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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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DOE OSTI2022

Angle-resolved polarimetry of hybrid perovskite emission for photonic technologies

Coupling between light and matter strongly depends on the polarization of the electromagnetic field and the nature of excitations in a material. As hybrid perovskites emerge as a promising class of materials for light-based technologies such as LEDs, LASERs, and photodetectors, it is critical to understand how their microstructure changes the intrinsic properties of the photon emission process. While the majority of optical studies have focused on the spectral content, quantum efficiency and lifetimes of emission in various hybrid perovskite thin films and nanostructures, few studies have investigated other properties of the emitted photons such as polarization and emission angle. Here, we use angle-resolved cathodoluminescence microscopy to access the full polarization state of photons emitted from large-grain hybrid perovskite films with spatial resolution well below the optical diffraction limit. In this work, mapping these Stokes parameters as a function of the angle at which the photons are emitted from the thin film surface, we reveal the effect of a grain boundary on the degree of polarization and angle at which the photons are emitted. Such studies of angle- and polarization-resolved emission at the single grain level are necessary for future development of perovskite-based flat optics, where effects of grain boundaries and interfaces need to be mitigated.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

NASA NTRS1991

Cryogenic Limb Array Etalon Spectrometer (CLAES) - Experiment description

The CLAES measurement concept, instrument design, and performance are presented, and the scientific capabilities and measurement modes are discussed. The CLAES experiment involves remote measurement of earth-limb emission spectra. Characteristic vibration-rotation line spectral radiances are obtained between 3.5 and 13 microns and inverted through an iterative relaxation process to yield pressure, temperature, and species mixing ratio. The UARS limb-viewing instruments, including CLAES, combined with the 57-deg orbit inclination, allow for measurements to 80-deg latitudes. CLAES requires high spectral resolution and high radiometric sensitivity to isolate and accurately measure weak emissions from trace species such as HCl and NO against intense backgrounds from abundant emitters such as CO2, H2O, and O3. Accuracy and precision of retrieved quantities, observational modes, and calibration modes are also discussed.

Roche, Aidan E.↗

NASA NTRS1985

The R Aquarii system at optical and radio wavelengths

New continuum observations of all radio components of the R Aquarii system at 2, 6, and 20 cm are reported which allow determination of polarization properties, integrated flux levels, spectral indices, and hence the emission mechanisms of the individual components. Complementary wide-band optical observations are also reported to help determine the nature and structure of the compact double radio source (CDRS) and the R Aquarii radio jet. The results of these observations are discussed in detail with regard to models currently or previously proposed for the R Aquarii system. It is concluded that the compact H II region spectral index is about +0.6, indicative of a thermal and optically thick expanding wind from the long-period variable. The radio jet emission is shown to be optically thin, thermal, cospatial with optical emission, and stable over the last few years. The CDRS is shown to be an extragalactic background object.

Hollis, J. M.↗

DOE OSTI2022

Gas and Cosmic-Ray Properties in the MBM 53, 54, and 55 Molecular Clouds and the Pegasus Loops Revealed by H i Line Profiles, Dust, and Gamma-Ray Data

In studying the interstellar medium (ISM) and Galactic cosmic rays (CRs), uncertainty of the interstellar gas density has always been an issue. To overcome this difficulty, we used a component decomposition of the 21 cm H i emission line and used the resulting gas maps in an analysis of γ-ray data obtained by the Fermi Large Area Telescope (LAT) for the MBM 53, 54, and 55 molecular clouds and the Pegasus loop. We decomposed the ISM gas into intermediate-velocity clouds, narrow-line and optically thick H i, broad-line and optically thin H i, CO-bright H 2 , and CO-dark H 2 using detailed correlations with the H i line profiles from the HI4PI survey, the Planck dust-emission model, and the Fermi-LAT γ-ray data. We found the fractions of the optical depth correction to the H i column density and CO-dark H 2 to be nearly equal. We fitted the CR spectra directly measured at/near the Earth and the measured γ-ray emissivity spectrum simultaneously. We obtained a spectral break in the interstellar proton spectrum at ~7 GeV, and found that the γ-ray emissivity normalization agrees with the AMS-02 proton spectrum within 10%, relaxing the tension with the CR spectra previously claimed.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1991

G33.6 + 0.1 - A shell type supernova remnant with unusual structure

The morphology of Supernova Remnant G33.6 + 0.1 (Kes 79) has been studied in the X-rays with Einstein and in the radio wavelengths using the VLA. Multifrequency high resolution observations of the VLA at 327, 1500, and 5000 MHz are used to study the radio spectrum and polarization. The radio emission shows well formed outer shell structure and very bright central emission. Although the overall distribution of spectral index (about -0.6 to -0.75) is consistent with that of shell type remnants, the bright filamentary emission along the 'inner ring' has relatively flatter spectrum (alpha about -0.4). Both radio and X-rays show strong central emission; existence of a plerion near the center cannot be ruled out. The X-ray image does not show the characteristic limb brightening for shell type SNRs. The X-ray and radio morphology may be understood in terms of very thick shell and the bright central emission as due to reverse shock.

Velusamy, T.↗

NASA NTRS1992

Passive microwave signatures of simulated pancake ice and young pressure ridges

Surface-based passive microwave observations of simulated pancake ice and of a first-year pressure ridge are described. The observed emissivity spectra are very similar to those observed on several field experiments in the polar regions. Certain spectral features such as a maximum emissivity at 37 GHz for pancake ice and a polarization ratio very close to zero for ridged ice are distinct from those of new, young, and first-year ice. They suggest possible signatures which may help to characterize these ice types using passive microwave techniques.

Grenfell, T. C.↗

NASA NTRS2018

An Overall Assessment of JPSS-2 VIIRS Radiometric Performance Based on Pre-Launch Testing

The Visible Infrared Imaging Radiometer Suite (VIIRS) on-board the second Joint Polar Satellite System (JPSS) completed its sensor level testing in February 2018. The JPSS-2 (J2) mission is scheduled to launch in 2022 and will be very similar to its two predecessor missions, the Suomi National Polar-orbiting Partnership (SNPP) mission, launched on 28 October 2011 and JPSS-1 (renamed NOAA-20) launched on 18 November 2017. VIIRS instrument has 22 spectral bands covering the spectrum between 0.4 and 12.6 μm: 14 reflective solar bands (RSB), 7 thermal emissive bands (TEB) and one day-night band (DNB). It is a cross-track scanning radiometer capable of providing global measurements through observations at two spatial resolutions, 375 m and 750 m at nadir for the imaging bands and moderate bands, respectively. This paper will provide an overview of J2 VIIRS characterization methodologies and calibration performance during the pre-launch testing phases performed by the National Aeronautics and Space Administration (NASA) VIIRS Characterization Support Team (VCST) to evaluate the at-launch baseline radiometric performance and generate the parameters needed to populate the sensor data record (SDR) Look-Up-Tables (LUTs). Our analysis results confirmed the good performance of J2 VIIRS, in general as good as previous VIIRS instruments and all non-compliances are expected to have low impact on data quality. Key sensor performance metrics include the signal to noise ratio (SNR), radiance dynamic range, reflective and emissive bands calibration performance, polarization sensitivity, spectral performance, response versus scan-angle (RVS) and scattered light response. A set of performance metrics generated during the pre-launch testing program will be compared to both the SNPP and JPSS-1 VIIRS sensors.

Oudrari, Hassan↗

NASA NTRS2018

Evaluation of Soil Moisture Estimated from IASI Measurements

A simple yet effective scheme to estimate volumetric soil moisture (VSM) using infrared (IR) land surface emissivity retrieved from satellite IR spectral radiance measurements was recently developed, assuming other parameters impacting the radiative transfer (e.g., temperature, vegetation coverage, and surface roughness) are known for an acceptable time and space reference location. This scheme was applied to a decade of global IR emissivity data retrieved from MetOp-A Infrared Atmospheric Sounding Interferometer measurements. Global datasets of monthly-mean 0.25° spatial-grid VSM, estimated from IR emissivity data (denoted as IR-VSM), are assembled to compare with those routinely provided by satellite microwave (MW) multi-sensor measurements (obtained from the ESA CCI website). The IR-VSM dataset is used to demonstrate its spatial variations as well as seasonal-cycles and inter-annual variability which are spatially coherent and consistent with that from MW measurements. Herein we report on some initial evaluation of the IR-VSM absolute values using in-situ measurements available from the Soil Climate Analysis Network of the USDA website. From the 114 ground station locations, we infer a mean bias between monthly-mean in-situ VSM and satellite derived IR-VSM of 0.005 (m3/m3) over the past decade, despite the differences between physical measurements. The absolute accuracy of IR-VSM is also evaluated using an independent source of soil moisture measurements.

Zhou, Daniel K.↗

DOE OSTI2026

Spectral and small-signal electroluminescence analysis of carrier dynamics in dual-color InGaN/GaN light-emitting diodes

Here, we study carrier transport, distribution, and recombination in dual-color c-plane InGaN/GaN LEDs using spectral analysis and small-signal electroluminescence (SSEL). The emissions from green and blue quantum wells (QWs) were experimentally separated and analyzed. Spectral analysis and SSEL independently demonstrate that emission from the green QW is dominant at low current densities, consistent with its narrower bandgap, while emission from the blue QW is more significant at higher current densities, consistent with its reduced quantum confined Stark effect and larger wavefunction overlap. In addition, we demonstrate that the carrier recombination in the QWs is non-uniform, with carrier transport dramatically affecting the carrier distribution between QWs and the recombination in a specific QW. Finally, our measurements suggest that the effective active region contributing most strongly to radiative recombination corresponds to approximately two to three QWs on the p-GaN side, indicating limited carrier transport to more distant QWs in the structures studied.

36 MATERIALS SCIENCE↗

NASA NTRS2005

Unveiling the Engines in QSOs: Multi-Wavelength Study

UV/optical emission lines offer some of the most detailed information obtainable about the intrinsic properties of quasars. Studies of the density, ionization and metal abundance of gas near the accreting black hole are probed through an intriguing but poorly understood complex of correlations between emission lines and overall quasar spectral energy distributions that has long suffered from a lack of large, consistently measured samples. As part of a broader effort to expand and systematize the data upon which these studies are built, we proposed to NASA to model, fit, and measure UV/optical emission line parameters in large samples of quasar spectra. As part of the project, we developed an automated measurement technique that accounts for galactic reddening, includes iron emission blends, galactic and intrinsic absorption lines, and performs multi-component fits to the emission line profiles. We present measured line parameters (equivalent width and FWHM) for a large number of (28) different UV/optical lines, including upper limits for undetected lines.

Green, Paul↗

NASA NTRS1981

Analysis of solar X-ray emission line profiles

The high spatial and spectral resolution solar X-ray observations of an active region in which an X-ray and radio gradual rise and fall was in progress are reported. The correlations of highly collimated X-ray scans with the magnetic data indicate the presence of a hot localized region of X-ray emission near the end of the magnetic neutral line. A thermal interpretation of the continuum observed from this region is consistent with an emission temperature of 3 x 10 to the 48th/cu cm and an electron temperature of 10 to the 7th K. A model of the temperature distribution of the X-ray emitting material within the collimator field of view is derived using the resonance lines of Ne X, Ne IX, and Fe XVII. Most of the emission measure is at temperatures less than 2,000,000 K, but some high-temperature material with an electron temperature between 5,000,000 K and 7,000,000 K is required.

Burek, A. J.↗

DOE OSTI2020

Two-Photon Spontaneous Emission in Atomically Thin Plasmonic Nanostructures

The ability to harness light-matter interactions at the few-photon level plays a pivotal role in quantum technologies. Single photons—the most elementary states of light—can be generated on demand in atomic and solid state emitters. Two-photon states are also key quantum assets, but achieving them in individual emitters is challenging because their generation rate is much slower than competing one-photon processes. We demonstrate that atomically thin plasmonic nanostructures can harness two-photon spontaneous emission, resulting in giant far field two-photon production, a wealth of resonant modes enabling tailored photonic and plasmonic entangled states, and plasmon-assisted single-photon creation orders of magnitude more efficient than standard one-photon emission. We unravel the two-photon spontaneous emission channels and show that their spectral line shapes emerge from an intricate interplay between Fano and Lorentzian resonances. Enhanced two-photon spontaneous emission in two-dimensional nanostructures paves the way to an alternative efficient source of light-matter entanglement for on-chip quantum information processing and free-space quantum communications.

36 MATERIALS SCIENCE↗

NASA NTRS1987

Radio detection of the Be star Psi Persei

The results of a VLA survey for radio emission from a sample of Be stars having strong excess emission in the IRAS bands are presented. Radio emission was detected from one star, Psi Persei. The radio flux density, together with nearly simultaneous ultraviolet and near-infrared observations, argue strongly against a spherically symmetric model for the circumstellar envelope, thus favoring equatorial disk models. In general, it is found that the spectral index of the excess emission increases between the radio and far-infrared, suggesting either increased acceleration of the outflow at large distances from the star, partial recombination of the outer regions of the disk, or divergence of the equatorial disk at large radii.

Taylor, A. R.↗

NASA NTRS1988

The submillimeter spectral break in Seyfert galaxies

Observations have been made of four Seyfert 1 galaxies at 155 microns and three at 370 microns. Two of the galaxies were detected at 155 microns, but none was detected at 370 microns. The 155 microns data and the strong upper limits at 370 microns show that the infrared continua decrease sharply beyond 100-155 microns. These observations depict a clear spectral difference between radio-loud and radio-quiet active galactic nuclei. The limits on the 100-370 microns spectral slope are consistent either with synchrotron self-absorption of a nonthermal source or with thermal dust emission similar to that arising from the disks of normal galaxies. The 155 microns flux from NGC 4151 is spatially extended through a radius of at least 48 arcsec, arguing for substantial dust emission at wavelengths greater than 80 microns and an even shorter cutoff wavelength for nonthermal emission from the active nucleus. The spectral breaks implied by our data suggest that the nuclear nonthermal sources must be smaller than about 10 light hours.

Engargiola, G.↗

NASA NTRS1995

TIMS observations of surface emissivity in HAPEX-Sahel

The Thermal Infrared Multispectral Scanner (TIMS) was flown on the NASA C-130 aircraft for a series of 12 flights during HAPEX-Sahel at altitudes ranging from 0.25 to 6 km (0.6 to 15 m resolution). TIMS provides coverage of the 8 to 12 micrometer thermal infrared band in 6 contiguous channels. Thus it is possible to observe the spectral behavior of the surface emissivity over this wavelength interval.

Schmugge, Thomas↗

DOE OSTI2022

Exploring the MeV sky with a combined coded mask and Compton telescope: the Galactic Explorer with a Coded aperture mask Compton telescope (GECCO)

The sky at MeV energies is currently poorly explored. Here we present an innovative mission concept that builds upon the heritage of past and current missions improving the sensitivity and, very importantly, the angular resolution. This consists in combining a Compton telescope and a coded-mask telescope. We delineate the motivation for such a concept and we define the scientific goals for such a mission. The Galactic Explorer with a Coded Aperture Mask Compton Telescope (GECCO) is a novel concept for a next-generation telescope covering hard X-ray and soft gamma-ray energies. The potential and importance of this approach that bridges the observational gap in the MeV energy range are presented. With the unprecedented angular resolution of the coded mask telescope combined with the sensitive Compton telescope, a mission such as GECCO can disentangle the discrete sources from the truly diffuse emission. Individual Galactic and extragalactic sources are detected. This also allows to understand the gamma-ray Galactic center excess and the Fermi Bubbles, and to trace the low-energy cosmic rays, and their propagation in the Galaxy. Nuclear and annihilation lines are spatially and spectrally resolved from the continuum emission and from sources, addressing the role of low-energy cosmic rays in star formation and galaxy evolution, the origin of the 511 keV positron line, fundamental physics, and the chemical enrichment in the Galaxy. Such an instrument also detects explosive transient gamma-ray sources, which, in turn, enables identifying and studying the astrophysical objects that produce gravitational waves and neutrinos in a multi-messenger context. By looking at a poorly explored energy band it also allows discoveries of new astrophysical phenomena.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2022

Exploring the MeV Sky With A Combined Coded Mask and Compton Telescope: the Galactic Explorer With A Coded Aperture Mask Compton Telescope (GECCO)

Elena Orlando↗

NASA NTRS1995

Deep ROSAT HRI observations of the Orion nebula region

We present results from three deep ROSAT high-resolution imager observations of the Orion Nebula star-forming region. The X-ray images contain over 1500 cataloged stars in a roughly 0.8 sq deg region centered on the Trapezium. In all, 389 distinct X-ray sources have been detected, at least two-thirds of which are associated with a single proper-motion cluster member. X-ray emission is detected from stars of all spectral types, from massive O- and B-type components of the Trapezium to the coolest, low-mass pre-main-sequence (PMS) stars. In this paper we focus primarily on X-ray emission from the late-type PMS stars. Of the approximately 100 late-type cluster members with measured spectral types, approximately three-fourths have been detected; we have derived X-ray luminosity upper limits for the remaining stars. We found coronal X-ray emission turns on around spectral type F6, with the upper envelope of activity increasing with deceasing effective temperature. When plotted in an X-ray luminosity versus bolometric luminosity diagram, late-type PMS stars lie below a 'saturation' line corresponding to L(sub x)/L(sub bol) approximately 10(exp -3). For approximately solar-mass PMS stars, we find a median X-ray luminosity approximately 1 x 10(exp 30) ergs/s. The late G, K, and M stars exhibit nearly a two order of magnitude spread in X-ray luminosity and in L(sub x)/L(sub bol) at a given effective temperature. Plots of X-ray activity versus v sin i rotational velocity and rotational period appear to show no clear dependence of activity on rotation. However, because only a small fraction of late-type PMS stars in the Orion Nebula have measured v sin i or P(sub rot) and because of uncertainties in L(sub x) and L(sub x)/L(sub bol), we believe the data are not conclusive on this point. Light curves of the detected X-ray sources have revealed at least 10 strong X-ray flares with characteristic rise times greater than or approximately equal to 1 hr and decay times ranging from approximately 2 to 12 hr. All the flares have X-ray energies in excess of 3 x 10(exp 35) ergs. Many of the X-ray sources associated with late-type cluster members have been observed in more than one ROSAT HRI exposure, allowing us to look for variability on the approximately 1 yr timescale between HRI observations. A statistical analysis of the resulting count rate ratios suggests that at least one-fourth of the late-type cluster stars are significantly variable on this timescale.

Gagne, Marc↗