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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
NASA NTRS2000

Coherent Doppler Laser Radar: Technology Development and Applications

NASA's Marshall Space Flight Center has been investigating, developing, and applying coherent Doppler laser radar technology for over 30 years. These efforts have included the first wind measurement in 1967, the first airborne flights in 1972, the first airborne wind field mapping in 1981, and the first measurement of hurricane eyewall winds in 1998. A parallel effort at MSFC since 1982 has been the study, modeling and technology development for a space-based global wind measurement system. These endeavors to date have resulted in compact, robust, eyesafe lidars at 2 micron wavelength based on solid-state laser technology; in a factor of 6 volume reduction in near diffraction limited, space-qualifiable telescopes; in sophisticated airborne scanners with full platform motion subtraction; in local oscillator lasers capable of rapid tuning of 25 GHz for removal of relative laser radar to target velocities over a 25 km/s range; in performance prediction theory and simulations that have been validated experimentally; and in extensive field campaign experience. We have also begun efforts to dramatically improve the fundamental photon efficiency of the laser radar, to demonstrate advanced lower mass laser radar telescopes and scanners; to develop laser and laser radar system alignment maintenance technologies; and to greatly improve the electrical efficiency, cooling technique, and robustness of the pulsed laser. This coherent Doppler laser radar technology is suitable for high resolution, high accuracy wind mapping; for aerosol and cloud measurement; for Differential Absorption Lidar (DIAL) measurements of atmospheric and trace gases; for hard target range and velocity measurement; and for hard target vibration spectra measurement. It is also suitable for a number of aircraft operations applications such as clear air turbulence (CAT) detection; dangerous wind shear (microburst) detection; airspeed, angle of attack, and sideslip measurement; and fuel savings through headwind minimization. In addition to the airborne and space platforms, a coherent Doppler laser radar system in an unmanned aerial vehicle (UAV) could provide battlefield weather and target identification.

Kavaya, Michael J.↗
DOE OSTI2023

Melting line and thermal equation of state of fcc-cobalt: A combined experimental and computational approach

The melting line of cobalt has been investigated both experimentally, using synchrotron X-ray diffraction coupled with laser-heated diamond anvil cells, and theoretically, using ab initio simulations. Over the investigated pressure and temperature range – between 30 and 100 GPa and from ambient temperature up to 4000 K – the hexagonal close-packed structure, stable at ambient conditions, is replaced at high temperature by the face-centered cubic structure, observed stable till melting. The melting temperatures obtained by the two methods are in remarkable agreement and the melting line can be well described by a Simon–Glatzel equation of the form T$_m$ = 1768(K)(P(GPa)/35.62+1) 0.64 . Finally, from the obtained results it was possible to determine a thermal equation of state for the cubic face-centered phase of Co.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Lidar simulation

The feasibility of measuring atmospheric water vapor via orbital lidar is estimated. The calculation starts with laser radar equations representing backscatter with and without molecular line absorption; the magnitudes of off-line backscatter are demonstrated. Extensive prior data on water line strengths are summarized to indicate the available sensitivity to water vapor concentration. Several lidar situations are considered starting with uniform and perturbed atmospheres at 0, 3, 10 and 20 kM (stratosphere) altitudes. These simulations are indicative of results to be obtained in ground truth measurements (ground-based and airborne). An approximate treatment of polar observations is also given. Vertical atmospheric soundings from orbit and from ground stations are calculated. Errors are discussed as regards their propagation through the lidar equation to render the measured water vapor concentration imprecise; conclusions are given as to required laser energy and feasible altitude resolution.

Source record↗
NASA NTRS1986

Simulator scene display evaluation device

An apparatus for aligning and calibrating scene displays in an aircraft simulator has a base on which all of the instruments for the aligning and calibrating are mounted. Laser directs beam at double right prism which is attached to pivoting support on base. The pivot point of the prism is located at the design eye point (DEP) of simulator during the aligning and calibrating. The objective lens in the base is movable on a track to follow the laser beam at different angles within the field of vision at the DEP. An eyepiece and a precision diopter are movable into a position behind the prism during the scene evaluation. A photometer or illuminometer is pivotable about the pivot into and out of position behind the eyepiece.

Haines, R. F.↗
DOE OSTI2025

Quantum Information for Fusion Energy Sciences (Final Technical Report)

The simulation of plasma dynamics is a critical area of Fusion Energy Sciences (FES) due to it’s usefulness in predicting, controlling, and confining plasmas in the context of potential fusion reactors. The simulation of plasmas is a computationally difficult problem in both classical and quantum physics, motivating investigation into the potential of quantum computers to simulate these systems. This project took several concrete steps towards this goal by developing tools for improving the control, characterization, and calibration of quantum gates on a superconducting quantum computer, developing error suppression and mitigation tools to reduce errors on the quantum computer, and utilizing these advancements to simulate reduced models of plasma dynamics on the quantum computer. In order to efficiently simulate plasma physics, an optimal control method which synthesizes, directly at the pulse level, any quantum gate on qubit and qutrit systems was developed. Using four superconducting transmon quantum processors at Rigetti and LLNL, it was demonstrated that any arbitrary quantum gate on qubits and qutrits could be implemented with high fidelity, leading to a significantly reduced length of a gate sequence. A problem of interest in FES is the nonlinear optical process of laser pulse compression within a plasma. Since quantum physics is linear, simulating nonlinear operations is not naturally feasible on a quantum computer, however it is possible to simulated a quantized version of the nonlinear process. A quantization approach to convert nonlinear wave-wave interaction problems to Hamiltonian simulation problems was developed and demonstrated using two qubits on a Rigetti device. In this experiment, a number of error suppression and mitigation techniques were investigated to determine how best to utilize the finite quantum resources. This study provides an example of how plasma problems may be solved on near-term, noisy quantum computing platforms and identified a promising set of techniques. Building on the insights of these experiments, the investigation turned to linear electron-plasma wave physics. A connection was identified between a local one-dimensional lattice spin model and linear wave phenomena, allowing a plasma physics problem to be efficiently mapped to the quantum computer. In this framework, reflection and transmission of plasma waves at a sharp boundary was studied, as well as the propagation of waves through an inhomogeneous plasma medium. In addition to the suite of error suppression and mitigation techniques developed, this experiment introduced the use of a digital-analog gate scheme designed to efficiently simulate the plasma Hamiltonian. With hardware available at the conclusion of the project, simulation at the scale of 9 qubits and 15 timesteps (60 entangling layers) was achieved.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2005

Characteristics of the Swirling Flow Generated by an Axial Swirler

An experimental investigation was conducted to study the aerodynamic characteristics of the confined, non-reacting, swirling flow field. The flow was generated by a helicoidal axial-vaned swirler with a short internal convergent-divergent venturi, which was confined within 2-inch square test section. A series of helicoidal axial-vaned swirlers have been designed with tip vane angles of 40 deg., 45 deg., 50 deg., 55 deg., 60 deg. and 65 deg.. The swirler with the tip vane angle of 60 deg. was combined with several simulated fuel nozzle insertions of varying lengths. A two-component Laser Doppler Velocimetry (LDV) system was employed to measure the three-component mean velocities and Reynolds stresses. Detailed data are provided to enhance understanding swirling flow with different swirl degrees and geometries and to support the development of more accurate physicaVnumerica1 models. The data indicated that the degree of swirl had a clear impact on the mean and turbulent flow fields. The swirling flow fields changed significantly with the addition of a variety of simulated fuel nozzle insertion lengths

Fu, Yongqiang↗
NASA NTRS1974

Rain droplet erosion mechanisms in transparent plastic materials

Tests were conducted to determine the damaging effects of rain erosion on optically transparent materials. The rotating arm test equipment used for the tests is described. Typical transparent materials such as those found in windshields, infrared windows, lasers, and television systems were tested. Nominal velocities of 400, 500, and 600 miles per hour and rainfall conditions of one inch per hour simulated rainfall were used in the tests. It was determined that an 80 percent reduction in laser transmittance can occur in plastics submitted to rain erosion. Significant results of the environmental tests are explained.

Schmitt, G. F., Jr.↗
DOE OSTI2024

Broadband Frequency Conversion of Spectrally Incoherent Pulses and Initial Laser-Plasma Instabilities Mitigation Experiments

There is a need for efficient broadband frequency conversion schemes from the infrared, where optical pulses are efficiently amplified by solid-state laser materials, to the ultraviolet, a wavelength range more suitable for inertial confinement fusion (ICF). The current schemes are inadequate for broadband, spectrally incoherent optical pulses composed of a large number of frequency components distributed over a large frequency range. Implementing novel technologies that generate optical pulses with a large number of spectral components improves the laser-target interaction. In particular, it has long been believed that broad bandwidth mitigates the electron-plasma-wave instabilities that generate suprathermal electrons, which degrade ICF performance by increasing the fuel adiabat and reducing the shell areal density. It is important to develop a platform to demonstrate hot electron suppression caused by the larger available bandwidth, which has not previously been feasible in the laboratory. Experimentally measuring and theoretically assessing these effects with adequately benchmarked simulation codes are paramount to the design and development of novel laser facilities aiming at producing energy via laser fusion. The Laboratory for Laser Energetics is building a new laser facility, the Fourth-generation Laser for Ultrabroadband eXperiments (FLUX), to generate high-energy nanosecond laser pulses with fractional bandwidth larger than 1% in the ultraviolet and perform combined experiments with the 60-beam Omega facility. This large increase in bandwidth from the ~ 0.1% currently available on high-energy laser systems, is achieved by combining amplification in nonlinear optical parametric amplifiers (OPAs) around 1053 nm (1w) with nonlinear frequency conversion to the ultraviolet (around 351 nm, 3w). The novel scheme for frequency conversion is based on the noncollinear sum-frequency generation (SFG) of the angularly dispersed amplified 1w output with a narrowband 2w pulse, which is also used to pump the OPA system. The proposal funded scientific and engineering studies necessary to implement this novel laser facility, accelerated the SFG deployment by funding additional project team resources (shop time, engineers, and technicians), and funded preliminary experiments on the Omega Laser.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1989

Atomic oxygen effects on spacecraft materials: The state of the art of our knowledge

In the flight materials exposure data base extensive quantitative data is available from limited exposures in a narrow range of orbital environments. More data is needed in a wider range of environments as well as longer exposure times. Synergistic effects with other environmental factors; polar orbit and higher altitude environments; and real time materials degradation data is needed to understand degradation kinetics and mechanism. Almost no laboratory data exists from high fidelity simulations of the LEO environment. Simulation and test system are under development, and the data base is scanty. Theoretical understanding of hyperthermal atom surface reactions in the LEO environment is not good enough to support development of reliable accelerated test methods. The laser sustained discharge, atom beam sources are the most promising high fidelity simulation-test systems at this time.

Koontz, Steven L.↗
DOE OSTI2024

GrainGNN: A dynamic graph neural network for predicting 3D grain microstructure

We propose GrainGNN, a surrogate model for the evolution of polycrystalline grain structure under rapid solidification conditions in metal additive manufacturing. High fidelity simulations of solidification microstructures are typically performed using multicomponent partial differential equations (PDEs) with moving interfaces. The inherent randomness of the PDE initial conditions (grain seeds) necessitates ensemble simulations to predict microstructure statistics, e.g., grain size, aspect ratio, and crystallographic orientation. Here, currently such ensemble simulations are prohibitively expensive and surrogates are necessary.In GrainGNN, we use a dynamic graph to represent interface motion and topological changes due to grain coarsening. We use a reduced representation of the microstructure using hand-crafted features; we combine pattern finding and altering graph algorithms with two neural networks, a classifier (for topological changes) and a regressor (for interface motion). Both networks have an encoder-decoder architecture; the encoder has a multi-layer transformer long-short-term-memory architecture; the decoder is a single layer perceptron.We evaluate GrainGNN by comparing it to high-fidelity phase field simulations for in-distribution and out-of-distribution grain configurations for solidification under laser power bed fusion conditions. GrainGNN results in 80%–90% pointwise accuracy; and nearly identical distributions of scalar quantities of interest (QoI) between phase field and GrainGNN simulations compared using Kolmogorov-Smirnov test. GrainGNN's inference speedup (PyTorch on single x86 CPU) over a high-fidelity phase field simulation (CUDA on a single NVIDIA A100 GPU) is 150×–2000× for 100-initial grain problem. Further, using GrainGNN, we model the formation of 11,600 grains in 220 seconds on a single CPU core.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Nanosecond Laser Drying in Wafer Foundries for Significant Energy Efficiency Improvement

Surface drying is a critical process in microelectronics wafer fabrication. In order to reduce and eliminate watermarks, many surface drying processes have been studied and used. Most of the wafer foundries currently use drying processes based on Isopropyl Alcohol (IPA), which causes serious safety (fire), health, environmental, and energy efficiency issues. The long-term goal of this project is to develop a fast, effective, chemical-free, and extremely energy efficient wafer drying technology that employs nanosecond laser-induced sub-surface evaporation and explosion. The objectives of this project are to 1) experimentally develop and verify the laser surface drying method, explore and identify how and to what extent various physical parameters influence the drying efficiency and effectiveness; and 2) understand and optimize the underlying thermodynamics in the proposed laser surface drying, including micro/nanoscale sub-surface superheating, evaporation, explosion, and photo/thermochemical bond breaking via atomistic modeling and experimental characterization. Toward these objectives, five tasks have been accomplished successfully, including 1) develop in-lab laser surface drying setup and study the effect of varied laser parameters, 2) use multiscale hybrid-modeling to study and understand the physics of water behavior during drying toward process optimization, 3) investigate the effect of drying conditions on the drying effectiveness, 4) develop a large-scale laser drying scanning system with automatic scanning, and 5) conduct large-scale simulation to study the effect of dopant level and develop strategies for system development toward industry deployment.

42 ENGINEERING↗
NASA NTRS1984

Free-jet feasibility study of a thermal acoustic shield concept for AST/VCE application-dual stream nozzles. Comprehensive data report. Volume 2: Laser velocimeter and suppressor. Base pressure data

Acoustic and diagnostic data that were obtained to determine the influence of selected geometric and aerodynamic flow variables of coannular nozzles with thermal acoustic shields are summarized in this comprehensive data report. A total of 136 static and simulated flight acoustic test points were conducted with 9 scale-model nozzles. Aerodynamic laser velocimeter measurements were made for four selected plumes. In addition, static pressure data in the chute base region of the suppressor configurations were obtained to assess the influence of the shield stream on the suppressor base drag.

Janardan, B. A.↗
DOE OSTI2026

Burn mode signatures enabled by high dynamic range fusion reaction history

The evolution of the fusion burn of a compressed inertial confinement fusion (ICF) implosion gives information about the evolution of the temperature, mass, and volume of the hot spot. Currently, the fusion reaction history has been measured with about a decade of dynamic range, giving information about just the peak of the fusion burn. There are proposals for extending the dynamic range to 1000×, measuring the rising edge of the burn earlier in time. Using fusion hot spot theory and a set of ICF simulations, we identify and categorize different stages of fusion burn and what signatures could be measured. For ice layered implosions, the details, conditions, and dynamics of the fusion burn propagation could be observed. For double shell and OMEGA scale implosions, the evolution of the final compression and rebounding shock before ignition could be observed. Higher dynamic range expands investigation into the logarithmic derivative, α, as a signature of various mechanisms.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Suppressing the enhancement of stimulated Raman scattering in inhomogeneous plasmas by tuning the modulation frequency of a broadband laser

The stimulated Raman scattering (SRS) instability can inhibit the performance of laser driven inertial confinement fusion (ICF) implosions by scattering light into unwanted directions or by generating hot electrons that preheat the target fuel. In principle, ICF target designs can avoid parameter regimes conducive to large, linear SRS gains. In practice, kinetic inflation—the nonlinear enhancement of SRS due to electron trapping in the excited plasma wave—makes this difficult. Here we show that laser bandwidth in the form of frequency modulation can either decrease or increase the inflationary SRS (iSRS) threshold in inhomogeneous plasmas depending on the maximum chirp of the laser pulse. The threshold, mapped out by a series of particle-in-cell simulations, exhibits a minimum when the frequency change within the pulse cancels the spatial detuning due to density inhomogeneities along the trajectory of the scattered light. In conclusion, by tuning the pump laser parameters away from this minimum, the iSRS threshold can be larger than at zero bandwidth, providing a path to mitigating kinetic inflation in ignition relevant plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Absorption of relativistic multi-picosecond laser pulses in wire arrays

We study the interaction of intense multi-picosecond laser pulses with arrays of carbon wires attached to solid substrates. Here, we find that laser absorption in wire arrays resembles that in flat targets with very large uniform plasma density gradients. Performing two-dimensional particle-in-cell simulations, we optimize target parameters like wire thickness and -distance for energy absorption of a 2picosecond laser pulse with a large focal spot; this has implications for x-ray- and charged particle source development.

43 PARTICLE ACCELERATORS↗
NASA NTRS1985

ICIASF '85 - International Congress on Instrumentation in Aerospace Simulation Facilities, 11th, Stanford University, CA, August 26-28, 1985, Record

Developments related to laser Doppler velocimetry are discussed, taking into account a three-component dual beam laser-Doppler-anemometer to be operated in large wind tunnels, a new optical system for three-dimensional laser-Doppler-anemometry using an argon-ion and a dye laser, and a two-component laser Doppler velocimeter by switching fringe orientation. Other topics studied are concerned with facilities, instrumentation, control, hot wire/thin film measurements, optical diagnostic techniques, signal and data processing, facilities and adaptive wall test sections, data acquisition and processing, ballistic instrument systems, dynamic testing and material deformation measurements, optical flow measurements, test techniques, force measurement systems, and holography. Attention is given to nonlinear calibration of integral wind tunnel balances, a microcomputer system for real time digitized image compression, and two phase flow diagnostics in propulsion systems.

Source record↗
NASA NTRS1988

Aeroacoustics of advanced STOVL aircraft plumes

This paper summarizes a basic and well-controlled experimental study involving flow visualization and noise measurements to define the acoustic and flow fields of single plumes impinging on a simulated ground plane. The flow visualization was made by strobing a laser light source at the discrete frequencies generated by the impingement of the jets and measured by a nearfield microphone. This enabled visualization of instability waves generated by the interaction between the plumes and the sound generated during impingement, and also by dynamic coupling between the two plumes. These data were acquired as a function of distance between the ground and the nozzle exit. Nearfield acoustic data were acquired simultaneously. Data for nozzle diameters of 0.265 in. and 0.4 in. are described. For selected nozzles, effects of exit boundary layer characteristics and nozzle protrusion through a simulated aircraft body are also presented.

Ahuja, K. K.↗