Holographic characterization of aerospace components
Pulsed laser holographic applications to aerospace components nondestructive testing, inspecting electron beam welds and internal structural flaws
Erf, R. K.↗
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Holographic interferometry
Holographic interferometry application to laser NDT of objects with nonoptical surfaces, describing techniques and industrial uses
Wuerker, R. F.↗
Summary of the nondestructive evaluation session
Advanced material systems and designs require improved nondestructive evaluation (NDE) techniques for quality control, failure analysis and properties monitoring. Some advanced NDE techniques such as infrared scanning systems, laser holographic applications and the use of the Mossbauer effect are outlined. Applications of these techniques are discussed for evaluating the new space shuttle external insulation materials, aircraft structures and engine components, and precursors to crack initiation and growth.
Stinebring, R. C.↗
In vivo blood-flow mapping
Application of laser doppler techniques to commercially available, low loss fiber optics allows direct reading of blood velocity within tiny blood vessels.
Frazer, R. E.↗
Intensities and N2 collision-broadening coefficients measured for selected H2O absorption lines between 715 and 732 nm
Intensities and N2 collision-broadening coefficients are measured for 62 water vapor absorption lines between 715 and 732 nm potentially applicable to laser remote sensing of atmospheric water vapor. Absolute line strengths and widths were determined from spectra corrected for instrument resolution, air-path absorption and Lorentz and Doppler broadening for pure water vapor and water vapor-nitrogen mixtures in a multipass absorption cell with a base path length of 25 m (White cell). Line strengths are observed to range from 4 x 10 to the -25th to 4 x 10 to the -23rd kayser/molecule per sq cm, and collision broadening coefficients are found to be approximately equal to 0.1 kayser/atm.
Wilkerson, T. D.↗
NASA technical advances in aircraft occupant safety
NASA's aviation safety technology program examines specific safety problems associated with atmospheric hazards, crash-fire survival, control of aircraft on runways, human factors, terminal area operations hazards, and accident factors simulation. While aircraft occupants are ultimately affected by any of these hazards, their well-being is immediately impacted by three specific events: unexpected turbulence encounters, fire and its effects, and crash impact. NASA research in the application of laser technology to the problem of clear air turbulence detection, the development of fire resistant materials for aircraft construction, and to the improvement of seats and restraint systems to reduce crash injuries are reviewed.
Enders, J. H.↗
Lasing characteristics of gas mixtures involving UFG: Application to nuclear pumping of lasers
Intense blue-green fluorescence from a structured band centered at lambda approximately 484 nm was observed from Ar, CF3I and NF3 gas mixtures excited by an electron beam. This emission was tentatively assigned to the E yields A transition of the iodine monofluoride (IF) molecule. The fluorescence efficiency of the IF(E yields A) band and the IF (E) state radiative lifetime were estimated to be approximately 6% and 15 ns, respectively. The emission band structure, the short IF(E) radiative lifetime and the Franck-Condon shift between the E and A states suggest that IF is an attractive candidate for a blue-green laser.
Verdeyen, J. T.↗
Composite wall concept for high temperature turbine shrouds: Survey of low modulus strain isolator materials
Plasma sprayed yttria stabilized zirconium oxide turbine seal specimens, incorporating various low modulus porous metal strain isolator pads between the zirconium oxide and a dense metal substrate, were subjected to cyclic thermal shock testing. Specimens that had a low modulus pad composed of sintered FeNiCrAlY fibermetal survived 1000 thermal shock cycles without spalling of the ceramic. A figure of merit for the low modulus pad materials taking into consideration the elastic modulus, thermal conductivity, strength, and oxidation resistance of the pad was proposed, and showed reasonable agreement with the thermal shock results. A potential surface distress problem on the zirconium oxide, associated with nonuniform temperature distribution and rapid stress relaxation was identified. One approach to solving the surface distress problem through application of laser surface fusion of the zirconium oxide layer showed some promise, but improvements in the laser surface fusion process are necessary to prevent process associated damage to the ceramic.
Bill, R. C.↗
The application of free-electron lasers to the transmission of energy in space
Previously announced in STAR as N82-25499
Segall, S. B.↗
Application of VLBI and satellite laser ranging to geodynamics
The NASA Crustal Dynamics Project has developed very-long baseline interferometer (VLBI) systems and satellite laser ranging (SLR) systems for geodynamics measurements. In VLBI, a radio noise signal from a distant quasar is received by two or more radio antennas and coherently recorded. These recordings are cross-correlated to determine the relative signal delays between stations which are used to derive the vector baselines between the stations. The SLR systems accurately determine the range to a retroreflector satellite as a function of time with short laser pulses. These range measurements from several stations to the same satellite are used in orbit analysis programs to determine the position of the stations and the vector baselines between the stations. Measurements with these systems have achieved precisions of a few centimeters in length for distances of several thousand km. These systems are now operating in a global network for measuring the relative motion of the N. American, Pacific, S. American, Nazca, Eurasian and Australian tectonic plates. Highly mobile VLBI and SLR systems are being operated at many sites in the active earthquake areas in western N. America in order to determine the crustal deformation and strain accumulation.
Coates, R. J.↗
Performance of OOK and low-order PPM modulations in optical communications when using APD-based receivers
The paper computes direct detection laser communications receiver performance when using avalanche photodiode (APD) detectors. The performances are compared in terms of bit error probability vs average signal required per bit when the transmitter uses either on-off keying (OOK) or low-order PPM formats. It is shown that QPPM requires 3 dB less signal than OOK, while BPPM requires the same or slightly more than OOK for the same performance. Optimum APD gain values range from 200 to 400. When using QPPM, k(eff) = 0.006, and optimum gain, 60 signal counts/bit are required at 500 Mbits/s for a 0.000001 bit error probability. It is concluded that QPPM may be an attractive signaling format for some fiber or free space laser communication applications.
Abshire, J. B.↗
Mixing layer control for tangential slot injection in turbulent flows
Tangential injection into turbulent flows is one of the most promising methods of minimizing skin friction and providing thermal protection. The technique also has application to laser hardening. The effectiveness of the injected material can be increased if the spreading rate of the resulting mixing region can be reduced. Various techniques which have been shown to be effective in manipulating the rate of growth of mixing layers under certain conditions have been applied to a slot configuration having a thick external turbulent boundary layer. These include geometry modifications to the slot lip trailing edge and acoustic excitation of the slot exit plane over a wide range of frequencies. Neither of these approaches produced any noticeable effect on the downstream evolution of the mixing layer. This lack of effectiveness is attributed to the dominating influence of the well-developed incoming turbulent boundary layer. The placement of large-eddy breakup devices in this boundary layer upstream of the injection point did produce significantly lower velocities in the near-wall region of the flow downstream of the slot exit.
Mcinville, R. M.↗
A holographic interferometric study of an axisymmetric shock-wave/boundary-layer strong interaction flow
The results of a holographic interferometric and analytical examination of shock wave/turbulent boundary layer interactions occurring in a flow near a cone-cylinder intersection are reported. A Mach 2.85 flow with an Re of 18 million was used, along with cone angles of 12.5, 20 and 30 deg. Negligible, incipient and large scale separations were observed. The subsonic layer of the boundary always remained thin and was usually penetrated by the shock wave. An Abel transform, applied to the interferometric traces, yielded a great deal of data on the density field when combined with data from application of laser velocimeter, pressure tap and oil flow techniques.
Dunagan, S. E.↗
Symposium (International) on Combustion, 20th, University of Michigan, Ann Arbor, MI, August 12-17, 1984, Proceedings
The present conference on combustion phenomena considers topics in automotive engine combustion, turbulent reacting flows, the modeling of practical combustion systems, reaction kinetics, combustion-generated particulates, combustion diagnostics, coal combustion process characteristics, fire-related phenomena, explosion/detonation phenomena, spray combustion, ignition/extinction, laminar flames, pollutant formation processes, practical combustor devices, and rocket propellant combustion. Attention is given to the contributions of combustion science to piston engine design, modeling and measurement techniques for turbulent combustion, the specific effects of energy, collisions, and transport processes in combustion chemistry kinetics, the formation of large molecules, particulates and ions in premixed hydrocarbon flames, the application of laser diagnostics to combustion systems, spark ignition energies for dust-air mixtures, the controlling mechanisms of flow-assisted flame spread, the ignition and combustion of coal-water slurries, spontaneous ignition of methane, turbulent and accelerating dust flames, and the temperature sensitivity of double base propellants.
Source record↗
Application of an InGaAsP diode laser to probe photodissociation dynamics - I(asterisk) quantum yields from n- and i-C3F7I and CH3I by laser gain vs absorption spectroscopy
Initial measurements on I-asterisk yields of alkyl iodides at 266 nm are reported using gain vs. absorption spectroscopy with an InGaAsP diode probe laser. The results are 102 percent + or - 4 percent, 102 percent + or - 7 percent, and 73 percent + or - 4 percent for n-C3F7I, i-C3F7I, and CH3I respectively. Future prospects for the development of diode laser systems and for their use in dynamical studies are discussed.
Hess, W. P.↗
Use of induced fluorescence measurements to assess aluminum-organic interactions in acidified lakes
The application of laser fluorosensing to the tracing of metals in acid lakes is proposed. The effects of the metals on the dissolving organic carbon (DOC) fluorescence is studied using laboratory mixed water samples and natural water samples from Hamilton and Big Moose Lakes in New York. The operation of the laser fluorosensing system employed in the experiment is described. The DOC fluorescence was quenched by Al, Cu, and Fe, and the relation between pH and the quenching rate is examined. The humic substances fluorescence spectra are analyzed to estimate the concentrations of DOC in water and the relative concentration of Al. The interference problems caused by chemical competition between metal ions and ligands, and changes in the background DOC fluorescence are discussed. It is noted that an airborne laser fluorescence is useful for detecting elevated concentrations of metals.
Vodacek, A.↗
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.↗
The use of molten salts as physical models for the study of solidification in metals and semiconductors
It is presently noted that molten salts possess attributes rendering them attractive as physical models of cast metals in solidification studies. Molten alkali halides have an approximately correct Prandtl number for this modeling of metallic melts, and are transparent to visible light. Attention is given to solidification in the LiCl-KCl system, in order to determine whether such phenomena as solute rejection can be observed and characterized through the application of laser schlieren imaging.
Koziol, Jurek K.↗