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Spatial phase-shift reconstruction technique for measurement of complex mode vibration by dual-reference-stepped strobe phase holographic interferometry

This paper presents a method for measuring the complex mode of a vibrating structure using two separate dual reference stepped strobe phase (0, 90 degrees) holograms and a new spatial phase shifting technique during reconstruction. Spatial phase shifting is accomplished by scanning a pencil of a laser conjugate reconstruction beam in four equal steps across the hologram; four shifted phase real images are obtained for each of the two holograms and each set of four images is processed to get the unwrapped phase distribution. The vibration amplitude and phase are then obtained using these two phase distributions. The new spatial phase shifting technique greatly simplifies data acquisition and optical readout since only a single reconstruction beam is used to reconstruct both wavefronts for each hologram. The theory and experimental results are presented.