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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Performance analysis and technical assessment of coherent lidar systems for airborne wind shear detection

Detailed computer simulations of the lidar wind-measuring process have been conducted to evaluate the use of pulsed coherent lidar for airborne windshear monitoring. NASA data fields for an actual microburst event were used in the simulation. Both CO2 and Ho:YAG laser lidar systems performed well in the microburst test case, and were able to measure wind shear in the severe weather of this wet microburst to ranges in excess of 1.4 km. The consequent warning time gained was about 15 sec.

Huffaker, R. Milton↗
NASA NTRS1988

Applications of spaceborne laser ranger on EOS

An account is given of the design concept and potential applications in science and engineering of the spaceborne laser ranging and altimeter apparatus employed by the Geodynamics Laser Ranging System; this is scheduled for 1997 launch as part of the multiple-satellite Earth Observing System. In the retrograding mode for geodynamics, the system will use a Nd:YAG laser's green and UV output for distance determination to ground retroreflectors. Engineering applications encompass land management and long-term ground stability studies relevant to nuclear power plant, pipeline, and aqueduct locations.

Degnan, John J.↗
NASA NTRS1988

Mid-infrared solid-state lasers and laser materials

An account is given of NASA-Langley's objectives for the development of advanced lasers and laser materials systems applicable to remote sensing in the mid-IR range. Prominent among current concerns are fiber-optic spectroscopy, eye-safe solid-state lasers for both Doppler sensing and mid-IR wavelength-generation laser pumping, and nonlinear optics generating tunable mid-IR radiation. Ho:YAG lasers are noted to exhibit intrinsic advantages for the desired applications, and are pumpable by GaAlAs laser diodes with a quantum efficiency approaching 2.

Barnes, Norman P.↗
NASA NTRS1988

Integrated spectrum analyzer/wavemeter for pulsed, tunable lasers

A compact instrument for single shot spectrum analysis and real time wavelength measurement of pulsed, tunable lasers has been built. Its accuracy and limitations are discussed, along with its potential applications. Results of tests with a narrow-line Nd:YAG-pumped dye laser are also presented.

Cotnoir, Leo J.↗
NASA NTRS1988

Room-temperature operation of a Co:MgF2 laser

A normal-mode, pulsed Co:MgF2 laser has been operated at room temperature for the first time. Continuous tuning from 1750 to 2500 nm with pulse energies up to 70 mJ and 46-percent slope efficiency was obtained with a 1338-nm Nd:YAG pump laser.

Welford, D.↗
NASA NTRS1988

Efficient monolithic MgO:LiNbO3 singly resonant optical parametric oscillator

A monolithic MgO:LiNbO3 singly resonant optical parametric oscillator (OPO) was operated as both a standing-wave and a ring-geometry resonator. The OPO was pumped by the second harmonic of an amplified single-mode diode-laser-pumped Nd:YAG laser. Pump depletions of greater than 60 percent were observed when pumping four times greater than the 35-W threshold. The OPO output at the resonant signal tuned with temperature from 834 to 958 nm, while the corresponding idler tuned from 1.47 to 1.2 microns. The spectral characteristics of the OPO signal output and the relative merits of a standing wave versus a ring geometry are discussed.

Kozlovsky, W. J.↗
NASA NTRS1988

Transient photoconductivity in the ferromagnetic semiconductor CdCr2Se4

The transient photoconductive response time of the ferromagnetic semiconductor CdCr2Se4 was measured to be smaller than 90 ps, the response time of the scope. The measurements were performed at room temperature (300 K) for 0.53 and 1.06 microns excitations using a mode locked frequency-doubled YAG laser.

Walser, A. D.↗
NASA NTRS1988

An analysis of the temperature distribution in finite solid-state laser rods

An expression for the time-dependent temperature distribution in a finite solid-state laser rod, for an arbitrary distribution of pump energy, has been derived. The specific case of end pumping by circular (constant) or Gaussian beams is included. This formulation was used to predict the time evolution of temperature in Ti:sapphire laser rods and in Nd:YAG rods of specific dimensions.

Farrukh, Usamah O.↗
NASA NTRS1989

Theory of the optimally coupled Q-switched laser

The general equations describing Q-switched laser operation are transcendental in nature and require numerical solutions, which greatly complicates the optimization of real devices. Here, it is shown that, using the mathematical technique of Lagrange multipliers, one can derive simple analytic expressions for all of the key parameters of the optimally coupled laser, i.e., one which uses an optimum reflector to obtain maximum laser efficiency for a given pump level. These parameters can all be expressed as functions of a single dimensionless variable z, defined as the ratio of the unsaturated small-signal gain to the dissipative (nonuseful) optical loss, multiplied by a few simple constants. Laser design tradeoff studies and performance projections can be accomplished quickly with the help of several graphs and a simple hand calculator. Sample calculations for a high-gain Nd:YAG and a low-gain alexandrite laser are presented as illustrations of the technique.

Degnan, John J.↗
NASA NTRS1988

Monolithic nonplanar ring lasers - Resistance to optical feedback

The sensitivity of a monolithic unidirectional nonplanar ring laser to optical feedback depends on the polarization eigenmodes of the resonator, which are complicated functions of the resonator geometry. Resonator geometries that increase the loss difference between the two directions of propagation around the ring improve the resistance of the lasers to optical feedback. Here, measurements on Nd:YAG nonplanar ring lasers having two different ring geometries are discussed. Currently, 1 percent optical feedback produces a 10 percent reduction in useful output power for the more feedback-resistant oscillator, a tenfold improvement over previous designs.

Nilsson, Alan C.↗
NASA NTRS1989

Cloud top liquid water from lidar observations of marine stratocumulus

Marine stratus clouds were simultaneously observed by nadir Nd:YAG lidar measurements and in situ cloud physics measurements. A procedure was applied to derive the two-dimensional vertical cross section of the liquid water from within the cloud top lidar observations. A comparison to direct in-cloud liquid water observations gave good results. The liquid water retrieval was limited to an effective optical depth of 1.5. The true cloud optical thickness was also obtained from the retrieval procedure to a corresponding limit of 3.8. The optical thickness of the observed marine stratus clouds was predominantly below 3.0.

Spinhirne, J. D.↗
NASA NTRS1990

Direct solar-pumped iodine laser amplifier

The optimum conditions of a solar pumped iodine laser are found in this research for the case of a continuous wave operation and a pulsed operation. The optimum product of the pressure(p) inside the laser tube and the tube diameter(d) was pd=40 approx. 50 torr-cm on the contrary to the case of a high intensity flashlamp pumped iodine laser where the optimum value of the product is known to be pd=150 torr-cm. The pressure-diameter product is less than 1/3 of that of the high power iodine laser. During the research period, various laser materials were also studied for solar pumping. Among the laser materials, Nd:YAG is found to have the lowest laser threshold pumping intensity of about 200 solar constant. The Rhodamine 6G was also tested as the solar pumped laser material. The threshold pumping power was measured to be about 20,000 solar constant. The amplification experiment for a continuously pumped iodine laser amplifier was performed using Vortek solar simulator and the amplification factors were measured for single pass amplification and triple pass amplification of the 15 cm long amplifier tube. The amplification of 5 was obtained for the triple pass amplification.

Han, Kwang S.↗
NASA NTRS1990

Development of eye-safe lidar for aerosol measurements

Research is summarized on the development of an eye safe Raman conversion system to carry out lidar measurements of aerosol and clouds from an airborne platform. Radiation is produced at the first Stokes wavelength of 1.54 micron in the eye safe infrared, when methane is used as the Raman-active medium, the pump source being a Nd:YAG laser at 1.064 micron. Results are presented for an experimental study of the dependence of the 1.54 micron first Stokes radiation on the focusing geometry, methane gas pressure, and pump energy. The specific new technique developed for optimizing the first Stokes generation involves retroreflecting the backward-generated first Stokes light back into the Raman cell as a seed Stokes beam which is then amplified in the temporal tail of the pump beam. Almost 20 percent conversion to 1.54 micron is obtained. Complete, assembled hardware for the Raman conversion system was delivered to the Goddard Space Flight Center for a successful GLOBE flight (1989) to measure aerosol backscatter around the Pacific basin.

Singh, Upendra N.↗
NASA NTRS1989

Recent advances in efficient long-life, eye-safe solid state and CO2 lasers for laser radar applications

The key problems in the development of eye-safe solid-state lasers are discussed, taking into account the energy transfer mechanisms between the complicated energy level manifolds of the Tm, Ho, Er ion dopants in hosts with decreasing crystal fields such as YAG or YLF. Optimization of energy transfer for efficient lasing through choice of dopant concentration, power density, crystal field and temperature is addressed. The tailoring of energy transfer times to provide efficient energy extraction for short pulses used in DIAL and Doppler lidar is considered. Recent advances in Pt/SnO2 oxide catalysts and other noble metal/metal oxide combinations for CO2 lasers are discussed. Emphasis is given to the dramatic effects of small quantities of H2O vapor for increasing the activity and lifetime of Pt/SnO2 catalysts and to increased lifetime operation with rare isotope (C-12)(O-18)2 lasing mixtures.

Hess, R. V.↗
NASA NTRS1989

Parametric amplification in AgGaSe2

AgGaSe2 has been grown, annealed, and characterized for the mid-IR. Characterization includes measurement of the average power-limiting factors including absorption and the variation of the refractive indices with temperature. Using specially annealed crystals 20 mm long and a Ho:YAG pump, parametric amplification at 3.39 microns has achieved a gain of 2.9 with a peak power input of only 8 MW/sq cm.

Barnes, Norman P.↗
NASA NTRS1990

Blackbody absorption efficiencies for six lamp pumped Nd laser materials

Utilizing high resolution spectra, the absorption efficiencies for six Nd laser materials were calculated as functions of the effective blackbody temperature of the lamp and laser crystal size. The six materials were Nd:YAG, Nd:YLF, Nd:Q-98 Glass, Nd:YVO4, Nd:BEL, and Nd:Cr:GSGG. Under the guidelines of this study, Nd:Cr:GSGG's absorption efficiency is twice the absorption efficiency of any of the other laser materials.

Cross, Patricia L.↗
NASA NTRS1989

Spectroscopic investigation of Cr to Tm energy transfer in yttrium aluminum garnet crystals

A series of experiments has been conducted in order to examine the nature of the energy transfer process between the Cr(3+) and Tm(3+) ions in YAG. Data are obtained on various samples doped with Cr(3+) and/or Tm(3+). These data include absorption, luminescence, excitation spectra and time-resolved response to pulsed excitation. The measurements were carried out over a range of temperatures from 78 to 350 K. The rate of nonradiative energy transfer from Cr(3+) to Tm(3+) depends on temperature, and in the region from 200 to 350 K, this dependence is due primarily to the thermal variation in the radiative decay probability of the Cr ion.

Armagan, G.↗
NASA NTRS1989

Architectural design of a ground-based deep-space optical reception antenna

An architectural design of a ground-based antenna (telescope) for receiving optical communications from deep space is presented. Physical and optical parameters, and their effect on the performance and cost considerations, are described. The channel capacity of the antenna is 100 kbits/s from Saturn and 5 Mbits/s from Mars. A novel sunshade is designed to permit optical communication even when the deep-space laser source is as close to the sun as 12 deg. Inserts in the tubes of the sunshade permit operations at solar elongations as small as 6 or 3 deg. The Nd:YAG source laser and the Fraunhofer filter (a narrow-band predetection optical filter) are tuned to match the Doppler shifts of the source and background. A typical Saturn-to-earth data link can reduce its source power requirement from 8.2 W to 2 W of laser output by employing a Fraunhofer filter instead of a conventional multilayer dielectric filter.

Kerr, E. L.↗