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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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NASA NTRS1992

A Remote Laser Mass Spectrometer for Lunar Resource Assessment

The use of lasers as a source of excitation for surface mass spectroscopy has been investigated for some time. Since the laser can be focused to a small spot with intensity, it can vaporize and accelerate atoms of material. Using this phenomenon with a time-of-flight mass spectrometer allows a surface elemental mass analysis of a small region with each laser pulse. While the technique has been well developed for Earth applications, space applications are less developed. NASA Langley recently began a research program to investigate the use of a laser to create ions from the lunar surface and to analyze the ions at an orbiting spacecraft. A multijoule, Q-switched Nd:YAG laser would be focused to a small spot on the lunar surface, creating a dense plasma. This plasma would eject high-energy ions, as well as neutrals, electrons, and photons. An experiment is being set up to determine the characteristics of such a laser mass spectrometer at long flight distances. This experiment will determine the character of a future flight instrument for lunar resource assessment.

Deyoung, R. J.↗
NASA NTRS1993

Laser-based firing systems for prompt initiation of secondary explosives

Motivated by issues of weapon safety and security, laser based firing systems for promptly initiating secondary explosives have been under active development at Sandia National Laboratories for more than four years. Such a firing system consists of miniaturized, Q-switched, solid-state laser, optical detonators, optical safety switches, and elements for splitting, coupling, and transmitting the laser output. Potential system applications pose significant challenges in terms of server mechanical and thermal environments and packaging constraints, while requiring clear demonstration of safety enhancements. The Direct Optical Initiation (DOI) Program at Sandia is addressing these challenges through progress development phases during which the design, fabrication, and testing of prototype hardware is aimed at more difficult application requirements. A brief history of the development program, and a summary of current and planned activities, will be presented.

Meeks, Kent D.↗
NASA NTRS1992

Diode pumped, regenerative Nd:YAG ring amplifier for space application

The study reviews the research and development of a prototype laser used to study one possible method of short-pulse production and amplification, in particular, a pulsed Nd:YAG ring laser pumped by laser diode arrays and injected seeded by a 100-ps source. The diode array pumped, regenerative amplifier consists of only five optical elements, two mirrors, one thin film polarizer, one Nd:YAG crystal, and one pockels cell. The pockels cell performed both as a Q-switch and a cavity dumper for amplified pulse ejection through the thin film polarizer. The total optical efficiency was low principally due to the low gain provided by the 2-bar pumped laser head. After comparison with a computer model, a real seed threshold of about 10 exp -15 J was achieved because only about 0.1 percent of the injected energy mode-matched with the ring.

Coyle, D. B.↗
NASA NTRS1993

Long-pulse-length 2-micron diode-pumped YLiF4 laser

A diode-pumped Ho:Tm:YLiF4 laser at room temperature has achieved an optical efficiency of 5.9 percent under normal-mode operation. Long pulse lengths, of the order of 1 microsec, have been obtained by use of 4-m ring resonator, with laser energy output of 15 mJ in single Q-switched pulses for an input energy of 2.078 J.

Jani, Mahendra G.↗
NASA NTRS1995

Integrated optical components in thin films of polymers

The results will be reported on the study of integrated optical components based on nonlinear optical polymeric films. Polymers poly(methyl methacrylate) (PMMA) and polyimide (PI) doped with organic laser dyes 4-dicyanomethylene-2-methyl-6-p dimethylaminostyryl-4H pyran (DCM) and 1, 3, 5, 7, 8 - pentamethyl-2,6 -diethyl-pyrromethene -BF2-complex (Pyrommethene 567, PM-567) were selected as materials for light guiding films. Additionally, UV polymerized polydiacetylene (PDA) on glass substrate was used as a waveguide material. Optical waveguides were fabricated using spin coating of preoxidized silicon wafers (1.5 micrometer silicon oxide layer) with organic dye/polymer solution followed by soft baking. the modes in slab waveguides were studied using prism coupling techniques. Measured values of mode coupling angles in multimode waveguides were used to calculate film thickness and refractive index for different polarizations. Refractive index anisotropy was found in PDA waveguide. The optimal conditions of spin coating for single mode waveguide fabrication were estimated. Propagation losses were measured by collecting the light scattered from the trace of a propagating mode either by scanning photo detector or by CCD camera. Different types of light coupling techniques were used including end-dire coupling, prism and grating coupling. Mechanical printing technique was developed for coupling grating fabrication resulting in gratings with 4% diffraction efficiency. The gratings demonstrated good stability with diffraction efficiency relaxation rate 2.4 dB/hour at a temperature approximately 15-20 C below glass transition point. Dye doped waveguides were transversally pumped with frequency doubled Nd:YAG Q-switched laser producing intensive light emission with apparent 6 kW/sq cm pump threshold and spectrum narrowing near 617 nm peak in the case of DCM doped waveguide. PM-567 doped waveguide pumped with CW Ar(+) laser (514 nm wavelength) far below threshold (0.1 W/sq.cm pump power) demonstrated emission spectrum narrowing near 616 nm peak with 18% power conversion slope efficiency. In this case emission spectrum modification was caused by the enhanced light absorption along the direction of propagating waveguide modes. Changing length, thickness, and other morphlogical waveguide parameters one can modify emission spectrum in predictable direction. The results show that polymeric waveguides, especially based on high temperature polymers such as Pl, can be used to produce a varietiy of active and passive silicon compatible integrated optical components for aerospace applications.

Sarkisov, Sergey↗
NASA NTRS1995

Design and development of an all-solid-state laser unit for microgravity combustion applications

The laser-induced fluorescence (LIF) technique is a sensitive and noninvasive method for imaging of flames and for monitoring of temperature and the presence of transient molecular species in flames. Our research effort has two major objectives: (1) to use LIF to study the fundamentals of microgravity combustion via spectroscopic characterization of free radicals, and (2) to design and develop an all-solid-state portable laser unit for combustion studies in a microgravity environment. Well-characterized free radicals, namely hydroxyl (OH) and methoxy (CH3O), have analytically convenient bands that can be laser-excited in the 280-298 nm spectral region with the newly discovered solid-state tunable laser, which is based on the LiCaAIF6:Ce3+(LiCAF:Ce) single crystal pumped by the quadrupled (266 nm) output of a Q-switched YAG:Nd laser. The 266 nm YAG radiation (of about 10 mJ pulse energy) was split into two beams of about equal intensity, one used for photolysis of the free radical precursor and the other used for pumping the laser crystal. Tunability of the LiCAF:Ce laser was provided by a step-motor-driven Littrow-mounted diffraction grating. Laser excitation spectra of the CH3O radical was recorded in the 291.5-296.5 nm region with 0.15 cm(exp -1) resolution. Laboratory experiments have thus successfully shown that the idea of using the LiCAF:Ce laser as a dual-purpose photolysis and excitation source can pay rich dividends and that such a laser can be the center piece of an all-solid-state portable device that can be used for routine analytical investigations of microgravity combustion phenomena.

Kamal, Mohammed M.↗
NASA NTRS1996

Dual-rod Cr: LiSAF oscillator/amplifier for remote sensing applications

A dual rod configuration is used to achieve 16W average power operation from a flashlamp-pumped Cr:LiSAF laser oscillator. A double-pass dual-rod amplifier configuration was used to amplify 141(mu)J pulses from a Q-switched diode-pumped LiSAF oscillator by a factor of (approximately)120. This experiment established a small signal gain of 13.4% per cm at 820 nm. Improved slope efficiency (7.4% electrical-to-light) and pulse repetition frequency (40Hz) were achieved with a single-rod oscillator using improved Cr:LiSAF material.

Early, J. W.↗
NASA NTRS1996

High Spectral Resolution Lidar Measurements Using an I2 Absorption Filter

The University of Wisconsin high spectral resolution lidar (HSRL) measures optical properties of the atmosphere by separating the Doppler-broadened molecular backscatter return from the unbroadened aerosol return. The HSRL was modified to use an I2 absorption cell The modified HSRL transmitter uses a continuously pumped, Q-switched, injection seeded, frequency doubled Nd:YAG laser operating at a 4 kHz pulse repetition rate. This laser is tunable over a 124 GHz frequency range by temperature tuning the seed laser under computer control.

Eloranta, E. W.↗
NASA NTRS1995

Diode-Pumped Long-Pulse-Length Ho:Tm:YLiF4 Laser at 10 Hz

An optical efficiency of 0.052 under normal mode operation for diode-pumped Ho:Tm:YLiF4 at a pulse repetition frequency of 10 Hz has been achieved. Laser output energy of 30 mJ in single Q-switched pulses with 600-ns pulse length were obtained for an input energy of 3 J. A diffusion-bonded birefringent laser rod consisting of Ho:Tm-doped and undoped pieces of YLF was utilized for 10-Hz operation.

Jani, Mahendra G.↗
NASA NTRS1997

Laser-Induced Damage Threshold and Certification Procedures for Optical Materials

This document provides instructions for performing laser-induced-damage-threshold tests and pass-fail certification tests on optical materials used in pulsed-laser systems. The optical materials to which these procedures apply include coated and uncoated optical substrates, laser crystals, Q-switches, polarizers, and other optical components employed in pulsed-laser systems.

Source record↗
NASA NTRS1997

Improvement in Suppression of Pulsed Nd:YAG Laser Light With Iodine Absorption Cells for Filtered Rayleigh Scattering Measurements

Filtered Rayleigh scattering using iodine absorption cells is an effective technique for obtaining density, temperature, and velocity measurements in high speed confined flows. By tuning a single frequency laser to a strong iodine absorption line, stray scattered laser light can be greatly suppressed. For example, the minimum transmission predicted by an iodine absorption model calculation is less than 10(exp -5) at the 18788.44/cm line using a 200 mm absorption cell containing iodine vapor at 0.46 T. Measurements obtained by other researches using a CW Nd:YAG laser agree with the model calculations. However, measurements made by us and by others using Q-switched, injection-seeded, frequency doubled Nd:YAG lasers only show minimum transmission of about 3 x 10(exp -3). This greatly reduces the applicability of the filtered Rayleigh scattering technique using these lasers in experiments having large amounts of stray scattered laser light. The purposes of the present study are to characterize the spectrum of the excess light transmitted by the iodine cell and to make changes to the laser to reduce the transmitted laser light. Transmission data as a function of laser frequency for the iodine absorption line at 18788.44/cm are presented. A planar mirror Fabry-Perot interferometer was used to characterize the frequency spectrum of the light passed through the cell. Measurements taken with the laser tuned to the center of the iodine absorption line show the light transmitted through the iodine cell to have a component with a bandwidth of about 40 GHz. This is probably caused by other modes in the laser that exist in spite of the single frequency injection beam. A second broadband component was also observed, possibly caused by the laser flash lamps or by fluorescence. An intracavity etalon was installed in the laser oscillator cavity to suppress the 40 GHz component. Measurements taken with the etalon tuned to the injection frequency showed a reduction in the transmitted laser light. This improvement allows the iodine cell to block significantly more of the stray laser light in filtered Rayleigh scattering experiments. Examples are given of filtered Rayleigh scattering measurements showing the effect of the etalon on measurements taken in a Mach 3 flow in the NASA Lewis 4 inch by 10 inch supersonic wind tunnel.

Seasholtz, Richard G.↗
NASA NTRS1998

Design and Performance of a Miniature Lidar Wind Profiler (MLWP)

The directional velocity of the wind is one of the most critical components for understanding meteorological and other dynamic atmospheric processes. Altitude-resolved wind velocity measurements, also known as wind profiles or soundings, are especially necessary for providing data for meteorological forecasting and overall global circulation models (GCM's). Wind profiler data are also critical in identifying possible dangerous weather conditions for aviation. Furthermore, a system has yet to be developed for wind profiling from the surface of Mars which could also meet the stringent requirements on size, weight, and power of such a mission. Obviously, a novel wind profiling approach based on small and efficient technology is required to meet these needs. A lidar system based on small and highly efficient semiconductor lasers is now feasible due to recent developments in the laser and detector technologies. The recent development of high detection efficiency (50%), silicon-based photon-counting detectors when combined with high laser pulse repetition rates and long receiver integration times has allowed these transmitter energies to be reduced to the order of microjoules per pulse. Aerosol lidar systems using this technique have been demonstrated for both Q-switched, diode-pumped solid-state laser transmitters (lambda = 523 nm) and semiconductor diode lasers (lambda = 830 nm); however, a wind profiling lidar based on this technique has yet to be developed. We will present an investigation of a semiconductor-laser-based lidar system which uses the "edge-filter" direct detection technique to infer Doppler frequency shifts of signals backscattered from aerosols in the planetary boundary layer (PBL). Our investigation will incorporate a novel semiconductor laser design which mitigates the deleterious effects of frequency chirp in pulsed diode lasers, a problem which has limited their use in such systems in the past. Our miniature lidar could be used on a future Mars lander and perhaps find its own niche in terrestrial applications due to its potential low cost an small size.

Cornwell, Donald M., Jr.↗
NASA NTRS1998

2-Micron Diode-Pumped Pulsed Laser Transmitter for SPARCLE: A Coherent Wind Lidar Shuttle Mission

To enable a tropospheric vector wind velocity profiling from space with a pulsed Doppler lidar, a diode-pumped, room temperature Ho:Tm:YLF coherent pulsed transmitter has been developed at NASA Langley Research Center. This pulsed laser transmitter will be a part of coherent wind lidar shuttle mission SPARCLE. The acronym stands for SPAce Readiness Coherent Lidar Experiment and is primarily a technology demonstration mission and is expected to fly in 2001 as NASA's New Millennium Program (NMP) second Earth Orbiter (EO-2) mission. The laser transmitter for SPARCLE is a Ho:Tm:YLF power oscillator operating at eye-safe wavelength of 2.05 microns. The Q-switched output energy is 125 mJ at six Hz, and it has a near-transform limited beam with a pulse width of 170 ns. The high power and high beam quality of this laser makes it well suited as a coherent wind lidar transmitter on a space platform. When the output of this power oscillator is amplified by using four diode-pumped Ho:Tm:YLF amplifiers, an output energy of 600 mJ at 10 Hz is achieved. This is the highest energy ever produced at 10 Hz, and is at least an order of magnitude greater than previously achieved for a 2-micron diode-pumped laser at room temperature.

Singh, Upendra N.↗
NASA NTRS1999

Photon-Counting Multikilohertz Microlaser Altimeters

Spaceborne laser altimeters in planetary orbit typically use high energy (approximately 100 mJ) solid state lasers, large telescopes (50 to 100 cm), and high detection thresholds to achieve unambiguous surface returns with few or no ifalse alarmsi resulting from solar background noise. As a result of this conservative design philosophy, spacecraft prime power weight, or size constraints typically restrict operations to modest repetition rates on the order of a few tens of Hz which, at a typical ground velocity of 7 Km/sec, limits along-track spatial sampling to one sample every few hundred meters. The surface return rate of an Earth-orbiting altimeter can be increased by up to two orders of magnitude for a given laser output power by emitting the available photons in a high frequency (few KHz) train of low energy (< 1 mJ) pulses, as produced by passively Q-switched solid state "microlasers", and using single photon detection. while simultaneously using much smaller telescope diameters on the order of 10 cm. Simple onboard software algorithms, based on post-detection Poisson filtering techniques, can be employed to identify and extract the surface data from solar background noise prior to onboard data storage or transmission to a ground station. Under NASAis Instrument Incubator Program, we have begun the design and construction of a scanning airborne instrument to demonstrate the potential advantages of the technique for future space missions.

Degnan, John J.↗
NASA NTRS1998

The Laser Vegetation Imaging Sensor (LVIS): An Airborne Laser Altimeter for Mapping Vegetation and Topography

The Laser Vegetation Imaging Sensor (LVIS) is an airborne laser altimeter designed to quickly and extensively map surface topography as well as the relative heights of other reflecting surfaces within the laser footprint. Since 1997, this instrument has primarily been used as the airborne simulator for the Vegetation Canopy Lidar (VCL) mission, a spaceborne mission designed to measure tree height, vertical structure and ground topography (including sub-canopy topography). LVIS is capable of operating from 500 m to 10 km above ground level with footprint sizes from 1 to 60 m. Laser footprints can be randomly spaced within the 7 degree telescope field-of-view, constrained only by the operating frequency of the ND:YAG Q-switched laser (500 Hz). A significant innovation of the LVIS altimeter is that all ranging, waveform recording, and range gating are performed using a single digitizer, clock base, and detector. A portion of the outgoing laser pulse is fiber-optically fed into the detector used to collect the return signal and this entire time history of the outgoing and return pulses is digitized at 500 Msamp/sec. The ground return is then located using software digital signal processing, even in the presence of visibly opaque clouds. The surface height distribution of all reflecting surfaces within the laser footprint can be determined, for example, tree height and ground elevation. To date, the LVIS system has been used to monitor topographic change at Long Valley caldera, CA, as part of NASA's Topography and Surface Change program, and to map tree structure and sub-canopy topography at the La Selva Biological Research Station in Costa Rica, as part of the pre-launch calibration activities for the VCL mission. We present results that show the laser altimeter consistently and accurately maps surface topography, including sub-canopy topography, and vegetation height and structure. These results confirm the measurement concept of VCL and highlight the benefits of airborne prototypes of spaceborne instruments.

Bryan, J.↗
NASA NTRS1999

High Efficiency End-Pumped Ho:Tm:YLF Disk Amplifier

Space based coherent lidar for global wind measurement requires an all solid state laser system with high energy, high efficiency and narrow linewidth that operates in the eye safe region. A Q-switched, diode pumped Ho:Tm:YLF 2 micrometer laser with output energy of as much as 125 mJ at 6 Hz with an optical-to-optical efficiency of 3% has been reported. Single frequency operation of the laser was achieved by injection seeding. The design of this laser is being incorporated into NASA's SPARCLE (SPAce Readiness Coherent Lidar Experiment) wind lidar mission. Laser output energy ranging from 500 mJ to 2 J is required for an operational space coherent lidar. We previously developed a high energy Ho:Tm:YLF master oscillator and side pumped power amplifier system and demonstrated a 600-mJ single frequency pulse at a repetition rate of 10 Hz. Although the output energy is high, the optical-to-optical efficiency is only about 2%. Designing a high energy, highly efficient, conductively cooled 2-micrometer laser remains a challenge. In this paper, the preliminary result of an end-pumped amplifier that has a potential to provide a factor 3 of improvement in the system efficiency is reported.

Yu, Jirong↗
NASA NTRS2000

Photon-Counting Microlaser Rangers, Transponders, and Altimeters

Unlike current manned systems, NASA's next generation SLR2000 Satellite Laser Ranging (SLR) station is fully autonomous. eye-safe, relatively compact and inexpensive. and, during daytime tracking operates at signal-to-noise ratios several orders of magnitude below unity. Tiny, passively Q-switched microlasers generate ultra-short pulses with output energies on the order of 100 micron-J at few kHz rates to achieve mm-level ranging precision to satellite altitudes of 20,000 km. Special ranging receivers, combined with Poisson statistical analysis of the received photon distribution, enable the system to rapidly and reliably identify and extract the single photon laser echoes from the solar background. The enhanced rate of return, combined with a uniform signal strength, can actually drive down both systematic and random range errors. The new SLR2000 technology has already spawned exciting new applications. Compact microlaser altimeters, capable of mapping the surface of a planet or other celestial body at multikilohertz rates, is one such application, and a high altitude, airborne version is currently being developed under NASA's Instrument Incubator Program. Interplanetary microlaser transponders would be capable of performing decimeter ranging or subnanosecond time transfer to spacecraft throughout the inner Solar System. resulting in improved knowledge of planetary motions and liberations and enhanced General Relativity experiments.

Degnan, John J.↗
NASA NTRS2000

Photon-Counting Multikilohertz Microlaser Altimeters for Airborne and Spaceborne Topographic Measurements

We consider the optimum design of photon-counting microlaser altimeters operating from airborne and spaceborne platforms under both day and night conditions. Extremely compact Q-switched microlaser transmitters produce trains of low energy pulses at multi-kHz rates and can easily generate subnanosecond pulse-widths for precise ranging. To guide the design, we have modeled the solar noise background and developed simple algorithms, based on Post-Detection Poisson Filtering (PDPF), to optimally extract the weak altimeter signal from a high noise background during daytime operations. Practical technology issues, such as detector and/or receiver dead times, have also been considered in the analysis. We describe an airborne prototype, being developed under NASA's instrument Incubator Program, which is designed to operate at a 10 kHz rate from aircraft cruise altitudes up to 12 km with laser pulse energies on the order of a few microjoules. We also analyze a compact and power efficient system designed to operate from Mars orbit at an altitude of 300 km and sample the Martian surface at rates up to 4.3 kHz using a 1 watt laser transmitter and an 18 cm telescope. This yields a Power-Aperture Product of 0.24 W-square meter, corresponding to a value almost 4 times smaller than the Mars Orbiting Laser Altimeter (0. 88W-square meter), yet the sampling rate is roughly 400 times greater (4 kHz vs 10 Hz) Relative to conventional high power laser altimeters, advantages of photon-counting laser altimeters include: (1) a more efficient use of available laser photons providing up to two orders of magnitude greater surface sampling rates for a given laser power-telescope aperture product; (2) a simultaneous two order of magnitude reduction in the volume, cost and weight of the telescope system; (3) the unique ability to spatially resolve the source of the surface return in a photon counting mode through the use of pixellated or imaging detectors; and (4) improved vertical and transverse spatial resolution resulting from both (1) and (3). Furthermore, because of significantly lower laser pulse energies, the microaltimeter is inherently more eyesafe to observers on the ground and less prone to internal optical damage, which can terminate a space mission prematurely.

Degnan, John J.↗