RESUMO
A technique is described for recording and reconstructing two- and three-dimensional color images utilizing a fringe-modulated speckle pattern. A multiple-aperture imaging system generates the modulated speckles and produces an image plane hologram in which the various complex waveforms, passing through the individual apertures, operate simultaneously as object and reference beams. This holographic recording system is considerably less sensitive to external vibration than conventional off-axis holography and requires much less stringent temporal- and spatial-coherence specifications for its light source.
RESUMO
The measurement of ultrasonic surface wave (USW) velocity is difficult using the pulse overlap method (POM) in the presence of an externally applied stress. Coupling variations between the sample and the transducer cause nonuniform distortions of the two received pulses which makes the overlap condition difficult to determine over an extended stress range. The adaptation in this paper of a single transducer configuration to generate and detect the USW eliminates coupling variations between two or more transducers. In addition, two parallel, precisely positioned and contoured grooves are laser scribed on the sample surface to provide the necessary overlap echoes. Since both echoes are reflected only once by identical grooves and are equally affected by the distortions due to coupling variations, the overlap condition is relatively unaffected by the external stress and the accuracy of the USW velocity measurement is increased significantly.
