The data acquisition from the shape of an object is a must to complete its quantitative
displacement measurement analysis. Over the past years whole field of view optical non-invasive
testing has been widely used in many areas, from industrial ones to, for instance, biomedical
research topics. To measure the surface contour from the tympanic membrane (TM) of ex-vivo cats
digital holographic interferometry (DHI) is used in combination with a two-illumination
positions method: the shape is directly measured from the phase change between two source
positions by means of a digital Fourier transform method. The TM shape data in conjunction with
its displacement data renders a complete and accurate description of the TM deformation, a
feature that no doubt will serve to better comprehend the hearing process. Acquiring knowledge
from the tissue shape indicates a mechanical behavior and, indirectly, an alteration in the
physiological structure due to middle ear diseases or damages in the tissue that can
deteriorate sound transmission. The TM shape contour was successfully measured by using two
source positions within DHI showing that the TM has a conical shape. Its maximum depth was
found to be 2 mm, considering the umbo as the reference point with respect to the TM annulus
plane, where the setup is arranged in such a manner that it is capable of measuring a height of
up to 7 mm.
Electronic speckle pattern interferometry has been used to study resonant in-plane vibrations of a thin square metal plate. An in-plane sensitive arrangement is used with dual-beam illumination from a pulsed laser. Fringe patterns are formed which show a cosinusoidal intensity profile. These fringe patterns inherently carry phase information, which is extracted using the single phase step technique and analyzed to determine the amplitude and phase for the horizontal and vertical components of in-plane vibration. These are automatically combined to yield the total in-plane vibration mode. The final result is displayed as vectors drawn over an image of the object.
Addition fringes are obtained in real time from electronic speckle pattern interferometry (ESPI) by use of a twin-pulsed laser when two pulses are fired during a single field of a CCD camera. This enables object deformations to be studied in harsh environmental conditions. However, the fringe patterns have poor visibility because optical noise is additive. To our knowledge automatic phase extraction from addition fringes has not previously been achieved: Low-pass filtering to suppress random speckle noise also eliminates the fringes because of their low visibility. Two phase-stepping algorithms that calculate phase from ESPI fringes without the need for a preprocessing filter are presented. In the first ESPI subtraction fringes are considered, for which an improvement in accuracy is seen, and in the second ESPI addition fringes are considered, which, we believe, has enabled the phase to be extracted for the first time. The algorithms are demonstrated with theoretical data and with experimental ESPI fringepatterns recorded with a cw laser. As presented, they form the first step toward a procedure that can beused with twin-pulsed ESPI.
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