Additive-Subtractive Phase-Modulated Speckle Interferometry: Fringe Visibility under Partial Decorrelation

Sridhar Krishnaswamy*, Bruno F. Pouet, Tom C. Chatters

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Additive-subtractive phase modulated speckle interferometry (ASPM-SI) is a technique that minimizes the susceptibility of speckle methods to environmental noise while providing fringes of good visibility. The method requires the acquisition of two consecutive video frames of additive-speckle images of the same two deformed states of an object at a rapid enough rate such that ambient noise is not a problem. The additive-speckle images as expected are of very poor visibility due to the presence of the self-interference term. An interframe phase-modulation is introduced and the two additive-speckle images are digitally subtracted to improve the fringe visibility by removing the self-interference term. The ASPM-SI method works with in-plane and out-of-plane deformation sensitive ESPI as well as with displacement-gradient sensitive speckle-shearing interferometry. It is shown that the ASPM-SI scheme has higher visibility than conventional additive-SI and performs consistently better than subtractive-SI schemes in the presence of partial interframe speckle decorrelating optical noise. Furthermore, it is shown that the fringe visibility of the out-of-plane displacement sensitive interferometer which uses a protected reference beam separate from the object beam can be made to be essentially unity even at complete interframe decorrelation.

Original languageEnglish (US)
Pages (from-to)179-197
Number of pages19
JournalOptics and Lasers in Engineering
Issue number2-3 SPEC. ISS.
StatePublished - 1997

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics
  • Mechanical Engineering
  • Electrical and Electronic Engineering


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