Maximal fraction of acceptable measurements in phase-shifting speckle interferometry: a theoretical study

The interference between a uniform reference wave and a speckle object wave results in variable fringe contrast and background level. Taking these variations into account, we optimize system parameters of phase-shifting speckle interferometry. The results show that the optimal reference intensity should always be equal to one fourth of the detector’s saturation level. The optimal reference to the object-intensity ratio shows an increase from one up to, in most practical cases, six as a chosen interference dynamic range increases from its minimum value. The dependence of a maximal fraction of acceptable measurements on the dynamic range is calculated. Numerical examples indicate that we may hope for a readout accuracy in the range of 1/50th to 1/100th of a fringe period and still cover more than half of the image area with acceptable data. These data are taken without spatial averaging and have maximum resolution.