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At least 91 records · Page 5

All sources NASA NTRS DOE OSTI

NASA NTRS1991

Laser welding in space

Autogenous welds in 304 stainless steel were performed by Nd-YAG laser heating in a simulated space environment. Simulation consists of welding on the NASA KC-135 aircraft to produce the microgravity and by containing the specimen in a vacuum chamber. Experimental results show that the microgravity welds are stronger, harder in the fusion zone, have deeper penetration and have a rougher surface rippling of the weld pool than one-g welds. To perform laser welding in space, a solar-pumped laser concept that significantly increases the laser conversion efficiency and makes welding viable despite the limited power availability of spacecraft is proposed.

Kaukler, W. F.↗

NASA NTRS1989

A space-based combined thermophotovoltaic electric generator and gas laser solar energy conversion system

This paper describes a spaceborne energy conversion system consisting of a thermophotovoltaic electric generator and a gas laser. As a power source for the converson, the system utilizes an intermediate blackbody cavity heated to a temperature of 2000-2400 K by concentrated solar radiation. A double-layer solar cell of GaAs and Si forms a cylindrical surface concentric to this blackbody cavity, receiving the blackbody radiation and converting it into electricity with cell conversion efficiency of 50 percent or more. If the blackbody cavity encloses a laser medium, the blackbody radiation can also be used to simultaneously pump a lasing gas. The feasibility of blackbody optical pumping at 4.3 microns in a CO2-He gas mixture was experimentally demonstrated.

Yesil, Oktay↗

NASA NTRS1979

Radiation energy conversion in space

Topics discussed at the third NASA conference on radiant energy conversion are reviewed. The unconcentrated-photovoltaic-generation version of a solar power satellite is described, noting that it will consist of a 21.3 x 5.3-sq-km silicon-solar-cell array expected to provide 17 Gw of electrical power, with 1 km in diam transmitters oriented to beam 2.45 GHz microwave power to two receiving/rectifying 'rectennas' on earth. The Solares space-energy-system concept, designed for providing a large fraction of the world's energy needs at costs comparable to those of future coal/nuclear alternative, is considered, as are subsystems for improving the economics of the solar power satellite. A concept proposing the use of relativistic-electron-storage rings for electron-beam energy transmission and storage, and a report on the production of a high temperature plasma with concentrated solar radiation are taken into account. Laser-conversion systems, including the direct-solar-pumped space laser, and the telec-powered spacecraft, are discussed.

Billman, K. W.↗

NASA NTRS1995

Tunable CW diode-pumped Tm,Ho:YLiF4 laser operating at or near room temperature

A conversion efficiency of 42% and slope efficiency of 60% relative to absorbed pump power are obtained from a continuous wave diode-pumped Tm,Ho:YLiF4 laser at 2 microns with output power of 84 mW at a crystal temperature of 275 K. The emission spectrum is etalon tunable over a range of7 nm (16.3/cm) centered on 2.067 microns with fine tuning capability of the transition frequency with crystal temperature at a measured rate of -0.03/(cm)K. The effective emission cross-section is measured to be 5 x 10(exp -21) cm squared. These and other aspects of the laser performance are disclosed in the context of calculated atmospheric absorption characteristics in this spectral region and potential use in remote sensing applications. Single frequency output and frequency stabilization are achieved using an intracavity etalon in conjunction with an external reference etalon.

Mcguckin, Brendan T.↗

NASA NTRS1972

Laser power stations in orbit.

Potential laser applications for space-borne power generation are discussed in the light of the current state of the art. The feasible ranges of various laser classes with standing waves are estimated. Power and efficiency, mirror factors, phased-array performance and beam patterns are analyzed as selection characteristics. Other topics include the maximum receiving-element size, energy conversion, pointing and tracking, causes of deformation, and mirror distortions. It is theorized that a nuclear-fueled laser satellite could beam power to distances twice the earth-sun distance with predictable pointing accuracies.

Hansen, C. F.↗

NASA NTRS1978

Preliminary results on the conversion of laser energy into electricity

A preliminary experiment was performed to investigate conversion of 10.6 micron laser energy to electrical energy via a laser-sustained argon plasma. Short-circuit currents of 0.7 A were measured between a thoriated-tungsten emitter and collector electrodes immersed in the laser-sustained argon plasma. Open-circuit voltages of about 1.5 V were inferred from the current-voltage load characteristics. The dominant mechanism of laser energy conversion is uncertain at this time. Much higher output powers appear possible.

Thompson, R. W.↗

NASA NTRS1986

Space-based laser-driven MHD generator: Feasibility study

The feasibility of a laser-driven MHD generator, as a candidate receiver for a space-based laser power transmission system, was investigated. On the basis of reasonable parameters obtained in the literature, a model of the laser-driven MHD generator was developed with the assumptions of a steady, turbulent, two-dimensional flow. These assumptions were based on the continuous and steady generation of plasmas by the exposure of the continuous wave laser beam thus inducing a steady back pressure that enables the medium to flow steadily. The model considered here took the turbulent nature of plasmas into account in the two-dimensional geometry of the generator. For these conditions with the plasma parameters defining the thermal conductivity, viscosity, electrical conductivity for the plasma flow, a generator efficiency of 53.3% was calculated. If turbulent effects and nonequilibrium ionization are taken into account, the efficiency is 43.2%. The study shows that the laser-driven MHD system has potential as a laser power receiver for space applications because of its high energy conversion efficiency, high energy density and relatively simple mechanism as compared to other energy conversion cycles.

Choi, S. H.↗

NASA NTRS1981

Free electron lasers for transmission of energy in space

A one-dimensional resonant-particle model of a free electron laser (FEL) is used to calculate laser gain and conversion efficiency of electron energy to photon energy. The optical beam profile for a resonant optical cavity is included in the model as an axial variation of laser intensity. The electron beam profile is matched to the optical beam profile and modeled as an axial variation of current density. Effective energy spread due to beam emittance is included. Accelerators appropriate for a space-based FEL oscillator are reviewed. Constraints on the concentric optical resonator and on systems required for space operation are described. An example is given of a space-based FEL that would produce 1.7 MW of average output power at 0.5 micrometer wavelength with over 50% conversion efficiency of electrical energy to laser energy. It would utilize a 10 m-long amplifier centered in a 200 m-long optical cavity. A 3-amp, 65 meV electrostatic accelerator would provide the electron beam and recover the beam after it passes through the amplifier. Three to five shuttle flights would be needed to place the laser in orbit.

Segall, S. B.↗

DOE OSTI2023

Engineered current-density profile diode laser

The present technology can be used to control the current injection profile in the longitudinal direction of a high-power diode laser in order to optimize current densities as a function of position in the cavity to promote higher reliable output power and increase the electrical to optical conversion efficiency of the device beyond the level which can be achieved without application of this technique. This approach can be utilized, e.g., in the fabrication of semiconductor laser chips to improve the output power and wall plug efficiency for applications requiring improved performance operation.

Leisher, Paul O.↗

DOE OSTI2024

Engineered current-density profile diode laser

Leisher, Paul O.↗

NASA NTRS1972

Efficient second harmonic generation of picosecond laser pulses.

Efficient conversion to the second harmonic (SH) using KD2PO4 and CsH2AsO4 crystals inside a folded cavity of a high-power-dye mode-locked neodymium-glass laser is reported. For the first time, frequency-doubled picosecond light pulses have been obtained in CsH2AsO4 with peak powers of the order of 1 GW/sq cm at 0.531 micron for an effective pump power density of 4 GW/sq cm.

Rabson, T. A.↗

NASA NTRS2001

Frequency conversion system

Laser diode pumped mid-IR wavelength sources include at least one high power, near-IR wavelength, injection and/or sources wherein one or both of such sources may be tunable providing a pump wave output beam to a quasi-phase matched (QPM) nonlinear frequency mixing (NFM) device. The NFM device may be a difference frequency mixing (DFM) device or an optical parametric oscillation (OPO) device. Wavelength tuning of at least one of the sources advantageously provides the ability for optimizing pump or injection wavelengths to match the QPM properties of the NFM device enabling a broad range of mid-IR wavelength selectivity. Also, pump powers are gain enhanced by the addition of a rare earth amplifier or oscillator, or a Raman/Brillouin amplifier or oscillator between the high power source and the NFM device. Further, polarization conversion using Raman or Brillouin wavelength shifting is provided to optimize frequency conversion efficiency in the NFM device.

Sanders, Steven↗

NASA NTRS1976

Laser engines operating by resonance absorption

Basic tutorial article on the thermodynamic feasibility of laser engines at the present state of the art. Three main options are considered: (1) laser power applied externally to a heat reservoir (boiler approach); (2) internal heating of working fluid by resonance absorption; and (3) direct conversion of selective excitation into work. Only (2) is considered practically feasible at present. Basic concepts and variants, efficiency relations, upper temperature limits of laser engines, selection of absorbing gases, engine walls, bleaching, thermodynamic cycles of optimized laser engines, laser-powered turbines, laser heat pumps are discussed. Photon engines and laser dissociation engines are also considered.

Garbuny, M.↗

NASA NTRS1991

Investigation of loss processes of Tm and Tm,Ho in YAG

The loss of excitation from various manifolds of Tm and Tm,Ho in YAG as a function of temperature and concentration is studied. Two probable loss mechanisms - a Tm up-conversion and a Ho up-conversion - are identified. A 785-nm CW diode laser with 400-nW peak power was focused to a small spot on the sample. The emission from the sample observed at 90 deg was monitored through a monochromator with slits open to 3 mm. Intensity of emission was measured by varying the power of the excitation source using a set of neutral density filters. Power is reported as the percentage of the peak power, and the intensity curves were normalized below 20 percent of transmission. The fact that there is emission above the pump energy indicates an up-conversion from excited manifolds. Nonlinear changes in the intensity of the emission from the Tm 3F4 manifold with the pump power reveals a loss of excitation from this manifold. The linear dependence of the 5I7 manifold emission with pump power at low Tm and high Ho concentrations and the gain of energy in the 5I6 manifold of Ho indicate that the 5I7 manifold loss is due to the coupling of Tm and Ho ions.

Armagan, G.↗

NASA NTRS1993

Tunable CW diode-pumped Tm,Ho:YLiF4 laser operating at or near room temperature

A conversion efficiency of 42 percent and slope efficiency of 60 percent relative to absorbed pump power are obtained from a continuous wave diode-pumped Tm,Ho:YLiF4 laser at 2 microns with output power of 84mW at a crystal temperature of 275K. The emission spectrum is etalon tunable over a range of 7nm (16.3 cm(sup -1) centered on 2.067 microns with fine tuning capability of the transition frequency with crystal temperature at a measured rate of -0.03/(cm)K. The effective emission cross-section is measured to be 5 x 10(sup -21) cm squared. These and other aspects of the laser performance are disclosed in the context of calculated atmospheric absorption characteristics in this spectral region and potential use in remote sensing applications. Single frequency output and frequency stabilization are achieved using an intracavity etalon in conjunction with an external reference etalon.

Mcguckin, Brendan T.↗

NASA NTRS1992

Efficient CW diode-pumped Tm, Ho:YLF laser with tunability near 2.067 microns

A conversion efficiency of 42 percent and slope efficiency of approximately 60 percent relative to absorbed pump power are reported from a continuous wave diode-pumped Tm, Ho:YLF laser at 2 microns with output power of 84 mW at sub-ambient temperatures. The emission spectrum is etalon tunable over a range of 16/cm centered on 2.067 microns, with fine tuning capability of the transition frequency with crystal temperature at a measured rate of about -0.03/cm-K. The effective emission cross section is measured to be 5 x 10 exp -21 sq cm. These and other aspects of the laser performance are discussed in the context of calculated atmospheric absorption characteristics in this spectral region and potential use in remote sensing applications.

Mcguckin, B. T.↗

NASA NTRS1992

Laser prospects for SPS and restoration of the ozone layer

Large-scale applications of high-power lasers are considered (special experiments are described to confirm the feasibility of these applications) to achieve also large-scale environmental advantages. The possibility of producing electric energy by Laser-Solar Power Satellites in the near future is discussed. A full-scale experimental L-SPS satellite is suggested as a module of a global space energy network. Electric power of about 10 MW at the surface of the Earth is achievable as a result of energy conversion of laser radiation. L-SPS is based on the greatest advantages of present optics and laser techniques. Specialized-scale experiments are carried out and described. L-SPS project could provide real electricity for consumers not later than by highly developed fusion techniques, and the environmental aftereffects are quite favorable. A new method of power supply for satellites is suggested, based on the connection of an on-board electric circuit directly with the ground-based power grid by means of laser beams.

Kruzhilin, Yuri↗

NASA NTRS1993

Proceedings of the 12th Space Photovoltaic Research and Technology Conference (SPRAT 12)

The Twelfth Space Photovoltaic Research and Technology conference was held at the NASA Lewis Research Center from 20 to 22 Oct. 1992. The papers and workshops presented in this volume report substantial progress in a variety of areas in space photovoltaics. Topics covered include: high efficiency GaAs and InP solar cells, GaAs/Ge cells as commercial items, flexible amorphous and thin film solar cells (in the early stages of pilot production), high efficiency multiple bandgap cells, laser power converters, solar cell and array technology, heteroepitaxial cells, betavoltaic energy conversion, and space radiation effects in InP cells. Space flight data on a variety of cells were also presented.

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