<title>Holographic measurement of deformation using carrier fringe and FFT techniques</title>

Abstract

This paper describes a carrier fringe technique for measuring surface deformation. In contrast to conventional holography and fringe analysis, this holographic system is based on the fibre optics and automatic spatial carrier fringe pattern analysis techniques. Carrier fringes are generated by simply translating the object beam between two exposures. Single-mode optic fibres are used to transfer both the object and reference beams. The use of optical fibres offers advantages in the field of optical holography. The Fast Fourier Transform (FFT) method is used to process the interferograms. This method offringe pattern analysis is a successful technique for extracting phase information from fringe patterns which result from the interference of tilted wavefronts. The paper also introduces the tile level, minimum spanning tree and phase unwrapping techniques. The method is illustrated by measuring the centrally loaded disk. A correction is made for the non uniform spacing of the carrier fringes, which was introduced by a slight inclination of object. The results are given for disk, including the perspective plot of the out of plane deformation field, the maps of wrapped and unwrapped phase, and a contour map of the unwrapped phase.