Combining TV holography recording with acoustic phase stepping and image processing, we measure the integrated density distribution in sound fields that propagate in air. We record a given number of two-dimensional cross sections that are tomographically backprojected to give the amplitude and phase distributions of the emitted sound field. The validity of the procedure is demonstrated.
Using a Nd:YAG laser in single and double pulse mode, the dynamic behavior of bubbles generated by a small airgun, placed in a water tank, has been investigated. Single pulse holograms of the bubble have been obtained with the purpose of investigating the shape and smoothness of the surface. Interferometric holography, or double pulse holography, of the bubble has been performed in order to detect the pressure wave from the gun at the early stages of the bubble expansion. The optical phase delay of the laser beams traversing the test section is caused by a local change in the refractive index of the water in the tank due to the acoustic disturbance. A theory for relating the change of the refractive index to bubble parameters is presented. Modeling of interferometric holograms has been performed with the aim of qualitatively comparing them with the recorded holograms. From the holograms it is observed that the surface of the bubble is relatively smooth during the first expansion. During the contraction, and the following oscillations, the bubble surface becomes highly nonsmooth and chaotic due to the developed turbulence in the surrounding water.
A vibrating sound source causes periodic variations of the refractive index in the surrounding medium. A light wave passing through the sound field will experience a corresponding variation of its path length which can be measured by interferometric techniques like TV holography. One TV-holography recording represents the integrated optical pathlength in one direction. The sound source is rotated to record cross sections of the field as seen from different directions. By tomographic backprojection of these recordings, afterward the amplitude and phase of the sound field in any plane of the volume are reconstructed.
A vibrating sound source causes periodic pressure variations in the air. The pressure variations lead to corresponding variations in the refractive index of the air which can be measured using interferometric techniques like TV-holography. Each measurement maps a cross-section of the integrated sound fields. To obtain a complete map of the volume distribution of sound field we record cross-sections from different directions. Using tomographical hackprojection of these recordings, we reconstruct the amplitude and phase of the sound field in any plane of the volume. Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx I I J SPIE Vol. 2358 Vibration Measurements (1 994) I 309 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx
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