  We propose to use a Nomarski imaging interferometer to measure the
out-of-plane displacement field of MEMS. It is shown that the measured optical
phase arises both from height and slope gradients. Using four integrating
buckets a more efficient approach to unwrap the measured phase is presented,
thus making the method well suited for highly curved objects. Slope and height
effects are then decoupled by expanding the displacement field on a functions
basis, and the inverse transformation is applied to get a displacement field
from a measure of the optical phase map change with a mechanical loading. A
measurement reproducibility of about 10 pm is achieved, and typical results are
shown on a microcantilever under thermal actuation, thereby proving the ability
of such a set-up to provide a reliable full-field kinematic measurement without
surface modification.
