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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 NTRS2008

Laser Sounder for Measuring Atmospheric CO2 Concentrations: Progress Toward Ascends

The next generation of space-based, active remote sensing instruments for measurement of tropospheric CO2 promises a capability to quantify global carbon sources and sinks at regional scales. Active (laser) methods will extend CO2 measurement coverage in time, space, and perhaps precision such that the underlying mechanisms for carbon exchange at the surface can be understood with .sufficient detail to confidently project the future of carbon-climate interaction and the influence of remediative policy actions. The recent Decadal Survey for Earth Science by the US National Research Council has recommended such a mission called the Active Sensing of CO2 Emissions over Nights, Days, and Seasons (ASCENDS) for launch in 2013-2016. We have been developing a laser technique for measurement of tropospheric CO2 for a number of years. Our immediate goal is to develop and demonstrate the method and instrument technology that will permit measurements of the CO2 column abundance over a horizontal path and from aircraft at the few-ppmv level. Our longer-term goal is to demonstrate the required capabilities of the technique, develop a space mission approach, and design the instrument for an ASCENDS-type mission. Our approach is to use a dual channel laser absorption spectrometer (i.e., differential absorption in altimeter mode), which continuously measures from a near-polar circular orbit. We use several co-aligned tunable fiber laser transmitters allowing simultaneous measurement of the absorption from a CO2 line in the 1570 nm band, O2 extinction in the oxygen A-band (near 765 nm), and aerosol backscatter in the same measurement path. We measure the energy of the laser echoes at nadir reflected from land and water surfaces, day and night. The lasers have spectral widths much narrower than the gas absorption lines and are turned on and off the selected CO2 and O2 lines at kHz rates. The gas extinction and column densities for the CO2 and O2 gases are estimated from the ratio of the on and off-line singnals via the DIAL technique. We used pulsed laser signals, photon counting detectors, and time gating to isolate the laser returns from the surface, and to reject photons scattered from thin clouds and aerosols. High signal-to-noise ratios are required and the CO2 estimates can be sensitive to small drifts or other errors in the instrument, so the absorption estimates need to be quite stable for hours. We have constructed a breadboard version of the CO2 sensor that uses a low power fiber laser and a 20 cm diameter telescope. We have used it to make measurements of CO2 absorption in the laboratory and over 200-m to 2-km long open horizontal paths. These have been done in several sessions extending over multiple days, which allows us to assess the measurement stability and to compare absorption variations to readings from an external in situ CO2 sensor. We have also calculated characteristics of the technique for space including its expected measurement performance for different modulation types, and have performed an initial space mission accommodation study. We sill describe these results in the presentation.

Abshire, J. B.↗
NASA NTRS1975

Tunable lasers and their application in analytical chemistry

The impact that laser techniques might have in chemical analysis is examined. Absorption, scattering, and heterodyne detection is considered. Particular emphasis is placed on the advantages of using frequency-tunable sources, and dye solution lasers are regarded as the outstanding example of this type of laser. Types of spectroscopy that can be carried out with lasers are discussed along with the ultimate sensitivity or minimum detectable concentration of molecules that can be achieved with each method. Analytical applications include laser microprobe analysis, remote sensing and instrumental methods such as laser-Raman spectroscopy, atomic absorption/fluorescence spectrometry, fluorescence assay techniques, optoacoustic spectroscopy, and polarization measurements. The application of lasers to spectroscopic methods of analysis would seem to be a rewarding field both for research in analytical chemistry and for investments in instrument manufacturing.

Steinfeld, J. I.↗
NASA NTRS1981

Progress of the LASSO experiment

The LASSO (Later Synchronisation from Stationary Orbit) experiment, designed to demonstrate the feasibility of achieving time synchronization between remote atomic clocks with an accuracy of one nanosecond or better by using laser techniques for the first time is described. The experiment uses groundbased laser stations and the SIRIO-2 geostationary satellite to be launched towards the end of 1981. The qualification of the LASSO on-board equipment is discussed with a brief description of the electrical and optical test equipment used. The progress of the operational organization is included.

Serene, B. E. H.↗
NASA NTRS1986

Lidar stratospheric ozone measurements at the observatoire de Haute Provence (France)

Strastospheric ozone monitoring is of particular importance to confirm present day theories predicting a maximal ozone depletion, due to chlorofluorocarbon emission, in the 35 to 45 km altitude range. Measurements presently rely on both ground based and satellite-borne passive experiments. Such systems have been recently shown to have intrinsic limitations mainly due to atmospheric aerosol presence and calibration problems. During the last few years, active lidar profiling of the ozone vertical distribution by the Differential Absorption Laser technique (DIAL) in the UV wavelength range has been developed using two different laser sources: a Nd-YAG pumped dye laser which enables a large tuning range of the UV emitted wavelengths; and exciplex laser sources using xenon chloride as an active medium and emitting at 308 nm, the off wavelength being usually generated by Raman shifting techniques. Advantages and limitations of using both of these systems are briefly discussed.

Godin, S.↗
NASA NTRS1989

Test techniques for cryogenic wind tunnels

Some of the testing techniques developed for transonic cryogenic tunnels are presented. Techniques are emphasized which required special development or were unique because of the opportunities offered by cryogenic operation. Measuring the static aerodynamic coefficients normally used to determine component efficiency is discussed. The first topic is testing of two dimensional airfoils at transonic Mach numbers and flight values of Reynolds number. Three dimensional tests of complete configurations and sidewall mounted wings are also described. Since flight Reynolds numbers are of interest, free transition must be allowed. A discussion is given of wind tunnel and model construction effects on transition location. Time dependent phenomena, fluid mechanics, and measurement techniques are examined. The time dependent, or unsteady, aerodynamic test techniques described include testing for flutter, buffet, and oscillating airfoil characteristics. In describing non-intrusive laser techniques, discussions are given regarding optical access, seeding, forward scatter lasers, two-spot lasers, and laser holography. Methods of detecting transition and separation are reported and a new type of skin friction balance is described.

Lawing, Pierce L.↗
NASA NTRS1983

Measurements and predictions for nonevaporating sprays in a quiescent environment

Yule et al. (1982) have conducted a study of vaporizing sprays with the aid of laser techniques. The present investigation has the objective to supplement the measurements performed by Yule et al., by considering the limiting case of a spray in a stagnant environment. Mean and fluctuating velocities of the continuous phase are measured by means of laser Doppler anemometry (LDA) techniques, while Fraunhofer diffraction and slide impaction methods are employed to determine drop sizes. Liquid fluxes in the spray are found by making use of an isokinetic sampling probe. The obtained data are used as a basis for the evaluation of three models of the process, including a locally homogeneous flow (LHF) model, a deterministic separated flow (DSF) model, and a stochastic separated flow (SSF) model. It is found that the LHF and DSF models do not provide very satisfactory predictions for the test sprays, while the SSF model does provide reasonably good predictions of the observed structure.

Solomon, A. S. P.↗
NASA NTRS1984

Laser balancing system for high material removal rates

A laser technique to remove material in excess of 10 mg/sec from a spinning rotor is described. This material removal rate is 20 times greater than previously reported for a surface speed of 30 m/sec. Material removal enhancement was achieved by steering a focused laser beam with moving optics to increase the time of laser energy interaction with a particular location on the circumferential surface of a spinning rotor. A neodymium:yttrium aluminum garnet (Nd:YAG) pulse laser was used in this work to evaluate material removal for carbon steel, 347 stainless steel, Inconal 718, and titanium 6-4. This technique is applicable to dynamic laser balancing.

Jones, M. G.↗
NASA NTRS1998

Stable Isotope Laser Spectrometer for Exploration of Mars

On Earth, measurements of the ratios of stable carbon isotopes have providet much information about geological and biological processes. For example, fractionation of carbon occur in biotic processes and the retention of a distinctive 2-4% contrast in C-13/C-12 between organic carbon and carbonates in rocks as old as 3.8 billion years constitutes some of the firmest evidence for the antiquity of life on the Earth. We have developed a prototype tunable diode laser spectrometer which demonstrates the feasibility of making accurate in situ isotopic ratio measurements on Mars. This miniaturized instrument, with an optical path length of 10 cm should be capable of making accurate C-13/C-12 and N-15/N-14 measurements. Gas samples for measurement are to be produced by pyrolysis using soil samples as small as 50 mg. Measurements of C-13/C-12, O-18/O-16 and N-15/N-14 have been made to a precision of better than 0.1%, and various other isotopes are feasible. This laser technique, which relies on the extremely narrow emission linewidth of tunable diode lasers (less than 0.001/ cm),has favorable features in comparison to mass spectrometry, the standard method of accurate isotopic ratio measurement. The miniature instrument could be ready to deploy c 2003 or other Mars lander missions.

Sauke, Todd B.↗
NASA NTRS1990

New Space Domain Processing Technique for Pulsed Laser Velocimetry

A new and fast data processing technique for pulsed-laser-velocimetry data is described. A simplified cross correlation algorithm was developed which uses the time history information of the recorded particle images. It is shown that, the use of the particle time history information (which can be obtained using an electronic camera to record the particle exposures) facilitates high speed processing and unambiguous velocity vector information. It was found that a complex convection vortex flow can be recorded and completely processed in less than 2 min on a personal computer, producing a two-dimensional map of the flow field containing over 300 velocity vectors.

Wernet, Mark P.↗
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.↗
DOE OSTI2025

Ink-based laser powder bed fusion of barium titanate

Barium titanate (BTO) is a lead-free functional ceramic that is widely used in sensors, transducers, and actuators. The increasing demand for complex geometries and quick design iterations motivates the use of additive manufacturing techniques. Laser powder bed fusion (L-PBF) additive manufacturing technique enables the net-shape or near-net-shape fabrication of metals and alloys. Ceramic L-PBF remains challenging due to their high melting temperature. Here, to address this challenge, a nanoparticle ink feedstock was incorporated into the L-PBF process to allow low power melting of BTO. Key print parameters (i.e. laser power, scanning speed, and hatching spacing) were optimized to fabricate millimeter-scale BTO parts. The printed BTO samples possessed an inhomogeneous equiaxed-columnar-cellular microstructure. Semiconducting current-voltage behavior was observed in as-printed samples, which was attributed to the creation of oxygen vacancies. The piezoelectric d 33 coefficient was measured to be 4.6 pC/N.

Dielectrics↗
DOE OSTI2024

Highly cascaded first-order fiber Bragg gratings in highly multimode optical fibers for distributed temperature sensing under harsh environment conditions

This study presents a pioneering technique for fabricating highly cascaded first-order fiber Bragg gratings (FBGs) using a femtosecond laser-assisted point-by-point inscription method in highly multimode optical fibers, specifically Sapphire crystalline fiber, and pure silica coreless fiber. Notably, it marks the first successful demonstration of a distributed array comprising 10 FBGs within highly multimode fibers. This achievement is facilitated by a high-power laser technique that yields larger reflectors characterized by a Gaussian intensity profile. These first-order FBGs offer various advantages, including enhanced reflectivity, reduced fabrication time, and simplified spectral characteristics, enhancing their accessibility for interpretation when contrasted with higher-order FBGs. In addition to that it encompasses a comprehensive analysis of the robustness and efficacy of these FBGs, with particular emphasis on their ability to endure extreme temperatures. These FBGs demonstrate an advantageous capability for localized multi-point temperature monitoring, reaching temperatures up to 1500°C with sapphire crystalline fiber and 1100°C with pure silica coreless fiber. This resilience makes them suitable for deployment in harsh environmental conditions. This innovative approach substantially broadens the potential applications of highly multimode optical fibers, particularly in the arena of sensing and communication, where challenges related to thermal gradients and harsh environments prevail. Furthermore, these groundbreaking first-order FBGs signify a substantial advancement in the realm of distributed temperature sensing, offering supreme capabilities for temperature monitoring and signal stability. As such, our work holds the promise of a substantial impact on industries and applications that demand unwavering reliability under extreme conditions.

47 OTHER INSTRUMENTATION↗
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↗
DOE OSTI2023

High frequency beam oscillation keyhole dynamics in laser melting revealed by in-situ x-ray imaging

The metal additive manufacturing industry is actively developing instruments and strategies to enable higher productivity, optimal build quality, and controllable as-built microstructure. A beam controlling technique, laser oscillation has shown potential in all these aspects in laser welding; however, few attempts have been made to understand the underlying physics of the oscillating keyholes/melt pools which are the prerequisites for these strategies to become a useful tool for laser-based additive manufacturing processes. Here, to address this gap, we utilized a synchrotron-based X-ray operando technique to image the dynamic keyhole oscillation in Ti-6Al-4V using a miniature powder bed fusion setup. We found good agreement between the experimental observations and simulations performed with a validated Lattice Boltzmann multiphysics model. The study revealed the continuous and periodic fluctuations in the characteristic keyhole parameters that are unique to the oscillating laser beam processing and responsible for the chevron pattern formation at solidification. In particular, despite the intrinsic longer-range fluctuation, the oscillating technique displayed potential for reducing keyhole instability, mitigating porosity formation, and altering surface topology. These insights on the oscillating keyhole dynamics can be useful for the future development and application of this technique.

36 MATERIALS SCIENCE↗
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.↗