Automated analysis of holointerferograms for the determination of surface displacement

Holographic deformation measurements by Fourier transform technique with automatic phase unwrapping

“…The phase function must be a slowly varying function compared to the variation introduced by the carrier frequency. (1) In interferometry, the interference fringes of tilted wavefronts can be described by g(x,y) = a(x,y) + b(x,y) cos[2iruox + (x,y)1 ,…”

“…Optical fibers offer advantages in the field of optical holography79: 1 . They require much less space than a conventional system and allow almost unlimited freedom in selecting object and reference beam angles.…”

The Use of Carrier Fringes and FFT in Holographic Nondestructive Testing

“…whether the surface has moved toward or away from the observer, 1-2 and in assigning the correct fringe orders. In overcoming these difficulties, the carrier fringe technique [1][2][3][4][5][6] is frequently used. The basic principle of the technique is to introduce a known set of linear carrier fringes which modulates the conventional deformation fringes.…”

“…The fast Fourier transform (FFT) method of fringe pattern analysis is successfully used for extracting phase information from fringe patterns caused by the interference of tilted wavefronts. [2][3][4][5][6] Tilting the wavefront generates a linearised fringe pattern which facilitates the use of computerized automatic analysis. The FFT method for computing phases can produce phase maps automatically without the need for locating fringe centers or assigning fringe orders.…”

<title>Numerical analysis of fringe patterns for structural engineering problems</title>

“…This method imposes monotonicity of phase change across the measurement field. Optically, the carrier fringe can be obtained by rotating either the object or the reference beam [7]. The same result can be achieved numerically: an array, having equal numerical values along columns and varying from a maximum to a minimum along rows, must be added to the array representing the image.…”