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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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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Development of Genesis Solar Wind Sample Cleanliness Assessment: Initial Report on Sample 60341 Optical Imagery and Elemental Mapping

Since 2005 the Genesis science team has experimented with techniques for removing the contaminant particles and films from the collection surface of the Genesis fragments. A subset of ~40 samples have been designated as "cleaning matrix" samples. These are small samples to which various cleaning approaches are applied and then cleanliness is assessed optically, by TRXRF, SEM, ToF-SIMS, XPS, ellipsometry or other means [1-9]. Most of these sam-ples remain available for allocation, with cleanliness assessment data. This assessment allows evaluation of various cleaning techniques and handling or analytical effects. Cleaning techniques investigated by the Genesis community include acid/base etching, acetate replica peels, ion beam, and CO2 snow jet cleaning [10-16]. JSC provides surface cleaning using UV ozone exposure and ultra-pure water (UPW) [17-20]. The UPW rinse is commonly used to clean samples for handling debris between processing by different researchers. Optical microscopic images of the sample taken before and after UPW cleaning show what has been added or removed during the cleaning process.

Gonzalez, C. P.↗
DOE OSTI2025

Competing and Anisotropic Exchange Interactions in the Kagome Lattice Ferromagnet Co 3 Sn 2 S 2

The kagome lattice ferromagnet, Co 3 Sn 2 S 2 , serves as template for a host of materials that exhibit exotic topological states, as well as a giant anomalous Hall state—a momentous realization in condensed matter physics. The anisotropic exchange interactions are probed by applying external magnetic fields in various directions along major crystal axes and the magneto-optical response is recorded. When magnetic fields are applied along the a–b plane, long-range magnetism forms and grows with increasing temperature. This counterintuitive behavior does not take place when the magnetic field is applied at a slight angle off the a–b plane. In fact, the opposite effect is observed for this exact configuration, as well as for other fields arrangements. Ab initio theoretical calculations reveal that anisotropic exchange interactions are the underlying mechanism leading to this peculiar behavior. Furthermore, the long-range ferromagnetic order along the c-axis is thought to coexist with an antiferromagnetic, or spin glass, state in the a–b plane, before becoming paramagnetic above the Curie temperature (T c ). These two coexisting magnetic states are thought to compete as the temperature approaches T c , with the antiferromagnetic state gaining strength compared to the ferromagnetic order.

Barua, Arup [University of South Florida, Tampa, F↗
DOE OSTI2024

Properties of V-defect injectors in long wavelength GaN LEDs studied by near-field electro- and photoluminescence

The efficiency of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on uniformity of hole distribution between the QWs. Typically, transport between the QWs takes place via carrier capture into and thermionic emission out of the QWs. In InGaN/GaN QWs, the thermionic hole transport is hindered by the high quantum confinement and polarization barriers. To overcome this drawback, hole injection through semipolar QWs located at sidewalls of V-defects had been proposed. However, in the case of the V-defect injection, strong lateral emission variations take place. In this work, we explore the nature of these variations and the impact of the V-defects on the emission spectra and carrier dynamics. The study was performed by mapping electroluminescence (EL) and photoluminescence (PL) with a scanning near-field optical microscope in LEDs that contain a deeper well that can only be populated by holes through the V-defects. Applying different excitation schemes (electrical injection and optical excitation in the far- and near-field), we have shown that the EL intensity variations are caused by the lateral nonuniformity of the hole injection. We have also found that, in biased structures, the PL intensity and decay time in the V-defect regions are only moderately lower that in the V-defect-free regions thus showing no evidence of an efficient Shockley-–Read–Hall recombination. In the V-defect regions, the emission spectra experience a red shift and increased broadening, which suggests an increase of the In content and well width in the polar QWs close to the V-defects.

Electroluminescence↗
NASA NTRS1993

Hubble Space Telescope prescription retrieval

Prescription retrieval is a technique for directly estimating optical prescription parameters from images. We apply it to estimate the value of the Hubble Space Telescope primary mirror conic constant. Our results agree with other studies that examined primary-mirror test fixtures and results. In addition they show that small aberrations exist on the planetary-camera repeater optics.

Redding, David↗
NASA NTRS1971

Thermomagnetic recording and magnetic-optic playback system

A magnetic recording and magneto-optic playback system is disclosed wherein thermomagnetic recording is employed. A transparent isotropic film is heated along a continuous path by a focused laser beam. As each successive area of the path is heated locally to the vicinity of its Curie point in the presence of an applied magnetic field, a magneto-optic density is established proportional to the magnetic field and fixed in place as the area cools once the laser beam moves on to an adjacent area. To play back the recorded data, the intensity of the laser beam is reduced to avoid reaching the vicinity of the Curie point of the film as it is scanned by the laser beam in the same manner as for recording. A Faraday effect analyzer and photo detector are employed as a transducer for producing an output signal.

Lewicki, G. W.↗
NASA NTRS1976

Determination of strains in optical windows of a high-pressure chamber by holographic interferometry and finite element analysis

Holographic interferometry and finite element analysis have been applied to determine the strain in a large optical window installed in a high-pressure chamber. Two different shapes of windows were chosen, and the outside and inside surface strains of the windows were followed as a function of internal pressure by taking double exposed holograms at 69-bar intervals up to 483 bars. The results were compared with the values calculated by a standard finite element code with an assumption of no displacement at the load-bearing edge. The agreement between two results was found to be good for both cases.

Soga, N.↗
NASA NTRS1988

Active phase compensation system for fiber optic holography

Fiber optic delivery systems promise to extend the application of holography to severe environments by simplifying test configurations and permitting the laser to be remotely placed in a more benign location. However, the introduction of optical fiber leads to phase stability problems. Environmental effects cause the pathlengths of the fibers to change randomly, preventing the formation of stationary interference patterns which are required for holography. An active phase control system has been designed and used with an all-fiber optical system to stabilize the phase difference between light emitted from two fibers, and to step the phase difference by 90 deg without applying any constraints on the placement of the fibers. The accuracy of the phase steps is shown to be better than 0.02 deg., and a stable phase difference can be maintained for 30 min. This system can be applied to both conventional and electro-optic holography, as well as to any system where the maintenance of an accurate phase difference between two coherent beams is required.

Mercer, Carolyn R.↗
NASA NTRS1989

Active phase compensation system for fiber optic holography

Fiber optic delivery systems promise to extend the application of holography to severe environments by simplifying test configurations and permitting the laser to be remotely placed in a more benign location. However, the introduction of optical fiber leads to phase stability problems. Environmental effects cause the pathlengths of the fibers to change randomly, preventing the formation of stationary interference patterns which are required for holography. An active phase control system has been designed and used with an all-fiber optical system to stabilize the phase difference between light emitted from two fibers, and to step the phase difference by 90 deg without applying any constraints on the placement of the fibers. The accuracy of the phase steps is shown to be better than 0.02 deg., and a stable phase difference can be maintained for 30 min. This system can be applied to both conventional and electro-optic holography, as well as to any system where the maintenance of an accurate phase difference between two coherent beams is required.

Mercer, Carolyn R.↗
NASA NTRS1986

Lateral shift of an optical beam due to leaky surface-plasmon excitations

A leaky-wave theory is applied to the study of the lateral shift of a bounded optical beam reflected from a prism-air-metal (and prism-metal-air) layered configuration with surface-plasmon excitations. The locations of the pole and the zero of the reflection coefficient for the leaky surface-plasmon mode are calculated as one varies the thickness of the center layer. The excited surface-plasmon mode is leaky because of the presence of the prism. Both the real part and the imaginary part of the pole are affected by the energy leakage. The detailed structure of the reflected intensity and the forward and backward shifts of the reflected beam are illustrated.

Chuang, S. L.↗
NASA NTRS1988

Optical properties of cometary grains

An analysis of visible/near IF polarimetry of Comet Halley leads to a variation of the complex refractive index m = n - i x k of grain material with wavelength, i.e., a slight decrease of n from 1.39 at lambda = 0.37 micrometer to 1.37 at lambda = 2.2 micrometers, in constrast to an increase of k from 0.024 at lambda = 0.37 micrometer to 0.042 at lambda 2.2 micrometers. The mass distribution of grains reported by Mazets et al. from in situ measurements of Vega 2 was applied in the analysis. Combining these optical constants with those of astronomical silicate proposed by Draine, cometary silicate is presented as a candidate for cometary grains. The complex refractive index of the proposed cometary silicate is shown. Based on Mie theory, an emission coefficiency of each of the grains in computed as well as its temperature, as functions of grain radius and sun comet (grain) distance. It is found that the tentative thermal spectrum from these cometary silicates, where the mass distribution of grains reported by Mazets from Vega 2 was applied, fits very well to the IR spectrum of Comet Halley. This means that cometary silicate can explain not only the phase angle and wavelength dependences of visible/near IF polarization, but also the thermal emission.

Mukai, Tadashi↗
NASA NTRS2012

Global and Regional Trends of Aerosol Optical Depth over Land and Ocean Using SeaWiFS Measurements from 1997 to 2010

Both sensor calibration and satellite retrieval algorithm play an important role in the ability to determine accurately long-term trends from satellite data. Owing to the unprecedented accuracy and long-term stability of its radiometric calibration, the SeaWiFS measurements exhibit minimal uncertainty with respect to sensor calibration. In this study, we take advantage of this well-calibrated set of measurements by applying a newly-developed aerosol optical depth (AOD) retrieval algorithm over land and ocean to investigate the distribution of AOD, and to identify emerging patterns and trends in global and regional aerosol loading during its 13-year mission. Our results indicate that the averaged AOD trend over global ocean is weakly positive from 1998 to 2010 and comparable to that observed by MODIS but opposite in sign to that observed by AVHRR during overlapping years. On a smaller scale, different trends are found for different regions. For example, large upward trends are found over the Arabian Peninsula that indicate a strengthening of the seasonal cycle of dust emission and transport processes over the whole region as well as over downwind oceanic regions. In contrast, a negative-neutral tendency is observed over the desert/arid Saharan region as well as in the associated dust outflow over the north Atlantic. Additionally, we found decreasing trends over the eastern US and Europe, and increasing trends over countries such as China and India that are experiencing rapid economic development. In general, these results are consistent with those derived from ground-based AERONET measurements.

Hsu, N. C.↗
DOE OSTI2026

Insights from a coupled thermo-hydro-mechanical analysis of a layered high-temperature thermal energy storage reservoir

Coupled thermal-hydraulic-mechanical (THM) modeling is applied to investigate the performance of a seasonal high-temperature aquifer thermal energy storage operation based on data and conditions from current site investigations at the Geostorage Forsthaus pilot project in Bern (Switzerland). The model includes subhorizontal sand lenses of various lengths and dips that are embedded in a low permeability clay matrix. Thermal energy storage is simulated by seasonal injection and withdrawal of hot (up to 90 °C) water from a main well, with reservoir pressure regulated by two auxiliary wells at a distance of about 70 m from the main well. The results show how targeted injection into deeper permeable storage formations, along with active deep well pressure control, can effectively minimize geomechanical impact and the potential risk of damaging subsurface storage and sealing formations, or even surface facilities. With such pressure control, the subsurface mechanical responses are dominated by thermal strain and stress, which can be monitored with subsurface fiber optics. The study demonstrates how coupled THM modeling can be applied for the design of a safe and efficient thermal energy storage operation, and how subsurface fiber optic monitoring can be applied for performance confirmation, allowing for more confident operational forecasting.

Rutqvist, Jonny↗
NASA NTRSDate not supplied

Applications and Development Work for Digital Image Correlation Using High Speed Cameras

NASA, Army, and industry partners are working to advance optical measurement techniques used in highly dynamic rocket engine and missile test environments. This allows for direct component data collection during test and flight environments, significantly reduced analysis time, and associated cost savings. Digital Image Correlation (DIC) uses calibrated stereo cameras to collect three-dimensional (3-D) displacements, strains, and acceleration data by referencing a stochastic speckle pattern applied to the test object. These optical measurement techniques provide significantly improved data resulting in better performance predictions, model validation, and information about components during hot-fire tests and test flights.

Rachel Paden↗
NASA NTRS2011

From X-Ray Telescopes to Neutron Focusing

In the case of neutrons the refractive index is slightly less than unity for most elements and their isotopes. Consequently, thermal and cold neutrons can be reflected from smooth surfaces at grazing-incidence angles. Hence, the optical technologies developed for x-ray astronomy can be applied for neutron focusing. The focusing capabilities of grazing incidence neutron imaging optics have been successfully demonstrated using nickel mirrors. The mirrors were fabricated using an electroformed nickel replication process at Marshall Space Flight Center. Results of the neutron optics experiments will be presented. Challenges of the neutron imaging optics as well as possible applications of the optics will be discussed.

Gubarev, M. V.↗
NASA NTRS1982

Sensitivity of constrained linear inversions to the selection of the Lagrange multiplier

The influence of the choice of the Lagrange multiplier on constrained linear inversions is explored, with reference made to applications in inferring the columnar aerosol size distributions from spectral aerosol optical depth measurements. A range of the Lagrange multiplier is examined to find all positive solutions for the solution vector, which represents modifying factors to the assumed form of the size distribution. An iterative method is devised to constrain the calculations to consideration of only positive quantities and a requirement that the regression fit to data be consistent with measurement errors. The determination of the variances and covariances is formulated and applied to existing data sets for optical depth. Variances in the solution are found to be large for particle radii when the information content of the data is small.

King, M. D.↗
NASA NTRS1991

Recent results on structural control of an active precision structure

This paper describes recent results in structural control of an active precision truss structure at JPL. The goal is to develop practical control methodology and to apply to active truss structures intended for high precision space-based optics applications. The active structure considered incorporates piezoelectric active members which apply control forces internal to the structure and thereby improve the structure's dimensional stability. Two approaches to structural control system design were investigated. The first approach uses only noncollocated measurements of acceleration at the location of a simulated optical component to achieve structural stabilization. The second approach is essentially the same as the first one except that a viscous damper was used in place of a truss member on the structure to improve the dampings of selected flexible modes. The corresponding experimental closed-loop results are presented in this paper.

Chu, C. C.↗
NASA NTRS2001

A Multi-Band Analytical Algorithm for Deriving Absorption and Backscattering Coefficients from Remote-Sensing Reflectance of Optically Deep Waters

A multi-band analytical (MBA) algorithm is developed to retrieve absorption and backscattering coefficients for optically deep waters, which can be applied to data from past and current satellite sensors, as well as data from hyperspectral sensors. This MBA algorithm applies a remote-sensing reflectance model derived from the Radiative Transfer Equation, and values of absorption and backscattering coefficients are analytically calculated from values of remote-sensing reflectance. There are only limited empirical relationships involved in the algorithm, which implies that this MBA algorithm could be applied to a wide dynamic range of waters. Applying the algorithm to a simulated non-"Case 1" data set, which has no relation to the development of the algorithm, the percentage error for the total absorption coefficient at 440 nm a (sub 440) is approximately 12% for a range of 0.012 - 2.1 per meter (approximately 6% for a (sub 440) less than approximately 0.3 per meter), while a traditional band-ratio approach returns a percentage error of approximately 30%. Applying it to a field data set ranging from 0.025 to 2.0 per meter, the result for a (sub 440) is very close to that using a full spectrum optimization technique (9.6% difference). Compared to the optimization approach, the MBA algorithm cuts the computation time dramatically with only a small sacrifice in accuracy, making it suitable for processing large data sets such as satellite images. Significant improvements over empirical algorithms have also been achieved in retrieving the optical properties of optically deep waters.

Lee, Zhong-Ping↗