Abstract: This paper presents a method for measuring the complexmode of a vibrating structure using two separate dualreference stepped strobe phase (0, 90 degrees)holograms and a new spatial phase shifting techniqueduring reconstruction. Spatial phase shifting isaccomplished by scanning a pencil of a laser conjugatereconstruction beam in four equal steps across thehologram; four shifted phase real images are obtainedfor each of the two holograms and each set of fourimages is processed to get the unwrapped phasedistribution. The vibration amplitude and phase arethen obtained using these two phase distributions. Thenew spatial phase shifting technique greatly simplifiesdata acquisition and optical readout since only asingle reconstruction beam is used to reconstruct bothwavefronts for each hologram. The theory andexperimental results are presented. !6
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