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Proceedings Paper

Improvement of speckle correlation fringes by adaptive correction using twisted nematic LCD
Author(s): Erwin Hack; Phanindra Narayan Gundu
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Paper Abstract

Subtraction correlation fringes in Digital Speckle Pattern Interferometry are described as a smoothly varying intensity distribution multiplied with high-frequency noise that is due to the random distribution of speckle intensity and speckle phase across the image plane. Although intensity modulation and speckle phase can be eliminated by phase stepping or other phase retrieval methods, noise is not eliminated completely due to the limited dynamic range of image processing, given by the saturation level of the camera, the digitisation depth and the electronic noise. Digital image processing techniques have been developed to reduce the speckle noise from the fringe pattern, but in most cases the fringes are not restored completely. In this paper the speckle noise is reduced before image digitisation by reducing the range of either the modulation intensity values or the speckle phase values, or both, in the interference pattern. This is done adaptively by using programmable twisted nematic LCDs. Since the manipulation is performed for each pixel independently in the reference beam, the imaging quality is retained and no blurring occurs. We quantitatively discuss the improvement and limitation of the method. The experimental verification is performed using an amplitude-only or phase-only spatial light modulator in a conventional ESPI setup.

Paper Details

Date Published: 15 September 2006
PDF: 6 pages
Proc. SPIE 6341, Speckle06: Speckles, From Grains to Flowers, 63410L (15 September 2006); doi: 10.1117/12.695289
Show Author Affiliations
Erwin Hack, Empa (Switzerland)
Phanindra Narayan Gundu, Empa (Switzerland)

Published in SPIE Proceedings Vol. 6341:
Speckle06: Speckles, From Grains to Flowers
Pierre Slangen; Christine Cerruti, Editor(s)

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