Single phase-step algorithm for phase difference measurement using ESPI

The paper describes a new algorithm that uses only two mutually phase-stepped interferograms per deformation state in order to retrieve module 2 pi the phase signal due to deformation. It is suited for use in ESPI where the initial phase in the interference term is the phase of speckle that varies randomly over the imaging sensor. Any phase step value except those close to multiples of pi can be applied. Practical advantages of the algorithm are outlined. An analysis of phase measurement uncertainty is presented, results are discussed and compared with those from standard phase-shifting algorithms. Obtained results prove that measurement uncertainties smaller 2 pi/20 are feasible.