Systematic errors of phase-shifting speckle interferometry

A theoretical and numerical investigation of the systematic phase errors in phase-shifting speckle interferometry is presented. The theoretical invest igation analyzes the behavior of some systematic error induced by intensity variations in two cases of data-computing techniques. The first case deals with the technique in which the phase change is computed, unwrapped, and t hen linearly filtered; the second case deals with the technique in which th e data are linearly filtered before the arctangent calculation and then unw rapped. With the first filtering technique it is shown that it is preferabl e when the phase change is of relatively low spatial frequency, leading to a particularly accurate method. With the second case it is demonstrated tha t an important parameter of speckle interferometry is the modulation factor of the interference frame that induces phase errors when the data are filt ered before the arctangent calculation. We show that this technique is bett er than the first when the phase change is composed of high-spatial-frequen cy variations. The theoretical investigation of the two techniques is compa red with numerical simulations, considering the frequency characteristics o f the phase change, and this shows a good match between theory and simulati ons. (C) 2001 Optical Society of America.