Unambiguous profilometry by fringe-order identification in white-light phase-shifting interferometry

Abstract

This paper proposes a white-light phase-shifting method for interferometry, in which the absolute phase of each point is measured individually. During the axial scanning of the sample, eight phase-shifted intensities are recorded, while the fringe visibility is maximum. A seven-point algorithm, which compensates for the variation in the fringe visibility due to the coherence envelope, allows the computation of the relative 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 deduced from the evolution of the fringe envelope between two consecutive PZT positions and from the computed relative phase. This method allows unambiguous profilometry with a nanometric resolution by using a phase-shifting method. Furthermore, both the necessary storage memory and the computation time can be significantly reduced by comparing with already-demonstrated white-light profilers working in the same resolution range.