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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 1,081 records · Page 60

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NASA NTRS1982

The two-photon absorptivity of rotational transitions in the A2 Sigma hyperon + (v prime = O) - X-2 pion (v prime prime = O) gamma band of nitric oxide

A predominantly single-mode pulsed dye laser system giving a well characterized spatial and temporal output suitable for absolute two-photon absorptivity measurements was used to study the NO gamma(0,0) S11 + R21 (J double prime = 7-1/2) transition. Using a calibrated induced-fluorescence technique, an absorptivity parameter of 2.8 + or - 1.4 x 10 to the minus 51st power cm to the 6th power was obtained. Relative strengths of other rotational transitions in the gamma(0,0) band were also measured and shown to compare well with predicted values in all cases except the O12 (J double prime = 10-1/2) transition.

Gross, K. P.↗

NASA NTRS1983

Wedge coupling of lasers into multimode fibers

Design and experimental data for obtuse-angled wedges used in coupled configurations of diode lasers and multimode fibers are presented. An analytic definition of the connection between the wedge angle and the fiber acceptance half-angle is developed, along with a formula for the minimum half-angle. An inequality is defined for determining the bevel angle of the output end of the fiber to eliminate end reflections. The fiber parameters are accounted for in the bevel. The formulations were tested in comparison with the performance of a coupled CDH laser system and good agreement was found in the output spectrum.

Ladany, I.↗

NASA NTRS1982

Gravito-inertial sensitivity of the spider - Araneus sericatus

The gravito-inertial transfer function of the orb-weaving spider was evaluated by changes in the cardiac reflex. A non-intrusive method, using a laser system recorded the cardiac pulse. Between 1.001 and 1.5 Gz the data are 'best-fit' by a log function (r-squared 0.92). The response of the neurogenic heart is seen to be a good dependent variable for invetebrate research. The arachnid lyriform organ has those qualities which complement the obtained gravity function. It is hypothesized that the cardiac pump maintains the spiders equilibrium in the gravito-inertial field.

Finck, A.↗

NASA NTRS1982

NASA geodynamics program

The goals of the NASA geodynamics program comprise the study of the interior structure and composition of the earth, its crustal motions and deformations, the rotational dynamics, and the terrestrial potential fields. Laser ranging an VLBI techniques are being applied in cooperation with 16 other countries. Reflectors on the moon are illumined with laser beams from earth, which are also bounced off the Lageos and French Starlette satellites, permitting monitoring of polar motion, earth rotation, and distance to the moon within 5 cm. Mobile laser systems are being deployed for developing a gravity field model and examining crustal deformation regionally. The VLBI installations use quasars as reference objects and the GPS satellites will give position accuracy within 1-2 cm. Satellite-to-satellite tracking, Magsat, and Shuttle timing experiment data are providing geopotential field data and timing synchronization.

Fischetti, T. L.↗

NASA NTRS1985

Thermal-Expansion Measurement

Precise stable laser system determines coefficients of thermal expansion. Dual-beam interferometer arrangement monitors changes in sample length as function of temperature by following changes inoptical path lengths.

Davis, J. H.↗

NASA NTRS1984

The reflection of airborne UV laser pulses from the ocean

It is experimentally shown here for the first time that the normalized laser backscatter cross-section of the sea surface is a function of elevation or height position on teh ocean wave. All data were taken off-nadir, resulting in incidence angles of about 6.5 deg measured relative to the normal to mean sea level (MSL). In the limited data sets analyzed to date, the normalized backscatter cross-section was found to be higher in wave crest regions and lower in wave troughs for a swell-dominated sea over which the wind speed was 5 m/s. The reverse was found to be the case for a sea that was driven by a 14 m/s wind. These isolated results show that the MSL, as measured by an off-nadir and/or multibeam type satellite laser altimeter, will be found above, at, or below the true MSL, depending on the local sea conditions existing in the footprint of the altimeter. Airborne nadir-pointed laser altimeter data for a wide variety of sea conditions are needed before a final determination can be made of the effect of sea state on the backscatter cross-section as measured by a down-looking satellite laser system.

Hoge, F. E.↗

NASA NTRS1985

Transitions of the type 2s-2p in highly ionized Cu, Zn, Ga, and Ge

Transitions of the type 2s-2p in the F I, O I, N I, and C I isoelectronic sequences of copper, zinc, gallium, and germanium have been identified in the spectra from plasmas produced by the Omega laser system at the University of Rochester. The wavelengths are in the range 50 to 112 A and are measured using silicon and oxygen lines as wavelength standards for gallium and using several lines from the F I, O I, and Na I isoelectronic sequences as wavelength standards for copper, zinc, and germanium. The energy levels that are determined from the measured wavelengths are also presented. Based on these measurements, the wavelengths for a number of magnetic-dipole transitions within the ground configurations of the F I, O I, and N I isoelectronic sequences are predicted.

Behring, W. E.↗

NASA NTRS1985

International Symposium on Remote Sensing of Environment, Third Thematic Conference: Remote Sensing for Exploration Geology, Colorado Springs, CO, April 16-19, 1984, Proceedings. Volumes 1 & 2

A photogeologic and remote sensing model of porphyry type mineral sytems is considered along with a Landsat application to development of a tectonic model for hydrocarbon exploration of Devonian shales in west-central Virginia, remote sensing and the funnel philosophy, Landsat-based tectonic and metallogenic synthesis of the southwest United States, and an evolving paradigm for computer vision. Attention is given to the neotectonics of the Tibetan plateau deduced from Landsat MSS image interpretation, remote sensing in northern Arizona, the use of an airborne laser system for vegetation inventories and geobotanical prospecting, an evaluation of Thematic Mapper data for hydrocarbon exploration in low-relief basins, and an evaluation of the information content of high spectral resolution imagery. Other topics explored are related to a major source of new radar data for exploration research, the accuracy of geologic maps produced from Landsat data, and an approach for the geometric rectification of radar imagery.

Source record↗

NASA NTRS1986

Application of an InGaAsP diode laser to probe photodissociation dynamics - I(asterisk) quantum yields from n- and i-C3F7I and CH3I by laser gain vs absorption spectroscopy

Initial measurements on I-asterisk yields of alkyl iodides at 266 nm are reported using gain vs. absorption spectroscopy with an InGaAsP diode probe laser. The results are 102 percent + or - 4 percent, 102 percent + or - 7 percent, and 73 percent + or - 4 percent for n-C3F7I, i-C3F7I, and CH3I respectively. Future prospects for the development of diode laser systems and for their use in dynamical studies are discussed.

Hess, W. P.↗

NASA NTRS1987

Innovative methods for the measurement of I* quantum yields and kinetics by diode laser gain-versus-absorption

The quantum yields of a variety of candidate molecules for solar lasant materials to produce I* were tested. The absorption spectrum was measured for each compound and the I* yield determined by the diode laser or by infrared emission, using C3F7I as a standard. The results of these measurements are summarized. A GaAsInP diode laser system was developed to probe I and I* atoms to obtain yields and kinetics. A technique of gain-versus-absorption spectroscopy was investigated to measure quantum yields with high accuracy. The errors in the yield data were reduced to +/- 2% or less. In addition, experiments were set up to measure the rates of F-sublevel changing collisions in both the I ground state and the I* excited state. Finally, experiments and modelling were carried out to explore the possibility of measuring the recombination rates of I* with C3F7 radicals.

Leone, Stephen R.↗

NASA NTRS1987

A method of atmospheric density measurements during Shuttle entry using UV laser Rayleigh scattering

A detailed study is described of the performance capabilities and the hardware requirements for a method in which ambient density is measured along the Space Shuttle flight path using on-board optical instrumentation. The technique relies on Rayleigh scattering of light from a pulsed, ultraviolet, ArF excimer laser operating at a wavelength of 193 nm. The method is shown to be capable of providing direct measurements of ambient density with an uncertainty of less than 1 percent and with a spatial resolution of 1 km, over an altitude range from 50 to 90 km. In addition, extensions of this concept are discussed that allow measurements of the shock wave location and the density profile within the shock layer. Two approaches are identified that appear to be feasible, in which the same laser system is used for the extended measurements as that required for the ambient density measurements.

Mckenzie, Robert L.↗

NASA NTRS1988

Laser investigations for payload G-652 prior to filing pre-flight accommodation requirements

In anticipation of presenting the preflight accommodations requirements to NASA for approval, the physics, biology, electronic and chemistry aspects of laser experiments which are most advantageous to the flight are investigated. Preliminary laboratory evaluation was targeted with the realization that future flights of the shuttle may begin in 1988. It is the consensus that during the holding time before the resumption of flights, there is an extra margin of perfection which is possible and that the period prior to flight is advantageous technologically. The problems that can be encountered in space flown laser systems are addressed and the analysis of data is offered as a model for preflight accommodation requirement filing.

Bellina, Joseph↗

NASA NTRS1988

Diode laser-pumped solid-state lasers

An evaluation is made of the consequences for solid-state lasers of novel diode laser-pumping technology. Diode laser-pumped neodymium lasers have operated at an electrical-to-optical efficiency of 10 percent in a single spatial mode, with linewidths of less than 10 kHz, and with a spectral power brightness sufficiently great to allow frequency extension by harmonic generation in nonlinear crystals; this has yielded green and blue sources of coherent radiation. Q-switched operation with kW peak powers and mode-locked operation with 10-picosec pulse widths have also been demonstrated. All-solid-state lasers at prices comparable to those of current flash-lamp-pumped laser systems are foreseen, as are power levels exceeding 1 kW, for coherent radar, global satellite sensing, and micromachining.

Byer, Robert L.↗

NASA NTRS1988

Characteristics and kinetics of laser-pumped Ti:sapphire oscillators

The experimental performance of a gain-switched Ti:sapphire laser oscillator pumped by a frequency-doubled Q-switched Nd:YAG laser system is presented for a variety of operating conditions. A theoretical model developed for this oscillator predicts well its performance. The observed curved input-output energy plots for the oscillator result from the kinetics of gain switching and fluorescence decay during the gain buildup period. Fluorescence decay also produces observed oscillator thresholds higher than those normally predicted by the standard gain-equals-loss condition. Gain-switched parasitic modes, with a higher threshold but shorter round-trip time than the resonator mode, cause the resonator mode to oscillate only over a finite range of pump energies. Spectroscopic investigations show that the Ti:sapphire cross-section spectrum is well fit by a Poisson distribution, giving a peak cross section of 3 x 10 to the -19th sq cm for the pi polarization.

Eggleston, John M.↗

NASA NTRS1988

Atmospheric transmission coefficients for laser pulses with spectral widths of a few tenths of a nanometer over the wavelength region from 800 to 860 nanometers

Effective atmospheric transmission spectra were calculated from 800 to 860 nanometers for laser sources with spectral widths of a few tenths of a nanometer. In this spectral region, the atmospheric absorption lines (water lines) have linewidths of a few hundredths of a nanometer, so that the transmission coefficient for a relatively wide laser pulse must be computed by taking a weighted average over the pulse spectral width. Laser spectral widths of several tenths of a nanometer are shown to reduce the effective absorption by water lines to as little as 10 to 20 percent, even when the laser is centered on a line or overlaps several lines. Thus, the effect of absorption by atmospheric water lines may be greatly reduced for laser communication systems using laser diode array transmitters, for which the pulse spectral width may be a few tenths of a nanometer.

Safren, H. G.↗

NASA NTRS1989

Holographic interferometry with an injection seeded Nd:YAG laser and two reference beams

The performance of twin injection seeded Nd:YAG lasers is compared with the performance of an argon-ion laser for recording dual-reference-beam holograms in AGFA 8E56 emulsion. Optical heterodyning is used to measure interference, and the results are expressed in terms of heterodyning signal level and intensity signal-to-noise. The Nd:YAG laser system is to be used for optical inspections of structures for cracks, defects, gas leaks, and structural changes.

Decker, Arthur J.↗

NASA NTRS1988

Free-flying experiment to measure the Schawlow-Townes linewidth limit of a 300 THz laser oscillator

Recent advances in laser diode-pumped solid state laser sources permit the design and testing of laser sources with linewidths that approach the Schawlow-Townes limit of 1 Hz/mW of output power. Laser diode pumped solid state ring oscillators have been operated with CW output power levels of 25 mW at electrical efficiencies that exceed 6 percent. These oscillators are expected to operate for lifetimes that approach those of the laser diode sources which is now approaching 20,000 hours. The efficiency and lifetime of these narrow linewidth laser sources will enable space measurements of gravity waves, remote sensing applications (including local range rate and measurements), and laser sources for frequency and time standards. A free-flight experiment, 'SUNLITE', is being designed to measure the linewidth of this all-solid-state laser system.

Byer, R. L.↗

NASA NTRS1988

Doppler and range determination for deep space vehicles using active optical transponders

This paper describes and analyzes two types of laser system employing active transponders that could accurately determine Doppler and range to deep space vehicles from earth-orbiting satellites. The first is a noncoherent optical system in which the Doppler effect on an intensity-modulating subcarrier is measured. The second is a coherent optical system in which the Doppler effect of the optical carrier itself is measured. Doppler and range measurement errors are mathematically modeled and, for three example systems, numerically evaluated.

Kinman, Peter W.↗