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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 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
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 NTRS1987

Determining Optical Axes of Uniaxial Crystals

Polarizing-microscope concept adapted for thick samples. Optical axis of crystal usually found by examining sample thinner than 1 mm between crossed polarizing plates. Frequently impractical to cut off small sample of crystal for testing, technique modified to accommodate large crystals. Ability to circumvent effect of birefringence has applications where laser beams must be transmitted through uniaxial crystals, as in laser diagnostics of contained flows in systems requiring windows for optical access.

Schock, H. J.↗
NASA NTRS1986

Multiple scattering depolarization in marine stratus clouds: Lidar experiments

The depolarization of ruby lidar backscattering caused by multiple scattering in marine stratus clouds was examined systematically from a field site on the southern California coast. Investigated were the effects on the linear depolarization (delta) of lidar receiver field of view (FOV), elevation angle and laser beam pointing errors. An approximately linear increase in maximum delta values was observed with increasing receiver FOV, and the importance of accurate transmitter/receiver beam alignment was demonstrated during experiments in which the laser axis was deliberately misaligned. An elevation angle dependence to the delta values was observed as a consequence of the natural vertical inhomogeneity of water cloud content above the cloud base. Time histories of the depolarization characteristics of dissipating stratus clouds revealed significant spatial and temporal variability in delta values attributed to cloud composition variations. Employing a 1 mrad transmitter FOV, maximum delta values of 0.21 nd 0.33 were observed with 1 and 3 mrad receiver FOVs, respectively, from the low stratus clouds. The fundamental causes and effects on the lidar equation of multiple scattering are also discussed.

Sassen, K.↗
NASA NTRS1990

Free-space laser communication technologies II; Proceedings of the Meeting, Los Angeles, CA, Jan. 15-17, 1990

Various papers on free-space laser communication technologies are presented. Individual topics addressed include: optical intersatellite link experiment between the earth station and ETS-VI, the Goddard optical communications program, technologies and techniques for lasercom terminal size, weight, and cost reduction, laser beam acquisition and tracking system for ETS-VI laser communication equipment, analog dividers for acquisition and tracking signal normalization, fine pointing mechanism using multilayered piezoelectric actuator for optical ISL system, analysis of SILEX tracking sensor performance, new telescope concept for space communication, telescope considered as a very high gain antenna, design of compact transceiver optical systems for optical intersatellite links, ultralightweight optics for laser communications, highly sensitive measurement method for stray light and retroreflected light, depolarization effects on free space laser transceiver communication systems, in-orbit measurements of microaccelerations of ESA's communication satellite Olympus, high-performance laser diode transmitter for optical free space communication, diode-pumped Nd:host laser transmitter for intersatellite optical communications, single-frequency diode-pumped laser for free-space communication.

Begley, David L.↗
NASA NTRS2012

Optical Phase Recovery and Locking in a PPM Laser Communication Link

Free-space optical communication holds great promise for future space missions requiring high data rates. For data communication in deep space, the current architecture employs pulse position modulation (PPM). In this scheme, the light is transmitted and detected as pulses within an array of time slots. While the PPM method is efficient for data transmission, the phase of the laser light is not utilized. The phase coherence of a PPM optical signal has been investigated with the goal of developing a new laser communication and ranging scheme that utilizes optical coherence within the established PPM architecture and photon-counting detection (PCD). Experimental measurements of a PPM modulated optical signal were conducted, and modeling code was developed to generate random PPM signals and simulate spectra via FFT (Fast Fourier Transform) analysis. The experimental results show very good agreement with the simulations and confirm that coherence is preserved despite modulation with high extinction ratios and very low duty cycles. A real-time technique has been developed to recover the phase information through the mixing of a PPM signal with a frequency-shifted local oscillator (LO). This mixed signal is amplified, filtered, and integrated to generate a voltage proportional to the phase of the modulated signal. By choosing an appropriate time constant for integration, one can maintain a phase lock despite long dark times between consecutive pulses with low duty cycle. A proof-of-principle demonstration was first achieved with an RF-based PPM signal and test setup. With the same principle method, an optical carrier within a PPM modulated laser beam could also be tracked and recovered. A reference laser was phase-locked to an independent pulsed laser signal with low-duty-cycle pseudo-random PPM codes. In this way, the drifting carrier frequency in the primary laser source is tracked via its phase change in the mixed beat note, while the corresponding voltage feedback maintains the phase lock between the two laser sources. The novelty and key significance of this work is that the carrier phase information can be harnessed within an optical communication link based on PPM-PCD architecture. This technology development could lead to quantum-limited efficient performance within the communication link itself, as well as enable high-resolution optical tracking capabilities for planetary science and spacecraft navigation.

Aveline, David C.↗
NASA NTRS2015

ICESat-2 ATLAS Beam Steering Mechanism (BSM)

This work covers the design and test of a beam steering mechanism (BSM) used to accurately guide a laser on the Advanced Topographic Laser Altimeter System (ATLAS) down to Earth in order to measure elevation. It describes the main components in the BSM that allows it to perform and meet stringent requirements. Requirements of the BSM include two-axis steering of the transmitted laser beam, +-5000 uRad mechanical motion in each axis, and 1.5 uRad RMS pointing stability among many other requirements. The BSM uses four voice coil actuators in order to locate the mirror at the angle we need. There are four Differential Position Sensors that determine the position and angle of the mirror at all times. These sensors were verified through optical testing in both ambient and thermal conditions. Testing and extensive analyses were performed on the two-axis flexure throughout the program to check flexure thickness, positive margins, and infinite life. The mirror mount design has been modified to eliminate radial preload, while incorporating a titanium wave spring to provide an axial preload of 10.8N. The BSM underwent multiple tests in order to verify all components work as required under various conditions.

000000↗
DOE OSTI2020

Effect of cross-beam energy transfer on target-offset asymmetry in direct-drive inertial confinement fusion implosions

The unintentional mispositioning of inertial confinement fusion (ICF) capsules from the center of laser beam convergence has long been shown in simulations to generate large ℓ = 1 asymmetry and significantly degrade implosion symmetry and fusion yields. Experimental yields on the OMEGA Laser System, however, have shown much less sensitivity to this initial target offset. This paper presents simulations of offset ICF implosions improved by including a physics model of cross-beam energy transfer (CBET), a mechanism of laser energy scattering from one beam to another. Room-temperature OMEGA implosion experiments with prescribed target offsets are simulated with and without CBET, illustrating that CBET mitigates the ℓ = 1 implosion asymmetry from target offset. Here, comparison of simulations to multiple complementary experimental observables indicates the addition of CBET physics in offset simulations is necessary to match experimental results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

A multi-terawatt two-color beam for high-power field-controlled nonlinear optics

Two-color laser beams are instrumental in light-field control and enhancement of high-order harmonic, spectral supercontinuum, and terahertz radiation generated in gases, plasmas, and solids. Here we demonstrate a multi-terawatt two-color beam produced using a relativistic plasma mirror, with 110 mJ at 800 nm and 30 mJ at 400 nm. Both color components have high spatial quality and can be simultaneously focused, provided that the plasma mirror lies within a Rayleigh range of the driving fundamental beam. Favorable scaling of second-harmonic generation by plasma mirrors at relativistic intensities suggests them as an excellent tool for multi-color waveform synthesis beyond the petawatt level.

42 ENGINEERING↗
NASA NTRS1980

Errors incurred in a plane-wave-type expansion of a Gaussian beam

The multipole expansion obtained by Morita et al. (1968) of the Gaussian laser beam used to levitate an aerosol particle in order that its complete phase matrix may be measured is compared with that of Tsai and Pogorzelski (1975) in order to demonstrate the effect of the incorrect expansion used by Morita. Errors incurred by the use of an equation in which one side satisfies the scalar wave equation while the other side does not and can be reduced to a plane wave amplitude are calculated as functions of the inverse of the wave number times the beam waist, the wave number times the radial spherical coordinate and the angular spherical coordinate. Errors on the order of a few percent, considered undetectable are obtained in the squared-field amplitudes due to the expansion, however, they are found to become significant (several tens of percent) when the angle is zero. It is concluded that the expansion of Morita should only be used in the regions where the spherical angle is less than 0.01 and its product with the wave number and the radial spherical coordinate is less than unity.

Kattawar, G. W.↗
DOE OSTI2021

Effect of cross-beam energy transfer on target-offset asymmetry in direct-drive inertial confinement fusion implosions

The unintentional mispositioning of inertial confinement fusion (ICF) capsules from the center of laser beam convergence has long been shown in simulations to generate large ℓ = 1 asymmetry and significantly degrade implosion symmetry and fusion yields. Experimental yields on the OMEGA Laser System, however, have shown much less sensitivity to this initial target offset. This paper presents simulations of offset ICF implosions improved by including a physics model of cross-beam energy transfer (CBET), a mechanism of laser energy scattering from one beam to another. Room-temperature OMEGA implosion experiments with prescribed target offsets are simulated with and without CBET, illustrating that CBET mitigates the ℓ = 1 implosion asymmetry from target offset. Comparison of simulations to multiple complementary experimental observables indicates the addition of CBET physics in offset simulations is necessary to match experimental results.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1977

Production of dense plasmas in a hypocycloidal pinch apparatus

A high-power pinch apparatus consisting of disk electrodes was developed, and diagnostic measurements to study its mechanism of dense plasma production have been made. The collapse fronts of the current sheets are well organized, and dense plasma foci are produced on the axis with radial stability in excess of 5 microsec. A plasma density greater than 10 to the 18th power per cu cm is determined with Stark broadening and CO2 laser absorption. Essentially complete absorption of a high-energy CO2 laser beam has been observed. A plasma temperature of approximately 1 keV is measured with differential transmission of soft X-rays through thin foils. The advantages of this apparatus over the coaxial plasma focus are improvements in (1) plasma volume, (2) stability, (3) containment time, (4) access to additional heating by laser or electron beams, and (5) the possibility of scaling up to a multiple array for high-power operation.

Lee, J. H.↗
NASA NTRS1992

Phase stability of injection-locked beam of semiconductor lasers

An experiment on the phase stability of an injection locked beam was done by using AlGaAs semiconductor lasers. The coherence of two beams from master and slave lasers was measured by interference between the beams in the Twymann-Green interferometer. The phase change of the output beam of the slave laser as a function of the driving current was measured in a Mach-Zehnder interferometer consisting of the master and slave lasers, and a value of 2.5 radians/mA was obtained.

Kwon, Jin Hyuk↗
NASA NTRS1976

Modular high accuracy tracker for dual channel laser Doppler velocimeter

In the study described, a scanning dual-channel cross-beam laser Doppler velocimeter (developed for measuring simultaneously the two orthogonal components of flow velocity and turbulence intensity) was used to measure the instantaneous velocity characteristics of a model helicopter rotor and in a vortex wake survey experiment on a Boeing 747 aircraft model. Particular attention is given to a special purpose dual-loop frequency tracker developed to track and demodulate 10 microsecond wide pulse burst Doppler signals with a study cycle of 25% (or narrower signals at a higher duty cycle) generated by the laser Doppler velocimeter.

Fridman, J. D.↗
NASA NTRS1999

Single Bubble Sonoluminescence in Low Gravity and Optical Radiation Pressure Positioning of the Bubble

Several groups of researchers have demonstrated that high frequency sound in water may be used to cause the regular repeated compression and luminescence of a small bubble of gas in a flask. The phenomenon is known as single bubble sonoluminescence (SBSL). It is potentially important because light emitted by the bubble appears to be associated with a significant concentration of energy within the volume of the bubble. Unfortunately, the detailed physical mechanisms causing the radiation of light by oscillating bubbles are poorly understood and there is some evidence that carrying out experiments in a weightless environment may provide helpful clues. In addition, the radiation pressure of laser beams on the bubble may provide a way of simulating weightless experiments in the laboratory. The standard model of SBSL attributes the light emission to heating within the bubble by a spherically imploding shock wave to achieve temperatures of 50,000 K or greater. In an alternative model, the emission is attributed to the impact of a jet of water which is required to span the bubble and the formation of the jet is linked to the buoyancy of the bubble. The coupling between buoyancy and jet formation is a consequence of the displacement of the bubble from a velocity node (pressure antinode) of the standing acoustic wave that drives the radial bubble oscillations. One objective of this grant is to understand SBSL emission in reduced buoyancy on KC-135 parabolic flights. To optimize the design of those experiments and for other reasons which will help resolve the role of buoyancy, laboratory experiments are planned in simulated low gravity in which the radiation pressure of laser light will be used to position the bubble at the acoustic velocity node of the ultrasonic standing wave. Laser light will also be used to push the bubble away from the velocity node, increasing the effective buoyancy. The original experiments on the optical levitation and radiation pressure on bubbles in water by Unger and Marston noted above were carried out using a continuous wave (CW) beam of an Argon laser. For lateral stability the beam had a intensity minimum along its axis. Calculations of the optical radiation force on an SBSL bubble indicate that ion laser technology is a poor choice for providing the magnitude of the average optical radiation force required. Consequently it is necessary to examine various diode-pumped solid state laser technologies. The approach for this part of the research will be to achieve optical levitation of a quiescent bubble based on contemporary laser technology and then to strobe the laser synchronously with the SBSL bubble oscillations.

Thiessen, D. B.↗
DOE OSTI2020

Experimental investigation of laser ablation of stone polycrystalline targets

We report the results of an experimental investigation of ablation of stone polycrystalline targets of complex multicomponent composition, which imitate the substance of asteroids. The targets were irradiated by nanosecond pulses of a neodymium laser at an energy density Φ{sub L} of up to 5 × 10{sup 4} J cm{sup −2}. The experiments demonstrated the existence of two ablation regimes, with the boundary between them lying at Φ{sub L} ≈ 4000 J cm{sup −2}. The regime change is characterised by a change in the form of the dependence of the surface mass density of removed target material on the laser energy density and by the appearance of a minimum in the dependence of specific energy of destruction on Φ{sub L}. This is supposedly related to the passage from a one-dimensional plasma plume expansion to the three-dimensional one and the corresponding decrease in the efficiency of energy transfer from the laser beam to the target due to a lowering of laser-produced plasma density. Our experiments also showed the existence of a maximum in impulse coupling coefficient C{sub m} as a function of laser energy density (C{sub m} ≈ 6.3 × 10{sup −5} N W{sup −1} for Φ{sub L} = Φ{sub opt} ≈ 25 J cm{sup −2}). Maxima were also recorded in the dependences of the ablation efficiency and average ablation flow velocity on Φ{sub L}. For Φ{sub L} > Φ{sub opt}, the decrease in the function C{sub m}(Φ{sub L}) turns out to be much steeper than for metals and polymer materials. The difference is supposedly due to the lower strength and lower plasticity of the polycrystalline stone targets. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Two-stage nonlinear compression of high-power femtosecond laser pulses

Two-stage compression of laser pulses with a power of 250 TW is experimentally realised by broadening their spectrum during self-phase modulation in fused silica and subsequent dispersion compensation upon reflection from chirping mirrors. A five-fold decrease in the duration is demonstrated, from 75 to 15 fs, with a B-integral value of about 5 at each stage. It is possible to avoid small-scale self-focusing due to self-filtering of the laser beam during free propagation in vacuum. With optimal parameters of the dispersive mirror, the pulse can be compressed to a duration of less than 5 fs. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Cloud Particle Imager (CPI) and 3-View Cloud Particle Imager (3V-CPI) Instrument Handbook

The cloud particle imager (CPI) is a U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) user facility instrument for measuring the concentration and size of cloud droplet and ice crystals. Hydrometeors entering the tube will be detected by a system of two continuous wave lasers that are perpendicular to each other, monitoring the sample volume. When a hydrometeor obscures both laser beams it is inside the sample volume and a third laser is triggered to illuminate the hydrometeor and a camera records a two-dimensional image. The CPI records images with a resolution of 2.3 μm. Since the camera has 1024 x 1024 pixels, the maximum detectable size is 2.3 mm x 2.3 mm.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1995

Prototype Holographic Atmospheric Scanner for Environmental Remote Sensing (PHASERS)

A ground-based atmospheric lidar system that utilizes a Holographic Optical Telescope and Scanner has been developed and successfully operated to obtain atmospheric backscatter profiles. The Prototype Holographic Atmospheric Scanner for Environmental Remote Sensing is built around a volume phase reflection Holographic Optical Element. This single optical element both directs and collimates the outgoing laser beam as well as collects, focuses, and filters the atmospheric laser backscatter, while offering significant weight savings over existing telescope mirror technology. Conical scanning is accomplished as the HOE rotates on a turntable sweeping the 1.2 mrad field of view around a 42deg cone. During this technology demonstration, atmospheric aerosol and cloud return signals have been received in both stationary and scanning modes. The success of this program has led to the further development of this technology for integration into airborne and eventually satellite earth observing scanning lidar telescopes.

Guerra, David V.↗