Review and Comparison of Different Multi-Channel Spatial-Phase Shift Algorithms of Electronic Speckle Pattern Interferometry

Electronic Speckle Pattern Interferometry (ESPI) is the most sensitive and accurate method for 3D deformation measurement in micro and sub micro-level. ESPI measures deformation by evaluating the phase difference of two recorded speckle interferograms under different loading conditions. By a spatial phase shift technique, ESPI allows for the rapid, accurate and continuous 3D deformation measurement. Multi-channel and carrier frequency are the two main methods of spatial phase shift. Compared with carrier frequency method, which is subject to the problem of spectrum aliasing, multi-channel method is more flexible in use. For extracting the phase value of speckles, four-step algorithm and five-step arbitrary phase algorithm are commonly used. Different algorithms have different spatial resolution, operational requirements, and phase image quality. In order to better understand the impact of different algorithms, we present a comparison of these methods of spatial phase measurement in terms of quality and operability. Besides, this paper also conducts experimental research and discussion on the relationship between speckle and corresponding pixels. Basic theory, brief derivation and optical layouts for the three algorithms will be presented. The potentials and limitations of the multi-channel spatial phase shift ESPI system will be demonstrated by examples of precise measurement of deformation.