55 research outputs found

    Applications of high power lasers

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    The use of computer generated, reflection holograms in conjunction with high power lasers for precision machining of metals and ceramics was investigated. The Reflection holograms which were developed and made to work at both optical wavelength (He-Ne, 6328 A) and infrared (CO2, 10.6) meet the primary practical requirement of ruggedness and are relatively economical and simple to fabricate. The technology is sufficiently advanced now so that reflection holography could indeed be used as a practical manufacturing device in certain applications requiring low power densities. However, the present holograms are energy inefficient and much of the laser power is lost in the zero order spot and higher diffraction orders. Improvements of laser machining over conventional methods are discussed and addition applications are listed. Possible uses in the electronics industry include drilling holes in printed circuit boards making soldered connections, and resistor trimming

    New measuring techniques using holographic and speckle interferometric recording

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    Electronic and photographic interferometric recording, and their combination, result in several novel optical measuring techniques. The interferometric properties of holographic and speckle processes in these techniques encompass fields such as lapse time, real time and time average holographic interferometry, two-wavelength and multiple-index speckle contouring, figure (moire) interference, photographic bleach processes and electronic processing. Each of these fields is analysed and conclusions are drawn in their interaction with the proposed techniques. A clear and simple approach to optical wave theory is intended with emphasis in scalar wave theory. [Continues.

    Optical measurement of local mass transfer coefficients in naturally convecting systems

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    Use of an incorparated hardening develpoer to produce a phase modulated hologram in a silver halide material

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    A holographic material is investigated which uses an incorporated hardening developer in a fine grain silver halide emulsion to first obtain a hardening modulation in the gelatin, and then convert the hardening modulation to a refractive index modulation by alcohol dehydration similar to the dichromated gel process. The hardening modulation is observed but conversion to a refractive index modulation by alcohol dehydration is not seen. The feasibility and problems of the material are evaluated

    Contributions to image reconstruction

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    The problem of image reconstruction from indirect measurements is considered. Reconstruction methods for the following types of measurement are presented in detail: (a) Radiant intensity at the image plane of the transmission electron microscope. (b) Radiant intensity of X-ray diffraction from paracrystalline and fibrous macromolecular specimens. (c) Projections which may be incomplete in linear extent, as well as sampled and finite in number. Image reconstruction from measurements (a) and (b) is affected by the phase problem. It is shown how: (a) Off-set holography might be achieved in the electron microscope when examining a crystalline specimen or an aperiodic specimen deposited on to a crystalline substrate. A diffraction plane mask selects one of the diffracted beams from the crystal to act as the holographic reference. Microscope aberrations may be compensated after reconstruction from the hologram. An optical simulation of the process is reported. (b) Under certain conditions it is possible to deduce the continuous diffraction pattern of a molecule from measured crystal structure factor intensities. Theoretical results are derived for the diffraction from generalised helix-like structures. A recently proposed model of the DNA molecule is shown to be consistent with much of the available X-ray data. (c) Preprocessing of projection data may be effected efficiently when the data are measured with a fan beam of radiation. (d) Useful images may be' reconstructed from projections which are incomplete in the sense that they are "hollow" or "truncated". The modified back-projection method of image Reconstruction is analysed in detail. "Hollow" and "truncated" projections are defined to be projections which have their inner and outer parts missing, respectively. Theoretical considerations show that unambiguous reconstruction is possible from hollow but not from truncated projections. Practical methods are presented which preprocess the incomplete projections so that reconstructions can be obtained from them using the modified back-projection method. Examples showing reconstructions of a test object from computer-generated incomplete projections are used to demonstrate the effectiveness of the preprocessing methods

    Quantitative void characterization in structural ceramics using scanning laser acoustic microscopy

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    The ability of scanning laser acoustic microscopy (SLAM) to characterize artificially seeded voids in sintered silicon nitride structural ceramic specimens was investigated. Using trigonometric relationships and Airy's diffraction theory, predictions of internal void depth and size were obtained from acoustic diffraction patterns produced by the voids. Agreement was observed between actual and predicted void depths. However, predicted void diameters were generally much greater than actual diameters. Precise diameter predictions are difficult to obtain due to measurement uncertainty and the limitations of 100 MHz SLAM applied to typical ceramic specimens
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