Illustrations

This paragraph presents an illustration of the phase stepping method. We consider an interferogram with a fringe pattern such as the one represented on figure 13.

We now apply the phase stepping method with 4 phase steps separated by , generated (for example) with a piezoelectric transducer. Figure 14 shows the 4 shifted interferograms, obtained with phase steps of 0, , and respectively.

As we have seen previously, the phase can be calculated using the following relation:

Figure 15 shows the results obtained after applying the algorithm to the 4 shifted interferograms.

The phase is only obtained modulo , thus producing the phase jumps observed on the figure. When we apply a phase unwrapping algorithm, we obtain the result shown on figure 16.

The reader will note that the 0 value of the phase measurement is arbitrary and depends on the starting point of the phase unwrapping algorithm. This level can therefore be adjusted if it is possible to know a point in the phase map where the phase is really equal to 0.