A FOURIER-TRANSFORM TECHNIQUE TO OBTAIN PHASE DERIVATIVES IN INTERFEROMETRY

A Fourier transform technique to compute the phase derivatives directly from the wrapped (modulo 2pi) interferometric phase maps is presented. The phase discontinuities are eliminated by converting the wrapped phase map into a continuous fringe pattern and the phase derivative is obtained using a differentiator in the Fourier space. Sign information during the phase-to-fringe conversion process is preserved using a computer generated carrier. The proposed technique can be used to obtain phase derivatives, even when the phase map is ill-conditioned for phase unwrapping, due to the presence of noise. This technique can be used with advantage in areas such as experimental stress analysis, where the phase derivative (proportional to strain) and not the continuous phase (proportional to displacement) is the quantity of interest.