Search NASA⌕ Search

SEARCH · Search NASA

Results for “Optical diffusers”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Simultaneous Retrieval of Aerosol and Surface Optical Properties from Combined Airborne- and Ground-Based Direct and Diffuse Radiometric Measurements

This paper presents a new method for simultaneously retrieving aerosol and surface reflectance properties from combined airborne and ground-based direct and diffuse radiometric measurements. The method is based on the standard Aerosol Robotic Network (AERONET) method for retrieving aerosol size distribution, complex index of refraction, and single scattering albedo, but modified to retrieve aerosol properties in two layers, below and above the aircraft, and parameters on surface optical properties from combined datasets (Cloud Absorption Radiometer (CAR) and AERONET data). A key advantage of this method is the inversion of all available spectral and angular data at the same time, while accounting for the influence of noise in the inversion procedure using statistical optimization. The wide spectral (0.34-2.30 m) and angular range (180 ) of the CAR instrument, combined with observations from an AERONET sunphotometer, provide sufficient measurement constraints for characterizing aerosol and surface properties with minimal assumptions. The robustness of the method was tested on observations made during four different field campaigns: (a) the Southern African Regional Science Initiative 2000 over Mongu, Zambia, (b) the Intercontinental Transport Experiment-Phase B over Mexico City, Mexico (c) Cloud and Land Surface Interaction Campaign over the Atmospheric Radiation Measurement (ARM) Central Facility, Oklahoma, USA, and (d) the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) over Elson Lagoon in Barrow, Alaska, USA. The four areas are dominated by different surface characteristics and aerosol types, and therefore provide good test cases for the new inversion method.

Gatebe, C. K.↗
NASA NTRS1995

Nucleation and growth of crystals under cirrus and polar stratospheric cloud conditions

Laboratory studies examine phase changes of hygroscopic substances which occur as aerosol in stratosphere and troposphere (sodium chloride, ammonium sulfate, ammonium bisulfate, nitric acid, sulfuric acid), under controlled conditions, in samples volume 1 to 10(exp -4) ml. Crystallization of salts from supersaturated solutions is examined by slowly evaporating a solution drop on a substrate, under controlled relative humidity, until self nucleation occurs; controlled nucleation of ice in a mm capillary U-tube gives a measured ice crystallization velocity at known supercooling. Two states of crystallization occur for regions where hydrates exist. It is inferred that all of the materials readily exist as supersaturated/supercooled solutions; the degree of metastability appears to be slightly enhanced by inclusion of aircraft produced soot. The crystallization velocity is taken as a measure of viscosity. Results suggest an approach to a glass transition at high molality, supersaturation and/or supercooling within the range of atmospheric interest. It is hypothesized that surface reactions occur more readily on solidified particles - either crystalline or glass, whereas volume reactions are more important on droplets with sufficiently low viscosity and volume diffusivity. Implications are examined for optical properties of such particles in the atmosphere. In a separate experiment, crystal growth was examined in a modified thermal vapor diffusion chamber over the range of cirrus temperature (-30 to -70 C) and under controlled supersaturation and air pressure. The crystals grew at a velocity of 1-2 microns/s, thickness 60-70 micron, in the form of thin column crystals. Design criteria are given for a system to investigate particle growth down to -100 C, (PSC temperatures) where nitric acid particles can be grown under similar control and in the form of hydrate crystals.

Hallett, John↗
NASA NTRS1996

Copper Gas Diffusers For Purging Line-Focus Laser Welds

Modified flow diffusers built for inert-gas purging of welds made with 5-kW CO(2) lasers operating with line-focus optics in conduction mode instead of with point-focus optics in customary keyhole mode. Diffusers made of copper components brazed together, robust enough to withstand strong reflections of line-focused laser energy.

Fonteyne, Steve L.↗
NASA NTRS1975

A modified Henyey method for computing radiative transfer hydrodynamics

The implicit hydrodynamic code of Kutter and Sparks (1972), which is limited to optically thick regions and employs the diffusion approximation for radiative transfer, is modified to include radiative transfer effects in the optically thin regions of a model star. A modified Henyey method is used to include the solution of the radiative transfer equation in this implicit code, and the convergence properties of this method are proven. A comparison is made between two hydrodynamic models of a classical Cepheid with a 12-day period, one of which was computed with the diffusion approximation and the other with the modified Henyey method. It is found that the two models produce nearly identical light and velocity curves, but differ in the fact that the former never has temperature inversions in the atmosphere while the latter does when sufficiently strong shocks are present.

Karp, A. H.↗
NASA NTRS2016

A Neural Network Approach to Infer Optical Depth of Thick Ice Clouds at Night

One of the roadblocks to continuously monitoring cloud properties is the tendency of clouds to become optically black at cloud optical depths (COD) of 6 or less. This constraint dramatically reduces the quantitative information content at night. A recent study found that because of their diffuse nature, ice clouds remain optically gray, to some extent, up to COD of 100 at certain wavelengths. Taking advantage of this weak dependency and the availability of COD retrievals from CloudSat, an artificial neural network algorithm was developed to estimate COD values up to 70 from common satellite imager infrared channels. The method was trained using matched 2007 CloudSat and Aqua MODIS data and is tested using similar data from 2008. The results show a significant improvement over the use of default values at night with high correlation. This paper summarizes the results and suggests paths for future improvement.

Minnis, P.↗
NASA NTRS1983

High-temperature, high-pressure optical cells

For measuring the thermal diffusivity of HgCdTe melts by the laser-pulse method, an infrared transparent cell with flat windows of sufficient strength to withstand the high-vapor pressure of mercury had to be developed. Since mercury telluride expands on freezing, certain difficulties arose in returning the cell to room temperature without cracking it. T08 commercial fused silica is used in the construction of the cell, and the cells are transparent for wavelengths from about 3.5 microns in the infrared to 260 nm in the ultraviolet. The construction procedure for the required cells has been laborious. However, the obtained cell has routinely withstood internal pressures in excess of 60 atm at 900 C. Attention is given to the design of the windows, aspects of cell construction, and questions of loading.

Holland, L. R.↗
NASA NTRS1989

Stoichiometric effects on the optical properties of LiInSe(2)

The diffuse reflectance of LiInSe(2) between 0.67 and 3.54 eV have been measured and the Kubelka-Munk theory was used to obtain the absorption coefficient from the data. The band gap in the samples is located at approximately 1.6 eV. The In and Se content of the samples was determined from atomic absorption measurements. Absorption peaks at 0.890 and 0.896 eV have been observed which are correlated, respectively, to the selenium and indium deficiencies in the samples.

Smith, Cecily J.↗
NASA NTRS2005

MASS CONTENT AND DYNAMICAL STATE OF 3 OPTICALLY SELECTED HIGH-Z CLUSTERS

As part of our analysis of the Chandra and XMM-Newton observations of the high redshift, optically selected cluster ElS0954-2023/22, we have identified Chandra sources in the field and measured their count rate and fluxes. From the 15 ksec Chandra ACIS-S observation, we detected eleven X-ray sources. Their positions and count rates are listed below. Our analysis also shows faint diffuse emission associated with the optically identified cluster. This information was used in a joint analysis of the XMM-Newton observation of the cluster emission to determine the luminosity and temperature of the diffuse cluster gas.

Mushotzky, Richard F.↗
NASA NTRS2001

Degradation of MODIS Optics During the First Year of On-Orbit Operation

The MODIS (Moderate Resolution Imaging Spectroradiometer) sensor on the NASA EOS (Earth Observing System) Terra spacecraft has completed more than one year of on-orbit operation since the instrument opened its Nadir door for the scene data collection on 24 February 2000. Its 20 reflective solar bands, from VIS (visible) to SWIR (shortwavelength infrared) (0.41 to 2.1 micron), are calibrated on-orbit by a solar diffuser (SD) and a solar diffuser stability monitor (SDSM). Degradation in the reflective solar bands has been observed in the reflectance of the on board solar diffuser and for the MODIS optics. Variations in degradation of up to 3% are evident between the two sides of the MODIS scan mirror. Degradation of the SD is tracked with the solar diffuser stability monitor, and degradation of the entire MODIS system is tracked by SD observations, adjusted for SD changes. Overall degradation at the shortest wavelengths (near 400 nm) are up to 3% for SD, and in excess of 10% for the MODIS system. Degradation of the SD and full MODIS system for the sensor's reflective solar bands will be described in this report.

Guenther, B.↗
NASA NTRS1975

An example of the use of laboratory results in the optics of the sea

A relation between the average cosine in underwater conditions and the coefficient of diffuse reflection is used to determine the optical characteristics of the sea. The cosine is considered equal to the ratio of the radiation flux through a horizontal cross section to the flux irradiating a spherical surface surrounding the observation point.

Timofeyeva, V. A.↗
NASA NTRS1992

Surface migration and volume diffusion in the AgGaSe2-Ag2Se system

Surface migration and volume diffusion in the Ag2Se-AgGaSe2 system were investigated using reactive diffusion couples which were analyzed by X-ray diffraction, optical microscopy, and electron probe microanalysis. The surface diffusivities of all mobile species are found to be much larger than volume diffusivities. The results of the study suggest that Se moves together with Ag and Ga to maintain binary (Ag2Se and Ga2Se3) stoichiometry and electroneutrality. The dominance of surface migration kinetics can account for the uniform annihilation of second-phase precipitates during heat treatments.

Kim, N.-H.↗
NASA NTRS2001

Diffusivity Measurements Made Instant and Easy

A compact common path interferometer (CPI) system has been developed to measure the diffusivity of liquid pairs. The CPI is an optical technique that can be used to measure changes in the gradient of the refraction index of transparent materials. It uses a shearing interferometer that shares the same optical path from a laser light source to the final imaging plane. The molecular diffusion coefficient of liquids can be determined from the physical relations between changes in the optical path length and liquid phase properties. When the data obtained by using the CPI have been compared with similar results from other techniques, the instrument has been demonstrated to be far superior to other instruments for measuring the diffusivity of miscible liquids while staying very compact and robust (ref. 1). Because of its compactness and ease of use, the CPI has been adopted for use in studies of interface dynamics as well as other diffusion-controlled process applications (ref. 2). This progress will permit experiments in microgravity that can quantitatively answer basic science questions about mass and thermal diffusion and their effect in transport processes. This instrument is a spinoff of a diagnostic development for microgravity fluid physics experiments at the NASA Glenn Research Center that has used optics and electronics existing in the fluid physics laboratory for feasibility studies. Optical diagnostic techniques have become an integral part of many areas of measurement applications in industrial and research laboratories. Many types of interferometers and their phase-shifted versions have been used as instruments for measuring optical wave fronts for lens testing and combustion and fluid flow diagnostics. One of these, the point diffraction interferometer, is considered to be robust (see, for example, ref. 3) because it has a common-path design. The point diffraction interferometer is difficult to align and has a limited measurement range for liquid-phase applications. Interferometry and schlieren techniques have been widely used for many years for gas-flow-visualization. On the other hand, the CPI, which is basically a Wollaston prism Polarizer in combination with an analyser (crystalline quartz retardation plate) is used instead of a point diffraction interferometer unit. The advantage of using the CPI over other optical techniques is that it can make quantitative measurements in liquids with the large index of refraction variations that often occur in interface dynamics studies. This can be simply accomplished by using different prism polarizers for each particular experimental condition.

Rashidnia, Nasser↗
NASA NTRS1982

X-ray emission from the Carina Nebula and the associated early stars

New Einstein observations of the Carina Nebula show the extent of the diffuse X-ray nebula to be 1.1 deg E-W by 0.7 deg N-S. The diffuse X-ray emission is generally associated with optically bright regions, but the correlation is not exact. Emission is strongest from regions bordering the apparently overlying dust lane, indicating an interaction between the energetic material of the optical nebula and the region containing the dust. The diffuse X-rays are from hot gas with temperatures of about 10 million K, and electron densities of 0.1-1/cu cm. The energy to heat this gas probably comes from strong stellar winds of the early stars embedded in the nebula. X-rays from 15 O and W-R stars in the Carina OBI association have been detected. Data are consistent with the hypothesis that X-ray luminosity is equal to about 2.0 x 10 to the -7th of bolometric luminosity for all O stars in this region with remarkably little scatter. X-ray emission from the three W-R stars observed is significantly different. In particular, the WN6 star, HD 93162, has an X-ray luminosity equal to about 2.0 x 10 to the -6th of bolometer luminosity, a factor of 30 higher than for two other W-R stars in this nebula, and perhaps the highest X-ray luminosity/bolometric luminosity of any W-R star for which X-ray observations have been made.

Seward, F. D.↗
DOE OSTI2025

Time-Domain Extreme-Ultraviolet Diffuse Scattering Spectroscopy of Nanoscale Surface Phonons

Here, we report the observation of dynamic fringe patterns in the diffuse scattering of extreme ultraviolet light from surfaces, following femtosecond optical excitation. At each point on the detector, the diffuse scattering intensity exhibits oscillations at well-defined frequencies that correspond to surface phonons with wave vectors determined by the scattering geometry, indicating that the optical excitation generates coherent surface phonons propagating in all directions and spanning a wavelength range from 60 to 300 nm. This phenomenon is observed on a variety of samples, including single-layer and multilayer metal films, as well as bulk semiconductors. The measured surface phonon dispersions show good agreement with theoretical calculations. By comparing signal amplitudes from samples with different surface morphologies, we find that the excitation mechanism is linked to the natural surface roughness of the samples. However, the signal is still detectable on extremely smooth surfaces with subnanometer roughness. Our findings demonstrate a simple and effective method for optically exciting coherent surface phonons with nanoscale wavelengths on a wide range of solid samples and establish a foundation for surface phonon spectroscopy in a wave vector range well beyond the limit of conventional surface Brillouin scattering.

Capotondi, F. [Elettra-Sincrotrone Trieste (Italy)↗
DOE OSTI2026

Crystal Growth of Quaternary RE 2 EuSi 2 S 8 ( RE = Ce–Nd, Sm, Gd, Tb) Using Flux-Assisted Boron Chalcogen Mixture (BCM) Method: Investigation of Magnetic and Luminescence Properties

A series of quaternary rare-earth containing thiosilicates with the general formula RE 2 EuSi 2 S 8 (RE = Ce–Nd, Sm, Gd, Tb) has been synthesized via the flux-assisted boron chalcogen mixture (BCM) crystal growth method. High-quality single crystals were obtained, and their crystal structures were determined by single-crystal X-ray diffraction. The RE 2 EuSi 2 S 8 series crystallizes in the trigonal system, adopting the space group R-3c. Polycrystalline samples were employed for physical property measurements, including magnetic susceptibility measurements, UV–visible diffuse reflectance, and photoluminescent response. Magnetic data of RE 2 EuSi 2 S 8 ( RE = Ce, Nd, and Gd) were collected over the 2–300 K temperature range. The samples were paramagnetic behavior with negative Weiss constants (θ W = −11.05, −10.55, and −1.35 K respectively). Their thermal stability was investigated using thermogravimetric analysis (TGA). Optical band gaps, estimated from diffuse reflectance spectra, were determined to be 2.2(1) eV for Ce 2 EuSi 2 S 8 , 1.8(1) eV for Nd 2 EuSi 2 S 8 , and 1.7(1) eV for Gd 2 EuSi 2 S 8 respectively. Finally, photoluminescence measurements were collected on Ce 2 EuSi 2 S 8 and Tb 2 EuSi 2 S 8 single crystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1992

The molecular hydrogen emission around L1551 IRS 5 - Shock-heated molecular gas at the base of the molecular outflow

Spatially resolved observations of the v = 1-0 S(1) molecular hydrogen emission toward L1551 IRS 5 using the grating spectrometer at KPNO are presented. The S(1) emission consists of a ridge component extending toward west along the optical jet from its peak on IRS 5 and a diffuse component which traces the innermost region of the cavity enclosed by the molecular outflow. The ridge component represents shock-heated molecular gas at the root of the optical jet. The diffuse component is too bright to be of scattered origin; it most likely arises from shock-heated gas within the cavity and could represent an acceleration process of the molecular outflow.

Yamashita, Takuya↗