Contrast-enhanced and phase-controlled stroboscopic additive fiber optic TV holography for whole field out-of-plane vibration analysis

A new technique for real-time contrast enhancement and phase control of fringes in additive stroboscopic TV Holography applied to out-of-plane vibration analysis and its implementation of a fiber optic electronic speckle pattern interferometer (FOESPI) are presented. Synchronous stroboscopic illumination, firing two pulses per object's vibration period, is combined with simultaneous interpulse (high frequency) and interframe (low frequency) phase modulation in the reference arm of the ESPI yielding a sequence of frames (interferograms) that are grabbed and processed in real-time. With this artifice both speckle and fringes phases are independently controlled by means of the parameters of modulation enabling speckle contrast inversion, as required to enhance the visibility of fringes by sequential subtraction, as well as dynamic fringe phase shifting to solve peak-valley ambiguity.