Quantitative and automatic analysis of interferometric fringe data using carrier fringe and FFT techniques

Abstract

Computerised analysis of optical fringe pattern is a rapidly developing approach to extract quantitative data from phase encoded intensity distribution. This thesis describes results of investigations of quantitative and automatic analysis of interference fringe data using carrier fringe and FFT techniques. Several automatic and semiautomatic fringe analysis algorithms that enable the reduction of fringe patterns to quantitative data have been reviewed and illustrated with some examples. A fresh holographic contouring approach by the movement of object beams through fibre optics is described. The use of fibre optics provides a simple method for obtaining contouring fringes in the holographic system. A carrier fringe technique for measuring surface deformation is described and verified by experiments. A theoretical analysis of the carrier fringe technique is given. The effects of carrier frequency on holographic fringe data has been investigated with computer generated holograms. In contrast to conventional holography and fringe analysis, this holographic system based on fibre optics and automatic spatial carrier fringe analysis technique. The FFT approach is used to process the interferograms. An excellent correlation between the theoretical deformation profile and that suggested by the technique is given. The accuracy of the measurement for a centrally loaded aluminum disk is 0.05pm. The design and construction of a computerised photoelastic stress measurement system is discussed. This full field, fully automated photoelastic stress measurement system is a new approach to photoelastic fringe analysis. Linear carrier fringes generated using quartz wedge are superimposed on fringes formed by the stressed model. The resultant fringes pattern is then captured using a CCD camera and stored in a digital frame buffer. A FFT method has been used to process the complete photoelastic fringe image over the whole surface of the model. The whole principal stress difference field has been calculated and plotted from one single video frame