Determination of the best phase step of the Carré algorithm in phase shifting interferometry

The Carré algorithm is a widely used phase shifting algorithm in optical interferometry because its phase step is arbitrary. It is important to determine the best phase step in order to minimize the phase measurement errors. A detailed error analysis is carried out to reveal the relationships between the phase measurement errors and the phase step, according to which a suitable phase step can be selected. A good and recommendable phase step is 110°, but it is only valid for minimizing the influence of the random intensity noises. For a better choice the behavior of the experimental system should be considered.