SFFT based phase demodulation for faster interference fringes analysis

Abstract

Try to take advantages of the high-resolution CCD/CMOS developed over the years for real-time three-dimensional deformation/geometry metrology system development, Fourier transform (FT) based algorithms have been integrated to convert interference fringes to wrapped phase maps and then to unwrapped phase maps. All of which led to easy implementation of the algorithms developed over the years to achieve extremely efficient FT computation. Sparse Fast Fourier Transform (SFFT) that only calculating the non-zero coefficient in frequency domain, includes calculations of imaginary part and log, was implemented to further accelerate the computation rate for the above-mentioned FT based operations. Coupling the SFFT accelerated phase map computation approach with Michelson interferometer and Electronic Speckle Pattern Interferometry (ESPI) for near real-time three-dimensional deformation measurement led to the newly developed system. The directions of object deformation are revealed by performing FT to the interference fringes obtained with pre-introduced spatial carrier frequency, which provides a way to retrieve the phase maps by using a single rather than several intensity maps. With only one image frame needed, the interference fringes caused by the deformation could be recorded for off-line phase maps computation if the computation efforts are longer than the recording frame rate. To apply the SFFT algorithm on phase retrieval, a conceptual framework was presented. The benefit of using SFFT as compared to FT was also demonstrated.