coordinated network, called MPL-Net, by the Cloud and Aerosol Lidar Group at NASA Goddard Space Flight Center (GSFC) using funding provided by the NASA Earth Observing System. tn addition to the funding provided by NASA EOS, the NASA CERES Ground Validation Group supplied four MPL systems to the project, and the NASA TOMS group contributed their MPL for work at GSFC. The Atmospheric Radiation Measurement Program (ARM) also agreed to make their data available to the MPL-Net project for processing. In addition to the initial NASA and ARM operated sites, several other independent research groups have also expressed interest in joining the network using their own instruments. Finally, a limited amount of EOS funding was set aside to participate in various field experiments each year. The NASA Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic Studies (SIMBIOS) project also provides funds to deploy their MPL during ocean research cruises. All together, the MPL-Net project has participated in four major field experiments since 2000. Most MPL-Net sites and field experiment locations are also co-located with sunphotometers in the NASA Aerosol Robotic Network. (AERONET). Therefore, at these locations data is collected on both aerosol and cloud vertical structure as well as column optical depth and sky radiance. Real-time data products are now available from most MPL-Net sites. Our real-time products are generated at times of AERONET aerosol optical depth (AOD) measurements. The AERONET AOD is used as input to our processing routines, which calculate the aerosol layer top height and extinction profile, and our MPL calibration value. A variety of other data products are available or under development. We present an overview of the MPL-Net project and discuss data products useful to the AERONET community. Results from several sites and field experiments will be presented.
Welton, Ellsworth J.↗
Molecular Modeling and Experimental Investigations of Nonlinear Optical Compounds Monosubstituted Derivatives of Dicyanovinylbenzene
A search for potential nonlinear optical compounds was performed using the Cambridge Structure Database and molecular modeling. We investigated a series of monosubstituted derivatives of dicyanovinylbenzene, since the nonlinear optical (NLO) properties of such derivatives (o-methoxy-dicyanovinylbenzene, DIVA) were studied earlier. The molecular geometry of these compounds was investigated with x-ray analysis and discussed along with the results of molecular mechanics and ab initio quantum chemical calculations. The influence of crystal packing on the planarity of the molecules of this series has been revealed. Two new compounds from the series studied, ortho-F and para-Cl-dicyanovinylbenzene, according to powder measurements, were found to be NLO compounds in the crystal state about 10 times more active than urea. The peculiarities of crystal structure formation in the framework of balance between van der Waals and electrostatic interactions have been discussed. The crystal shape of DIVA and two new NLO compounds have been calculated on the basis of the known crystal structure.
Timofeeva, Tatiana V.↗
Conceptual design and structural analysis of the spectroscopy of the atmosphere using far infrared emission (SAFIRE) instrument
The conceptual design and structural analysis for the Spectroscopy of the Atmosphere using Far Infrared Emission (SAFIRE) Instrument are provided. SAFIRE, which is an international effort, is proposed for the Earth Observing Systems (EOS) program for atmospheric ozone studies. A concept was developed which meets mission requirements and is the product of numerous parametric studies and design/analysis iterations. Stiffness, thermal stability, and weight constraints led to a graphite/epoxy composite design for the optical bench and supporting struts. The structural configuration was determined by considering various mounting arrangements of the optical, cryo, and electronic components. Quasi-static, thermal, modal, and dynamic response analyses were performed, and the results are presented for the selected configuration.
Moses, Robert W.↗
ORFEUS observations of AM Herculis
The Orbiting and Retrievable Far and Extreme UV Spectrometer (ORFEUS) telescope has observed AM Her in its high optical state at high spectral resolution in the 912-1176 A band. Spectra at two phases show O VI emission lines with a broad and narrow component structure similar to that of the optical emission lines. We find that the O VI lines are optically thick, and that the densities in the broad- and narrow-component regions differ by a factor of 100. The most puzzling aspect of the observations is the continuum, which is softer than expected, but does not show definite Lyman absorption lines. We discuss the implications for the 'soft X-ray excess' of AM Her stars.
Raymond, John C.↗
Compact programmable photonic variable delay devices
Optical variable delay devices for providing variable true time delay to multiple optical beams simultaneously. A ladder-structured variable delay device comprises multiple basic building blocks stacked on top of each other resembling a ladder. Each basic building block has two polarization beamsplitters and a polarization rotator array arranged to form a trihedron; Controlling an array element of the polarization rotator array causes a beam passing through the array element either going up to a basic building block above it or reflect back towards a block below it. The beams going higher on the ladder experience longer optical path delay. An index-switched optical variable delay device comprises of many birefringent crystal segments connected with one another, with a polarization rotator array sandwiched between any two adjacent crystal segments. An array element in the polarization rotator array controls the polarization state of a beam passing through the element, causing the beam experience different refractive indices or path delays in the following crystal segment. By independently control each element in each polarization rotator array, variable optical path delays of each beam can be achieved. Finally, an index-switched variable delay device and a ladder-structured variable device are cascaded to form a new device which combines the advantages of the two individual devices. This programmable optic device has the properties of high packing density, low loss, easy fabrication, and virtually infinite bandwidth. The device is inherently two dimensional and has a packing density exceeding 25 lines/cm.sup.2. The delay resolution of the device is on the order of a femtosecond (one micron in space) and the total delay exceeds 10 nanosecond. In addition, the delay is reversible so that the same delay device can be used for both antenna transmitting and receiving.
Yao, X. Steve↗
Photonic variable delay devices based on optical birefringence
Optical variable delay devices for providing variable true time delay to multiple optical beams simultaneously. A ladder-structured variable delay device comprises multiple basic building blocks stacked on top of each other resembling a ladder. Each basic building block has two polarization beamsplitters and a polarization rotator array arranged to form a trihedron; Controlling an array element of the polarization rotator array causes a beam passing through the array element either going up to a basic building block above it or reflect back towards a block below it. The beams going higher on the ladder experience longer optical path delay. An index-switched optical variable delay device comprises of many birefringent crystal segments connected with one another, with a polarization rotator array sandwiched between any two adjacent crystal segments. An array element in the polarization rotator array controls the polarization state of a beam passing through the element, causing the beam experience different refractive indices or path delays in the following crystal segment. By independently control each element in each polarization rotator array, variable optical path delays of each beam can be achieved. Finally, an index-switched variable delay device and a ladder-structured variable device are cascaded to form a new device which combines the advantages of the two individual devices. This programmable optic device has the properties of high packing density, low loss, easy fabrication, and virtually infinite bandwidth. The device is inherently two dimensional and has a packing density exceeding 25 lines/cm2. The delay resolution of the device is on the order of a femtosecond (one micron in space) and the total delay exceeds 10 nanosecond. In addition, the delay is reversible so that the same delay device can be used for both antenna transmitting and receiving.
Yao, X. Steve↗
Optical conductivity of alpha-Mn
The optical constants were measured at room temperature in the photon-energy range 0.6-6.5 eV on evaporated thin films. Evaporation conditions were chosen that gave the alpha-Mn crystal structure with relatively large grains. The optical conductivity was separated into intraband and interband contributions by fitting to the Drude formula at low energies. The results are anomalous in comparison to other 3d transition metals: the free-electron lifetime is exceptionally short (in agreement with the large dc resistivity of Mn), and the interband transitions seem unusually weak at the lower energies. Possible explanations related to the complicated crystal structure of alpha-Mn with its loss of point symmetry at the atom sites are discussed.
Scoles, K. J.↗
Optical conductivity of alpha-Mn
The optical constants were measured at room temperature in the photon-energy range 0.6 to 6.5 eV on evaporated thin films. Evaporation conditions were chosen that gave the alpha-Mn crystal structure with reasonably large grains. The optical conductivity was separated into intraband and interband contributions by fitting to the Drude formula at low energies. The results are anomalous in comparison to other 3d transition metals. The free-electron lifetime is exceptionally sort (in agreement with the large dc resistivity of Mn), and the interband transitions seem unusually weak at the lower energies. Possible explanations related to the complicated crystal structure of alpha-Mn are discussed.
Scoles, K. J.↗
Structural Model Validation - ALLVAR
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ALLVAR↗
Structural and electrical performance of a large concentrating solar cell panel.
Structural integrity and electrical-optical performance of large concentrating solar cell panel for spacecraft power supplies
SPACECRAFT POWER SUPPLY↗