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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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Solid, linear chain hydrocarbons with molecular weight ranging from about 300 to 2000 can serve as long-lived recording medium in optical memory system. Suitable recording hydrocarbons include microcrystalline waxes and low molecular weight polymers or ethylene.
When reference beam strikes target it undergoes Doppler shift dependent upon target velocity. To compensate, object beam is first reflected from rotating cylinder that revolves in direction opposite to target but at same speed. When beam strikes target it is returned to original frequency and is in phase with reference beam. Alternatively this motion compensator may act on reference beam.
Three-dimensional system uses two additional mirrors and path compensators. It is essentially three mutually-orthogonal one-dimensional systems with common focus. Laser beam is split into four parts, three of which are object beams; and fourth is reference beam. Size of each ellipse depends on magnitude of velocity vectors.
A program to apply holography for nondestructive testing of the X-248 rocket motor was undertaken. The objective was to establish the capability of holography in detecting known unbonding between liner and propellant. Holography was performed employing stressing techniques: (1) acoustical, (2) thermal, (3) radiative, and (4) static loading. Radiative stressing was successful in locating a large area of liner/propellant unbond. The results were correlated with destructive testing. Theoretical analysis provided an understanding of motor case holography in conjunction with radiative stressing.
A system for the analysis and measurement of thin films in which the light output of a laser is split into two beams is discribed. The first beam is focused to illuminate the entire area of a photographic plate and the second beam is colummated and directed through a relatively small portion of the photographic plate onto the sample with the film to be observed. The surface of the sample is positioned at a slight angle with respect to a plane normal to the second beam and the light reflected from the sample arrives back at the photographic plate in a region other than through which the second beam originally passes. By making two successive exposures during the deposition of material on the surface of the sample, holograms are recorded on the photographic plate. The plate is then developed and interference lines of the hologram provide a measurement of the film or material deposited between exposure.
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Explore the source record for details and available documents.
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Explore the source record for details and available documents.
A new experimental method was used to optically investigate the acoustic field radiated from supersonic jets. The method utilizes a pulse ruby laser to obtain double exposure holograms of the sound field of a supersonic jet. The jet remains on during both exposures thus eliminating the no-flow exposure. The time separation between the pulses can be varied depending on the spectral component of the radiation to be observed. Optical records were obtained for supersonic jets with exit Mach number 1.0, 1.5 and 2.0. It was found that high frequency acoustic radiation mainly originates from the regions near the nozzle exit, whereas the low frequency noise is generated from regions further downstream. These findings are consistent with the acoustic data obtained by other investigators.
The sensitivity of crystals of LiTaO3 to hologram formation was observed to vary with impurity concentration from a value comparable to the most sensitive doped LiNbO3 for an impure crystal to a value more than five orders of magnitude smaller for a purer crystal. Fatigue effects were observed upon write-erase cycling. These effects were dependent upon writing and erasure polarization and power and could be virtually eliminated by proper choice of optical parameters.
The sensitivity of LiTaO3 crystals to hologram formation has been observed to vary with impurity concentration. For a writing wavelength of 488.0 nm and power density of 1.1 W/sq cm, the sensitivity varied from a value comparable to the most sensitive doped LiNbO3 for an impure crystal to a value more than 5 orders of magnitude smaller for a purer crystal. Fatigue effects were observed upon write-erase cycling. These effects were dependent upon writing and erasure polarization and power density and could be minimized by proper choice of optical parameters.
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Problems associated with digital computer generation of holograms are discussed along with a criteria for producing optimum digital holograms. This criteria revolves around amplitude resolution and spatial frequency limitations induced by the computer and plotter process.
For a given wavelength, the angle of incidence for the optimum relative efficiency was sensibly the same for the various gratings independently of the Nb grooves/mm. In spite of the fact that all these gratings were blazed at the same wavelength this was not obvious a priori as the blaze angle varied from 1.71 deg for 600 gr/mm to 14.41 deg for the 5,000 gr/mm grating.
In reduced LiNbO3:Mn both the photorefractive sensitivity and the simultaneously measured photocurrent result from drift with a polarization-dependent effective 'internal field' of about 6 kV/cm. In reduced undoped LiTaO3 the observed difference in applied fields of the minimum photorefractive sensitivity and zero photocurrent imply charge transport is by a mechanism that cannot be completely described by diffusion and drift in an electric field. The direct measurement of the harmonic content of phase gratings written in several LiNbO3 and LiTaO3 crystals shows termination of charge-transport results from the space-charge field of the hologram.
A theory concerning the problem of fringe interpretation reported by Hecht et al. (1973) is extended and a simpler semiquantitative method for the assessment of the fringes is developed. According to the new method, the fringe contrast between any two points on an object, is determined on the basis of the difference of the path-length changes at each point. The theoretical development of the method is discussed and a description of experimental results is given.