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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Development of a broadband reflective phase retarder to generate circularly polarized light for MTW-OPAL and multipetawatt lasers

Here, our research focuses on designing metallic coatings to create broadband all-reflective phase retarders that generate circularly polarized (CP) light for the MTW-OPAL Laser System while ensuring the desired polarization state on the target. This all-reflective phase retarder can function as a phase retarder when used in an out-of-plane configuration, whereas it acts as a normal mirror set in an in-plane configuration. If the polarization of the beam is not purely s- or p-polarized, however, mirrors will in general introduce retardance, and therefore compensators or polarization-independent mirror pairs are needed to ensure the desired polarization at the target plane.

47 OTHER INSTRUMENTATION↗
NASA NTRS1984

Light polarization measurements - A method to determine the specular and diffuse light-scattering properties of both leaves and plant canopies

The contributions of diffuse and specular reflection to the total canopy reflection of sunlight are determined experimentally for wheat at two stages of development using spectroradiometer measurements obtained at 13 wavelengths in the 480-720-nm range with a polarizing film in maximum and minimum signal-amplitude positions. The data and computation techniques are presented in tables, diagrams, and graphs, and the need to take specular reflection into account in constructing models of light/canopy interaction is stressed.

Vanderbilt, V. C.↗
NASA NTRS1985

Specular, diffuse, and polarized light scattered by two wheat canopies

Using polarization measurements, the reflectance factor of two wheat canopies is divided into components due to specularly and diffusely reflected light. The data show that two key angles may be predicted, the angle of the polarizer for minimum flux and the angle of incidence of sunlight specularly reflected by a leaf to a sensor. The results show that specular reflection is a key aspect to radiation transfer by two canopies. Results suggest that the advent of heading in wheat may be remotely sensed from polarization measurements of the canopy reflectance.

Vanderbilt, V. C.↗
NASA NTRS2010

The Effect of Incident Light Polarization on Vegetation Bidirectional Reflectance Factor

The Laboratory-based Bidirectional Reflectance Factor (BRF) polarization study of vegetation is presented in this paper. The BRF was measured using a short-arc Xenon lamp/monochromator assembly producing an incoherent, tunable light source with a well-defined spectral bandpass at visible and near-infrared wavelengths of interest at 470 nm and 870 nm and coherent light source at 1.656 microns. All vegetation samples were measured using P and S linearly polarized incident light over a range of incident and scatter angles. By comparing these results, we quantitatively examine how the BRF of the samples depends on the polarization of the incident light. The differences are significant, depend strongly on the incident and scatter angles, and can be as high as 120% at 67 deg incident and 470nm. The global nature of Earth's processes requires consistent long-term calibration of all instruments involved in data retrieval. The BRF defines the reflection characteristics of Earth surface. It provides the reflectance of a target in a specific direction as a function of illumination and viewing geometry. The BRF is a function of wavelength and reflects the structural and optical properties of the surface. Various space and airborne radiometric and imaging remote sensing instruments are used in the remote sensing characterization of vegetation canopies and soils, oceans, or especially large pollution sources. The satellite data is validated through comparison with airborne, ground-based and laboratory-based data in an effort to fully understand the vegetation canopy reflectance, The Sun's light is assumed to be unpolarized at the top of the atmosphere; however it becomes polarized to some degree due to atmospheric effects by the time it reaches the vegetation canopy. Although there are numerous atmospheric correction models, laboratory data is needed for model verification and improvement.

Georgiev, Georgi T.↗
NASA NTRS1973

On the influence of the atmospheric dust on the zodiacal light polarization

Three color observations of the nightglow brightness and polarization were made to determine the brightness of zodiacal light at the ecliptic pole. On the assumption that the degree of polarization of zodiacal light is 0.20 at the ecliptic pole, the corresponding brightnesses are found to be 68, 70, and 96 G2 stars of the 10th magnitude per square deg. at 0.37, 0.53, and 0.58 micron. The large diurnal variations in observed intensity and direction of polarization are attributed to the effects of dust in the earth's atmosphere.

Divari, N. B.↗
NASA NTRS2000

Polarized light from star forming regions

Studies of polarized radiation from molecular clouds and the environments of protostars are providing information about the orientations and strengths of magnetic fields and the sizes andcompositions of dust grains in these environments.

Astronomical polarimetry cosmic dust instellar mag↗
DOE OSTI2020

The impact of light polarization effects on weak lensing systematics

ABSTRACT A fraction of the light observed from edge-on disc galaxies is polarized due to two physical effects: selective extinction by dust grains aligned with the magnetic field and scattering of the anisotropic starlight field. Since the reflection and transmission coefficients of the reflecting and refracting surfaces in an optical system depend on the polarization of incoming rays, this optical polarization produces both (a) a selection bias in favour of galaxies with specific orientations and (b) a polarization-dependent point spread function (PSF). In this work, we build toy models to obtain for the first time an estimate for the impact of polarization on PSF shapes and the impact of the selection bias due to the polarization effect on the measurement of the ellipticity used in shear measurements. In particular, we are interested in determining if this effect will be significant for Wide-Field Infrared Survey Telescope (WFIRST). We show that the systematic uncertainties in the ellipticity components are 8 × 10−5 and 1.1 × 10−4 due to the selection bias and PSF errors respectively. Compared to the overall requirements on knowledge of the WFIRST PSF ellipticity (4.7 × 10−4 per component), both of these systematic uncertainties are sufficiently close to the WFIRST tolerance level that more detailed studies of the polarization effects or more stringent requirements on polarization-sensitive instrumentation for WFIRST are required.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1989

Earth scenes in polarized light observed from the Space Shuttle

By means of a pair of boresighted and synchronized cameras fitted with orthogonally oriented polarizing filters and carried aboard the Space Shuttle, a large number of polarized images of the earth's surface have been obtained from orbital altitude. Selected pairs of images, both in color and in black and white, have been digitized and computer-processed to yield analogous images in each of the three Stokes parameters necessary for characterizing the state of linear polarization of the emergent light. Many of the images show surface properties more distinctly in degree and plane of polarization than in simple intensity alone. It is believed that these are the first, and certainly the most extensive, set of polarized images of the earth ever obtained from space. Selected pairs of the images are presented here along with some early results of analysis.

Whitehead, Victor S.↗
DOE OSTI2024

A Uniform Analysis of Debris Disks with the Gemini Planet Imager. I. An Empirical Search for Perturbations from Planetary Companions in Polarized Light Images

The Gemini Planet Imager (GPI) has excelled in imaging debris disks in the near-infrared. The GPI Exoplanet Survey imaged 24 debris disks in polarized H-band light, while other programs observed half of these disks in polarized J and/or K1 bands. Using these data, we present a uniform analysis of the morphology of each disk to find asymmetries suggestive of perturbations, particularly those due to planet–disk interactions. The multiwavelength surface brightness, disk color, and geometry permit the identification of any asymmetries such as warps or disk offsets from the central star. We find that 19 of the disks in this sample exhibit asymmetries in surface brightness, disk color, disk geometry, or a combination of the three, suggesting that for this sample, perturbations, as seen in scattered light, are common. The relationship between these perturbations and potential planets in the system is discussed. We also explore correlations among stellar temperatures, ages, disk properties, and observed perturbations. We find significant trends between the vertical aspect ratio and the stellar temperature, disk radial extent, and the dust grain size distribution power law, q. We also confirm a trend between the disk color and stellar effective temperature, where the disk becomes increasingly red/neutral with increasing temperature. Such results have important implications for the evolution of debris disk systems around stars of various spectral types.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2024

A Uniform Analysis of Debris Disks with the Gemini Planet Imager. I. An Empirical Search for Perturbations from Planetary Companions in Polarized Light Images

The Gemini Planet Imager (GPI) has excelled in imaging debris disks in the near-infrared. The GPI Exoplanet Survey imaged 24 debris disks in polarized H-band light, while other programs observed half of these disks in polarized J and/or K1 bands. Using these data, we present a uniform analysis of the morphology of each disk to find asymmetries suggestive of perturbations, particularly those due to planet–disk interactions. The multiwavelength surface brightness, disk color, and geometry permit the identification of any asymmetries such as warps or disk offsets from the central star. We find that 19 of the disks in this sample exhibit asymmetries in surface brightness, disk color, disk geometry, or a combination of the three, suggesting that for this sample, perturbations, as seen in scattered light, are common. The relationship between these perturbations and potential planets in the system is discussed. We also explore correlations among stellar temperatures, ages, disk properties, and observed perturbations. We find significant trends between the vertical aspect ratio and the stellar temperature, disk radial extent, and the dust grain size distribution power law, q. We also confirm a trend between the disk color and stellar effective temperature, where the disk becomes increasingly red/neutral with increasing temperature. Such results have important implications for the evolution of debris disk systems around stars of various spectral types.

Katie A Crotts↗
NASA NTRS1978

Discovery of polarized light scattered by dust around Alpha Orionis

Following the suggestion by Jura and Jacoby (1976), linearly polarized blue continuum starlight scattered by the dust shell around the M2 Iab star Alpha Orionis (Betelgeuse) has been discovered. The polarization has been traced in the NE, NW, SE, and SW directions and has positive (tangential) orientation. Some asymmetry of the optical depth in the shell exists 15 and 30 arcsec from the star. In the NE direction the polarization was measured as far as 90 arcsec (17,000 AU) from the star. The dependence of the average intensity of the scattered light from the nebula on angular distance from the star is more consistent with an inverse-square density law than with inverse 1.5 or inverse-cube laws. Assuming that the density is proportional to the inverse square of distance from the star, the scattering optical depth in blue light along a radius of 0.03 arcsec is no more than 0.15 + or - 0.05. Future observations of the wavelength dependence of polarization will allow a determination of grain size.

Mcmillan, R. S.↗
NASA NTRS1971

Multiple scattering of polarized light in planetary atmospheres. II - Sunlight reflected by terrestrial water clouds.

The intensity and polarization of sunlight reflected by terrestrial water clouds are computed with the doubling method. The calculations illustrate that this method can be effectively used in problems involving strongly anisotropic phase matrices. The method can, therefore, be used to derive information about planetary clouds, including those of the earth, from polarimetric observations. The results of the computations indicate that the polarization is more sensitive than the intensity to cloud microstructure, such as particle size and shape.

Hansen, J. E.↗
NASA NTRS1999

Efficient IR Transmission Diffraction Grating for Circularly Polarized Light

Numerical methods, using rigorous coupled wave theory, are used to design rectangular relief diffraction gratings for an infrared application which requires comparable first order efficiencies in the TE and TM polarization states. The depth, period, and fill factor of the grating are varied to identify optimal two level binary lamellar grating profiles which predict efficiencies for individual TM and TE polarizations above 75 percent, while keeping the difference between the two efficiencies within 10 percent. The application at hand is a rotating, transmissive diffractive scanner for space-based coherent lidar. The operating wavelength is 2.0 microns. A collimated, circularly polarized beam is incident on the diffractive scanner at the Bragg angle; 30 and 45 degree beam deflection angles being studied. Fused silica is the substrate material of choice. Selected designs are fabricated on 3 inch fused silica substrates using lithographic methods. The performance of the test pieces is measured and compared to theoretical predictions.

Cole, Helen↗
NASA NTRS1995

Optical-Fiber Fluorosensors With Polarized Light Sources

Chemiluminescent and/or fluorescent molecules in optical-fiber fluorosensors oriented with light-emitting dipoles along transverse axis. Sensor of proposed type captures greater fraction of chemiluminescence or fluorescence and transmits it to photodetector. Transverse polarization increases sensitivity. Basic principles of optical-fiber fluorosensors described in "Making Optical-Fiber Chemical Sensors More Sensitive" (LAR-14525), "Improved Optical-Fiber Chemical Sensors" (LAR-14607), and "Improved Optical-Fiber Temperature Sensors" (LAR-14647).

Egalon, Claudio O.↗
NASA NTRS2017

Si III OV Bright Line of Scattering Polarized Light That Has Been Observed in the CLASP and Its Center-to-Limb Variation

The CLASP (Chromospheric Lyman-Alpha Spectro- Polarimeter) rocket experiment, in addition to the ultraviolet region of the Ly alpha emission line (121.57 nm), emission lines of Si III (120.65 nm) and OV (121.83 nm) is can be observed. These are optically thin line compared to a Ly alpha line, if Rarere captured its polarization, there is a possibility that dripping even a new physical diagnosis chromosphere-transition layer. In particular, OV bright light is a release from the transition layer, further, three P one to one S(sub 0) is a forbidden line (cross-triplet transition between lines), it was not quite know whether to polarization.

spectropolarimeter↗
NASA NTRS2014

Detecting Super-Thin Clouds With Polarized Light

We report a novel method for detecting cloud particles in the atmosphere. Solar radiation backscattered from clouds is studied with both satellite data and a radiative transfer model. A distinct feature is found in the angle of linear polarization of solar radiation that is backscattered from clouds. The dominant backscattered electric field from the clear-sky Earth-atmosphere system is nearly parallel to the Earth surface. However, when clouds are present, this electric field can rotate significantly away from the parallel direction. Model results demonstrate that this polarization feature can be used to detect super-thin cirrus clouds having an optical depth of only ~0.06 and super-thin liquid water clouds having an optical depth of only ~0.01. Such clouds are too thin to be sensed using any current passive satellite instruments.

Sun, Wenbo↗