Windowed defocused photographic speckle vibration measurement.
The out-of-plane vibration of a rough surface causes an in-plane vibration of its speckle pattern when observed with a defocused optical photographic system. If the frequency of the oscillations is high enough, a time-averaged specklegram is recorded from which the amplitude of the vibration can be estimated. The statistical character of speckle distributions along with the pixel sampling and intensity analog-to-digital conversion inherent to electronic cameras degrade the accuracy of the amplitude measurement to an extent that is analyzed and experimentally tested in this paper. The relations limiting the mutually competing metrological features of a defocused speckle system are also deduced mathematically.
Department of Applied Physics, Faculty for Industrial Engineering, Polytechnic University of Madrid, Jose Gutierrez Abascal 2, 28006 Madrid, Spain. jose.diazdelacruz@upm.es
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Diazdelacruz