23 June 1995 Additive-subtractive speckle interferometry: phase measurements in noisy conditions
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In this paper, we propose a novel technique for quantitative phase measurements of vibrating structures based on additive-subtractive speckle interferometry. Additive fringe patterns (of poor visibility) corresponding to the object deformation are obtained by pulsing the laser illumination at times when the deformation is at its maximum and minimum amplitudes. A relative inter-pulse phase shift is introduced within each repetitive deformation cycle (e.g. +(pi) /2 for the maximum and -(pi) /2 for the minimum amplitudes respectively) to obtain two consecutive conjugate pairs of phase-shifted additive fringe patterns. Additionally, and inter-frame phase shift is introduced between the conjugate pairs of additive fringe patterns, which are then subtracted and rectified to provide a phase-shifted additive-subtractive fringe pattern of good visibility. Typically four such phase-shifted additive-subtractive fringe patterns with relative phase shift of (pi) /2 between each other are obtained, and these are used to calculate the deformation phase map from which the vibration measurement of a circular membrane. The ability of the technique to perform in relatively severe noisy environments is demonstrated.
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Lewis S. Wang and Sridhar Krishnaswamy "Additive-subtractive speckle interferometry: phase measurements in noisy conditions", Proc. SPIE 2545, Interferometry VII: Applications, (23 June 1995); doi: 10.1117/12.212666; https://doi.org/10.1117/12.212666

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