Two approaches to the blind phase shift extraction for two-step electronic speckle pattern interferometry

Abstract

A two-step electronic speckle pattern interferometry (ESPI) method with blind phase shift of a reference wave, in which the phase shift extraction is fulfilled by using both a correlation and a discrete Fourier transform (DFT) approaches, is presented here. In the correlation approach, the blind phase shift is calculated via the correlation coefficient between two similar speckle interferograms (SI) differing only by the reference wave phase shift. The DFT approach is based on the blind phase shift extraction from frequency components of SI Fourier spectra. Comparative analysis of these approaches has testified to their high performance. Moreover, it is shown that the correlation approach is more preferable for blind phase shift extraction from SIs with a rough surface than from interferograms with a smooth surface; hence, it is more convenient for ESPI than for phase-shifting interferometry. In addition, this approach provides a lesser level of systematic error of extracted phase shift in comparison with the DFT. The correlation approach was used for experimental definition of Poisson’s ratio for duralumin constructional material by the two-step ESPI method.