Abstract
A method is described whereby sound field distributions can be determined within optically transparent media with a focused beam of light. The optical methods that are well known employ a collimated beam of light and yield information that is averaged over the entire light-sound interaction region. With a focused light beam, however, the sound pressure at the focal region alone can be determined. The method makes use of either the periodic refraction of part of the light beam by the sound field or of acoustically induced birefringence, if it exists. The former has been described in a preliminary report by the authors [Intern. Symp. Acoust. Holography, 2nd March 1969]. The resolution obtainable is determined by the focal spot size and is approximately ΛF/D along the direction of the light beam, where Λ is the acoustic wavelength, F is the focal length of the lens, and D is the diameter of the light beam before focusing. The technique is useful for ultrasound microscopy and results of applications to acoustic imaging and holography will be presented.
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