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At least 199 records · Page 11

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NASA NTRS1987

Rb-Sr and Sm-Nd systematics of cherts and other siliceous deposits

An analysis of marine and lacustrine cherts demonstrates that Rb-Sr and Sm-Nd systems may be used in elucidating the origin and evolution of cherts, and that the Rb-Sr system may be used for dating. All samples have high Rb/Sr ratios, and though the site of these elements in cherts was not established, they appear to be correlated with Al content. Sm/Nd ratios were typical of continental sources, and the results show the Rb-Sr system in cherts to be isolated from the associated carbonate, with little Sr exchange. Data suggest that in many cases cherts are formed by dissolved SiO2 nucleating on clay-like material which preserves the isotropic characteristics of the detrital source, while in some cases it is possible that cherts were formed from silica-saturated waters from a nonmarine source.

Weis, D.↗

NASA NTRS1987

Continuous-wave operation of a room-temperature, diode-laser-pumped, 946-nm Nd:YAG laser

Single-stripe diode-laser-pumped operation of a continuous-wave 946-nm Nd:YAG laser with less than 10-mW threshold has been demonstrated. A slope efficiency of 16 percent near threshold was shown with a projected slope efficiency well above a threshold of 34 percent based on results under Rhodamine 6G dye-laser pumping. Nonlinear crystals for second-harmonic generation of this source were evaluated. KNbO3 and periodically poled LiNbO3 appear to be the most promising.

Fan, T. Y.↗

NASA NTRS1988

Nd and Sr isotope systematics of clastic metasediments from Isua, West Greenland - Identification of pre-3.8 Ga differentiated crustal components

A detailed Sm-Nd and Rb-Sr isotopic study of the Isua clastic metasediments has been performed in the context of recently established stratigraphy for the Isua section. Samples from the sequence B are investigated for the first time. A clear correlation between lithology and isotopic characteristics is pointed out. The results indicate the existence of at least three distinct components for each of the distinct sequences A and B. It is suggested that some of these components may be derived from continental crustal sources that predate the time of depositon of these sediments by as much as about 0.4 b.y. A large pre-3.8 Ga continental crust is also inferred by the data.

Jacobsen, Stein B.↗

NASA NTRS1988

Long-pulse generation with a stable-relaxation-oscillation Nd:YLF laser

A simple technique for long-pulse (0.2-2 microsec) generation with neodymium lasers has been demonstrated. Under the proper conditions, a normal-mode oscillator, operated in a single transverse mode, produces well-defined relaxation oscillations from which a single subpulse can be isolated for amplification. The characteristic subpulse temporal profile is ideal for saturated amplification without pulse shortening. Data are presented for a Nd:YLF system consisting of an oscillator followed by a 64-nm-long amplifier. Pulse energies in excess of 100 mJ were achieved with a small-signal gain of 630.

Harisson, J.↗

NASA NTRS1988

Efficient second harmonic generation of a diode-laser-pumped CW Nd:YAG laser using monolithic MgO:LiNbO3 external resonant cavities

56-percent efficient external-cavity-resonant second-harmonic generation of a diode-laser pumped, CW single-axial-mode Nd:YAG laser is reported. A theory of external doubling with a resonant fundamental is presented and compared to experimental results for three monolithic cavities of nonlinear MgO:LiNbO3. The best conversion efficiency was obtained with a 12.5-mm-long monolithic ring cavity doubler, which produced 29.7 mW of CW, single-axial model 532-nm radiation from an input of 52.5 mW.

Kozlovsky, William J.↗

NASA NTRS1989

Efficient Cavity-Dumped, Frequency-Doubled Nd:YAG Laser

New design expected to increase efficiency of cavity-dumped, frequency-doubled Nd:YAG laser. Frequency doubled outside primary laser resonator, and portion of fundamental-frequency light not used by doubler returned to primary laser cavity to increase efficiency. Applications of laser foreseen in data communictions, laser ranging, studies of atmosphere, remote sensing, and laboratory studies.

Robinson, D. L.↗

NASA NTRS1988

U-Th-Pb, Sm-Nd, Rb-Sr, and Lu-Hf systematics of returned Mars samples

The advantage of studying returned planetary samples cannot be overstated. A wider range of analytical techniques with higher sensitivities and accuracies can be applied to returned samples. Measurement of U-Th-Pb, Sm-Nd, Rb-Sr, and Lu-Hf isotopic systematics for chronology and isotopic tracer studies of planetary specimens cannot be done in situ with desirable precision. Returned Mars samples will be examined using all the physical, chemical, and geologic methods necessary to gain information on the origin and evolution of Mars. A returned Martian sample would provide ample information regarding the accretionary and evolutionary history of the Martian planetary body and possibly other planets of our solar system.

Tatsumoto, M.↗

NASA NTRS1988

Fast frequency tuning and phase locking of diode-pumped Nd:YAG ring lasers

A diode-pumped single-mode monolithic Nd:YAG ring-laser oscillator has been built which can be tuned piezoelectrically over several tens of MHz in a few microsecs. Frequency stability over 1 msec is better than 500 Hz. Two lasers have been electronically phase locked for periods of minutes with a phase noise of 29 mrad rms.

Kane, Thomas J.↗

NASA NTRS1988

OPO performance with a long pulse length, single frequency Nd:YAG laser pump

With the advent of new nonlinear materials and single-frequency pump sources, there is renewed interest in optical parametric oscillators (OPOs). A single-mode diode-laser-pumped monolithic Nd:YAG nonplanar ring laser that is both amplified and frequency doubled is used to pump a monolithic MgO:LiNbO3 pulsed singly resonant OPO. The OPO signal output was temperature tuned from 834 to 958 nm, producing an idler tuning from 1.47 to 1.2 microns. Efforts toward a CW all-solid-state doubly resonant OPO are also described.

Kozlovsky, W. J.↗

NASA NTRS1989

30 Hz-linewidth, diode-laser-pumped, Nd:GGG nonplanar ring oscillators by active frequency stabilisation

A heterodyne linewidth of less than 30 Hz for the beatnote between the outputs of two 282 THz Nd:GGG nonplanar ring oscillators (NPROs) is reported. The lasers were independently locked to adjacent axial modes of a high-finesse interferometer. The remnant frequency noise appears to be dominated by free spectral range fluctuations in the reference interferometer rather than by residual laser noise.

Day, T.↗

NASA NTRS1989

Os, Sr, Nd, and Pb isotope systematics of southern African peridotite xenoliths - Implications for the chemical evolution of subcontinental mantle

Isotope analyses of Os, Sr, Nd, and Pb elements were caried out on twelve peridotite xenoliths from the Jagersfontein, Letseng-la-terae, Thaba Patsoa, Mothae, and Premier kimberlites of southern Africa, to investigate the timing and the nature of melt extraction from the continental lithosphere and its relation to the continent formation and stabilization. The distinct Os and Pb isotopic characteristics found in these samples suggested that both the low- and the high-temperature peridotites reside in an ancient stable lithospheric 'keel' to the craton that has been isolated from chemical exchange with the sublithospheric mantle for time periods in excess of 2 Ga.

Walker, R. J.↗

NASA NTRS1989

Frequency fluctuations of a diode-pumped Nd:YAG ring laser

The spectral density of the frequency fluctuations of a diode-pumped single-mode monolithic Nd:YAG ring laser was measured by locking a Fabry-Perot resonator to the laser frequency. The fluctuations approach the limit due to spontaneous emission (the Schawlow-Townes limit) at frequencies above 80 kHz. The inherent frequency stability of these lasers makes them attractive as a potential light source for gravitational-wave interferometers.

Fritschel, Peter↗

NASA NTRS1990

Thermal and electric properties of Nd(1.85)Ce(0.15)CuO(4-y) and Pr(1.85)Ce(0.15)CuO(4-y)

Electric resistivity, magnetic susceptibility, thermoelectric power, and Hall coefficient of Nd(1.85)Ce(0.15)CuO(4-y) and Pr(1.85)Ce(0.15)CuO(4-y) whose onset temperature of the superconductivity are 24 K and 23 K were measured. Experimental results show many interesting features. In particular, the Hall coefficients are negative and relatively flat as a function of temperature. However, the temperature dependence of the thermoelectric power (TEP) for these two samples shows the positive sign for both samples in contrast to the previous results. Moreover TEP for both samples remains flat in the normal state below 250 K, but decreases rapidly above 250 K. TEP of only Pr(1.85)Ce(0.15)CuO(4-y) shows a peak near 50 K. Finally onset temperatures of sudden drop of TEP are higher than those of resistance drop. The physical properties of these samples produced at different conditions such as different heat treatment temperatures, atmospheres were also measured. TEP and resistance measurement show that oxygen deficiency is essential to produce better superconducting samples. Correlation between TEP and superconductivity for these different samples will be discussed.

Lim, Z. S.↗

NASA NTRS1990

Intensity noise in diode-pumped single-frequency Nd:YAG lasers and its control by electronic feedback

The power spectrum of the relative intensity noise (RIN) of single-frequency diode-pumped Nd:YAG lasers is observed to be shot-noise limited at frequencies above 20 MHz for a photocurrent of up to 4.4 mA. Relaxation oscillations result in noise 60-70 dB above shot noise at a few hundred kHz. These relaxation oscillations have been suppressed using electronic feedback.

Kane, Thomas J.↗

NASA NTRS1990

Theoretical model for a background noise limited laser-excited optical filter for doubled Nd lasers

A simple theoretical model for the calculation of the dependence of filter quantum efficiency versus laser pump power in an atomic Rb vapor laser-excited optical filter is reported. Calculations for Rb filter transitions that can be used to detect the practical and important frequency-doubled Nd lasers are presented. The results of these calculations show the filter's quantum efficiency versus the laser pump power. The required laser pump powers required range from 2.4 to 60 mW/sq cm of filter aperture.

Shay, Thomas M.↗

NASA NTRS1989

Optical inspection of space-propulsion components using an injection seeded Nd:YAG laser system

A dual-beam, injection-seeded, Nd:YAG laser has been demonstrated for detecting structural defects. This demonstration was part of an on-going project to use dual-reference-beam holographic interferometry to inspect space propulsion components for cracks, structural failures, structural changes, and gas leaks. Potential subjects for inspection include welds, duct work, casings, turbopumps, blades, composites, and ceramics. The maximum dimension of an inspected area ranges from a few centimeters to a meter. The entire optical inspection system is now ready for a demonstration application.

Decker, Arthur J.↗

NASA NTRS1990

SUNLITE program. Sub-Hertz relative frequency stabilization of two diode laser pumped Nd:YAG lasers locked to a Fabry-Perot interferometer

Two laser pumped Nd:YAG lasers were frequency stabilized to a commercial 6.327 GHz free spectral range Fabry-Perot interferometer yielding a best case beatnote linewidth of 330 MHz. In addition, a Fabry-Perot interferometer with a free spectral range of 680 MHz, a linewidth of 25 kHz, and a finesse of 27,500 was built, and when it was substituted in place of the commercial interferometer, it produced a robust and easily repeatable beatnote linewidth of 700 MHz.

Byer, R. L.↗

NASA NTRS1990

Stimulated Raman shifting of the Nd:YAG fourth harmonic (266 nm) in H2, HD, and D2

The dependence of the first Stokes stimulated Raman conversion efficiency of fourth-harmonic radiation from a Nd:YAG laser at 266 nm has been studied for the isotopic species H2, HD, and D2 as a function of gas pressure and laser energy using a low numerical aperture (about 0.0045) pumping geometry. While the laser energy threshold for first Stokes conversion varies significantly among the species, photon conversion efficiencies of at least 50 percent can be achieved for all of them for laser pump energies at 266 nm of 50 mJ/pulse or less. This study provides a new measurement of the differential cross section for stimulated Raman scattering in HD of 8.1 + or - 2.4 x 10 to the -29th sq cm/sr at 266 nm and at high pressures, and agreement is found with previous measurements of the cross sections for H2 and D2. The results have been used to optimize the laser transmitter system for a differential-absorption lidar to measure tropospheric ozone concentration profiles.

Haner, David A.↗