Search NASA⌕ Search

SEARCH · Search NASA

Results for “ND”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Submegahertz frequency-stablized Nd:YAG oscillator

The operation of a 5-msec, quasi-continuous wave (CW) 10-Hz repetition-rate pulsed single-frequency Nd:YAG oscillator with a feedback stabilized frequency bandwidth of less than 200 kHz is described. The major problems associated with frequency stabilization for quasi-CW operation, frequency chirp and maintenance of the frequency control signal, are described, and the design of a wide-bandwidth frequency locking system with a search and chirp compensation loop is given. This frequency stabilized oscillator is a potentially useful laser source for atmospheric wind velocity measurements by coherent lidar Doppler velocimetry, which require a laser source with less than 1 MHz linewidth, and also has applications in high-resolution nonlinear spectroscopic studies at Fourier-transform-limited linewidths.

Sun, Y. L.↗
NASA NTRS1982

Age and provenance of the target materials for tektites and possible impactites as inferred from Sm-Nd and Rb-Sr systematics

Chemical, trace element, and isotopic compositions of tektites are consistent with production by melting of sediments derived from the old terrestrial continental crust. Each tektite group is characterized by a uniform Nd model age, interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites. Sr model ages are variable within each group, reflecting Rb-Sr fractionation, and, in the favorable limit of very high Rb/Sr ratios, approach the time of sedimentation of the parent material which melted to form the tektites. Unlike tektites, which are dense homogeneous objects, sanidine spherules are porous, fine grained inhomogeneous objects. The leaching experiment employed by the present study shows that the sanidine spherules could have been formed by an oceanic impact involving basaltic crust and overlying sediments or seawater.

Shaw, H. F.↗
NASA NTRS1982

The geochemical coherence of Pu and Nd and the Pu-244/U-238 ratio of the early solar system

Two very different sets of Pu-244/U-238 ratios have been reported for early solar system materials, one high and the other low, and this paper examines how one of these groups may yield an incorrect ratio. Recently measured partition coefficients for Pu and Sm (Jones, 1981) are used to evaluate Pu-Nd fractionation during achondrite genesis, and Pu-244/U-238 ratios of chondrites, achondrites, and Ca-Al-rich inclusions are compared and discussed. A low Pu-244/U-238 ratio is favored, and some implications of this low ratio for galactic nucleosynthesis and meteorite age dating are briefly discussed.

Jones, J. H.↗
NASA NTRS1983

Sm-Nd isotopic systematics of the ancient Gneiss complex, southern Africa

In order to shed some new light on the question of the absolute and relative ages of the Ancient Gneiss Complex and Onverwacht Group, a Sm-Nd whole-rock and mineral isochron study of the AGC was begun. At this point, the whole-rock study of samples from the Bimodal Suite selected from those studied for their geochemical characteristics by Hunter et al., is completed. These results and their implications for the chronologic evolution of the Kaapvaal craton and the sources of these ancient rocks are discussed.

Carlson, R. W.↗
NASA NTRS1983

Nd:YAG holographic interferometer for aerodynamic research

A holographic interferometer system has been installed in the NASA Ames 2- by 2-Foot Transonic Wind Tunnel. The system incorporates a modern 10 pps, Nd:YAG pulsed laser which provides reliable operation and is easy to align. The spatial filtering requirements of the unstable resonator beam are described, as well as the integration of the system into the existing schlieren system. A two-plate holographic interferometer is used to reconstruct flow field data. For static wind tunnel models, the single exposure holograms are recorded in the usual manner; however, for dynamic models such as oscillating airfoils, synchronous laser hologram recording is used.

Craig, J. E.↗
NASA NTRS1985

Highly Efficient Nd:yag Lasers for Free-space Optical Communications

A highly efficient Nd:YAG laser end-pumped by semiconductor lasers as a possible free-space optical communications source is discussed. Because this concept affords high pumping densities, a long absorption length, and excellent mode-matching characteristics, it is estimated that electrical-to-optical efficiencies greater than 5% could be achieved. Several engineering aspects such as resonator size and configuration, pump collecting optics, and thermal effects are also discussed. Finally, possible methods for combining laser-diode pumps to achieve higher output powers are illustrated.

Sipes, D. L., Jr.↗
NASA NTRS1985

Monolithic, unidirectional single-mode Nd:YAG ring laser

A new solid-state laser has been designed which achieves high single-mode output power by using a unidirectional nonplanar resonator constructed from a single Nd:YAG crystal. When placed in a magnetic field, the laser provides a pump-limited, single-axial-mode output of 163 mW at 1064 nm. The laser has been specifically developed as an oscillator for a long-range coherent Doppler anemometer. Other applications include coherent communications, coherent optical radar, and inertial rotation sensing.

Kane, T. J.↗
NASA NTRS1986

Rb-Sr and Sm-Nd internal isochron ages of a subophitic basalt clast and a matrix sample from the Y75011 eucrite

Rb-Sr and Sm-Nd dating studies of the Yamato polymict eucrite Y75011, which contains several coarse-grained mesostasis-rich basaltic clasts with subophitic texture which are representative of pristine lavalike basalts extruded on the surface of the Howardite-Eucrite-Diogenite (HED) parent body, are reported. The results show that moderately evolved basaltic lavas were produced very early in the history of the HED parent body. Their preservation as clasts in the polymict eucrites suggests derivation from a different geological setting on the parent body than that occupied by the more thermally metamorphosed monomict eucrites. It is suggested that the preservation of pristine clasts in polymict eucrites may be due to their impact excavation to the surface of the parent body away from heat sources concentrated within impact craters.

Nyquist, L. E.↗
NASA NTRS1985

Nd:YAG and ruby based lidar systems for remote sensing of atmospheric aerosols

The application of solid-state lasers to the study of stratospheric and tropospheric aerosols is analyzed. A 48-inch mobile lidar which operates in the 0.6943, 1.06, 0.3472, and 0.5300 micron ranges is utilized to monitor the stratosphere. The detectors of the system consist of photomultipliers, and the dual-channel, computer-based data-acquisition-system which provides on-line plotting of scattering ratio profiles. The components of the 14-inch aperture, dual-wavelength airborne lidar system that operates with ruby and Nd:YAG transmitters are described. An 8-inch, down-looking airborne lidar with silicon diode or photomultiplier detectors was developed. The capabilities of the system alone and when combined with the 14-inch lidar are discussed. Examples of the data provided by the three lidar systems are presented, revealing the reliability and operational efficiency of the systems.

Fuller, W. H., Jr.↗
NASA NTRS1985

SM-ND isotopic studies of proterozoic anorthosites Systematics and implications

Sm-Nd isotopic studies of anorthosites can be used to provide information on their ages of crystallization and metamorphism, contamination history, and mantle sources. Proterozoic anorthosites in the Grenville and Nain Provinces of eastern North America crystallized between about 1100 and 1600 Ma, and some were metamorphosed at about 1000 Ma. Grenville Province anorthosite massifs were derived from depleted mantle. It is not clear whether massifs and related mafic intrusions throughout the Nain Province of Labrador were derived from enriched mantle, or were contaminated by early Archean (greater than 3500 Ma) silicic crustal materials, heretofore thought to be restricted to coastal Labrador.

Ashwal, L. D.↗
NASA NTRS1986

Aleutian terranes from Nd isotopes

Nd isotope ratios substantiate the identification of oceanic crustal terranes within the continental crustal basement of the Aleutian island arc. The oceanic terranes are exposed in the westernmost Aleutians, but to the east, they are completely buried by isotopically distinct arc-volcanic rocks. Analogous oceanic terranes may be important components of the terrane collages that comprise the continents.

Kay, R. W.↗
NASA NTRS1986

Pb, Sr, Nd, and Hf isotopic constraints on the origin of Hawaiian basalts and evidence for a unique mantle source

The isotopic Pb, Sr, Nd, and Hf compositions of rocks from nine Hawaiian volcanos are determined using the analytical procedures described by Tatsumoto and Unruh (1976) and Patchett and Tatsumoto (1980). The results are presented in graphs, tables, and maps and characterized in detail. The mantle plume, the oceanic lithosphere, and the depleted mantle are identified as distinct sources of the Hawaiian basalts, with different mechanisms responsible for the formation of shield-building tholeiites, late-stage alkalic rocks, and posterosional basalts. The uniqueness of the Hawaiian basalts and the possibility that the Koolau end member represents an undepleted 'primitive' mantle reservoir are considered.

Stille, P.↗
NASA NTRS1986

Diode-pumped continuous-wave Nd:glass laser

The paper reports on diode-laser pumping of monolithic Nd:glass laser oscillators. End pumping with a single-stripe diode laser, a threshold of 2.2 mW, and a slope efficiency of 42 percent were observed on a 2-mm-long oscillator with a mode radius of 35 microns. The oscillator generated 2.5 mW of single-ended output power in many axial modes.

Kozlovsky, W. J.↗
NASA NTRS1986

Plasma sprayed Fe(76)Nd(16)B(8) permanent magnets

Thin coatings (0.16 mm) and thick coatings (0.50 mm) of Fe(76)Nd(16)B(8) were deposited on stainless-steel substrates by low pressure plasma spraying. Microscopic examination of the coatings in a light microscope revealed excessive porosity, but good bonding to the substrate. Fracture cross sections examined in a scanning electron microscope showed the grains to be equiaxed and approximately 1 micron or less in diameter in the as-sprayed condition. The intrinsic coercivities of the as-sprayed coatings varied from 5.8 to 10.9 kOe. The effects of postspray heat treatments on the intrinsic coercivity are also given.

Overfelt, R. A.↗
NASA NTRS1987

Frequency stability and offset locking of a laser-diode-pumped Nd:YAG monolithic nonplanar ring oscillator

The frequency stability of laser-diode-pumped, monolithic Nd:YAG solid-state unidirectional nonplanar ring oscillators was studied by heterodyne measurements. CW single-axial- and transverse-mode power of 25 mW at 1064 nm was obtained at a slope efficiency of 19 percent. Two independent oscillators were offset-locked at 17 MHz with frequency fluctuations of less than + or - 40 kHz for periods of 8 min.

Kane, Thomas J.↗
NASA NTRS1987

Coherent laser radar at 1.06 micron using Nd:YAG lasers

A coherent laser radar system operating at the 1.06 micron Nd:YAG laser wavelength has been built and operated. A laser-diode-pumped monolithic ring laser served as the master oscillator. A single flash-lamp-pumped zigzag slab amplified the oscillator output to a power of 2.3 kW. Single-mode optical fiber was used to collect and mix the return signal with the local-oscillator output. Signals from clouds at a range of 2.7 km and from atmospheric aerosols at a range of 600 m were detected.

Kane, Thomas J.↗
NASA NTRS1987

Superconductivity above 90 K in the square-planar compound system ABa2Cu3O(6 + x) with A = Y, La, Nd, Sm, Eu, Gd, Ho, Er, and Lu

Superconductivity has been found in the 90-K range in ABa2Cu3O(6 + x) with A = La, Nd, Sm, Eu, Gd, Ho, Er, and Lu in addition to Y. The results suggest that the unique square-planar Cu atoms, each surrounded by four or six oxygen atoms, are crucial to the superconductivity of oxides in general. In particular, the high Tc of ABa2Cu3O(6 + x) is attributed mainly to the quasi-two-dimensional assembly of the CuO2-Ba-CuO(2 + x)Ba-CuO2 layers sandwiched between two A layers, with particular emphasis in the CuO(2 + x) layers. Higher-Tc oxides are predicted for compounds with bigger assemblies of CuO2 layers coupled by Ba layers.

Hor, P. H.↗