P. Sandoz et al., UNAMBIGUOUS PROFILOMETRY BY FRINGE-ORDER IDENTIFICATION IN WHITE-LIGHT PHASE-SHIFTING INTERFEROMETRY, J. mod. opt., 44(3), 1997, pp. 519-534
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.