written by Richard W. Peterson

Stroboscopic holographic inteferometry has been developed at an advanced undergraduatelevel allowing real-time imaging of standing sound waves in gas filled, closed tube resonators.  A heterodyne Mach-Zehnder interferometer was first built by students to show the feasibility of interferometric detection of sound waves in a small cell.  In the subsequent holographic study, the laser irradiance is modulated by an acousto-optic cell at frequencies near that of the standing wave, and a video camera records the fringe motion due to sound pressure changes.  Fractional fringe shifts are observed for an air filled cell, and multiple fringe shifts are imaged for the case of freon.  Sound reflections from the cell ends are easily observed, with non-sinusoidal waveforms dominating at high intensities due to position of resonator harmonics.

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Last Modified July 23, 2010

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