SEARCH · Search NASA

Results for “LASER SPECTROSCOPY”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5

All sources NASA NTRS DOE OSTI

NASA NTRS1976

Monitoring spacecraft atmosphere contaminants by laser absorption spectroscopy

Laser-based spectrophotometric methods which have been proposed for the detection of trace concentrations of gaseous contaminants include Raman backscattering (LIDAR) and passive radiometry (LOPAIR). Remote sensing techniques using laser spectrometry are presented and in particular a simple long-path laser absorption method (LOLA), which is capable of resolving complex mixtures of closely related trace contaminants at ppm levels is discussed. A number of species were selected for study which are representative of those most likely to accumulate in closed environments, such as submarines or long-duration manned space flights. Computer programs were developed which will permit a real-time analysis of the monitored atmosphere. Estimates of the dynamic range of this monitoring technique for various system configurations, and comparison with other methods of analysis, are given.

Steinfeld, J. I.↗

NASA NTRS1983

Laser optogalvanic spectroscopy of molecules

In laser optogalvanic (LOG) spectroscopy, a tunable laser is used to probe the spectral characteristics of atomic or molecular species within an electrical discharge in a low pressure gas. Optogalvanic signals arise when the impedance of the discharge changes in response to the absorption of laser radiation. The technique may, therefore, be referred to as impedance spectroscopy. This change in impedance may be monitored as a change in the voltage across the discharge tube. LOG spectra are recorded by scanning the wavelength of a chopped CW dye laser while monitoring the discharge voltage with a lock-in amplifier. LOG signals are obtained if the laser wavelength matches a transition in a species present in the discharge (or flame), and if the absorption of energy in the laser beam alters the impedance of the discharge. Infrared LOG spectroscopy of molecules has been demonstrated and may prove to be the most productive application in the field of optogalvanic techniques.

Webster, C. R.↗

DOE OSTI2020

Laser-Plasma Spectroscopy of Hydroxyl with Applications

This article discusses laser-induced laboratory-air plasma measurements and analysis of hydroxyl (OH) ultraviolet spectra. The computations of the OH spectra utilize line strength data that were developed previously and that are now communicated for the first time. The line strengths have been utilized extensively in interpretation of recorded molecular emission spectra and have been well-tested in laser-induced fluorescence applications for the purpose of temperature inferences from recorded data. Moreover, new experiments with Q-switched laser pulses illustrate occurrence of molecular recombination spectra for time delays of the order of several dozen of microseconds after plasma initiation. The OH signals occur due to the natural humidity in laboratory air. Centrifugal stretching of the Franck-Condon factors and r-centroids are included in the process of determining the line strengths that are communicated as a Supplementary File. Laser spectroscopy applications of detailed OH computations include laser-induced plasma and combustion analyses, to name but two applications. This work also includes literature references that address various diagnosis applications.

47 OTHER INSTRUMENTATION↗

NASA NTRS2001

Trace gas absorption spectroscopy using laser difference-frequency spectrometer for environmental application

A widely tunable infrared spectrometer based on difference frequency generation (DFG) has been developed for organic trace gas detection by laser absorption spectroscopy. On-line measurements of concentration of various hydrocarbons, such as acetylene, benzene, and ethylene, were investigated using high-resolution DFG trace gas spectroscopy for highly sensitive detection.

Non-NASA Center↗

NASA NTRS1974

Laser photoluminescence spectroscopy of photodissociation fragments

Laser induced photoluminescence spectroscopy has been used to study the energy partitioning among CN fragments produced by the photodissociation of C2N2. The CN radicals are produced in both the A 2Pi and the X 2Sigma+ states. The A state is formed primarily in the nu-prime = 0 level, and the X state is formed in the lower vibrational levels. Since the photodissociation process does not produce the maximum amount of vibrational excitation in the CN fragments, it is suggested that the excess energy goes into either translational and/or rotational excitation of the CN.

Jackson, W. M.↗

DOE OSTI2023

Xenon Detection Using Double-Pulse Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy has been proposed as a diagnostic tool for fuel failure monitoring in helium-cooled fast reactor designs. Here, we show preliminary results which indicate that using double-pulse laser induced breakdown spectroscopy, a sub-ppm sensitivity for xenon in a helium ambient can be achieved. We additionally propose future studies which could help elucidate the mechanisms which lead to the observed signal enhancement.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

NASA NTRS2010

Multivariate Methods for Prediction of Geologic Sample Composition with Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) uses pulses of laser light to ablate a material from the surface of a sample and produce an expanding plasma. The optical emission from the plasma produces a spectrum which can be used to classify target materials and estimate their composition. The ChemCam instrument on the Mars Science Laboratory (MSL) mission will use LIBS to rapidly analyze targets remotely, allowing more resource- and time-intensive in-situ analyses to be reserved for targets of particular interest. ChemCam will also be used to analyze samples that are not reachable by the rover's in-situ instruments. Due to these tactical and scientific roles, it is important that ChemCam-derived sample compositions are as accurate as possible. We have compared the results of partial least squares (PLS), multilayer perceptron (MLP) artificial neural networks (ANNs), and cascade correlation (CC) ANNs to determine which technique yields better estimates of quantitative element abundances in rock and mineral samples. The number of hidden nodes in the MLP ANNs was optimized using a genetic algorithm. The influence of two data preprocessing techniques were also investigated: genetic algorithm feature selection and averaging the spectra for each training sample prior to training the PLS and ANN algorithms. We used a ChemCam-like laboratory stand-off LIBS system to collect spectra of 30 pressed powder geostandards and a diverse suite of 196 geologic slab samples of known bulk composition. We tested the performance of PLS and ANNs on a subset of these samples, choosing to focus on silicate rocks and minerals with a loss on ignition of less than 2 percent. This resulted in a set of 22 pressed powder geostandards and 80 geologic samples. Four of the geostandards were used as a validation set and 18 were used as the training set for the algorithms. We found that PLS typically resulted in the lowest average absolute error in its predictions, but that the optimized MLP ANN and the CC ANN often gave results comparable to PLS. Averaging the spectra for each training sample and/or using feature selection to choose a small subset of wavelengths to use for predictions gave mixed results, with degraded performance in some cases and similar or slightly improved performance in other cases. However, training time was significantly reduced for both PLS and ANN methods by implementing feature selection, making this a potentially appealing method for initial, rapid-turn-around analyses necessary for Chemcam's tactical role on MSL. Choice of training samples has a strong influence on the accuracy of predictions. We are currently investigating the use of clustering algorithms (e.g. k-means, neural gas, etc.) to identify training sets that are spectrally similar to the unknown samples that are being predicted, and therefore result in improved predictions

Morris, Richard↗

NASA NTRS1991

Laser stark spectroscopy of SO2 with the HCN laser

The far infrared laser Stark spectrum of SO2 was investigated using the 337-micron line of the HCN laser. Two distinct families, one originating at low field and the other at high field, were observed. The high field transition is identified. A significant fourth-order Stark shift was observed for this transition in the presence of a large second-order Stark shift. The zero-field frequency of the assigned transition was obtained by accounting for the fourth-order contribution.

Sarker, J. C.↗

DOE OSTI2025

Analysis of Off-Gas Streams from Small- and Large-Scale Sparging Salt Vessels using Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is being developed as an analytical monitoring tool for molten salt reactor (MSR) systems. A mobile LIBS platform was configured on a small-scale salt vessel (~100 g of salt) and then transported 0.6 km to successfully monitor an engineering-scale pumped salt loop (~100 kg of salt). Several studies on monitoring salt aerosols, hydrogen isotopes, and noble gases were performed on the small-scale system. All these studies were then implemented for monitoring various tests on the engineering-scale loop. Aerosolized salts from both the storage tank and pump bowl were monitored using LIBS to assess bulk salt analyte ratios (Mg, Na, K) and evaluate impurities (H, O, Ca). In addition to monitoring salt aerosols, LIBS was used in tandem with a residual gas analyzer (RGA) and a Raman spectroscopy system to detect hydrogen isotopes as they were sparged through and subsequently depleted from the loop storage tank. Lastly, a similar test with noble gases (100 ppm Kr, 1000 ppm Xe) was performed, in which LIBS demonstrated a faster response than the RGA used in-line. The tests and results are summarized in this report with detailed publications to follow. Key takeaways are listed in the conclusion of the report.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2021

Laser ablation spectrometry for studies of uranium plasmas, reactor monitoring, and spent fuel safety

Nuclear security is one of the defining challenges of our time. Nuclear threats range from deliberate dispersal of radioactive material to contaminate the vital infrastructure to diversion and smuggling of special nuclear material for clandestine nuclear programs and nuclear terrorism, respectively. There is an associated need to develop and sustain the nuclear forensics capabilities, which requires the understanding of complex processes that occur in plasmas of nuclear materials. The area of nuclear safety has seen a resurgence of public interest, and there is a concomitant need to safely store used nuclear fuel and detect structural material failure in nuclear power systems, especially in innovative reactor designs envisioned for future adoption. Laser-produced plasmas are complicated extreme environments that can generate intense and rich, highly specific signatures of nuclear and radiological materials, which can then be explored in a wide range of applications. They include interdiction and rapid detection of nuclear materials, including their isotopic composition, detection over long distances, laboratory simulation of weapons effects, monitoring the condition of structural materials in dry cask storage containers, and novel instrumentation for nuclear power systems. We present a compilation of recent representative examples of the application of laser spectroscopy, and laser-induced breakdown spectroscopy in particular, to nuclear safety and security problems. A case is made that spectroscopic techniques based on laser-produced plasmas offer complementary, and sometimes unique, capabilities that motivate the continued exploration of their efficient production and understanding of the signatures they produce

(020.3260) Isotope shifts, (140.3440) Laser-induce↗

NASA NTRS1983

Infrared laser optogalvanic spectroscopy of molecules

Infrared laser optogalvanic spectra of portions of the NH3 nu3 band at 9.5 microns and the NO2 nu3 band at 6.2 microns have been recorded using CW tunable diode lasers to probe dc electrical discharges in pure NH3 and an NO2/He gas mixture. Two contributions to the optogalvanic signal are identified: one which corresponds to an increase in discharge impedance and is seen only for irradiation of the negative glow region; and a second which corresponds to a decrease in discharge impedance and is seen for irradiation of all other discharge regions and the volume outside the interelectrode region. Mechanisms by which infrared laser irradiation may cause impedance changes in the discharge are proposed.

Webster, C. R.↗

NASA NTRS1983

Tunable diode laser optogalvanic spectroscopy of molecules

The laser optogalvanic (LOG) technique for studying molecular spectra has been extended for the first time to the infrared wavelength region. Portions of the NH3 nu-2 band at 9.5 microns and the NO2 nu-3 band at 6.2 microns have been recorded at Doppler-limited resolution using CW tunable diode lasers to probe dc electrical discharges in pure NH3 and an NO2/He gas mixture. Using adjustable electrode positions and an orthogonal geometry between the probe laser and the discharge axis, two contributions to the optogalvanic signal are identified: one which corresponds to an increase in discharge impedance and is seen only for irradiation of the negative glow region; and a second which corresponds to a decrease in discharge impedance and is seen for irradiation of all other discharge regions.

Webster, C. R.↗

NASA NTRS2013

Monitoring Temperature in High Enthalpy Arc-heated Plasma Flows using Tunable Diode Laser Absorption Spectroscopy

A tunable diode laser sensor was designed for in situ monitoring of temperature in the arc heater of the NASA Ames IHF arcjet facility (60 MW). An external cavity diode laser was used to generate light at 777.2 nm and laser absorption used to monitor the population of electronically excited oxygen atoms in an air plasma flow. Under the assumption of thermochemical equilibrium, time-resolved temperature measurements were obtained on four lines-of-sight, which enabled evaluation of the temperature uniformity in the plasma column for different arcjet operating conditions.

Martin, Marcel Nations↗

DOE OSTI2021

Chirped laser dispersion spectroscopy for spectroscopic chemical sensing with simultaneous range detection

Spectroscopic chemical detection requires knowledge or determination of an optical path for accurate quantification of path-integrated concentration of species. Continuous- wave-laser-based spectroscopic systems operating in an open integrated-path remote sensing configuration are usually not equipped for optical path determination. Here we demonstrate a measurement technique capable of simultaneous spectroscopic chemical quantification and range finding. Here, the range-finding functionality is implemented with chirped laser dispersion spectroscopy. The methodology is potentially useful for remote chemical sensing in a hard-target LIDAR configuration and for automatic calibration of gas cells with unknown or varying lengths.

03 NATURAL GAS↗

NASA NTRS1988

Diode laser harmonic spectroscopy applied to in situ measurements of atmospheric trace molecules

With the emergence of lead-salt diode laser technology, a broad and important IR spectral region, roughly 3-30 microns, became accessible to tunable laser spectroscopy. More recent advances in fabrication techniques have provided experimenters with relatively high power quasi-single-mode high-temperature lasers that are readily adapted to compact automated instruments for field experiments. An especially attractive capability of diode lasers is the ease of using them for simultaneous multiconstituent sampling in the atmosphere. This paper presents a summary description of field instruments for atmospheric research which employ diode lasers and second-harmonic detection. Representative results obtained with some of these instruments are presented.

Loewenstein, Max↗

NASA NTRS1983

dc discharge cell for laser optogalvanic spectroscopy

A dc electrical discharge cell for laser optogalvanic spectroscopy has been designed and tested. Signal optimization is achieved through the use of adjustable electrode positions and an orthogonal geometry between the probe laser and the discharge axis. Results are presented for visible dye laser and infrared diode laser studies of selected neutral, radical, and ion species.

Webster, C. R.↗

DOE OSTI2021

Feed-forward spectral calibration methodology for line-scanned tunable laser absorption spectroscopy

A generalized feed-forward method for accurate tunable laser absorption spectroscopy includes generating a laser beam. The generated laser beam is directed down a reference path and a test/sample path. One or more parameters are extracted from the reference path. The one or more parameters, extracted from the reference path, are used as feed-forward, to adjust spectral analysis of the test/sample path to detect a composition and/or concentration of an analyte gas within the test/sample path. The extraction of the one or more parameters from the reference path and the spectral analysis of the test/sample path are performed substantially concurrently.

Green, William↗

NASA NTRS2016

Space Launch System Base Heating Test: Tunable Diode Laser Absorption Spectroscopy

This paper describes the Tunable Diode Laser Absorption Spectroscopy (TDLAS) measurement of several water transitions that were interrogated during a hot-fire testing of the Space Launch Systems (SLS) sub-scale vehicle installed in LENS II. The temperature of the recirculating gas flow over the base plate was found to increase with altitude and is consistent with CFD results. It was also observed that the gas above the base plate has significant velocity along the optical path of the sensor at the higher altitudes. The line-by-line analysis of the H2O absorption features must include the effects of the Doppler shift phenomena particularly at high altitude. The TDLAS experimental measurements and the analysis procedure which incorporates the velocity dependent flow will be described.

Parker, Ron↗