| 摘要 |
An acoustic imaging system which is particularly useful at low sound levels. A light beam is made to pass twice through a region where the light can interact with the acoustic wave perturbed by the object. As a result a light image is created which is modulated at twice the acoustic frequency. Thus, a portion of the light has a frequency which is raised while another portion of the light has its frequency decreased by the acoustic frequency. Therefore, the modulated light may readily be segregated from the unmodulated light, for example, by a suitable bandpass filter. Because the scattered light does not disturb the image it is feasible to use a higher light intensity so that an optical image is obtainable even at low acoustic intensity. Furthermore, the resolution is improved because the system has a large aperture.
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