UNAMBIGUOUS PROFILOMETRY BY FRINGE-ORDER IDENTIFICATION IN WHITE-LIGHT PHASE-SHIFTING INTERFEROMETRY

This paper proposes a white-light phase-shifting method for interferom etry, in which the absolute phase of each point is measured individual ly. During the axial scanning of the sample, eight phase-shifted inten sities are recorded, while the fringe visibility is maximum. A seven-p oint algorithm, which compensates for the variation in the fringe visi bility due to the coherence envelope, allows the computation of the re lative phase. Then, the absolute phase is computed from this relative phase, the piezoelectric transducer (PZT) position at the beginning of the data recording and from the fringe order. The fringe order is ded uced from the evolution of the fringe envelope between two consecutive PZT positions and from the computed relative phase. This method allow s unambiguous profilometry with a nanometric resolution by using a pha se-shifting method. Furthermore, both the necessary storage memory and the computation time can be significantly reduced by comparing with a lready-demonstrated white-light profilers working in the same resoluti on range.