Full-bandwidth phase-shifting methods as well as band-limited fringe carrier
techniques are both problematic when testing high-NA spherical surfaces
in Fizeau interferometers. Phase stepping is usually performed by moving a
sample and reference sphere relative to each other along the optical axis. At
a high NA the method suffers from phase-shift inhomogeneity across the sample
surface. Fringe carrier techniques rely on a minimum fringe frequency and
call for an off-axis position of the sample, which in turn introduces condenser
aberrations. Distortion of the imaging optics generates further apparent
aberrations. We propose to combine both principles. The
phase shifts are replaced by a set of very low tilts such that the sample is
virtually on axis. Initial wavefront estimates are generated by a fringe carrier
method. An adaptive Misell-type algorithm combines the interferometric
data and iteratively improves the reconstructed wavefront until full spatial
bandwidth is achieved.
© 2006 Optical Society of America
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