Abstract
A method for determining the position of the zero-order fringe in a metrological experiment with digital speckle pattern interferometry is proposed. It is based on an averaging procedure with shifted images obtained before and after a load is applied. This technique is a complement to the phase-shifting methods. Experimental examples are shown.
Highlights
Background of the TechniqueThe basic Digital speckle pattern interferometry (DSPI) equation describing the intensity difference in an image point between a reference frame and the current one is given by[8 ] (1)where 70 and 7r are the intensities of the object and the reference beams, respectively,
Where 70 and 7r are the intensities of the object and the reference beams, respectively,
P(x, y, z), suffering a displacement, d = d(x, y, z ), 8 is given by[9] where N(P) is the number of fringes in the image between a fixed point and P, X is the light wavelength, eB is a unit vector from P in the observation direction, is a unit vector from P in the illumination direction, and S is the sensitivity vector
Summary
Interferometry can be used to produce a fringe pattern that represents the field surface displacement of an object in response to some change in mechanical loading.[1]. Analogical[5] and digital[6] holographic contouring have used multiple illumination sources to modify the fringe structure as a means for reducing order assignment ambiguity Another technique for contouring with multiple digital images is to synthesize a particular fringe profile, namely, that of an approximate delta function.[7] That fringe corresponds to the zero-order interference fringe, showing the locus of places with a zero optical path difference between the two illuminating beams. Using such a single-fringe projection, we can eliminate order ambiguity.
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