Reducing phase singularities in speckle interferometry by coherence tailoring

TL;DR

This paper presents a method to reduce phase singularities in speckle interferometry by tailoring the spatial coherence of the light source, enabling more reliable phase unwrapping for rough object characterization.

Contribution

The authors introduce a coherence tailoring technique in a Michelson interferometer that physically averages speckle fields, significantly reducing phase singularities in raw phase measurements.

Findings

Significant reduction in phase singularities achieved.

Standard unwrapping algorithms become applicable.

Method applicable to rough surface measurements.

Abstract

Speckle interferometry is an established optical metrology tool for the characterization of rough objects. The raw phase, however, is impaired by the presence of phase singularities, making the unwrapping procedure ambiguous. In a Michelson setup, we tailor the spatial coherence of the light source, achieving a physical averaging of independent, mutually incoherent speckle fields. In the resulting raw phase, the systematic phase is preserved while the number of phase singularities is greatly reduced. Both interferometer arms are affected by the averaging. The reduction is sufficient to even allow the use of a standard unwrapping algorithm originally developed for smooth surfaces only.