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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Laser remote sensing techniques

The properties and advantages of remote sensing lasers are discussed. The theory of nonresonant techniques, which is based on the lidar equation and elastic backscatter, and their applications to aerosol and meteorological parameters are examined. The characteristics and applications of the differential absorption lidar technique, the fluorescence technique, and Raman scattering are described. The use of a laser heterodyne radiometer and fiber optics for remote sensing is studied. Future developments in the field of remote sensing, in particular the improvement of laser sources, the fabrication of compact remote sensing instruments, and space-borne applications for lidar, are considered.

Grant, William B.↗
NASA NTRS2015

Visualization of a Sweeping Jet by Laser Speckle Retro-reflective Background Oriented Schlieren

Sweeping jet actuators are currently being studied as a method of active flow control to increase the performance of wings and tails. Computational Fluid Dynamics simulations show that the jet does not sweep at a constant rate, instead spending more time at the minimum and maximum of its extent. As part of a test done to provide dynamic flow measurements for Computation Fluid Dynamics validation in NASA Ames Fluid Mechanics Lab, Particle Image Velocimetry (PIV) was performed on a single sweeping jet actuator designed by NASA and Boeing that was inset in a small airfoil. However, even at low jet pressures, the PIV could not be acquired at high enough frequencies to both spatially and temporally resolve the stickiness of the jet motion. Therefore, a small portion of the PIV laser was picked off and used to acquire flow visualization at higher frequencies through a new technique, laser speckle Retroreflective Background Oriented Schlieren (RBOS).

sweeping jet actuator↗
NASA NTRS2021

In Situ Mg/Ca Measurements on Foraminifera: Comparison Between Laser Ablation Inductively Coupled Plasma Mass Spectrometry and Wavelength-Dispersive X-Ray Spectroscopy by Electron Probe Microanalyzer

We present a comparison of two different techniques: Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and wavelength-dispersive X-Ray Spectroscopy by electron probe microanalyzer (EPMA) for obtaining Mg/Ca ratios in individual foraminifera shells. The goal is to assess the use of EPMA as an alternative technique for Mg/Ca analyses of single foraminiferal calcite shells. Foraminifera obtained from sediments (benthic, Uvigerina spp.) and from plankton tows (planktonic, Orbulina universa) were analyzed. All specimens were prepared in epoxy mounts and exposed in cross-section such that multiple high-resolution analyses could be completed on the shells using both techniques. We examined our data using statistical methods designed for the assessment and comparison of measurement techniques. In the case of Uvigerina, the mean difference for ratios obtained using EPMA and LA-ICP-MS is very small (−0.046 mmol mol−1) and scale independent. The Limits of Agreement (LoA, the standard deviation of the bias plus the mean bias) is [−0.315, 0.223] mmol mol−1. For samples with ratios lower than 13 mmol mol−1, we found a mean EPMA–LA-ICP-MS bias of −2.44 mmol mol−1 and a corresponding LoA of [−3.85, −1.04] mmol mol−1. For ratios higher than 13 mmol mol−1, there appears to be a scale dependent bias, meaning that the EPMA measured ratios become progressively larger than those of LA-ICP-MS as the Mg/Ca ratio increases, so the mean bias and LoA metrics are not meaningful. Results indicate that it is possible to use EPMA to collect Mg/Ca data, if the ratios are lower than ∼13 mmol mol−1.

EPMA↗
NASA NTRS2021

Data Processing of Miniaturized Laser Heterodyne Radiometer (mini-LHR) Ground Instrument Retrievals

The Miniaturized Laser Heterodyne Radiometer (mini-LHR) is a passive ground instrument that observes the mole fraction of carbon dioxide (CO) and methane (CH)in the atmospheric column by measuring their absorption of sunlight at 1.6 microns. A laser heterodyne radiometer is similar in design to the super heterodyne radio receiver that is well known by ham radio enthusiasts. While not previously a commercial technique, laser heterodyne radiometers have a history of measuring atmospheric trace gases that started in the 1960s. With the commercial availability of inexpensive, low-power, thumbnail-sized lasers developed for the telecommunications industry, it was possible to miniaturize this technique and ultimately commercialize it. The mini-LHR has been under development at NASA GSFC since 2009. During that time, in addition to signicant technical improvements, processing has also evolved and been streamlined. Here we present details of the processing approach for raw mini-LHR data to produce 30- and 60-minute data products of CH and CO column mole fractions. Processing occurs in two general stages: a python-based pre-processing of raw data, followed by ingestion into a Planetary Spectrum Generator (PSG) retrieval algorithm. Raw data processing involves removal of outliers, correcting for changes in air mass throughout the day, averaging scans, and ultimately converting averaged scans into transmittance vs. wavelength. The PSG retrieval simulates a spectra for the time/day/location of the scan with meteorological inputs from Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) data set and then perturbs the concentrations of CO and CH to obtain a t based on an iterative least-squares curve fitting procedure.

Giancarlo Roberto Zambrano↗
NASA NTRS1994

A laser-based sizing/velocimetry technique to investigate the secondary atomization of aluminum gel propellants

A laser-based, forward-scatter diagnostic technique, employing a single laser sheet, has been developed to simultaneously measure the size and velocity of individual 10-150 micron droplets in a dilute polydisperse droplet stream (less than 1000 particles/cc) and to detect the presence of burning aluminum in these same droplets. Spectral emission from aluminum vapor in the 390-400 nm wavelength region is used as an indication of burning aluminum. The technique utilizes a 4-mm uniformly illuminated probe volume, eliminating trajectory-dependent particle sizing and size-dependent system detection bias. Particle sizing is based on a correlation of particle size with near-forward scattered light intensity. Calculations show average particle sizing variation to be within 3.5% over the expected range of refractive indices. Calibrations using a range of optical pinholes (10-100 micron) were used to verify the above sizing correlation.

Mueller, D. C.↗
NASA NTRSDate not supplied

Ultrashort Pulse Laser Surface Processing Techniques for Sterilization of Metal Surfaces for Planetary Protection

To prevent forward contamination from microbes aboard spacecraft intended to search for extraterrestrial life, there is a need for effective sterilization methods. However, current techniques are both time-consuming and expensive. For example, dry heat sterilization requires removal from the assembly site and several days of treatment. Furthermore, some components such as optics and electronics are not compatible with current sterilization techniques. Here, we report the latest results in our development of a novel femtosecond laser processing technique for the rapid sterilization of spacecraft hardware. Femtosecond lasers produce extremely high photon fluxes (10^29 photons/sec*cm^2, ~0.03 J/cm^2) in extremely short pulses, which can inactivate even stress-tolerant microbial spores with minimal damage to the spacecraft surface. Aluminum coupons were inoculated with specific densities of Bacillus subtilis bacterial endospores. These coupons were treated with various laser illumination parameters. Afterward, metal coupon samples were assayed for viable spores using a polyvinyl alcohol (PVA) peel, serial dilution, and plating for colony-forming units (CFU). Results indicate that with high enough energy density and pulse counts, most bacterial spores are inactivated with minimal damage to the metal. The sterilization is dependent on both the fluence and pulse count. In addition, femtosecond pulses are more effective than longer pulses for inactivation. These experiments have consistently achieved 4-log reduction in viable spores. Sterilization has been achieved on both flat metal coupons and non-flat surfaces with microchannels, with a slight reduction in sterilization efficiency on the uneven surface. The application of air flow during laser processing was also investigated as a way to remove spores that are dislodged from the surface by the laser illumination, which would contribute to the reduction of spacecraft bioburden. With laser processing technology rapidly evolving, our results support the possibility of an extremely rapid, in-situ surface sterilization method for use in spacecraft assembly clean rooms.

Kaleb McQuillan↗
NASA NTRS1987

Dual laser diode array emission coherently summed in an external cavity

The output power from two ten-element laser diodes arrays has been efficiently summed in an external cavity to obtain a coherent, continuous wave beam. In this technique, laser emission from each front surface antireflection coated diode array is stimulated by injection of emission from a second such array. This method was also applied to single-element diode lasers. The output beam characteristics such as spectral distribution, far-field and near-field beam patterns, and overall efficiency have been measured.

Hemmati, Hamid↗
NASA NTRS1981

Optical detection of pulsed surface particle displacements

The detection of acoustic surface wave pulses by a wideband differential interferometric laser technique which is insensitive to low frequency noise is described. System bandwidth is determined by the relationship between acoustic wavelength and the variable spacing between two laser probe beams focused on the solid surface which supports the waves. Theoretical sensitivity to surface displacement amplitude is equal to, or better than, that of other electrooptical techniques. Response to an ideal step function displacement is analyzed and experimental measurements of gated 2.5 MHz pulses generated on an aluminized pyrex plate are discussed. Potential application in the characterization of acoustic emission in composites is described.

Zerwekh, P. S.↗
NASA NTRS1982

Resonant Doppler velocimetry in supersonic nitrogen flow

The development of the Resonant Doppler Velocimeter (RDV) is discussed. It is a new nonintrusive laser technique for flow diagnosis. The RDV technique is applied to supersonic nitrogen flow with sodium atoms as tracer particles. The measurements are achieved by shining a tunable single frequency laser beam into the flow. The resonant absorption spectrum of the seeded species is determined by observing the fluorescence signal intensity as a function of excitation wavelength. By comparing the peak absorption wavelength with a reference frequency marker, the flow velocity along the excitation beam can be obtained through the Doppler shift relation. By fitting the spectrum with a theoretical line profile, the static temperature and pressure of the flow an be determined.

Cheng, S. W. S.↗
NASA NTRS1987

Comparison of experimental and computational techniques for plane mixing layers

In this paper, results from two experimental and two computational investigations of plane turbulent mixing layers are presented and compared. The experimental results include flow visualization data using the smoke laser technique and mean flow and turbulence measurements obtained with hot X-wires and a two-component LDV. Reasonably good agreement is found among these techniques, at least for turbulence quantities up to second order. Reynolds-averaged computations are successful at capturing the complete evolution of the mixing layer, including wake effects in the near field and approach to self-preservation in the far field. The two-dimensional vortex method shows excellent qualitative and quantitative agreement with measured data for the forced mixing layer. For the unforced layer, the results seem to indicate that a three-dimensional computation may be necessary.

Mehta, R. D.↗
NASA NTRS1981

Optical detection of pulsed surface particle displacements

The detection of acoustic surface wave pulses by a wideband differential interferometric laser technique which is insensitive to low frequency noise is described. System bandwidth is determined by the relationship between acoustic wavelength and the variable spacing between two laser probe beams focused on the solid surface which supports the waves. Response to an ideal step function displacement is analyzed and experimental measurements of gated 2.5 MHz pulses generated on an aluminized pyrex plate are discussed.

Zewekh, P. S.↗
NASA NTRS1991

A survey of laser lightning rod techniques

The work done to create a laser lightning rod (LLR) is discussed. Some ongoing research which has the potential for achieving an operational laser lightning rod for use in the protection of missile launch sites, launch vehicles, and other property is discussed. Because of the ease with which a laser beam can be steered into any cloud overhead, an LLR could be used to ascertain if there exists enough charge in the clouds to discharge to the ground as triggered lightning. This leads to the possibility of using LLRs to test clouds prior to launching missiles through the clouds or prior to flying aircraft through the clouds. LLRs could also be used to probe and discharge clouds before or during any hazardous ground operations. Thus, an operational LLR may be able to both detect such sub-critical electrical fields and effectively neutralize them.

Barnes, Arnold A., Jr.↗
NASA NTRS1985

An airborne lidar instrument for detection of OH using the technique of laser-induced fluorescence

Under suitable laboratory conditions, it has been demonstrated that the laser-induced fluorescence (LIF) measurement technique is sensitive enough to detect single atoms and molecules. This potential sensitivity has provided motivation for the development of this technique for ambient OH measurements. The present paper is concerned with an airborne lidar instrument for measuring OH concentration as used for the NASA GTE/CITE (Global Tropospheric Experiment/Chemical Instrumentation Test and Evaluation) intercomparison experiments during the fall of 1983 and the spring of 1984. A description is given of a working airborne instrument for measurements of OH in ambient air. The detection sensitivity demonstrated in the experiments should be sufficient for routine measurements in areas in which the OH concentration is in the range of high 1,000,000 molecule per cu cm or higher.

Davis, L. I., Jr.↗
NASA NTRS1999

Non-Intrusive Laser-Induced Imaging for Speciation and Patternation in High Pressure Gas Turbine Combustors

The next generation of was turbine combustors for aerospace applications will be required to meet increasingly stringent constraints on fuel efficiency, noise abatement, and emissions. The power plants being designed to meet these constraints will operate at extreme conditions of temperature and pressure, thereby generating unique challenges to the previously employed diagnostic methodologies. Current efforts at NASA Glenn Research Center (GRC) utilize optically accessible, high pressure flametubes and sector combustor rigs to probe, via advanced nonintrusive laser techniques, the complex flowfields encountered in advanced combustor designs. The fuel-air mixing process is of particular concern for lowering NO(x) emissions generated in lean, premixed engine concepts. Using planar laser-induced fluorescence (PLIF) we have obtained real-time, detailed imaging of the fuel spray distribution for a number of fuel injector over a wide range of operational conditions that closely match those expected in the proposed propulsion systems. Using a novel combination of planar imaging, of fuel fluorescence and computational analysis that allows an examination of the flowfield from any perspective, we have produced spatially and temporally resolved fuel-air distribution maps. These maps provide detailed insight into the fuel injection at actual conditions never before possible, thereby greatly enhancing the evaluation of fuel injector performance and combustion phenomena.

Locke, Randy J.↗