Optical Imaging of a Complex Ultrasonic Field by Diffraction of a Laser Beam

Lockheed Palo Alto Research Laboratory, Palo Alto, California
Journal of Applied Physics (Impact Factor: 2.18). 04/1967; 5(4):1981 - 1983. DOI: 10.1063/1.1709800
Source: IEEE Xplore


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    ABSTRACT: A Doppler†like phenomenon for acoustic waves is investigated by studying the scattering of a plane acoustic wave from a moving elastic nonlinearity in a nonlinear acoustic medium. By using the Green's†function technique, the first†order waves scattered in both forward and backward directions are calculated in terms of radiations arising from secondary sources induced in the region of the moving elastic nonlinearity. Three typical profiles of the moving elastic nonlinearity (rectangular, sawtooth, and trapezoidal) are considered. A Doppler†frequency shift similar to that in the electromagnetic†wave case is found in the backward†scattered wave but not in the forward†scattered wave. This frequency shift depends on the phase velocity of the acoustic wave in the unperturbed medium and the velocity of the moving elastic nonlinearity but not on the detail profile of the elastic nonlinearity. The intensity of the frequency†shifted scattered wave depends very strongly on the wavenumber of the incident wave, width and detail profile of the elastic nonlinearity, and less strongly on the velocity of the elastic nonlinearity. A possible experimental structure for investigating the Doppler†like phenomenon is suggested. The application of the Doppler†like phenomenon as a tool for investigating dynamical properties of a moving elastic nonlinearity or an elastic shock wave in liquids or solids is also indicated.
    No preview · Article · Aug 1968 · The Journal of the Acoustical Society of America
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    ABSTRACT: A Huygens' expression in integral form is derived for the diffraction of light scattered by weak acoustic waves using convolution theorem. Approximate and closed form expressions are given for two cases: one is quasi-three-dimensional light scattering and the other is three-dimensional light scattering. Properties in the optical imaging of the acoustic field by the Bragg reflection of light are discussed on the basis of the approximate expressions. For the case of the quasi-three-dimensional light scattering, the optical image is aberration-free. On the other hand, for the case of the three-dimensional light scattering, the astigmatism and curvature of field exist in the optical image. Some examples of the optical image are shown and are compared with the theoretical predictions.
    No preview · Article · Jul 1972 · Japanese Journal of Applied Physics
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    ABSTRACT: Acoustic microscopy is a relative newcomer to the field of acoustic imaging which will seek to discriminate micron size structural detail and render visible mechanical microstructure. Although in an early stage of development, wide areas of application are anticipated in both the physical and biological sciences. Recent developments in acoustic microscopy techniques and applications are discussed. Due to the resolution requirement, the present efforts to develop experimentally useful systems employ optical methods of sound amplitude detection through various intermediate methods of coupling. The desired acoustic pattern can be displayed as a hologram or as a conventional image. Phase contrast and dark field techniques are also possible. Resolution better than 10 μm has already been reported and another order of magnitude improvement is only a few years off. Thus, acoustic resolution may soon be demonstrated that is equivalent to that obtained with optical microscopy. During the course of preliminary investigations, various interesting and meaningful contrasts have been demonstrated between acoustic and optical micrographs of the same specimens. These are presented as first examples of applications for acoustic microscopy.
    No preview · Article · Jun 1974 · The Journal of the Acoustical Society of America
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