Application of the acousto-optic effect to pressure measurements in ultrasound fields in water using a laser vibrometer

James Buick, J. A. Cosgrove, P.-A. Douissard, C A Greated , B. Gilabert

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    Abstract

    A non-intrusive measuring technique, applied to sensing and measuring acoustic waves at ultrasonic frequencies is considered. The method is optically based and so does not interfere with the ultrasound field. The measurement procedure relies on the acousto-optic effect, that is the change in refractive index which occurs with changing pressure in the ultrasound field. This change in refractive index is detected through the change in the path length of a laser beam propagating through the region of interest. Typically these changes are small corresponding to a physical change of the order of 10−6 m. Fourier analysis is used to separate the component of the signal corresponding to the pressure variation from background noise and vibrations which can be dominant. Application of the technique is illustrated for an underwater ultrasound transducer. Measurements are made using the optical technique and compared to measurements taken with a hydrophone. The effectiveness of the optical measuring technique is discussed. It is shown that the laser vibrometer produces a good estimation of the mean beam pressure provided an estimation of the beam width is available, a restriction which is often satisfied; and the acoustic field can be assumed to be approximately constant across the beam.
    Original languageEnglish
    Pages (from-to)3203-3207
    JournalReview of Scientific Instruments
    Volume75
    Issue number10
    Early online date20 Sep 2004
    DOIs
    Publication statusPublished - 2004

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