Abstract
In time-averaged digital holography (TADH), one records a hologram of a periodically oscillating object by using the exposure time typically much longer than the oscillating period. Problems arise when the total available exposure time is restricted or when the oscillation period is unknown. In this work we investigate effects of short exposure time to the quality of the recorded hologram and show that, to record high fidelity information in a shortest possible time, close estimates of the oscillating period and the phase are required. To that end we propose an advanced procedure based on short hologram exposures that allows obtaining such estimates. The procedure is efficient both in the number of recordings and their total exposure time.
Highlights
Time-averaged digital holography (TADH) is a powerful technique for detecting resonant vibrations of objects
The problem of recording holograms with exposures shorter than the vibration period occurs in TV holography, where the standard video system (25 or 30 frames per second) has a fixed exposure time which limits its use regarding the fidelity of measured fringe patterns in lower frequency range
We investigate the fidelity of the fringe information in relation to the exposure time of the recorded holograms
Summary
Time-averaged digital holography (TADH) is a powerful technique for detecting resonant vibrations of objects. The Bessel description of fringe information is accurate under the restriction of having the hologram exposure time τ either equal to or much greater than the period of vibration T Such a definition of τ is sufficient for most of the TADH applications. The problem of recording holograms with exposures shorter than the vibration period occurs in TV holography, where the standard video system (25 or 30 frames per second) has a fixed exposure time which limits its use regarding the fidelity of measured fringe patterns in lower frequency range. We propose a procedure for determining the frequency and the phase of an unknown harmonic vibration To accomplish this task, we investigate the fidelity of the fringe information in relation to the exposure time of the recorded holograms. We use the correlation measures to calibrate the phase synchronization of the system, and we find the minimum number of holograms required to record the complete information on the measured vibration
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