Laser-induced fluorescence in a molecular beam of iodine.
Argon ion laser passing through iodine molecular beam inducing resonance fluorescence usable for oscillation frequency stabilization of laser
Ezekiel, S.↗
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In situ detection of tropospheric OH, HO2, NO2, and NO by laser-induced fluorescence in detection chambers at reduced pressures
This report is a brief summary of the status of work on the grant entitled 'In situ detection of tropospheric OH, HO2, NO2, and NO by laser induced fluorescence in detection chambers at low pressures'. The first version of the instrument is essentially complete and operational for about six months, and we continue to make improvements on the instrument sensitivity and reliability. We are focusing our efforts on improving our understanding of the operating characteristics of the instrument - particularly the inlet transmission for OH and HO2, the exact character of the air flow around and within the instrument, and the efficiency of the chemical conversion of HO2 to OH. We are also in the process of converting this laboratory instrument into a field worthy instrument that we can take to remote sites for measurements.
Brune, William H.↗
Vacuum ultraviolet laser induced fluorescence on a Si atomic beam
A broadly applicable vacuum ultraviolet experiment is described for measuring radiative lifetimes of neutral and singly-ionized atoms in a beam environment to 5-percent accuracy using laser induced fluorescence. First results for neutral Si are reported.
O'Brian, T. R.↗
Environmental effects on laser-induced fluorescence spectra of natural waters
Laser fluorosensing can be used to monitor dissolved organic carbon (DOC), but analysis of the data can be hindered by several environmental phenomena. These phenomena include attenuation of the laser beam and differential attenuation of the fluorescence by the water column, variability in the molecular weight composition of the DOC, and temperature, pH, and metal ion effects on DOC fluorescence. These factors are discussed in terms of their effect on laboratory and remote field data analysis. Experimental results are provided. Analysis of fluorosensor data of DOC may be improved by compensating for the environmental factors. An improved methodology is discussed, and a suggestion is made for indirect monitoring of pH and metal ion concentration.
Vodacek, Anthony↗
Scanning delay generator for measurement of kinetic decays using laser-induced fluorescence techniques
An electronic device is described which generates a delayed pulse, where the delay is increased in a step-like manner. This device finds application in the measurement of kinetic decays, particularly when laser-induced fluorescent (LIF) detection of the decaying species is used. The circuit uses 15 low-power Schottky TTL chips and is contained within a dual width NIM module.
Halpern, J. B.↗
The Use of Laser-Induced Fluorescence to Characterize Discharge Cathode Erosion in a 30 cm Ring-Cusp Ion Thruster
Relative erosion rates and impingement ion production mechanisms have been identified for the discharge cathode of a 30 cm ion engine using laser-induced fluorescence (LIF). Mo and W erosion products as well as neutral and singly ionized xenon were interrogated. The erosion increased with both discharge current and voltage and spatially resolved measurements agreed with observed erosion patters. Ion velocity mapping identified back-flowing ions near the regions of erosion with energies potentially sufficient to generate the level of observed erosion. Ion production regions downstream of the cathode were indicated and were suggested as possible sources of the erosion causing ions.
Sovey, James S.↗
Simultaneous 100-kHz Acetone Planar Laser-Induced Fluorescence and OH* Chemiluminescence in a Linear Non-Premixed Detonation Channel
Reactant mixing and combustion are investigated in an optically accessible, self-excited linear detonation combustor. The mixing field is captured using 100 kHz planar laser-induced fluorescence (PLIF) imaging of acetone as a tracer in the fuel supply, while 100 kHz chemiluminescence imaging of excited-state hydroxyl (OH*) radicals simultaneously resolves the evolution of the detonation wave. Time sequences are acquired over multiple detonation cycles in each test, with acetone-PLIF images collected along multiple orthogonal planes to reveal the complex three-dimensional topography of the fuel distribution. The instantaneous and phase averaged acetone-PLIF images enable measurement of key fuel injection characteristics, such as the injector recovery time, fuel jet velocity, and refill height for a range of operating conditions. Instantaneous and phase-averaged measurements of acetone-PLIF with the time-coincident OH* chemiluminescence images also reveal a number key features, such as fuel stratification and weak detonation in the injector near field, incomplete combustion and deflagration behind the detonation wave, vitiation and deflagration of reactants ahead of the detonation wave, and fuel and oxidizer recovery time mismatch leading to combustion inefficiency. These measurements significantly enhance the ability to obtain detailed information on the intracycle and intercycle spatiotemporal evolution of the reactant refill process and its coupled effects on the detonation wave structure and propagation.
Propulsion↗
A Laser-Induced Fluorescence Instrument for Aircraft Measurements of Sulfur Dioxide in the Upper Troposphere and Lower Stratosphere
This work describes the development and testing of a new instrument for in situ measurements of sulfur dioxide (SO2) on airborne platforms in the upper troposphere and lower stratosphere (UTLS). The instrument is based on the laser-induced fluorescence technique and uses the fifth harmonic of a tunable fiber-amplified semiconductor diode laser system at 1084.5 nm to excite SO2 at 216.9 nm. Sensitivity and background checks are achieved in flight by additions of SO2 calibration gas and zero air, respectively. Aircraft demonstration was performed during the NASA Volcano Plume Investigation Readiness and Gas-Phase and Aerosol Sulfur (VIRGAS) experiment, which was a series of flights using the NASA WB-57F during October 2015 based at Ellington Field and Harlingen, Texas. During these flights, the instrument successfully measured SO2 in the UTLS at background (non-volcanic) conditions with a precision of 2 ppt at 10 s and an overall uncertainty determined primarily by instrument drifts of +/- (16% + 0.9 ppt).
tunable fiber-amplified semiconductor diode laser ↗
Plasma erosion rate diagnostics using laser-induced fluorescence
An optical technique for measuring the sputtering rate of a molybdenum surface immersed in a xenon plasma has been developed and demonstrated. This approach, which may be useful in real-time wear diagnostics for ion thrusters, relies on laser-induced fluorescence to determine the density of sputtered molybdenum atoms.
Gaeta, C. J.↗
Absolute Doppler shift calibration of laser induced fluorescence signals using optogalvanic measurements in a hollow cathode lamp
The paper investigates the use of optogalvanic (OG) measurements on the neutral 3P1 and 3P2 levels of argon in a hollow cathode lamp for the purpose of calibrating Doppler shifts of laser-induced fluorescence signals from an arcjet plume. It is shown that, even with non-Doppler-free OG detection, accuracy to better than 10 MHz is possible but that, depending on the experiment geometry, corrections of 10-35 MHz may be necessary to offset small axial drift velocities of neutral atoms in the hollow cathode lamp.
Ruyten, Wilhelmus M.↗
Combustion Zone Characterization of GO2/GH2 Rocket Using Laser-Induced Fluorescence of OH
A series of studies were undertaken to measure various parameters such as velocity, species concentration, and temperature downstream of a shear coaxial injector in an optically accessible uni-element rocket chamber. Techniques applied include: laser Doppler velocimetry (LDV) for velocity; laser light scattering (LLS) for flow visualization and estimating mixture fraction and density; laser induced fluorescence (LIF) of hydroxyl radials (OH) to determine the characteristics and extent of the reaction zone; and Raman spectroscopy to measure major species concentration and temperature.
Moser, M. D.↗
Laser-Induced Fluorescence Helps Diagnose Plasma Processes
Technique developed to provide in situ monitoring of rates of ion sputter erosion of accelerator electrodes in ion thrusters also used for ground-based applications to monitor, calibrate, and otherwise diagnose plasma processes in fabrication of electronic and optical devices. Involves use of laser-induced-fluorescence measurements, which provide information on rates of ion etching, inferred rates of sputter deposition, and concentrations of contaminants.
Beattie, J. R.↗
Stereoscopic Imaging in Hypersonics Boundary Layers using Planar Laser-Induced Fluorescence
Stereoscopic time-resolved visualization of three-dimensional structures in a hypersonic flow has been performed for the first time. Nitric Oxide (NO) was seeded into hypersonic boundary layer flows that were designed to transition from laminar to turbulent. A thick laser sheet illuminated and excited the NO, causing spatially-varying fluorescence. Two cameras in a stereoscopic configuration were used to image the fluorescence. The images were processed in a computer visualization environment to provide stereoscopic image pairs. Two methods were used to display these image pairs: a cross-eyed viewing method which can be viewed by naked eyes, and red/blue anaglyphs, which require viewing through red/blue glasses. The images visualized three-dimensional information that would be lost if conventional planar laser-induced fluorescence imaging had been used. Two model configurations were studied in NASA Langley Research Center's 31-Inch Mach 10 Air Wind tunnel. One model was a 10 degree half-angle wedge containing a small protuberance to force the flow to transition. The other model was a 1/3-scale, truncated Hyper-X forebody model with blowing through a series of holes to force the boundary layer flow to transition to turbulence. In the former case, low flowrates of pure NO seeded and marked the boundary layer fluid. In the latter, a trace concentration of NO was seeded into the injected N2 gas. The three-dimensional visualizations have an effective time resolution of about 500 ns, which is fast enough to freeze this hypersonic flow. The 512x512 resolution of the resulting images is much higher than high-speed laser-sheet scanning systems with similar time response, which typically measure 10-20 planes.
Danehy, Paul M.↗
Method for measuring temperatures and densities in hypersonic wind tunnel air flows using laser-induced O2 fluorescence
Laser-induced fluorescence in oxygen, in combination with Raman scattering, is shown to be an accurate means by which temperature, density, and their fluctuations owing to turbulence can be measured in air flows associated with high-speed wind tunnels. For temperatures above 60 K and densities above 0.01 amagat, the uncertainties in the temperature and density measurements can be less than 2 percent, if the signal uncertainties are dominated by photon statistical noise. The measurements are unaffected by collisional quenching and can be achieved with laser fluences for which nonlinear effects are insignificant. Temperature measurements using laser-induced fluorescence alone have been demonstrated at known densities in the range of low temperatures and densities which are expected in a hypersonic wind tunnel.
Laufer, Gabriel↗
A method for measuring temperatures and densities in hypersonic wind tunnel air flows using laser-induced O2 fluorescence
Laser-induced fluorescence in oxygen, in combination with Raman scattering, is shown to be an accurate means by which temperature, density, and their fluctuations due to turbulence can be measured in air flows associated with high-speed wind tunnels. For temperatures above 60 K and densities above 0.01 amagat, the uncertainty in the temperature and density measurements can be less than 2 and 3 percent, respectively, if the signal uncertainties are dominated by photon-statistical noise. The measurements are unaffected by collisional quenching and can be achieved with laser fluences for which nonlinear effects are insignificant. Temperature measurements using laser-induced fluorescence alone have been demonstrated at known densities in the range of low temperatures and densities which are expected in a hypersonic wind tunnel.
Laufer, Gabriel↗
Laser induced fluorescence applied to turbulent reacting flows
The saturated fluorescence method makes use of the great simplifications which occur when under conditions of intense radiation the excitation process becomes saturated. A description is presented of the saturated fluorescence method, taking into account rate equations and saturation, radiative transfer, the two-level system, a multilevel system, and measurements under saturation conditions. The detectability limits of the method are investigated. Fluorescence trapping is found to place an upper limit on the number density of the fluorescing species that can be measured without signal loss. Turbulence places time and spatial constraints on the measurements, but otherwise poses no difficulties. Saturated laser induced fluorescence spectroscopy appears to be a most promising method for measuring species concentrations in flames.
Daily, J. W.↗
High-Speed Visualization of Spray Breakup and Velocity Estimation in a Rotating Detonation Combustor Using Laser Induced Fluorescence
The underlying physical processes that liquid fuel sprays undergo in rotating detonation engines, particularly breakup and combustion, are not well understood nor are the coupling effects between the detonation and the spray. In this work, a single liquid jet of liquid fuel is inserted into a hydrogen-air RDC in order to study repetitive-one way coupled detonation interactions. High speed laser induced fluorescence of Jet-A at 300 kHz is used to visualize the dynamic processes inside the RDC for up to 10 ms per test. The employed imaging schemes allowed for unique insight into the spreading of liquid fuel in the azimuthal-axial directions via volumetric laser illumination. The Jet-A velocity field was estimated using OpenOpticalFlow and the impulse events observed colloquially agree with prior work on this test platform.
Instrumentation↗
High-Speed Visualization of Spray Breakup and Velocity Estimation in a Rotating Detonation Combustor Using Laser Induced Fluorescence
The underlying physical processes that liquid fuel sprays undergo in rotating detonation engines, particularly breakup and combustion, are not well understood nor are the coupling effects between the detonation and the spray. In this work, a single liquid jet of liquid fuel is inserted into a hydrogen-air RDC in order to study repetitive-one way coupled detonation interactions. High speed laser induced fluorescence of Jet-A at 300 kHz is used to visualize the dynamic processes inside the RDC for up to 10 ms per test. The employed imaging schemes allowed for unique insight into the spreading of liquid fuel in the azimuthal-axial directions via volumetric laser illumination. The Jet-A velocity field was estimated using OpenOpticalFlow and the impulse events observed colloquially agree with prior work on this test platform.
Instrumentation↗