Determination of fringe order in white-light interference microscopy

Abstract

Combining phase and coherence information for improved precision in white-light interference microscopy requires a robust strategy for dealing with the inconsistencies between these two types of information. We correct for these inconsistencies on every measurement by direct analysis of the difference map between the coherence and the phase profiles. The algorithm adapts to surface texture and noise level and dynamically compensates for optical aberrations, distortions, diffraction, and dispersion that would otherwise lead to incorrect fringe order. The same analysis also provides the absolute height data that are essential to relational measurements between disconnected surfaces.

Development of a time-resolved white-light interference microscope for optical phase measurements during fs-laser material processing

“…A common procedure is the phase-shifting algorithm [8]. Thereby four interferograms are captured sequentially in time at a path length difference of λ/4 and allows for the unambiguous relative phase determination of each pixel [9]. Single interferograms can not be analyzed by this technique.…”

An ultrafast phase modulator for 3D imaging

“…Low coherence interference microscopy combines an interferometer and microscopy into one instrument and is able to image 3D micro engineering surface structures 4 . In its usual operation the object is scanned along the vertical axis (z axis) by a piezoelectric translation stage and good contrast fringes will be obtained only when the optical path difference between the two paths of the interferometer is approximately zero.…”

Quadrature wavelength scanning interferometry

“…The surface height can be estimated from the fringe data as the location at which the envelope of the interference signal reaches the maximum intensity value. Further resolution improvement is possible by estimating the surface height from the phase of the interference signal and solving for the fringe order through the envelope peak [11][12][13]. The advantage of CSI technique over PSI is removal of 2π phase ambiguity.…”